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Biochemistry > MODULE 10: Chapter 10.1 > Flashcards

MODULE 10: Chapter 10.1 Flashcards

1
Q

What is the primary function of the citrate cycle?

A

To oxidize acetyl-CoA and transfer electrons to NAD⁺ and FAD, generating NADH and FADH2

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2
Q

Where do all the enzymes in the citrate cycle reside in eukaryotic cells?

A

In the mitochondrial inner membrane and matrix

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3
Q

What is produced from the oxidation of one acetyl-CoA in the citrate cycle?

A

2 CO2, 3 NADH, 1 FADH2, and 1 GTP

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4
Q

What are the shared intermediates between the citrate cycle and the electron transport system?

A

NADH and FADH2

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5
Q

What is the ATP currency exchange ratio for NADH in the mitochondria?

A

∼2.5 ATP per NADH

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6
Q

What is the ATP currency exchange ratio for FADH2?

A

∼1.5 ATP per FADH2

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7
Q

What does one turn of the citrate cycle produce in terms of ATP?

A

∼10 ATP for every acetyl-CoA molecule oxidized

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8
Q

What role does pyruvate dehydrogenase play in the citrate cycle?

A

Regulates the flux of acetyl-CoA into the cycle

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9
Q

What is the significance of oxaloacetate in the citrate cycle?

A

It is both the substrate for the first reaction and the product of the last reaction

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10
Q

Which enzyme catalyzes the first reaction in the citrate cycle?

A

Citrate synthase

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11
Q

What is fluoroacetate and its effect on the citrate cycle?

A

It is a potent inhibitor of the citrate cycle enzyme mitochondrial aconitase

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12
Q

What is the acronym used to remember the relationship between oxidation and reduction?

A

OIL RIG (Oxidation Is Loss, Reduction Is Gain)

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13
Q

What two half-reactions comprise a redox reaction?

A

Oxidation (loss of electrons) and reduction (gain of electrons)

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14
Q

What do compounds that accept electrons in a redox reaction called?

A

Oxidants (or oxidizing agents)

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15
Q

What do compounds that donate electrons in a redox reaction called?

A

Reductants (or reducing agents)

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16
Q

What is the net reaction of the citrate cycle?

A

Acetyl-CoA + 3 NAD⁺ + FAD + GDP + Pi + 2 H2O → CoA + 2 CO2 + 3 NADH + 3 H⁺ + FADH2 + GTP

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17
Q

What is the role of isocitrate dehydrogenase in the citrate cycle?

A

Catalyzes the oxidative decarboxylation of isocitrate to form NADH and release CO2

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18
Q

What is the result of the redox reactions in the citrate cycle?

A

Transfer of electron pairs to NAD⁺ and FAD

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19
Q

What is a distinguishing feature of the citrate cycle compared to linear pathways like glycolysis?

A

Oxaloacetate is both a substrate and a product, requiring regeneration

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20
Q

What does the citrate cycle generate through substrate-level phosphorylation?

A

1 GTP, which is converted to ATP

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21
Q

Who first described the citrate cycle?

A

Hans Krebs in 1937

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22
Q

What did Krebs use to piece together the citrate cycle?

A

The compound malonate, which inhibits succinate dehydrogenase

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23
Q

What is the relationship between carbohydrate and fatty acid metabolism?

A

High ATP and NADH levels inhibit pyruvate dehydrogenase, diverting acetyl-CoA to fatty acid synthesis

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24
Q

What is the biochemical basis for low-carbohydrate diets?

A

Limiting carbohydrates stimulates fatty acid metabolism to produce acetyl-CoA for the citrate cycle

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25
What is the significance of the electron transport system in the citrate cycle?
It couples the oxidation of NADH and FADH2 to the reduction of O2 to form H2O
26
What happens to the proton gradient generated by the electron transport system?
It is used by ATP synthase to synthesize ATP from ADP and Pi
27
What does the citrate cycle involve in terms of electron transfer?
The transfer of electron pairs (2 e−) to the electron carrier molecules NAD⁺ and FAD
28
How is NAD⁺ reduced to NADH + H⁺?
By giving up two hydrogen atoms: one as a hydride ion (CH−) and the other as a proton (H⁺)
29
How is FAD reduced?
By sequential addition of one hydrogen (1 e− and 1 H⁺) at a time to give FADH2
30
What are oxidoreductases?
Enzymes that catalyze biochemical redox reactions
31
What are the two primary energy-conversion reactions in metabolism?
* Phosphoryl transfers involving ATP * Redox reactions using NAD⁺/NADH and FAD/FADH2
32
What does the change in biochemical standard free energy (ΔG°′) measure?
The spontaneity of a reaction
33
What is the biochemical standard reduction potential (E°′)?
A measure of the electron affinity of a given conjugate redox pair
34
How is the reduction potential E°′ determined in the laboratory?
Using an electrochemical cell to measure the relative e− affinity of a test redox pair compared to the reference hydrogen half-reaction
35
What indicates a positive E°′ value?
Oxidants with a higher affinity for electrons than that of H⁺
36
What indicates a negative E°′ value?
Oxidants with a lower affinity for electrons than that of H⁺
37
What is the relationship between ΔE°′ and ΔG°′?
ΔE°′ is proportional to ΔG°′, where positive ΔE°′ values indicate spontaneous reactions (ΔG°′ < 0)
38
What is the Nernst equation used for?
To calculate the actual reduction potentials for conjugate redox pairs based on concentrations
39
What is the effect of the NAD⁺ to NADH ratio in the mitochondria on reduction potential?
It makes NAD⁺ reduction more favorable due to a higher NAD⁺ to NADH ratio
40
What does ΔE°′ of a redox reaction indicate?
The tendency of the reductant to donate electrons to the oxidant
41
True or False: Reactions with negative ΔE°′ values will proceed spontaneously.
False
42
What does the term 'citrate cycle' refer to?
Also called Krebs cycle or TCA cycle; a central pathway in oxidative respiration converting acetyl units to CO2
43
What role does pyruvate dehydrogenase play in metabolism?
It converts pyruvate to acetyl-CoA and CO2, linking glycolysis to the citrate cycle
44
What is the function of citrate synthase in the citrate cycle?
It converts four-carbon oxaloacetate and acetyl-CoA into citrate
45
Fill in the blank: The change in biochemical standard free energy (ΔG°′) is calculated using the equation ΔG°′ = -nFΔE°′, where n is the _______.
number of electrons transferred
46
What is the TCA cycle?
A central pathway in oxidative respiration that converts acetyl units to CO2 with the concomitant production of FADH2, NADH, and ATP. ## Footnote TCA stands for tricarboxylic acid.
47
What does pyruvate dehydrogenase do?
Converts pyruvate to acetyl-CoA and CO2 with the reduction of NAD⁺ to form NADH; links the glycolytic pathway to the citrate cycle. ## Footnote It is a large multi-subunit enzyme.
48
What is the function of citrate synthase?
Converts four-carbon oxaloacetate into five-carbon citrate and regenerates CoA. ## Footnote It is the first enzyme in the citrate cycle.
49
What is the role of isocitrate dehydrogenase?
Catalyzes the oxidative decarboxylation of isocitrate to form α-ketoglutarate, NADH, and CO2. ## Footnote This enzyme plays a critical role in the citrate cycle.
50
What does α-ketoglutarate dehydrogenase do?
Catalyzes the conversion of α-ketoglutarate to succinyl-CoA; it is a key regulator of the citrate cycle. ## Footnote It is a multi-subunit complex.
51
Define oxidation reaction.
The half of a redox reaction in which a molecule or functional group loses electrons.
52
Define reduction reaction.
The half of a redox reaction in which a molecule or functional group gains electrons.
53
What is an oxidant?
The molecule in a redox reaction that gains electrons by oxidizing a different molecule.
54
What is a reductant?
The molecule in a redox reaction that loses electrons by reducing a different molecule.
55
What is a conjugate redox pair?
The oxidized and reduced states of a molecule or ion; for example, NAD⁺ and NADH.
56
What is an oxidoreductase?
An enzyme that catalyzes a biochemical redox reaction.
57
What is a dehydrogenase?
A type of oxidoreductase that also results in the release of hydrogen ions.
58
What is an electrochemical cell?
An apparatus used to measure the reduction potential of a test redox pair, typically measured under standard conditions against a reference standard of H⁺/H2.
59
What does the Nernst equation calculate?
The reduction potential under nonstandard conditions.
60
Define biochemical standard reduction potential (E°′).
A measure of the tendency of a compound to accept or donate electrons under the conditions of 1 M concentration, 25 °C, pH 7, and 1 atm pressure.

Biochemistry (44 decks)

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