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Citric acid cycle Flashcards

1
Q

what is the primary function of TCA cycle?

A

the oxidation of acetylCoA to CO2

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2
Q

the citric acid cycle is also called…….

A

Krebs cycle

Tricarboxylic Acid Cycle

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3
Q

does TCA cycle requires oxygen?

A

yes, its an aerobic reaction..

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4
Q

the energy released from this reaction is saved as what?

A

NADH, FADH2, and GTP

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5
Q

true or false?

the TCA cycle accounts for more than two-third of the ATP generated from fuel oxidation!

A

true..

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6
Q

why is the TCA called amphibolic

A

cuz it plays both catabolic and anabolic pathways
for the catabolic reaction, acetylCoA is oxidized to CO2, H2O giving out energy
for the anabolic reactions, Intermediates of TCA cycle plays a role in synthesis like heme formation, FA synthesis, Cholesterol, Steroid synthesis.

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7
Q

the cellular respiration is a process in which the cell consume …………….. and produce ……………….. as a waste product.

A

O2, CO2

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8
Q

TRUE OR FALSE

the glycolysis provides more energy (ATP) from glucose than cellular respiration.

A

false

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9
Q

the cellular respiration occurs in three major stages, what are they?

A
  1. AcetylCoA production
  2. AcetylCoA oxidation
  3. Electron transfer and oxidative phosphorylation
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10
Q

in respiration stage 1:

Acetyl-CoA production happens, what is generated?

A

generates some ATP, NADH, FADH2

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11
Q

in respiration stage 2:

acetyl CoA oxidation happens, what is generated?

A

Generates more NADH, FADH2, and one GTP

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12
Q

in respiration stage 3:

oxidative phosphorylation happens, what is generated?

A

generates a lots of ATP

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13
Q

what is the catalyst or enzyme that is used when pyruvate is oxidized to Acetyl CoA?

A

pyruvate dehydrogenase complex (PDH)

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14
Q

the PDH is activated by what in the liver? and what in the brain and nerves?

A

in the liver by the insulin, and in the brain the nerves the enzyme is not responsive to hormones

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15
Q

as we know, Coenzymes are not a permanent part of the enzymes’ structure. They associate, fulfill a function, and dissociate, so what is the function of the CoA?

A

to accept and carry acetyl groups

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16
Q

what are the 5 coenzymes that catalyze the pyruvate to acetyl CoA?

A 
Thiamine Pyrophosphate (TPP),lipoic acid, and FAD are prosthetic groups
NAD+ and CoA-SH are co- enzymes
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17
Q

pyruvate dehydrogenase complex is a multi-enzyme complex, what are the advantages of it?

A

‒short distance between catalytic sites allows channeling of substrates from one catalytic site to another
‒channeling minimizes side reactions
‒ regulation of activity of one subunit affects the entire complex

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18
Q

true or false..

formation of acetyl CoA (product 1) happens in step 2 by enzyme 2.

A

false, it happens in step 3 in enzyme 2

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19
Q

true or false

the regeneration of the oxidized FAD cofactor forming NADH happens in step 5 in enzyme 3

A

true

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20
Q

what inhibits pyruvate dehydrogenase?

A

its inhibited by its products acetyl coa and NADH

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21
Q

what does pyruvate dehydrogenase kinase does?

A

Pyruvate dehydrogenase kinase (PDH Kinase) phosphorylates PDH and converts it to inactive form. Anything regulates kinase activity directly affect PDH activity.
the kinase is activated by ATP acetyl coa and NADH, the presence of these the PDH is inhibited

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22
Q

during starvation, which enzyme increase? pyruvate dehydrogenase kinase or phosphatase?

A

pyruvate dehydrogenase kinase increase, because it needs to minimize the glyconeogenesis and the energy have to be saved instead of being wasted..

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23
Q

during starvation, the result is the inhibition of pyruvate dehydrogenase, why its inhibited?

A

The resulting inhibition of Pyruvate Dehydrogenase prevents muscle and other tissues from catabolizing glucose & gluconeogenesis precursors.

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24
Q

in the muscle, what stimulates the phosphatase and activates pyruvate dehydrogenase?

A

calcium

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25
Q

what are the diseases involved in pyruvate dehydrogenase complex deficiency?

A

beri beri diseases: deficiency in the thiamine or niacin, no enough ATP is produced throught the TCA cycle if the PDH is inactive

lactic acidosis: deficiency in the E1 results in inability to convert pyruvate to acetyl CoA.

Leigh syndrome: gene mutation in the PDH that causes less mitochondrial production of ATP

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26
Q

where does the TCA cycle takes place ?

A

in the mitochondria matrix

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27
Q

in the citric acid cycle, step 1 is ?

A

Step 1: C-C bond formation to make citrate

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28
Q

in citric acid cycle, step 2 is ?

A

Step 2: Isomerization via dehydration/rehydration

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29
Q

in citric acid cycle, step 3-4 is ?

A

Steps 3–4: Oxidative decarboxylations to give 2 NADH

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30
Q

in the citric acid cycle, in step 5?

A

Step 5: Substrate-level phosphorylation to give GTP

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31
Q

in the citric acid cycle, in step 6?

A

Step 6: Dehydrogenation to give reduced FADH2

32
Q

in citric acid cycle, in step 7?

A

Step 7: Hydration

33
Q

in the citric acid cycle, in step 8?

A

Step 8: Dehydrogenation to give NADH

34
Q

what is the enzyme used in step 1 in the citric acid cycle? and what is special about this reaction?

A

citrate synthase

the only reaction with C-C bond

35
Q

what is the enzyme used in the second step?

36
Q

what is the enzyme used in the 3rd step?

A

isocitrate dehydrogenase

37
Q

what enzyme is used in the 4th step ?

A

alpha ketoglutarate dehydrogenase

38
Q

in the 5th step, the succinylcholine CoA is produced, what is special about this reaction?

A
  • Last oxidative decarboxylation. Carbons not directly from glucose because carbons lost came from oxaloacetate
  • Succinyl-CoA is another higher-energy thioester bond
  • Highly thermodynamically favorable/irreversible. Regulated by product inhibition
39
Q

the enzyme alpha ketoglutarate dehydrogenase is similar to another enzyme, what is this enzyme?

A

pyruvate dehydrogenase

40
Q

in step 5, the succinate synthesis happens, which enzyme is used in this reaction?

A

succinylcholine CoA synthetase

41
Q

in step 6, the fumarate is generated, what is the enzyme that runs this reaction?

A

succinate dehydrogenase

in this reaction, FADH2 is generated

42
Q

in step 7, malate is formed, what is the enzyme that runs this reaction?

43
Q

in step 8, oxaloacetate is generated, what is the enzyme used?

A

malate dehydrogenase

44
Q

what is the net result of the citric acid cycle?

A

2CO2 + 3NADH + FADH2 + GTP

45
Q

what is the TOTAL energy produced by the citric acid cycle?

46
Q

what are the enzymes that help in the regulation f the TCA cycle?

A

Those catalyze the reaction with highly negative △G°: citrate synthase (1st step), isocitratedhydrogenase (3rd step) α–ketoglutatrate dehydrogenase complex (4th step).

47
Q

what are the irrevesible steps of the TCA cycle ?

A

1st, 3rd and 4th steps are IRREVERSIBLE

High product concentration inhibits the cycle

48
Q

TCA cycle is used in many pathways, state them..

A
  1. amino acid synthesis
  2. fatty acid synthesis
  3. heme synthesis
  4. glyconeogenesis
  5. Neurotransmitter (brain)
49
Q 
Which of the following coenzymes is unique to α– ketoglutatrate dehydrogenase complex ?
A. NAD+ 
B. FAD 
C. GDP 
D. H2O
E. Lipoic Acid
A

e. lipoic acid

50
Q 
Coenyzme A is synthesized from which of the following vitamins?
A. Niacin
B. Riboflavin 
C. Vitamin A
E. VitaminC
D. Pantothenate
A

d. pantothenate

51
Q 
A patient diagnosed wşth the thiamine deficiency exhibited fatigue and muscle cramps. The muscle crampsi have been related tı an accumulation of metabolic acids. Which of the following metabolic acids is most likely yo accumulate in a thiamine defiency?
A. Isocitric acid
• B.Pyruvic acid
• C. Succinic acid
• D. Malic acid
• E. Oxaloacetic acid
52
Q 
How many NADH molecules are generated from the complete oxidation of one Glucose?
A. 5 
B. 7
D. 16
 E. 32
  C. 10
53
Q

In what form is the energy released from TCA cycle oxidation?

A

NADH
FADH2
GTP (guanosine triphosphate)

54
Q

TCA Cycle accounts for more than one-third of the adenosine

triphosphate (ATP) generated from fuel oxidation.

A

False

its two-third

55
Q

TCA has both catabolic and anabolic roles.

56
Q

Which of the following is not true?
A. Cellular respiration provides more energy (ATP) from glucose than
glycolysis
B. Only a small amount of energy available in glucose is captured in glycolysis
C. glycolysis captures energy stored in lipids and amino
acids
D. Cellular respiration is used by animals, plants, and many microorganisms

A

C
Cellular respiration captures energy stored in lipids and amino
acids

57
Q

What are the three basic steps of cellular respiration?

A
  1. Acetyl CoA production
  2. Acetyl CoA oxidation
  3. Electron transfer and oxidative phosphorylation
58
Q 
Acetyl CoA can be from all except
A. Fatty acid 
B. Ketone bodies
C. Amino acids
D. Acetate
E. Lactate
A

E. Lactate

59
Q

What is the enzyme that catalyzes the oxidative decarboxylation of pyruvate to form acetyl-CoA?

A

Pyruvate Dehydrogenase Complex (PDH)

60
Q

Which of the following is true about PDH?
A. PDH complex is part of TCA cycle
B. its is one of the enzymes in glycolysis
C. In the liver, it is activated by insulin, whereas in the brain and nerves, its not responsive to hormones
D. All

A

C
PDH complex is not part of the TCA
cycle but it supplies substrate for
the cycle.

61
Q

Which of the following is true about acetyl-CoA
A. Coenzymes are not a permanent part of the enzymes’ structure
B. The function of CoA is to accept and carry acetyl groups
C. CoA contains thiol group, pantothenic acid, and ribose 3 phosphate
D. All

62
Q 
Which of the following is not among the coenzymes required for conversion of pyruvate to Acetyl-CoA?
A. Thiamine Pyrophosphate (TPP)
B. lipoic acid 
C. Palmitate 
D.FAD
E.NAD+ 
F. CoA-SH
A 
C
Thiamine Pyrophosphate (TPP),lipoic acid, and FAD are prosthetic groups while NAD+ and CoA-SH are coenzyme
63
Q

Which of the following is not advantage of multienzyme complexes?
A. channeling minimizes side reactions
B. regulation of activity of one subunit affects the entire complex
C. short distance between catalytic sites allows channeling of substrates from one catalytic site to another
D. None

64
Q

Which of the following is true?
A. Enzyme 1 catalyze the first and second step
B. Enzyme 2 work in re oxidation of lipoamide cofactor
C. Enzyme 3 works in regenerating oxidized FAD cofactor forming NADH
D. Oxidation of aldehyde to carboxylic acid is performed by Enzyme 2
E.A and B
F.A and c

A

F
Enzyme 1 Step 1: Decarboxylation of pyruvate to an aldehyde
Step 2: Oxidation of aldehyde to a carboxylic acid
Enzyme 2 Step 3: Formation of acetyl-CoA (product 1)
Enzyme 3 Step 4: Re oxidation of the lipoamide cofactor
Step 5: Regeneration of the oxidized FAD cofactor
Forming NADH (product 2)

65
Q 
Which of the following match is true?
A.Pyruvate Dhydrogenase -E1
B.Dihydrolipoyl Dehydrogenase -E2
C.Dihydrolipoyl Trasnacetlylase E3
D.All
A

A

B and C are reversed.

66
Q

Which of the following is false
A.NADH competes with NAD+ for binding to E3
B.Acetyl CoA competes with CoA for binding to E2
C.PDH is inhibited by Acetyl CoA and NADH
D.Kinase is inhibited by ATP, Acetyl CoA, and NADH
E.None

A

D

Kinase is activated by ATP, Acetyl CoA and NADH. In the presence of these, PDH complex is turned off.

67
Q

Pyruvate dehydrogenase kinase (PDH Kinase) phosphorylates PDH and converts it to inactive form.
True/ False

68
Q

Which of the following is true about what happens during starvation?
I.PDH kinase increases while PDH phosphate decrease
II.Metabolism shift toward fat utilization
III.Gluconeogenesis is maximized
IV.Glucose is spared for use by the brain and RBC
A.I, II, III
B.I, III, IV
C.II, III, IV
D.I, II, IV

A

D

Gluconeogenesis is minimized.

69
Q

The increased cytosolic Ca 2+ stimulates the phosphatase, & dephosphorylation activates ……………

A
  • Pyruvate Dehydrogenase.
70
Q 
Which of the following is not one of Pyruvate Dehydrogenase Complex Deficiency?
A.Beri Beri Disease
B.Hemolytic anemia
C.Lactic Acidosis
D.Leigh syndrome
A

B

its glycolytic disorder

71
Q

Which of the following is not true?
A.a-ketoglutarate synthesis and oxaloacetate synthesis generates NADH
B.Synthesis of Succinyl CoA is irreversible
C.a-ketoglutarate dehydrogenase and pyruvate have similar complexes.
D.Succinate synthesis produces GTP and is a substrate-level phosphorylation
E.Fumarate synthesis produce FADH2
F.None

72
Q

What is the net product of the citric acid cycle?

A 
2 CO2
3 NADH
1 FADH2
1GTP
1 CoA
3 H+
73
Q

1 NADH=…….ATP

1 FADH2=……ATP

74
Q 
Which enzymes catalyze the reaction with high negative delta G (irreversible)?
A.citrate synthase ( 1st step)
B.Fumerase ( 7th step)
C.isocitratedhydrogenase (3rd step)
D.dehydrogenase complex (4th step)
E.All except B
F.All except D
75
Q 
Which of the following is wrongly matched with its function?
A.A-ketoglutarate - Aminoacid synthesis
B.Succinyl CoA- heme synthesis
C.Malate- fatty acid synthesis
D.Oxaloacetate- amino acid synthesis
A

C
Malate- gluconeogenesis
Citrate- fatty acid synthesis

76
Q

Which steps produce NADH?

A

Oxaloacetate synthesis (8th step)
a-ketoglutarate synthesis (3rd step)
Succinyl CoA synthesis (4th step)

Biochemistry 2 (7 decks)

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