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Biochem Exam 2 > Chapter 9 - The Krebs Cycle > Flashcards

Chapter 9 - The Krebs Cycle Flashcards

1
Q

Which is slower - glycolysis or the krebs cycle?

A

the krebs cycle

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2
Q

Is every oxygen molecule that we breathe utilized in the citric acid cycle?

A

no - but a lot are

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3
Q

What are the 2 electron carriers in the citric acid cycle?

A

NADH and FADH2

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4
Q

What is the NET ATP gain of glycolysis?

A

2 ATP

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5
Q

What is the sole substrate of the krebs cycle?

A

acetyl-coA

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6
Q

What is the pathway product of the krebs cycle?

A

CO2

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7
Q

The overall operation of the krebs cycle _____ the 2 acetyl carbons of acetyl coA completely to _____

A

OXIDIZES to CO2

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8
Q

High energy electrons are captured in which 2 cofactors?

A

NADH and Q (ubiquinone)

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9
Q

Formation of acetylcoA from pyruvate requires an enzyme exclusively found where?

A

in the mitochondria

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10
Q

Where is pyruvate formed? (glycolysis)

A

in the cytosol

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11
Q

Cytosolic pyruvate must….

A

cross the outer mitochondrial membrane and the inner mitochondrial membrane

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12
Q

How does pyruvate cross the outer mitochondrial membrane?

A

through a porin

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13
Q

How does pyruvate cross the inner mitochondrial membrane?

A

inner membrane is impermeable to most molecules so pyruvate entry requires a transport protein - the PYRUVATE TRANSPORTER

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14
Q

Where does the pyruvate transporter transport pyruvate? What other molecule?

A

into the MATRIX along with a HYDROGEN ION

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15
Q

What happens in the matrix space?

A

oxidation takes place

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16
Q

What is the first step of this oxidation?

A

conversion of pyruvate to acetyl-CoA

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17
Q

What enzyme catalyzes the conversion of pyruvate to acetyl-CoA?

A

pyruvate dehydrogenase complex

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18
Q

What is an enzyme complex?

A

a group of enzymes that catalyzes a metabolic sequence WITHOUT RELEASING INTERMEDIATES

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19
Q

Write the overall reaction catalyzed by the pyruvate dehydrogenase complex

A

pyruvate + NAD+ +CoA —> Acetyl-CoA + NADH + CO2

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20
Q

The reaction catalyzed by the pyruvate dehydrogenase complex is ______

A

irreversible

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21
Q

The conversion of pyruvate to acetyl-CoA requires ____ enzymes and ____ cofactors

A

3 enzymes and 6 cofactors

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22
Q

What are the 3 mobile cofactors in the conversion of pyruvate to acetyl-CoA?

A

NAD+, NADH, CoA

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23
Q

What are the 3 bound cofactors in the conversion of pyruvate to acetyl-CoA?

A

thiamine pyrophosphate, lipoic acid, and FAD

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24
Q

Do the bound cofactors appear in the reaction?

A

NO - they act as an extension of the enzyme to which they’re attached

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25
Q

The 3 enzymes catalyzing the conversion of pyruvate to acetyl-CoA are represented as ___,____, and ____

A

E1, E2, E3

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26
Q

What 2 enzymes are involved in the REGULATION of the pyruvate dehydrogenase complex?

A

PDH kinase
PDH phosphatase

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27
Q

What molecule represents the “swinging arm” of the pyruvate dehydrogenase complex?

A

the lipoamide attached to E2

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28
Q

What does a kinase enzyme do?

A

Adds a phosphate to a molecule (usually deactivates it)

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29
Q

What is the opposite of a kinase enzyme?

A

Phosphatase - takes the phosphate off (usually activates molecule)

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30
Q

What is the bound cofactor of E1?

A

TPP -

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31
Q

What is the bound cofactor of E2?

A

Lipoamide

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32
Q

What is the bound cofactor of E3?

A

FAD

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33
Q

What mobile cofactor does PDH kinase react with?

A

ATP

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34
Q

Of the 3 - E1, E2, E3 - which reacts with a mobile cofactor?

A

E3 - reacts with NAD+

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35
Q

Which mobile cofactor diffuses away and transports its carried electrons elsewhere?

A

NADH

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36
Q

Describe the cycle that leads to NAD+ gaining 2 electrons and becoming NADH

A

E3 gives an electron pair to FAD to become FADH2. FADH2 transfers its 2 electrons to NAD+ to become NADH

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37
Q

LIPOIC ACID GETS ____ THEN _____

A

Reduced than oxidized

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38
Q

Which enzyme - E1, E2, or E3 - grabs an acetyl group and gives it to CoA to become acetyl CoA?

A

E2

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39
Q

E1 kicks out ____ from TPP

A

CO2

40
Q

The citric acid cycle consists of ____ reactions

A

8

41
Q

What does TCA stand for?

A

Tricarboxylic acid

42
Q

Citric acid can also be called _____ acid. Why?

A

Tricarboxylic acid because it contains 3 carboxyl groups

43
Q

Many intermediates in the citric acid cycle can be——-

A

Utilized by other pathways

44
Q

Isocitrate is a ___ of citrate

A

Isomer

45
Q

Acitonase is _____ an isomerase enzyme

A

NOT

46
Q

Where is PDH located in the cell?

A

In the mitochondrial matrix

47
Q

Which bound cofactor can move/swing among E1,E2, and E3?

A

Lipoamide

48
Q

Enzymes in the krebs cycle generate energy through—-

A

oxidation

49
Q

How many CO2 molecules are releases in the Krebs cycle? They are released as a result of ______

A

2 CO2 molecules. released as a result of oxidation

50
Q

What enzyme catalyzes the formation of Acetyl-CoA from pyruvate?

A

the pyruvate dehydrogenase complex

51
Q

How is acetyl-coA formed?

A

Pyruvate from glycolysis gives up 2 of its carbons and reacts with CoEnzyme A to produce acetyl-CoA

52
Q

What are the byproducts of the formation of Acetyl CoA from pyruvate?

A

NADH and CO2

53
Q

What class of enzymes is the pyruvate dehydrogenase complex?

A

oxidoreductase enzyme

54
Q

Acetyl-CoA is a ____ carbon molecule

A

2

55
Q

What is the first step of the krebs cycle? (include enzyme name, # of carbons, etc)

A

Acetyl-CoA has TWO CARBONS and reacts with the 4 CARBON MOLECULE OXALOACETATE to form the 6 CARBON MOLECULE - CITRATE

catalyzed by citrate synthase

56
Q

What are the byproducts of the reaction catalyzed by citrate synthase?

A

Coenzyme-A bonded to a sulfhydryl functional group (SH)

57
Q

What is the second reaction of the krebs cycle? (include names, enzyme, etc)

A

citrate (6 CARBONS) is converted into its isomer - isocitrate (Also 6 CARBONS)

58
Q

What is the 3rd reaction in the krebs cycle? (include names, enzyme, # carbons, etc)

A

Isocitrate is converted into alpha ketoglutarate. Catalyzed by isocitrate dehydrogenase (5 CARBONS)

59
Q

What are the byproducts of the 3rd reaction in the krebs cycle?

A

NAD+ IN,

NADH + H+ + CO2 OUT

60
Q

What else can you say about the 3rd reaction in the krebs cycle?

A

1st oxidation reduction reaction (produces energy)

61
Q

What can you say about the 4th reaction of the Krebs Cycle?

A

VERY SIMILAR to the 3rd

62
Q

State the names, enzymes, byproducts, and # of carbons in the 4th step of the krebs cycle

A

alpha ketoglutarate (5 CARBONS) is converted into succinyl CoA (4 CARBONS) . Catalyzed by alpha ketoglutarate dehydrogenase.

byproducts = NAD+ in, NADH, CO2 and H+ out

63
Q

Succinyl-CoA is a ——– meaning it can do what?

A

Succinyl-CoA is a HIGH ENERGY MOLECULE, meaning it can partake in substrate level phosphorylation to produce ATP

64
Q

Describe the 5th step of the krebs cycle including names, enzyme, # carbons, BYPRODUCTS, etc

A

succinyl-CoA is converted into succinate (both have 4 carbons)

Succinyl CoA is a high energy molecule and is used for substrate level phosphorylation to produce ATP

GDP + Pi in
GTP + CoA-SH out

Catalyzed by Succinyl CoA SYNTHETASE

65
Q

What is the difference between synthase and synthetase enzymes?

A

synthetase uses energy such as ATP, GTP, etc

66
Q

Succinate dehydrogenase removes a ___ from ____. The Hydrogen is then accepted by _____

A

Succinate dehydrogenase removes a HYDROGEN from SUCCINATE. The hydrogen is then accepted by FAD

67
Q

What is the ONLY enzyme of the Krebs Cycle that is membrane bound?

A

Succinate dehydrogenase

68
Q

Describe the 6th reaction in the Krebs Cycle. Give all details

A

Succinate is converted to Fumurate by Succinate Dehydrogenase. Both are 4 carbons. Q is reduced to QH2

69
Q

What does Q stand for?

A

Ubiquinone

70
Q

Describe the 7th reaction in the krebs cycle. give all details

A

fumurate is converted into malate through a hydration reaction to saturate the double bond (addition of water)
catalyzed by fumarase

71
Q

Describe the 8th reaction in the krebs cycle. give all details

A

malate is oxidized into oxaloacetate (both 4 carbons). catalyzed by malate dehydrogenase. NAD+ Reduced to NADH + H+

72
Q

Throughout the Krebs Cycle when 4 C molecules keep getting converted into other 4C molecules, is energy lost or gained?

A

lost

73
Q

How many ATP are produced from oxidizing ONE molecule of Acetyl-CoA? Break it down.

A

12 ATP

3 NADH—->9ATP
1QH2——->2ATP
1GTP——–>1ATP
=12ATP

74
Q

The conversion of Glucose to pyruvate produces ____ total ATP when all is said and done. Break it down.

A

8 ATP

2ATP—> 2ATP
2NADH–> 6ATP
=8ATP

75
Q

How many ATP are produced from the conversion of pyruvate to Acetyl-CoA? Break it down

A

3 ATP
1 NADH—> 3ATP

76
Q

Normally ___(#) pyruvates is converted into ____(#) Acetyl-CoA, meaning that in reality ______ ATP is produced

A

2 pyruvates are converted into 2 Acetyl-CoA, thus producing 2 NADH molecules and 6 ATP in reality

77
Q

in reality, _____(#) Acetyl-CoA(s) are oxidized into _____(#) molecules of CO2, meaning that _____ATP are produced

A

2 Acetyl-CoA’s are oxidized into 4 molecules of CO2, meaning that 24 ATP are produced for every Krebs cycle

78
Q

Upon COMPLETE OXIDATION, how many ATP are produced? What is the formula to illustrate this reaction?

A

Glucose —-> 6CO2
38 ATP are produced

79
Q

Which enzyme catalyzes the step where Q is reduced to QH2?

A

Succinate dehydrogenase

80
Q

Which step in the Krebs Cycle generates GTP?

A

Succinyl-CoA —–> Succinate

catalyzed by succinate synthetase

81
Q

The outer mitochondrial membrane allows the passage of molecules smaller than…..

A

10kda

82
Q

Pyruvate is ____ to acetyl-CoA

A

oxidized

83
Q

What are the 2 levels of Krebs Cycle regulation?

A

-By its supply of substrate (Acetyl-CoA)
-By intrinsic activity

84
Q

What are the 3 major nutrients?

A

fats, carbohydrates, and proteins

85
Q

All major nutrients are converted into _____ for oxidation by the Krebs cycle

A

acetyl-CoA

86
Q

The Krebs cycle is the final common route for the complete ____ of foods into _____

A

complete oxidation of foods into CO2

87
Q

How is the oxidation of pyruvate to Acetyl-CoA regulated?

A

by PDH kinase and PDH phosphatase.
-phosphorylation/dephosphorylation of the E1 component of the pyruvate dehydrogenase complex

88
Q

What enzyme puts E1 in its INACTIVE form and how does it accomplish this?

A

PDH kinase inactivates E1 by placing a phosphate group on it

89
Q

PDH kinase is inhibited by ___ and stimulated by _____

A

PDH kinase is inhibited by PYRUVATE and stimulated by acetyl-CoA

90
Q

The phosphatase that catalyzes the dephosphorylation of E1-P is stimulated by…..

A

CALCIUM

91
Q

The citric acid cycle is known as a ________

A

Metabolic Hub

92
Q

Why is the citric acid cycle known as a metabolic hub?

A

its enzymes play a role in other metabolic pathways

93
Q

What other metabolic pathways do the enzymes of the krebs cycle play a role in?

A

Fatty Acid synthesis uses CITRATE

Amino acids can be converted into Krebs cycle intermediates (transamination)

94
Q

Glutamate can be converted into what intermediate of the Krebs Cycle?

A

alpha ketoglutarate

95
Q

Aspartate can be converted into what intermediate of the Krebs cycle?

A

oxaloacetate

Biochem Exam 2 (7 decks)

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