The citric acid cycle (Kreb Cycle) Flashcards by Alshayma Althani

Citric Acid Cycle is a series of eight reactions that oxidize ——- to ———

acetyl-CoA to 2CO2 molecules

How well did you know this?

Not at all

Perfectly

One cycle of Kreb cycle reactions lead to ? NADH, ? FADH2 and ? GTP

3 NADH, 1 FADH2 and 1 GTP

How well did you know this?

Not at all

Perfectly

Glycolysis takes place in the ———

cytoplasm

How well did you know this?

Not at all

Perfectly

TCA cycle takes place in the ————

Mitochondria

How well did you know this?

Not at all

Perfectly

The —– and —– generated during theKrebs cyclefuels the——————– which drives this process, ultimately producing?molecules of ATP

NADH and FADH
electron transportchain
38

How well did you know this?

Not at all

Perfectly

ATP produced in Glycolysis

2 ATP (from substrate-level phosphorylation)
6 ATP from 2NADH (from oxidative phosphorylation)

NET THEORETICAL MAXIMUM OF ATP = 8

How well did you know this?

Not at all

Perfectly

ATP produced in transition state

6 ATP from 2NADH (from oxidative phosphorylation)

NET THEORETICAL MAXIMUM OF ATP = 6

How well did you know this?

Not at all

Perfectly

ATP produced in krebs cycle

2 ATP (from substrate-level phosphorylation)
18 ATP from 6NADH, 4 ATP from 2FADH2 (from oxidative phosphorylation)

NET THEORETICAL MAXIMUM OF ATP = 24

How well did you know this?

Not at all

Perfectly

O2 consumption, ATP production and NADH re-oxidation are tightly regulated via:

Substrate availability
Product inhibition
Feedback inhibition

How well did you know this?

Not at all

Perfectly

Covalent modification by phosphorylation inhibit ——————- .

Pyruvate Dehydrogenase

How well did you know this?

Not at all

Perfectly

Name of enzymes that catalyzes each step in the citric acid cycle

Citrate Synthase
1- Citrate
Aconitase
2- Iso-Citrate
Iso-Citrate Dehydrogenase
3- α-Ketoglutarate
α-Ketoglutarate Dehydrogenase
4- Succinyl-CoA
Succinyl-CoA Synthase
5- Succinate
Succinic Dehydrogenase
6- Fumarate
Fumarase
7- Malate
Malate Dehydrogenase
8- Oxaloacetate

How well did you know this?

Not at all

Perfectly

The overall goal of the citric acid cycle is to oxidize
pyruvate, form reduced coenzymes and produce ATP.
a. True
b. False

a. True

How well did you know this?

Not at all

Perfectly

The citric acid cycle is an anaerobic pathway that
occurs in the mitochondria of eukaryotes.
a. True
b. False

b. False (aerobic)

How well did you know this?

Not at all

Perfectly

The mechanism of pyruvate dehydrogenase complex is
an example of channeling.
a. True
b. False

a. True

How well did you know this?

Not at all

Perfectly

ATP is consumed by the pyruvate dehydrogenase
complex during the synthesis of acetyl CoA.
a. True
b. False

b. False
produced

How well did you know this?

Not at all

Perfectly

The carbon atoms that enter the citric acid cycle via
acetyl CoA are the same ones released as carbon
dioxide during one round of the citric acid cycle.
a. True
b. False

b. False

The citric acid cycle can be viewed as a multi-step
catalyst simply because it returns to its original state
after each round of reactions.
a. True
b. False

a. True

The only reaction in the citric acid cycle to generate a
carbon-carbon bond is catalyzed by citrate synthase.
a. True
b. False

a. True

Isocitrate is more easily oxidized than citrate because
it has a secondary alcohol group, whereas citrate’s
alcohol group is tertiary.
a. True
b. False

a. True

The citric acid cycle oxidizes pyruvate and some of
the pathway intermediates are starting materials for
many biosynthetic pathways. This means the citric
acid cycle is a/an ______________.
a. amplifying pathway
b. strictly catabolic pathway
c. anaerobic pathway
d. amphibolic pathway

d. amphibolic pathway

An amphibolic pathway is a biochemical pathway that includes both anabolic and catabolic processes

In eukaryotes the enzymes of the citric acid cycle are
found in the _________.
a. cytosol
b. mitochondria
c. nucleus
d. endoplasmic reticulum

b. mitochondria

Which is not a component of the pyruvate
dehydrogenase complex?
catalyzed by pyruvate dehydrogenase.
a. dihydrolipoamide dehydrogenase
b. isocitrate dehydrogenase
c. pyruvate dehydrogenase
d. dihydrolipoamide acetyltransferase

b. isocitrate dehydrogenase

Which cofactor is not used by the pyruvate
dehydrogenase complex?
a. lipoamide
b. thiamine pyrophosphate
c. FAD
d. QH2

d. QH2

Which step in the citric acid cycle is a rearrangement
reaction?
a. succinyl CoA to succinate
b. fumarate to L-malate
c. citrate to isocitrate
d. glucose 1,6-bisphosphate to fructose 1,6-
bisphosphate

c. citrate to isocitrate

Which is not produced by the citric acid cycle? a. NADH b. FMN c. CO2 d. FADH2

b. FMN

Which enzyme does not catalyze a reaction that releases carbon dioxide? a. ‡-ketoglutarate dehydrogenase complex b. pyruvate dehydrogenase c. malate dehydrogenase d. isocitrate dehydrogenase

c. malate dehydrogenase

After passing through the citric acid cycle, one mole of pyruvate will result in the formation of ______ moles of carbon dioxide and _________ mole(s) of GTP. a. 2; 2 b. 2; 1 c. 3; 2 d. 3; 1

d. 3; 1

The step at which acetyl CoA enters the citric acid cycle is classified as a ___________ reaction. a. condensation b. substrate-level phosphorylation c. decarboxylation d. dehydrogenation

a. condensation

Which enzyme catalyzes the conversion of citrate to isocitrate? Write the chemical reaction catalyzed by this enzyme. a. aldolase b. citrate synthase c. citrate isomerase d. aconitase

d. aconitase

Which 5-carbon intermediate of the citric acid cycle is converted to a 4-carbon molecule with the release of carbon dioxide? a. fumarase b. Alpha-ketoglutarate c. succinate d. isocitrate

b. Alpha-ketoglutarate

The succinate dehydrogenase complex catalyzes. a. The formation of a single hydrogen bond in the oxidation of succinate to fumarate b. The formation of a double bond in the oxidation of succinate to fumarate c. Both a and b d. None of the above

b. The formation of a double bond in the oxidation of succinate to fumarate

Malonate a. Is a structural analogy of succinate b. Binds to the substrate binding site of the succinate dehydrogenase complex but does not react c. Undergoes an oxidation reaction d. Both a and b e. All of the above

d. Both a and b

NAD-dependent malate dehydrogenase a. Catalyzes the oxidation of malate to regenerate oxaloacetate b. Catalyzes the conversion of fumarase to malate c. Catalyzes a reaction which results in the formation of an NADH molecule d. All of the above e. a and c only

e. a and c only

Which of the following inhibit(s) pyruvate dehydrogenase kinase? a. Pyruvate b. NADH c. Acetyl-CoA d. All of the above

a. Pyruvate

Elevated calcium levels lead to a. Phosphorylation of the E1 subunit and an increase in flux through the pyruvate dehydrogenase complex. b. Dephosphorylation of the E1 subunit and a decrease in flux through the pyruvate dehydrogenase complex. c. Neither of the above

b. Dephosphorylation of the E1 subunit and a decrease in flux through the pyruvate dehydrogenase complex.

Each of the following catalyzed reactions of the citric acid cycle appears to be metabolically irreversible except: a. Citrate synthase b. Fumarase c. Isocitrate dehydrogenase d. Alpha ketoglutarate dehydrogenase complex

b. Fumarase

Which of the following allosterically activates mammalian isocitrate dehydrogenase? a. ADP b. NADH c. Calcium d. All of the above e. a and c only

e. a and c only

Each of the following leads to a biosynthetic pathway except: a. Alpha-ketoglutarate b. Succinyl CoA c. Oxaloacetate d. Citrate e. None of the above

e. None of the above

Which of the following is not a fate of a citric acid cycle intermediate? a. Alpha-ketoglutarate reversibly converting to glutamate b. The biosynthesis of porphyrins from succinyl CoA's interaction with glycine c. Oxaloacetate as a carbohydrate precursor d. None of the above

d. None of the above