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Citric acid cycle
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Overview of the citric acid cycle
The citric acid cycle (CAC) – also known as the tricarboxylic acid (TCA) cycle or the Krebs cycle[1][2] – is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins into carbon dioxide and chemical energy in the form of adenosine triphosphate (ATP). In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other biochemical reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest established components of cellular metabolism and may have originated abiogenically.[3][4]
The name of this metabolic pathway is derived from the citric acid (a type of tricarboxylic acid, often called citrate, as the ionized form predominates at biological pH[5]) that is consumed and then regenerated by this sequence of reactions to complete the cycle. The cycle consumes acetate (in the form of acetyl-CoA) and water, reduces NAD+ to NADH, and produces carbon dioxide as a waste byproduct. The NADH generated by the citric acid cycle is fed into the oxidative phosphorylation (electron transport) pathway. The net result of these two closely linked pathways is the oxidation of nutrients to produce usable chemical energy in the form of ATP.
In eukaryotic cells, the citric acid cycle occurs in the matrix of the mitochondrion. In prokaryotic cells, such as bacteria which lack mitochondria, the citric acid cycle reaction sequence is performed in the cytosol with the proton gradient for ATP production being across the cell's surface (plasma membrane) rather than the inner membrane of the mitochondrion
Contents
[hide]
1 Discovery
2 Evolution
3 Overview
4 Steps
5 Structure of intermediates in Fischer projections and polygonal model
6 Products
7 Efficiency
8 Variation
9 Regulation
10 Major metabolic pathways converging on the citric acid cycle
11 Citric acid cycle intermediates serve as substrates for biosynthetic processes
12 Interactive pathway map
13 Glucose feeds the TCA cycle via circulating Lactate
14 See also
15 References
16 External links
Discovery[edit]
Several of the components and reactions of the citric acid cycle were established in the 1930s by the research of Albert Szent-Györgyi, who received the Nobel Prize in Physiology or Medicine in 1937 specifically for his discoveries pertaining to fumaric acid, a key component of the cycle.[6] The citric acid cycle itself was finally identified in 1937 by Hans Adolf Krebs and William Arthur Johnson while at the University of Sheffield,[7] for which the former received the Nobel Prize for Physiology or Medicine in 1953, and for whom the cycle is sometimes named (Krebs cycle).[8]
Evolution[edit]
Components of the citric acid cycle were derived from anaerobic bacteria, and the TCA cycle itself may have evolved more than once.[9] Theoretically, several alternatives to the TCA cycle exist; however, the TCA cycle appears to be the most efficient. If several TCA alternatives had evolved independently, they all appear to have converged to the TCA cycle.[10][11]
Overview[edit]
Structural diagram of acetyl-CoA: The portion in blue, on the left, is the acetyl group; the portion in black is coenzyme A.
The citric acid cycle is a key metabolic pathway that connects carbohydrate, fat, and protein metabolism. The reactions of the cycle are carried out by eight enzymes that completely oxidize acetate, in the form of acetyl-CoA, into two molecules each of carbon dioxide and water. Through catabolism of sugars, fats, and proteins, the two-carbon organic product acetyl-CoA (a form of acetate) is produced which enters the citric acid cycle. The reactions of the cycle also convert three equivalents of nicotinamide adenine dinucleotide (NAD+) into three equivalents of reduced NAD+ (NADH), one equivalent of flavin adenine dinucleotide (FAD) into one equivalent of FADH2, and one equivalent each of guanosine diphosphate (GDP) and inorganic phosphate (Pi) into one equivalent of guanosine triphosphate (GTP). The NADH and FADH2 generated by the citric acid cycle are, in turn, used by the oxidative phosphorylation pathway to generate energy-rich ATP.
One of the primary sources of acetyl-CoA is from the breakdown of sugars by glycolysis which yield pyruvate that in turn is decarboxylated by the enzyme pyruvate dehydrogenase generating acetyl-CoA according to the following reaction scheme:
CH3C(=O)C(=O)O−pyruvate + HSCoA + NAD+ → CH3C(=O)SCoAacetyl-CoA + NADH + CO2
The product of this reaction, acetyl-CoA, is the starting point for the citric acid cycle. Acetyl-CoA may also be obtained from the oxidation of fatty acids. Below is a schematic outline of the cycle:
The citric acid cycle begins with the transfer of a two-carbon acetyl group from acetyl-CoA to the four-carbon acceptor compound (oxaloacetate) to form a six-carbon compound (citrate).
The citrate then goes through a series of chemical transformations, losing two carboxyl groups as CO2. The carbons lost as CO2 originate from what was oxaloacetate, not directly from acetyl-CoA. The carbons donated by acetyl-CoA become part of the oxaloacetate carbon backbone after the first turn of the citric acid cycle. Loss of the acetyl-CoA-donated carbons as CO2 requires several turns of the citric acid cycle. However, because of the role of the citric acid cycle in anabolism, they might not be lost, since many citric acid cycle intermediates are also used as precursors for the biosynthesis of other molecules.[12]
Most of the energy made available by the oxidative steps of the cycle is transferred as energy-rich electrons to NAD+, forming NADH. For each acetyl group that enters the citric acid cycle, three molecules of NADH are produced.
Electrons are also transferred to the electron acceptor Q, forming QH2 (Q = FAD+, QH2 = FADH2).
For every NADH and FADH2 that are produced in the citric acid cycle, 2.5 and 1.5 ATP molecules are generated in oxidative phosphorylation, respectively.
At the end of each cycle, the four-carbon oxaloacetate has been regenerated, and the cycle continues.
Steps[edit]
Two carbon atoms are oxidized to CO2, the energy from these reactions is transferred to other metabolic processes through GTP (or ATP), and as electrons in NADH and QH2. The NADH generated in the citric acid cycle may later be oxidized (donate its electrons) to drive ATP synthesis in a type of process called oxidative phosphorylation.[5] FADH2 is covalently attached to succinate dehydrogenase, an enzyme which functions both in the CAC and the mitochondrial electron transport chain in oxidative phosphorylation. FADH2, therefore, facilitates transfer of electrons to coenzyme Q, which is the final electron acceptor of the reaction catalyzed by the succinate:ubiquinone oxidoreductase complex, also acting as an intermediate in the electron transport chain.[13]
The citric acid cycle is continuously supplied with new carbon in the form of acetyl-CoA, entering at step 0 below.[14]
Substrates
Products
Enzyme
Reaction type
Comment
0 / 10 Oxaloacetate +
Acetyl CoA +
H2O Citrate +
CoA-SH Citrate synthase Aldol condensation irreversible,
extends the 4C oxaloacetate to a 6C molecule
1 Citrate cis-Aconitate +
H2O Aconitase Dehydration reversible isomerisation
2 cis-Aconitate +
H2O Isocitrate Hydration
3 Isocitrate +
NAD+ Oxalosuccinate +
NADH + H + Isocitrate dehydrogenase Oxidation generates NADH (equivalent of 2.5 ATP)
4 Oxalosuccinate α-Ketoglutarate +
CO2 Decarboxylation rate-limiting, irreversible stage,
generates a 5C molecule
5 α-Ketoglutarate +
NAD+ +
CoA-SH Succinyl-CoA +
NADH + H+ +
CO2 α-Ketoglutarate dehydrogenase Oxidative
decarboxylation irreversible stage,
generates NADH (equivalent of 2.5 ATP),
regenerates the 4C chain (CoA excluded)
6 Succinyl-CoA +
GDP + Pi Succinate +
CoA-SH +
GTP Succinyl-CoA synthetase substrate-level phosphorylation or ADP→ATP instead of GDP→GTP,[13]
generates 1 ATP or equivalent
Condensation reaction of GDP + Pi and hydrolysis of Succinyl-CoA involve the H2O needed for balanced equation.
7 Succinate +
ubiquinone (Q) Fumarate +
ubiquinol (QH2) Succinate dehydrogenase Oxidation uses FAD as a prosthetic group (FAD→FADH2 in the first step of the reaction) in the enzyme,[13]
generates the equivalent of 1.5 ATP
8 Fumarate +
H2O L-Malate Fumarase Hydration Hydration of C-C double bond
9 L-Malate +
NAD+ Oxaloacetate +
NADH + H+ Malate dehydrogenase Oxidation reversible (in fact, equilibrium favors malate), generates NADH (equivalent of 2.5 ATP)
10 / 0 Oxaloacetate +
Acetyl CoA +
H2O Citrate +
CoA-SH Citrate synthase Aldol condensation This is the same as step 0 and restarts the cycle. The reaction is irreversible and extends the 4C oxaloacetate to a 6C molecule
Mitochondria in animals, including humans, possess two succinyl-CoA synthetases: one that produces GTP from GDP, and another that produces ATP from ADP.[15] Plants have the type that produces ATP (ADP-forming succinyl-CoA synthetase).[14] Several of the enzymes in the cycle may be loosely associated in a multienzyme protein complex within the mitochondrial matrix.[16]
The GTP that is formed by GDP-forming succinyl-CoA synthetase may be utilized by nucleoside-diphosphate kinase to form ATP (the catalyzed reaction is GTP + ADP → GDP + ATP).[13]
Structure of intermediates in Fischer projections and polygonal model[edit]
The intermediates of citric cycle depicted in Fischer projections show the chemical changing step by step. Such image can be compared to polygonal model representation.[17]
Structure of intermediates of citric acid cycle showed using Fischer projections, left, and polygonal model, right. Two-carbon molecule acetyl in the activated form acetyl-CoA (AcoA), on the top, condensate with four carbon molecule oxaloacetate (OxA) to form citrate (Cit). The next intermediates are, respectively, cis-aconitate (CisA), isocitrate (IsoC), oxalosuccinate (OxS), alphaketoglutarate (AKG), succinyl-CoA (ScoA), succinate (Suc), fumarate (Fum), malate (Mal), so the oxaloacetate is regenerated. The process can be followed in more detail, with the two carbons of the acetyl group of acetyl-CoA showed in blue is incorporated from citrate to succinyl-CoA in specific part of the species, and after this step the carbon is no further distinguishable since succinate is a symmetric molecule. The enzymes involved in this pathway correspond to citrate synthase ((1), aconitase ((2), isocitrate dehydrogenase (3), alphaketoglutarate dehydrogenase (4), succinyl-CoA synthetase (5), succinate dehydrogenase (6), fumarase (7), and malate dehydrogenase (8). Coenzymes (CoA-SH, NAD+, NADH + H+, FAD, FADH2, ATP or GTP and ADP or GDP), CO2 and H2O were omitted in these representations. The productions of NADH and FADH2 from the oxidized forms of coenzymes are represented, respectively, as the release of “2H” and “[2H]”. The production of ATP or GTP from ADP or GDP is shown by the release of high energy phosphate “~P”.
Products[edit]
Products of the first turn of the cycle are one GTP (or ATP), three NADH, one QH2, and two CO2.
Because two acetyl-CoA molecules are produced from each glucose molecule, two cycles are required per glucose molecule. Therefore, at the end of two cycles, the products are: two GTP, six NADH, two QH2, and four CO2.
Description Reactants Products
The sum of all reactions in the citric acid cycle is: Acetyl-CoA + 3 NAD+ + Q + GDP + Pi + 2 H2O → CoA-SH + 3 NADH + 3 H+ + QH2 + GTP + 2 CO2
Combining the reactions occurring during the pyruvate oxidation with those occurring during the citric acid cycle, the following overall pyruvate oxidation reaction is obtained: Pyruvate ion + 4 NAD+ + Q + GDP + Pi + 2 H2O → 4 NADH + 4 H+ + QH2 + GTP + 3 CO2
Combining the above reaction with the ones occurring in the course of glycolysis, the following overall glucose oxidation reaction (excluding reactions in the respiratory chain) is obtained: Glucose + 10 NAD+ + 2 Q + 2 ADP + 2 GDP + 4 Pi + 2 H2O → 10 NADH + 10 H+ + 2 QH2 + 2 ATP + 2 GTP + 6 CO2
The above reactions are balanced if Pi represents the H2PO4− ion, ADP and GDP the ADP2− and GDP2− ions, respectively, and ATP and GTP the ATP3− and GTP3− ions, respectively.
The total number of ATP molecules obtained after complete oxidation of one glucose in glycolysis, citric acid cycle, and oxidative phosphorylation is estimated to be between 30 and 38.[18]
Efficiency[edit]
The theoretical maximum yield of ATP through oxidation of one molecule of glucose in glycolysis, citric acid cycle, and oxidative phosphorylation is 38 (assuming 3 molar equivalents of ATP per equivalent NADH and 2 ATP per FADH2). In eukaryotes, two equivalents of NADH are generated in glycolysis, which takes place in the cytoplasm. Transport of these two equivalents into the mitochondria consumes two equivalents of ATP, thus reducing the net production of ATP to 36. Furthermore, inefficiencies in oxidative phosphorylation due to leakage of protons across the mitochondrial membrane and slippage of the ATP synthase/proton pump commonly reduces the ATP yield from NADH and FADH2 to less than the theoretical maximum yield.[18] The observed yields are, therefore, closer to ~2.5 ATP per NADH and ~1.5 ATP per FADH2, further reducing the total net production of ATP to approximately 30.[19] An assessment of the total ATP yield with newly revised proton-to-ATP ratios provides an estimate of 29.85 ATP per glucose molecule.[20]
Variation[edit]
While the citric acid cycle is in general highly conserved, there is significant variability in the enzymes found in different taxa[21] (note that the diagrams on this page are specific to the mammalian pathway variant).
Some differences exist between eukaryotes and prokaryotes. The conversion of D-threo-isocitrate to 2-oxoglutarate is catalyzed in eukaryotes by the NAD+-dependent EC 1.1.1.41, while prokaryotes employ the NADP+-dependent EC 1.1.1.42.[22] Similarly, the conversion of (S)-malate to oxaloacetate is catalyzed in eukaryotes by the NAD+-dependent EC 1.1.1.37, while most prokaryotes utilize a quinone-dependent enzyme, EC 1.1.5.4.[23]
A step with significant variability is the conversion of succinyl-CoA to succinate. Most organisms utilize EC 6.2.1.5, succinate–CoA ligase (ADP-forming) (despite its name, the enzyme operates in the pathway in the direction of ATP formation). In mammals a GTP-forming enzyme, succinate–CoA ligase (GDP-forming) (EC 6.2.1.4) also operates. The level of utilization of each isoform is tissue dependent.[24] In some acetate-producing bacteria, such as Acetobacter aceti, an entirely different enzyme catalyzes this conversion – EC 2.8.3.18, succinyl-CoA:acetate CoA-transferase. This specialized enzyme links the TCA cycle with acetate metabolism in these organisms.[25] Some bacteria, such as Helicobacter pylori, employ yet another enzyme for this conversion – succinyl-CoA:acetoacetate CoA-transferase (EC 2.8.3.5).[26]
Some variability also exists at the previous step – the conversion of 2-oxoglutarate to succinyl-CoA. While most organisms utilize the ubiquitous NAD+-dependent 2-oxoglutarate dehydrogenase, some bacteria utilize a ferredoxin-dependent 2-oxoglutarate synthase (EC 1.2.7.3).[27] Other organisms, including obligately autotrophic and methanotrophic bacteria and archaea, bypass succinyl-CoA entirely, and convert 2-oxoglutarate to succinate via succinate semialdehyde, using EC 4.1.1.71, 2-oxoglutarate decarboxylase, and EC 1.2.1.79, succinate-semialdehyde dehydrogenase.[28]
Regulation[edit]
The regulation of the citric acid cycle is largely determined by product inhibition and substrate availability. If the cycle were permitted to run unchecked, large amounts of metabolic energy could be wasted in overproduction of reduced coenzyme such as NADH and ATP. The major eventual substrate of the cycle is ADP which gets converted to ATP. A reduced amount of ADP causes accumulation of precursor NADH which in turn can inhibit a number of enzymes. NADH, a product of all dehydrogenases in the citric acid cycle with the exception of succinate dehydrogenase, inhibits pyruvate dehydrogenase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and also citrate synthase. Acetyl-coA inhibits pyruvate dehydrogenase, while succinyl-CoA inhibits alpha-ketoglutarate dehydrogenase and citrate synthase. When tested in vitro with TCA enzymes, ATP inhibits citrate synthase and α-ketoglutarate dehydrogenase; however, ATP levels do not change more than 10% in vivo between rest and vigorous exercise. There is no known allosteric mechanism that can account for large changes in reaction rate from an allosteric effector whose concentration changes less than 10%.[5]
Calcium is also used as a regulator in the citric acid cycle. Calcium levels in the mitochondrial matrix can reach up to the tens of micromolar levels during cellular activation.[29] It activates pyruvate dehydrogenase phosphatase which in turn activates the pyruvate dehydrogenase complex. Calcium also activates isocitrate dehydrogenase and α-ketoglutarate dehydrogenase.[30] This increases the reaction rate of many of the steps in the cycle, and therefore increases flux throughout the pathway.
Citrate is used for feedback inhibition, as it inhibits phosphofructokinase, an enzyme involved in glycolysis that catalyses formation of fructose 1,6-bisphosphate, a precursor of pyruvate. This prevents a constant high rate of flux when there is an accumulation of citrate and a decrease in substrate for the enzyme.
Recent work has demonstrated an important link between intermediates of the citric acid cycle and the regulation of hypoxia-inducible factors (HIF). HIF plays a role in the regulation of oxygen homeostasis, and is a transcription factor that targets angiogenesis, vascular remodeling, glucose utilization, iron transport and apoptosis. HIF is synthesized consititutively, and hydroxylation of at least one of two critical proline residues mediates their interaction with the von Hippel Lindau E3 ubiquitin ligase complex, which targets them for rapid degradation. This reaction is catalysed by prolyl 4-hydroxylases. Fumarate and succinate have been identified as potent inhibitors of prolyl hydroxylases, thus leading to the stabilisation of HIF.[31]
Major metabolic pathways converging on the citric acid cycle[edit]
Several catabolic pathways converge on the citric acid cycle. Most of these reactions add intermediates to the citric acid cycle, and are therefore known as anaplerotic reactions, from the Greek meaning to "fill up". These increase the amount of acetyl CoA that the cycle is able to carry, increasing the mitochondrion's capability to carry out respiration if this is otherwise a limiting factor. Processes that remove intermediates from the cycle are termed "cataplerotic" reactions.
In this section and in the next, the citric acid cycle intermediates are indicated in italics to distinguish them from other substrates and end-products.
Pyruvate molecules produced by glycolysis are actively transported across the inner mitochondrial membrane, and into the matrix. Here they can be oxidized and combined with coenzyme A to form CO2, acetyl-CoA, and NADH, as in the normal cycle.[32]
However, it is also possible for pyruvate to be carboxylated by pyruvate carboxylase to form oxaloacetate. This latter reaction "fills up" the amount of oxaloacetate in the citric acid cycle, and is therefore an anaplerotic reaction, increasing the cycle’s capacity to metabolize acetyl-CoA when the tissue's energy needs (e.g. in muscle) are suddenly increased by activity.[33]
In the citric acid cycle all the intermediates (e.g. citrate, iso-citrate, alpha-ketoglutarate, succinate, fumarate, malate and oxaloacetate) are regenerated during each turn of the cycle. Adding more of any of these intermediates to the mitochondrion therefore means that that additional amount is retained within the cycle, increasing all the other intermediates as one is converted into the other. Hence the addition of any one of them to the cycle has an anaplerotic effect, and its removal has a cataplerotic effect. These anaplerotic and cataplerotic reactions will, during the course of the cycle, increase or decrease the amount of oxaloacetate available to combine with acetyl-CoA to form citric acid. This in turn increases or decreases the rate of ATP production by the mitochondrion, and thus the availability of ATP to the cell.[33]
Acetyl-CoA, on the other hand, derived from pyruvate oxidation, or from the beta-oxidation of fatty acids, is the only fuel to enter the citric acid cycle. With each turn of the cycle one molecule of acetyl-CoA is consumed for every molecule of oxaloacetate present in the mitochondrial matrix, and is never regenerated. It is the oxidation of the acetate portion of acetyl-CoA that produces CO2 and water, with the energy thus released captured in the form of ATP.[33]
In the liver, the carboxylation of cytosolic pyruvate into intra-mitochondrial oxaloacetate is an early step in the gluconeogenic pathway which converts lactate and de-aminated alanine into glucose,[32][33] under the influence of high levels of glucagon and/or epinephrine in the blood.[33] Here the addition of oxaloacetate to the mitochondrion does not have a net anaplerotic effect, as another citric acid cycle intermediate (malate) is immediately removed from the mitochondrion to be converted into cytosolic oxaloacetate, which is ultimately converted into glucose, in a process that is almost the reverse of glycolysis.[33]
In protein catabolism, proteins are broken down by proteases into their constituent amino acids. Their carbon skeletons (i.e. the de-aminated amino acids) may either enter the citric acid cycle as intermediates (e.g. alpha-ketoglutarate derived from glutamate or glutamine), having an anaplerotic effect on the cycle, or, in the case of leucine, isoleucine, lysine, phenylalanine, tryptophan, and tyrosine, they are converted into acetyl-CoA which can be burned to CO2 and water, or used to form ketone bodies, which too can only be burned in tissues other than the liver where they are formed, or excreted via the urine or breath.[33] These latter amino acids are therefore termed "ketogenic" amino acids, whereas those that enter the citric acid cycle as intermediates can only be cataplerotically removed by entering the gluconeogenic pathway via malate which is transported out of the mitochondrion to be converted into cytosolic oxaloacetate and ultimately into glucose. These are the so-called "glucogenic" amino acids. De-aminated alanine, cysteine, glycine, serine, and threonine are converted to pyruvate and can consequently either enter the citric acid cycle as oxaloacetate (an anaplerotic reaction) or as acetyl-CoA to be disposed of as CO2 and water.[33]
In fat catabolism, triglycerides are hydrolyzed to break them into fatty acids and glycerol. In the liver the glycerol can be converted into glucose via dihydroxyacetone phosphate and glyceraldehyde-3-phosphate by way of gluconeogenesis. In many tissues, especially heart and skeletal muscle tissue, fatty acids are broken down through a process known as beta oxidation, which results in the production of mitochondrial acetyl-CoA, which can be used in the citric acid cycle. Beta oxidation of fatty acids with an odd number of methylene bridges produces propionyl-CoA, which is then converted into succinyl-CoA and fed into the citric acid cycle as an anaplerotic intermediate.[34]
The total energy gained from the complete breakdown of one (six-carbon) molecule of glucose by glycolysis, the formation of 2 acetyl-CoA molecules, their catabolism in the citric acid cycle, and oxidative phosphorylation equals about 30 ATP molecules, in eukaryotes. The number of ATP molecules derived from the beta oxidation of a 6 carbon segment of a fatty acid chain, and the subsequent oxidation of the resulting 3 molecules of acetyl-CoA is 40.
Citric acid cycle intermediates serve as substrates for biosynthetic processes[edit]
In this subheading, as in the previous one, the TCA intermediates are identified by italics.
Several of the citric acid cycle intermediates are used for the synthesis of important compounds, which will have significant cataplerotic effects on the cycle.[33] Acetyl-CoA cannot be transported out of the mitochondrion. To obtain cytosolic acetyl-CoA, citrate is removed from the citric acid cycle and carried across the inner mitochondrial membrane into the cytosol. There it is cleaved by ATP citrate lyase into acetyl-CoA and oxaloacetate. The oxaloacetate is returned to mitochondrion as malate (and then converted back into oxaloacetate to transfer more acetyl-CoA out of the mitochondrion).[35] The cytosolic acetyl-CoA is used for fatty acid synthesis and the production of cholesterol. Cholesterol can, in turn, be used to synthesize the steroid hormones, bile salts, and vitamin D.[32][33]
The carbon skeletons of many non-essential amino acids are made from citric acid cycle intermediates. To turn them into amino acids the alpha keto-acids formed from the citric acid cycle intermediates have to acquire their amino groups from glutamate in a transamination reaction, in which pyridoxal phosphate is a cofactor. In this reaction the glutamate is converted into alpha-ketoglutarate, which is a citric acid cycle intermediate. The intermediates that can provide the carbon skeletons for amino acid synthesis are oxaloacetate which forms aspartate and asparagine; and alpha-ketoglutarate which forms glutamine, proline, and arginine.[32][33]
Of these amino acids, aspartate and glutamine are used, together with carbon and nitrogen atoms from other sources, to form the purines that are used as the bases in DNA and RNA, as well as in ATP, AMP, GTP, NAD, FAD and CoA.[33]
The pyrimidines are partly assembled from aspartate (derived from oxaloacetate). The pyrimidines, thymine, cytosine and uracil, form the complementary bases to the purine bases in DNA and RNA, and are also components of CTP, UMP, UDP and UTP.[33]
The majority of the carbon atoms in the porphyrins come from the citric acid cycle intermediate, succinyl-CoA. These molecules are an important component of the hemoproteins, such as hemoglobin, myoglobin and various cytochromes.[33]
During gluconeogenesis mitochondrial oxaloacetate is reduced to malate which is then transported out of the mitochondrion, to be oxidized back to oxaloacetate in the cytosol. Cytosolic oxaloacetate is then decarboxylated to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase, which is the rate limiting step in the conversion of nearly all the gluconeogenic precursors (such as the glucogenic amino acids and lactate) into glucose by the liver and kidney.[32][33]
Because the citric acid cycle is involved in both catabolic and anabolic processes, it is known as an amphibolic pathway.
Interactive pathway map[edit]
Click on genes, proteins and metabolites below to link to respective articles. [§ 1]
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|{{{bSize}}}px|alt=TCA Cycle edit]]
TCA Cycle edit
Jump up ^ The interactive pathway map can be edited at WikiPathways: "TCACycle_WP78".
Glucose feeds the TCA cycle via circulating Lactate[edit]
The metabolic role of lactate is well recognized, including as a fuel for tissues and tumors. In the classical Cori cycle, muscles produce lactate which is then taken up by the liver for gluconeogenesis. New studies suggest that lactate can be used as a source of carbon for the TCA cycle.[36]
See also[edit]
Calvin cycle
Glyoxylate cycle
Reverse (Reductive) Krebs cycle
References[edit]
Jump up ^ Lowenstein JM (1969). Methods in Enzymology, Volume 13: Citric Acid Cycle. Boston: Academic Press. ISBN 0-12-181870-5.
Jump up ^ Krebs HA, Weitzman PD (1987). Krebs' citric acid cycle: half a century and still turning. London: Biochemical Society. p. 25. ISBN 0-904498-22-0.
Jump up ^ Wagner, Andreas (2014). Arrival of the Fittest (first ed.). New York: Penguin Group. p. 100. ISBN 9781591846468.
Jump up ^ Lane, Nick (2009). Life Ascending: The Ten Great Inventions of Evolution. New York: W.W. Norton & Co. ISBN 0-393-06596-0.
^ Jump up to: a b c Voet D, Voet JG (2004). Biochemistry (3rd ed.). New York: John Wiley & Sons, Inc. p. 615.
Jump up ^ "The Nobel Prize in Physiology or Medicine 1937". The Nobel Foundation. Retrieved 2011-10-26.
Jump up ^ Krebs, HA; Johnson, WA (April 1937). "Metabolism of ketonic acids in animal tissues". The Biochemical Journal. 31 (4): 645–60. PMC 1266984  . PMID 16746382.
Jump up ^ "The Nobel Prize in Physiology or Medicine 1953". The Nobel Foundation. Retrieved 2011-10-26.
Jump up ^ Gest H (1987). "Evolutionary roots of the citric acid cycle in prokaryotes". Biochem. Soc. Symp. 54: 3–16. PMID 3332996.
Jump up ^ Meléndez-Hevia E, Waddell TG, Cascante M (September 1996). "The puzzle of the Krebs citric acid cycle: assembling the pieces of chemically feasible reactions, and opportunism in the design of metabolic pathways during evolution". J. Mol. Evol. 43 (3): 293–303. doi:10.1007/BF02338838. PMID 8703096.
Jump up ^ Ebenhöh O, Heinrich R (January 2001). "Evolutionary optimization of metabolic pathways. Theoretical reconstruction of the stoichiometry of ATP and NADH producing systems". Bull. Math. Biol. 63 (1): 21–55. doi:10.1006/bulm.2000.0197. PMID 11146883.
Jump up ^ Wolfe RR, Jahoor F (February 1990). "Recovery of labeled CO2 during the infusion of C-1- vs C-2-labeled acetate: implications for tracer studies of substrate oxidation". Am. J. Clin. Nutr. 51 (2): 248–52. PMID 2106256.
^ Jump up to: a b c d Stryer L, Berg J, Tymoczko JL (2002). Biochemistry. San Francisco: W.H. Freeman. ISBN 0-7167-4684-0.
^ Jump up to: a b Jones RC, Buchanan BB, Gruissem W (2000). Biochemistry & molecular biology of plants (1st ed.). Rockville, Md: American Society of Plant Physiologists. ISBN 0-943088-39-9.
Jump up ^ Johnson JD, Mehus JG, Tews K, Milavetz BI, Lambeth DO (October 1998). "Genetic evidence for the expression of ATP- and GTP-specific succinyl-CoA synthetases in multicellular eucaryotes". J. Biol. Chem. 273 (42): 27580–6. doi:10.1074/jbc.273.42.27580. PMID 9765291.
Jump up ^ Barnes SJ, Weitzman PD (June 1986). "Organization of citric acid cycle enzymes into a multienzyme cluster". FEBS Lett. 201 (2): 267–70. doi:10.1016/0014-5793(86)80621-4. PMID 3086126.
Jump up ^ Bonafe, CFS; de Jesus MB; Bispo JAC (January–February 2018), "The Polygonal Model: A Simple Representation of Biomolecules as a Tool for Teaching Metabolism", Biochemistry and Molecular Biology Education, 46 (1): 66–75, doi:10.1002/bmb.21093 CS1 maint: Date format (link)
^ Jump up to: a b Porter RK, Brand MD (September 1995). "Mitochondrial proton conductance and H+/O ratio are independent of electron transport rate in isolated hepatocytes". Biochem. J. 310 (2): 379–82. doi:10.1042/bj3100379. PMC 1135905  . PMID 7654171.
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Jump up ^ "Citric acid cycle variants at MetaCyc".
Jump up ^ Sahara T, Takada Y, Takeuchi Y, Yamaoka N, Fukunaga N (March 2002). "Cloning, sequencing, and expression of a gene encoding the monomeric isocitrate dehydrogenase of the nitrogen-fixing bacterium, Azotobacter vinelandii". Biosci. Biotechnol. Biochem. 66 (3): 489–500. doi:10.1271/bbb.66.489. PMID 12005040.
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^ Jump up to: a b c d e f g h i j k l m n o Stryer, Lubert (1995). "Citric acid cycle.". In: Biochemistry (Fourth ed.). New York: W.H. Freeman and Company. pp. 509–527, 569–579, 614–616, 638–641, 732–735, 739–748, 770–773. ISBN 0 7167 2009 4.
Jump up ^ Halarnkar PP, Blomquist GJ (1989). "Comparative aspects of propionate metabolism". Comp. Biochem. Physiol., B. 92 (2): 227–31. doi:10.1016/0305-0491(89)90270-8. PMID 2647392.
Jump up ^ Ferre, P.; F. Foufelle (2007). "SREBP-1c Transcription Factor and Lipid Homeostasis: Clinical Perspective". Hormone Research. 68 (2): 72–82. doi:10.1159/000100426. PMID 17344645. Retrieved 2010-08-30. this process is outlined graphically in page 73
Jump up ^ TY - JOUR AU - Hui, Sheng AU - Ghergurovich, Jonathan M. AU - Morscher, Raphael J. AU - Jang, Cholsoon AU - Teng, Xin AU - Lu, Wenyun AU - Esparza, Lourdes A. AU - Reya, Tannishtha AU - Le Zhan, AU - Yanxiang Guo, Jessie AU - White, Eileen AU - Rabinowitz, Joshua D. TI - Glucose feeds the TCA cycle via circulating lactate JA - Nature PY - 2017/10/18/online VL - advance online publication SP - EP - PB - Macmillan Publishers Limited, part of Springer Nature. All rights reserved. SN - 1476-4687 UR - https://dx.doi.org/10.1038/nature24057 L3 - 10.1038/nature24057 M3 - Letter L3 - http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature24057.html#supplementary-information ER -
External links[edit]
An animation of the citric acid cycle at Smith College
Citric acid cycle variants at MetaCyc
Pathways connected to the citric acid cycle at Kyoto Encyclopedia of Genes and Genomes
Introduction at Khan Academy
metpath: Interactive representation of the citric acid cycle
[show]
v
t
e
Metabolism, catabolism, anabolism
General
Metabolic pathway
Metabolic network
Primary nutritional groups
Energy
metabolism
Aerobic respiration
Glycolysis → Pyruvate decarboxylation → Citric acid cycle → Oxidative phosphorylation (electron transport chain + ATP synthase)
Anaerobic respiration
Electron acceptors are other than oxygen
Fermentation
Glycolysis →
Substrate-level phosphorylation
ABE
Ethanol
Lactic acid
Specific
paths
Protein metabolism
Protein synthesis
Catabolism
Carbohydrate metabolism
(carbohydrate catabolism
and anabolism)
Human
Glycolysis ⇄ Gluconeogenesis
Glycogenolysis ⇄ Glycogenesis
Pentose phosphate pathway
Fructolysis
Galactolysis
Glycosylation
N-linked
O-linked
Nonhuman
Photosynthesis
Anoxygenic photosynthesis
Chemosynthesis
Carbon fixation
Xylose metabolism
Radiotrophism
Lipid metabolism
(lipolysis, lipogenesis)
Fatty acid metabolism
Fatty acid degradation (Beta oxidation)
Fatty acid synthesis
Other
Steroid metabolism
Sphingolipid metabolism
Eicosanoid metabolism
Ketosis
Reverse cholesterol transport
Amino acid
Amino acid synthesis
Urea cycle
Nucleotide
metabolism
Purine metabolism
Nucleotide salvage
Pyrimidine metabolism
Other
Metal metabolism
Iron metabolism
Ethanol metabolism
[show]
v
t
e
Citric acid cycle metabolic pathway
Acetyl-CoA
+ H2O
Oxaloacetate
NADH +H+
NAD+
Malate
H2O
Fumarate
FADH2
FAD
Succinate
CoA + ATP (GTP)
Pi + ADP (GDP)
Succinyl-CoA
NADH + H+ + CO2
CoA NAD+
Citrate
H2O
cis-Aconitate
H2O
Isocitrate
NAD(P)+
NAD(P)H + H+
Oxalosuccinate
CO2
2-oxoglutarate
[show]
v
t
e
Metabolism map
Carbon
Fixation
Photo-
respiration
Pentose
Phosphate
Pathway
Citric
Acid Cycle
Glyoxylate
Cycle
Urea
Cycle
Fatty
Acid
Synthesis
Fatty
Acid
Elongation
Beta
Oxidation
Peroxisomal
Beta
Oxidation

Glyco-
genolysis
Glyco-
genesis
Glyco-
lysis
Gluconeo-
genesis
Decarb-
oxylation
Fermentation
Keto-
lysis
Keto-
genesis
feeders to
Gluconeo-
genesis
Direct / C4 / CAM
Carbon Intake
Light Reaction
Oxidative
Phosphorylation
Amino Acid
Deamination
Citrate
Shuttle
Lipogenesis
Lipolysis
Steroidogenesis
MVA Pathway
MEP Pathway
Shikimate
Pathway
Transcription &
Replication
Translation
Proteolysis
Glycosy-
lation

Sugar
Acids
Double/Multiple
Sugars & Glycans
Simple
Sugars
Inositol-P
Amino Sugars
& Sialic Acids
Nucleotide Sugars
Hexose-P
Triose-P
Glycerol
P-glycerates
Pentose-P
Tetrose-P
Propionyl
-CoA
Succinate
Acetyl
-CoA
Pentose-P
P-glycerates
Glyoxylate
Photosystems
Pyruvate
Lactate
Acetyl
-CoA
Citrate
Oxalo-
acetate
Malate
Succinyl
-CoA
α-Keto-
glutarate
Ketone
Bodies
Respiratory
Chain
Serine Group
Alanine
Branched-chain
Amino Acids
Aspartate
Group
Homoserine
Group
& Lysine
Glutamate
Group
& Proline
Arginine
Creatine
& Polyamines
Ketogenic &
Glucogenic
Amino Acids
Amino Acids
Shikimate
Aromatic Amino
Acids & Histidine
Ascorbate
(Vitamin C)
δ-ALA
Bile
Pigments
Hemes
Cobalamins (Vitamin B12)
Various
Vitamin B's
Calciferols
(Vitamin D)
Retinoids
(Vitamin A)
Quinones (Vitamin K)
& Carotenoids (Vitamin E)
Cofactors
Vitamins
& Minerals
Antioxidants
PRPP
Nucleotides
Nucleic
Acids
Proteins
Glycoproteins
& Proteoglycans
Chlorophylls
MEP
MVA
Acetyl
-CoA
Polyketides
Terpenoid
Backbones
Terpenoids
& Carotenoids (Vitamin A)
Cholesterol
Bile Acids
Glycero-
phospholipids
Glycerolipids
Acyl-CoA
Fatty
Acids
Glyco-
sphingolipids
Sphingolipids
Waxes
Polyunsaturated
Fatty Acids
Neurotransmitters
& Thyroid Hormones
Steroids
Endo-
cannabinoids
Eicosanoids
Major metabolic pathways in metro-style map. Click any text (name of pathway or metabolites) to link to the corresponding article.
Single lines: pathways common to most lifeforms. Double lines: pathways not in humans (occurs in e.g. plants, fungi, prokaryotes). Orange nodes: carbohydrate metabolism. Violet nodes: photosynthesis. Red nodes: cellular respiration. Pink nodes: cell signaling. Blue nodes: amino acid metabolism. Grey nodes: vitamin and cofactor metabolism. Brown nodes: nucleotide and protein metabolism. Green nodes: lipid metabolism.
[show]
v
t
e
Metabolism: Citric acid cycle enzymes
Cycle
Citrate synthase
Aconitase
Isocitrate dehydrogenase
Oxoglutarate dehydrogenase
Succinyl CoA synthetase
Succinate dehydrogenase (SDHA)
Fumarase
Malate dehydrogenase and ETC
Anaplerotic
to acetyl-CoA
Pyruvate dehydrogenase complex (E1, E2, E3)
(regulated by Pyruvate dehydrogenase kinase and Pyruvate dehydrogenase phosphatase)
to α-ketoglutaric acid
Glutamate dehydrogenase
to succinyl-CoA
Methylmalonyl-CoA mutase
to oxaloacetate
Pyruvate carboxylase
Aspartate transaminase
Mitochondrial
electron transport chain/
oxidative phosphorylation
Primary
Complex I/NADH dehydrogenase
Complex II/Succinate dehydrogenase
Coenzyme Q
Complex III/Coenzyme Q - cytochrome c reductase
Cytochrome c
Complex IV/Cytochrome c oxidase
Coenzyme Q10 synthesis: COQ2
COQ3
COQ4
COQ5
COQ6
COQ7
COQ9
COQ10A
COQ10B
PDSS1
PDSS2
Other
Alternative oxidase
Electron-transferring-flavoprotein dehydrogenase
Authority control
LCCN: sh85073260
GND: 4148058-2
Retrieved from "https://en.wikipedia.org/w/index.php?title=Citric_acid_cycle&oldid=821028427"
Categories:
Biochemistry
Cellular respiration
Exercise physiology
Metabolic pathways
Citric acid cycle
1937 in biology
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Paranormal Activity (film series)
From Wikipedia, the free encyclopedia
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Paranormal Activity
Directed by
Oren Peli (PA1)
Tod Williams (PA2)
Henry Joost and Ariel Schulman (PA3 and 4)
Gregory Plotkin (PA: TGD)
Christopher B. Landon (PA: TMO)
Produced by
Oren Peli (PA1-TGD)
Jason Blum (PA1-TGD)
Akiva Goldsman (PA2 and 3)
Steven Schneider (PA1, 3 and 4)
Written by
Oren Peli (PA1)
Michael R. Perry (PA2)
Christopher B. Landon (PA2, 3, 4 and TMO)
Tom Pabst (PA2)
Jason Pagan (PA: TGD)
Andrew Stark (PA: TGD)
Adam Robitel (PA: TGD)
Gavin Heffernan (PA: TGD)
Starring
Katie Featherston (PA1-2, 4 and TMO)
Micah Sloat (PA1-2, 4 and TMO)
Sprague Grayden (PA2)
Brian Boland (PA2)
Molly Ephraim (PA2)
Lauren Bittner (PA3)
Chris Smith (PA3)
Chloe Csengery (PA3, TGD and TMO)
Jessica Tyler Brown (PA3)
Kathryn Newton (PA4)
Matt Shively (PA4)
Aiden Lovekamp (PA4)
Brady Allen (PA4)
Stephen Dunham (PA4)
Alexondra Lee (PA4)
Andrew Jacobs (PA: TMO)
Jorge Diaz (PA: TMO)
Gabrielle Walsh (PA: TMO)
Chris J. Murray (PA: TGD)
Brit Shaw (PA: TGD)
Dan Gill (PA: TGD)
Ivy George (PA: TGD)
Olivia Taylor Dudley (PA: TGD)
Production
company
Blumhouse Productions
Distributed by
Paramount Pictures
Release date
2007 – 2015
Running time
444 minutes (total)
Country
United States
Language
English
Budget
$28 million
Box office
$889.7 million
Paranormal Activity is an American supernatural horror film series consisting of six films and an unofficial film. Created by Oren Peli, the original film was widely released in 2007.
The films are based around a family haunted by a demon that stalks, terrifies and ultimately murders several members of the family and other bystanders during the course of the films. The series makes use of production cameras set up and used like security cameras or other recording devices in an attempt to present the films as found footage. The series has received mixed reviews, with the first and third films receiving generally positive critical reception, while the second film and fifth film receiving more lukewarm receptions and the fourth and sixth received mostly negative reception. The series is a strong financial success, making strong profits based on return on investment. The series as a whole has earned over thirty times the overall budget.
Contents
[hide]
1 Films
1.1 Paranormal Activity (2007)
1.2 Paranormal Activity 2 (2010)
1.3 Paranormal Activity 3 (2011)
1.4 Paranormal Activity 4 (2012)
1.5 Paranormal Activity: The Marked Ones (2014)
1.6 Paranormal Activity: The Ghost Dimension (2015)
2 Unofficial film
2.1 Paranormal Activity 2: Tokyo Night
3 Cast
4 Crew
5 Development
6 Reception
6.1 Box office performance
6.2 Critical and public response
7 Video game
8 References
Films[edit]
Paranormal Activity (2007)[edit]
Main article: Paranormal Activity
Set in 2006, a young couple, Katie and Micah, who have recently moved to a new house in San Diego, California, are terrorized by a demon that Katie believes has been following her all her life. The film is designed to look like a found footage-styled film with Micah filming the activity in their house.
Paranormal Activity 2 (2010)[edit]
Main article: Paranormal Activity 2
Set again in 2006, several weeks before the events of the first film, Katie's sister, Kristi and her family, who reside in Carlsbad, California, experience strange activity after Kristi's baby son, Hunter, is born. The film uses security cameras and a hand-held camera used in some scenes to film the activity in the house.
Paranormal Activity 3 (2011)[edit]
Main article: Paranormal Activity 3
Set in 1988, focuses on a younger Katie and Kristi, who live with their mother, Julie, and Julie's boyfriend, Dennis, in Santa Rosa, California, as they encounter "Toby" the demon for the first time. Concerned, Dennis decides to set up a few cameras around the house, one of which is attached to a small oscillating fan that moves the camera back and forth. The film also uses a hand-held camera.
Paranormal Activity 4 (2012)[edit]
Main article: Paranormal Activity 4
Set in 2011, the film focuses on Alex Nelson and her family residing in a neighborhood in Henderson, Nevada. The family begin to experience haunting concerning Alex's adopted brother, Wyatt, after Katie and her mysterious son, Robbie, move in across the street. Alex is helped by her boyfriend, Ben, to film the activity via MacBook webcams, Video camera, iPhone camera and Kinect technology. "Toby" is mentioned once in the film.
Paranormal Activity: The Marked Ones (2014)[edit]
Main article: Paranormal Activity: The Marked Ones
Set in 2012, the film follows a Latino community in Oxnard, California, where a group of high school graduates deal with the demon of a mysterious cult who have "marked" one of them. They document their experiences using basic tools of recording and with clues from the previous films to try to understand what is happening to them. The Marked Ones is the last film in the series to feature Katie Featherston.
Paranormal Activity: The Ghost Dimension (2015)[edit]
Main article: Paranormal Activity: The Ghost Dimension
Set in 2013, follows the Fleeges, a family of three who, after having relocated to a house in Santa Rosa, California, discover several tapes that show Katie and Kristi in the midst of their initiation ritual to enter a demonic coven 21 years before. The family begin to be haunted by the demon when the daughter, Leila, is targeted as she was born on the same date as of a boy from Paranormal Activity 2, Hunter. Along with normal recorders, the family also discover a unique video recorder that can show supernatural happenings, which they use to record the increasing paranormal activities.
Unofficial film[edit]
Paranormal Activity 2: Tokyo Night[edit]
Main article: Paranormal Activity 2: Tokyo Night
A Japanese Paranormal Activity sequel was released in 2010. It follows Haruka Yamano, who was in a car accident that broke her legs. She stayed home with her brother while their father was away as strange activity started happening in the house. It is later revealed that Haruka killed the possessed Katie in the car accident, causing the demon to transfer to her.
Cast[edit]
Character
Films
Unofficial Film
Paranormal Activity
Paranormal Activity 2
Paranormal Activity 3
Paranormal Activity 4
Paranormal Activity:
The Marked Ones
Paranormal Activity:
The Ghost Dimension
Paranormal Activity 2:
Tokyo Night
2007
2010
2011
2012
2014
2015
2010
Katie
Katie Featherston Mentioned as Katie Higgins Katie Featherston
(archive footage only)
Chloe Csengery Chloe Csengery
Micah
Micah Sloat Micah Sloat Micah Sloat
(archive footage only)
Kristi Rey
Sprague Grayden Archive footage, uncredited
Jessica Tyler Brown Jessica Tyler Brown
Daniel Rey
Brian Boland Archive footage, uncredited
Ali Rey
Molly Ephraim Molly Ephraim
Hunter Rey
Wyatt Nelson
Jackson Xenia Prieto (infant)
William Juan Prieto (toddler) Aiden Lovekamp (boy)
William Juan Prieto (toddler, archive footage, uncredited) Aiden Lovekamp (boy)
Martine
Vivis Cortez
Dennis
Chris Smith Archive footage, uncredited
Julie
Lauren Bittner Archive footage, uncredited
Lois
Hallie Foote Hallie Foote (uncredited) Hallie Foote
Randy Rosen
Dustin Ingram
Lisa
Johanna Braddy
Toby
Unseen and mentioned Mentioned Mark Steger
Alex Nelson
Kathryn Newton Mentioned only
Ben
Matt Shively
Robbie
Brady Allen
Doug Nelson
Stephen Dunham Mentioned only
Holly Nelson
Alexondra Lee Mentioned only
Jesse Arista
Andrew Jacobs
Hector Estrella
Jorge Diaz
Marisol Vargas
Gabrielle Walsh
Irma Arista
Renée Victor
Arturo Lopez
Richard Cabral
Ryan Fleege
Chris J. Murray
Emily Fleege
Brit Shaw
Mike Fleege
Dan Gill
Leila Fleege
Ivy George
Skyler
Olivia Taylor Dudley
Crew[edit]
Crew / Detail
Films
Paranormal Activity
Paranormal Activity 2
Paranormal Activity 3
Paranormal Activity 4
Paranormal Activity:
The Marked Ones
Paranormal Activity:
The Ghost Dimension
2007
2010
2011
2012
2014
2015
Director
Oren Peli Tod Williams Henry Joost
Ariel Schulman Christopher B. Landon Gregory Plotkin
Producer(s)
Jason Blum
Oren Peli Akiva Goldsman
Jason Blum
Oren Peli Steven Schneider
Jason Blum
Oren Peli Jason Blum
Oren Peli
Writer(s)
Oren Peli Christopher B. Landon
Michael R. Perry
Tom Pabst Christopher B. Landon Adam Robitel
Andrew Stark
Jason Pagan
Gavin Heffernan
Editor
Oren Peli Gregory Plotkin Michel Aller
Cinematography
Oren Peli Michael Simmonds Magdalena Gorka Doug Emmett Gonzalo Amat John Rutland
Production company
Blumhouse Productions
Distributor
Paramount Pictures
MPAA rating
R
Running time
86 minutes 91 minutes 84 minutes 87 minutes 84 minutes 88 minutes
Release date
October 14, 2007 October 22, 2010 October 21, 2011 October 19, 2012 January 3, 2014 October 23, 2015
Development[edit]
First-time director Oren Peli had been afraid of ghosts his whole life, even fearing the comedy film Ghostbusters, but intended to channel that fear into something positive and productive. Peli took a year to prepare his own house for shooting, going so far as to repaint the walls, add furniture, put in a carpet, and build a stairwell. In this time, he also did extensive research into paranormal phenomena and demonology, stating, "We wanted to be as truthful as we could be." The reason for making the supernatural entity in the story a demon was a result of the research pointing to the most malevolent and violent entities being "demons". The phenomena in the film take place largely at night—the vulnerability of being asleep, Peli reasoned, taps into a human being's most primal fear, stating, "If something is lurking in your home there's not much you can do about it." Attempting to focus on believability rather than action and gore, Peli chose to shoot the picture with a home video camera. In deciding on a more raw and stationary format (the camera was almost always sitting on a tripod or something else) and eliminating the need for a camera crew, a "higher degree of plausibility" was created for the audience as they were "more invested in the story and the characters". Peli says that the dialogue was "natural" because there was no real script. Instead, the actors were given outlines of the story and situations to improvise, a technique known as "retroscripting" used in the making of The Blair Witch Project. In casting the movie, Peli auditioned "a few hundred people" before finally meeting Katie Featherston and Micah Sloat. He originally auditioned them individually and later called them back to audition together. Peli was impressed with the chemistry between the actors, saying, "If you saw the footage, you would've thought they had known each other for years." During a guest appearance on The Jay Leno Show on November 3, 2009, Sloat and Featherston explained they each saw the casting call on LACasting. Featherston noted they were originally paid $500 for their work. The film was shot out of sequence due to Peli's self-imposed seven-day shooting schedule, though Peli would have preferred the story unfold for the actors as he had envisioned it. Sloat, who controlled the camera for a good deal of the film, was a former cameraman at his university's TV station. "It was a very intense week", Peli recalled, stating that the film would be shot day and night, edited at the same time, and would have the visual effects applied to it as the acting footage was being finalized.
Paramount and DreamWorks hired screenwriter Michael R. Perry to create Paranormal Activity 2. Oren Peli, the director of the first film, served as a producer for this prequel. Kevin Greutert, director of Saw VI, was initially hired to direct the prequel; however, Lions Gate Entertainment exercised a clause in Greutert's contract to have him direct the final film in the Saw film series. Both of the actors from the first film, Katie Featherston and Micah Sloat, reprise their roles in the prequel. Tod "Kip" Williams directed Paranormal Activity 2, which started production in May 2010 and was released in October the same year.
Paranormal Activity 3 and 4 were directed by Henry Joost and Ariel Schulman, documentary filmmakers who were well known for their feature debut Catfish. Production on the third entry began in June, 2011, with a release October 21 of the same year. Filming for the fourth film commenced in June, 2012, with a release of October 19.
A Latin American-themed fifth film, Paranormal Activity: The Marked Ones was released on January 3, 2014. Oren Peli, the creator of the franchise, returned to produce the film, while Christopher B. Landon, a screenwriter who had worked on the prior three entries in the series served as the writer and director.
The sixth and final film in the series, Paranormal Activity: The Ghost Dimension,[1] was announced to be released on October 25, 2013.[2] However, in August 2013, the release date was pushed back to October 24, 2014.[3] On September 17, 2014, the film's title was finalized and the release date was set on March 27, 2015,[4] later changed to October 23, 2015.[1] In September 2013, it was confirmed that Gregory Plotkin, a film editor who has edited every release in the series since Paranormal Activity 2, will make his directorial debut with the fifth film.[5][6] Oren Peli, the creator of the franchise and Jason Blum will return to produce the fifth film. In late September 2013, Paramount hired Almanac writers Jason Pagan and Andrew Stark to write the screenplay.[7] Though series writer Christopher B. Landon told that several sequels would follow The Ghost Dimension to wrap up the story,[8] producer Jason Blum later confirmed that the film will indeed be the last in the series.[9] He said:
"It’s coming to an end. This is it, the finale. We’re saying it before the movie opens. We’re not going to grind this horror franchise into the ground. This will keep Paranormal Activity as part of this culture and this particular time in a really fantastic way… All the questions that everyone has asked from the past ‘Paranormal Activity’ films: What does Toby look like? What’s the backstory to the families? These questions have been teased out. Now they will be answered."
Reception[edit]
Box office performance[edit]
Film
Release date
Box office gross
Box office ranking
Budget
Ref(s)
North America
Other territories
Worldwide
All time
North America
All time
worldwide
Paranormal Activity October 14, 2007 $107,918,810 $85,436,990 $193,355,800 #486 $15,000 [10]
Paranormal Activity 2 October 22, 2010 $84,752,907 $92,759,125 $177,512,032 #687 $3 million [11]
Paranormal Activity 3 October 21, 2011 $104,028,807 $103,011,037 $207,039,844 #514 #528 $5 million [12]
Paranormal Activity 4 October 19, 2012 $53,900,335 $88,917,657 $142,817,992 #1,253 $5 million [13]
Paranormal Activity: The Marked Ones January 3, 2014 $32,462,372 $58,442,482 $90,904,854 #2,142 $5 million [14]
Paranormal Activity: The Ghost Dimension October 23, 2015 $18,300,124 $59,799,429 $78,099,553 #3,288 $10 million [15]
Total
$401,384,320
$488,366,720
$889,730,075
$28,015,000
List indicator(s)
A dark grey cell indicates the information is not available for the film.
Critical and public response[edit]
Film
Rotten Tomatoes
Metacritic
CinemaScore
Paranormal Activity 83% (192 reviews)[16] 68 (24 reviews)[17] N/A
Paranormal Activity 2 58% (131 reviews)[18] 53 (23 reviews)[19] B[20]
Paranormal Activity 3 69% (118 reviews)[21] 59 (25 reviews)[22] C+[20]
Paranormal Activity 4 24% (103 reviews)[23] 40 (22 reviews)[24] C[20]
Paranormal Activity: The Marked Ones 37% (78 reviews)[25] 42 (19 reviews)[26] C-[20]
Paranormal Activity: The Ghost Dimension 14% (66 reviews)[27] 30 (13 reviews)[28] C[20]
Video game[edit]
A video game called Paranormal Activity: The Lost Soul was released on August 15, 2017 on PC, PS4, and Xbox One. The game was engineered for use VR and made use of the PlayStation VR for the PlayStation as well as Oculus Rift and HTC Vive for PC, but VR was not required for play.[29]
References[edit]
^ Jump up to: a b Ge, Linda (January 27, 2015). "New 'Paranormal Activity,' 'Friday the 13th' Pushed Back; 'The Ring' Reboot Gets Release Date". TheWrap. Retrieved January 27, 2015.
Jump up ^ Kilday, Gregg (November 20, 2012). "Paramount Sets Release Date for 'Paranormal Activity 5'". The Hollywood Reporter.
Jump up ^ "Paramount Sets Dates for 'Paranormal Activity 5,' Retitled Latino Spin-Off". TheWrap. August 8, 2013. Retrieved August 9, 2013.
Jump up ^ Lang, Brent (September 17, 2014). "'Paranormal Activity: The Ghost Dimension' Moved to 2015". Variety. Retrieved September 17, 2014.
Jump up ^ Chavez, Kellvin (September 27, 2013). "Gregory Plotkin to Direct 'Paranormal Activity 5'". Latino Review.
Jump up ^ Fleming Jr., Mike (September 26, 2013). "Gregory Plotkin Scares up Directing Debut on 'Paranormal 5.'". Retrieved September 26, 2013.
Jump up ^ Kit, Borys (September 25, 2013). "'Paranormal Activity 5' Snags 'Almanac' Writers (Exclusive)". Retrieved September 25, 2013.
Jump up ^ Lussier, Germain (January 6, 2014). "Exclusive: 'Paranormal Activity' Creators Have Planned an Ultimate Ending for the Series". /Film. Retrieved May 17, 2014.
Jump up ^ "Paranormal Activity: The Ghost Dimension Ends the Series". Slashfilm.
Jump up ^ "Paranormal Activity (2007)". Box Office Mojo. More than one of |website= and |work= specified (help)
Jump up ^ "Paranormal Activity 2 (2010)". Box Office Mojo. More than one of |website= and |work= specified (help)
Jump up ^ "Paranormal Activity 3 (2011)". Box Office Mojo. More than one of |website= and |work= specified (help)
Jump up ^ "Paranormal Activity 4 (2012)". Box Office Mojo. More than one of |website= and |work= specified (help)
Jump up ^ "Paranormal Activity: The Marked Ones". Box Office Mojo. More than one of |website= and |work= specified (help)
Jump up ^ "Paranormal Activity: The Ghost Dimension". Box Office Mojo. More than one of |website= and |work= specified (help)
Jump up ^ "Paranormal Activity". Rotten Tomatoes. Flixster. Retrieved 2012-06-20.
Jump up ^ "Paranormal Activity Reviews, Ratings, and Credit". Metacritic. CBS Interactive. Retrieved 2012-10-22.
Jump up ^ "Paranormal Activity 2". Rotten Tomatoes. Flixster. Retrieved 2012-06-20.
Jump up ^ "Paranormal Activity 2 Reviews, Ratings, and Credit". Metacritic. CBS Interactive. Retrieved 2012-10-22.
^ Jump up to: a b c d e "CinemaScore". cinemascore.com. Retrieved March 8, 2015.
Jump up ^ "Paranormal Activity 3". Rotten Tomatoes. Flixster. Retrieved 2012-06-20.
Jump up ^ "Paranormal Activity 3 Reviews, Ratings, and Credit". Metacritic. CBS Interactive. Retrieved 2012-10-22.
Jump up ^ "Paranormal Activity 4". Rotten Tomatoes. Flixster. Retrieved 2012-11-26.
Jump up ^ "Paranormal Activity 4 Reviews, Ratings, and Credit". Metacritic. CBS Interactive. Retrieved 2012-10-22.
Jump up ^ "Paranormal Activity: The Marked Ones". Rotten Tomatoes. Flixster. Retrieved 2014-01-03.
Jump up ^ "Paranormal Activity: The Marked Ones Reviews, Ratings, and Credit". Metacritic. CBS Interactive. Retrieved 2014-01-03.
Jump up ^ "Paranormal Activity: The Ghost Dimension". Rotten Tomatoes. Flixster. Retrieved 2015-10-24.
Jump up ^ "Paranormal Activity: The Ghost Dimension Reviews, Ratings, and Credit". Metacritic. CBS Interactive. Retrieved 2015-10-24.
Jump up ^ "'Paranormal Activity' VR Game Coming in 2016 -". bloody-disgusting.com.
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