TCA Cycle Flashcards
Does the citric acid cycle generate more ATP from glucose than glycolysis
Yes
The citric acid cycle requires ______ conditions
Aerobic
The citric acid cycle takes place in the
Mitochondria
Glycolysis takes place in the
Cytosol
The function of the citric acid cycle is
harvesting of high energy electrons from carbon fuels
what is the carbon source for citric acid cycle
acetyl CoA (via acetyl group)
Is the outer membrane of the mitochondria fairly smooth
yes
The inner mitochondrial membrane is highly convoluted, forming folds called
cristae
What is the function of cristae
it greatly increases the inner membrane’s surface area
what are the products of the citric acid cycle
- 2 CO2
- 1 GTP
- 3 NADH
- 1 FADH2
In the citric acid cycle a four carbon compound ______ condenses with a two-carbon _____ to yield a six-carbon tricarboxylic acid
- oxaloacetate
- acetyl unit
in the citric acid cycle CO2 is released by two successive
- oxidative decarboxylations
how many total electrons does citric acid cycle produce
8 electrons
Carboydrates—glucose— can be converted to pyruvate in
glycolysis
Pyruvate from glycolysis can be converted to
acetyle CoA
under anaerobic conditions pyruvate is converted to
lactate or ethanol
Aerobic conditions resulte in pyruvate entering the
mitochondria
Pyruvate dehydrogenase component abbreviation
E1
Dihydrolipoyl transacetylase abbreviation
E2
Dihydrolipoyl dehydrogenase abbreviation
E3
What is the prosthetic group of E1
TPP (Thiamine pyrophosphate)
What is the prosthetic group of E2
Lipoamide (Lipoic acid)
What is the prosthetic group of E3
FAD
E1 catalyzes
oxidative decarboxylation of pyruvate
E2 catalyzes
transfer of acetyl group to CoA
E3 catalyzes
Regeneration of the oxidized form of lipoamide
The dehydrogenase complex is composed of
E1 (pyruvate dehydrogenase component), E2 (Dihydrolipoyl transacetylase), E3 (Dihydrolipoyl dehydrogenase)
Acetyl CoA formation from pyruvate requires
3 enzymes and 5 coenzymes
- Catalytic cofactors (TPP, Lipoic acid, FAD)
Stoichiometric cofactors
- CoA, NAD+ (cofactors that function as substrates)
What are the 3 steps in the production of Acetyl CoA from pyruvate
- Decarboxylation
- Oxidation
- Transfer acetyl group to coenzyme A
What is the rate limiting step of Acetyl CoA synthesis
Decarboxylation
decarboxylation and oxidation of pyruvate in the formation of acetyl CoA are catalyzed by
E1 (pyruvate dehydrogenase component)
The transfer of acetyl group to Coenzyme A is catalyzed by
E2 (dihydrolipoyl transcetylase)
Acetyllipoamide has an energy rich
thioester bond
in the oxidation step of acetyl CoA synthesis the hydroxyethyl group attached to TPP is _____ to an acetyl group while being simultaneously transferred to
oxidized, lipoamide (a derivative of lipoic acid that is linked to the side chain of a lysine residue by an amide linkage)
What is preserved as the acetyl group is transferred form acetyllipoamide to CoA to form acetyl CoA
The energy-rich thioester bond
What is the function of E3
dihydrolipoyl dehydrogenase (E3) oxidizes dihydrolipoamide to lipoamide (two electrons are transferred to an FAD prothetic group of the enzyme and then to NAD+)
Why is the electron transfer potential of FAD in E3 increased
because it is tightly associated with the enzyme
Pyruvate dehydrogenase complex has how many copies of E1
24
Pyruvate dehydrogenase complex has how many copies of E2
24
Pyruvate dehydrogenase complex has how many copies of E3
12
Each E2 subunit is a ____ containing ____ distinct domains
trimer, 3
Flexible arm of ____ containing lipoid allows all domains of the complex to work together
E2
Aconitase catalyzes
Citrate —–> Isocitrate
Isocitrate dehydrogenase catalyzes
isocitrate + (NAD+) ——> Alpha-Ketoglutarate + NADH + (H+) + CO2
Alpha-ketoglutarate dehydrogenase complex catalyzes
alpha-ketoglutarate + (NAD+) + CoA ———> Succinyl CoA + NADH + (H+) + CO2
Succinyl CoA synthetase catalyzes
Succinyl CoA + GDP + Pi ——> Succinate + GTP + CoA
Succinate dehydrogenase catalyzes
Succinate + FAD —–> Fumarate + FADH2
Fumarase catalyzes
Fumarate + H2O —> Malate
Malate dehydrogenase catalyzes
Malate + (NAD+) —> OAA + NADH + H+
Citrate synthase catalyzes
OAA+ H2O + Acetly CoA —–> Citrate + CoA
what is the only step that directly yields a GTP in the TCA cylce
Succinyl CoA ——> Succinate
catalyzed by Succinyl CoA synthetase
inhibitors of PHD E2
NADH
ACetyl CoA
ATP
Induces PDH E2
Pyruvate, ADP
Succinyl CoA contains a ______ bond
high energy thioester bond (similar to ATP)
Succinate dehydrogenase is located
in the inner mitochondrial membrane and directly associated with ETC and TCA
FADH2 is actually not released form succinate dehydrogenase but electrons are passed directly to ____ in ETC
Coenzyme Q
Malate has a positive fee energy and therfore the reaction malate—–> OAA is driven by the use of the
products:
- OAA-citrate synthase
- NADH- ETC
Phosphorylated PDH is the ___ form therefore ____ activates it and ____ deactivates it
inactive, kinase deactivates it
phosphatase activates it
Phosphatases (which activate PDH) are stimulated by ___ and ____ and
ADP, Calcium, and insulin
Isocitrate dehydrogenase regulation
- inhibited by: ATP and NADH
- Induced by: ADP
Alpha ketogluturate dehydrogenase regulation
-inhibited by ATP, Succinyl CoA, and NADH
Inhibition of Isocitrate dehydrogenase leads to a build up of _____ which can transport to the cytosol and inhibit
citrate ( easily converted from isocitrate)
can signal phosphofructokinase and inhibit glycolysis
a buildup of alpha-ketoglutarate can be used for
synthesis of amino acids and purine bases , glutamate
Citrate from the TCA can be used for biosynthesis of
Fatty acids, sterols
succinyl CoA from the TCA can be used for biosynthesis of
Porphyrins, heme, chlorophyll
OAA from the TCA can be used for biosynthesis of
Glucose, Aspartate, purines, pyrimidines,
_____ amino acids are a source for TCA intermediates
branched chain amino acids
amino acids converted to pyruvate
- alanine
- serine
- Glycine
- Threonine
- Cysteine
- Tryptophan
Amino acids converted to OAA
Aspartate
Asparagine
Amino acids converted to alpha-ketoglutarate
glutamate glutamine proline histidine arginine
Amino acids converted to fumarate
phenylalanine
tyrosine
Amino acids converted to succinyl-CoA
Methionine
isoleucine
Valine
Amino acids converted to acetyl CoA
Leucine Isoleucine lysine phenylalanine tyrosine tryptophan threonine