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Biochemistry > The citric acid cycle (Kreb Cycle) > Flashcards

The citric acid cycle (Kreb Cycle) Flashcards

1
Q

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

A

acetyl-CoA to 2CO2 molecules

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2
Q

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

A

3 NADH, 1 FADH2 and 1 GTP

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3
Q

Glycolysis takes place in the ———

A

cytoplasm

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4
Q

TCA cycle takes place in the ————

A

Mitochondria

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5
Q

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

A

NADH and FADH
electron transportchain
38

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6
Q

ATP produced in Glycolysis

A

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

NET THEORETICAL MAXIMUM OF ATP = 8

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7
Q

ATP produced in transition state

A

6 ATP from 2NADH (from oxidative phosphorylation)

NET THEORETICAL MAXIMUM OF ATP = 6

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8
Q

ATP produced in krebs cycle

A

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

NET THEORETICAL MAXIMUM OF ATP = 24

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9
Q

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

A

Substrate availability
Product inhibition
Feedback inhibition

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10
Q

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

A

Pyruvate Dehydrogenase

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11
Q

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

A

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

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12
Q

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

A

a. True

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13
Q

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

A

b. False (aerobic)

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14
Q

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

A

a. True

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15
Q

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

A

b. False
produced

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16
Q

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

A

b. False

17
Q

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

a. True

18
Q

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

A

a. True

19
Q

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

a. True

20
Q

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

A

d. amphibolic pathway

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

21
Q

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

A

b. mitochondria

22
Q

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

A

b. isocitrate dehydrogenase

23
Q

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

A

d. QH2

24
Q

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

A

c. citrate to isocitrate

25
Q

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

A

b. FMN

26
Q

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

A

c. malate dehydrogenase

27
Q

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

A

d. 3; 1

28
Q

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

a. condensation

29
Q

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

A

d. aconitase

30
Q

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

A

b. Alpha-ketoglutarate

31
Q

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

A

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

32
Q

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

A

d. Both a and b

33
Q

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

A

e. a and c only

34
Q

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

A

a. Pyruvate

35
Q

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

A

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

36
Q

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

A

b. Fumarase

37
Q

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

A

e. a and c only

38
Q

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

A

e. None of the above

39
Q

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

A

d. None of the above

Biochemistry (10 decks)

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