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Biochemistry 3630 > Ch 14 Citric Acid Cycle > Flashcards

Ch 14 Citric Acid Cycle Flashcards

1
Q

Where does the citric acid cycle occur?

A

In mitochondria

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2
Q

What are the alternative names for the citric acid cycle?

A

Tricarboxylic acid (TCA) cycle, Kreb’s cycle

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3
Q

Who discovered the citric acid cycle and in what year?

A

Sir Hans Adolf Krebs, 1937

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4
Q

What is the net result of each round of the citric acid cycle?

A

Loss of two carbons as CO2 for each acetyl-CoA that enters the cycle

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5
Q

What are the three types of high-energy products produced in the citric acid cycle?

A
  • 1 GTP
  • 3 NADH
  • 1 FADH2
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6
Q

What does NADH stand for?

A

Nicotinamide adenine dinucleotide

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7
Q

What are the oxidized and reduced forms of NAD?

A

NAD+ (oxidized), NADH (reduced)

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8
Q

What are the oxidized and reduced forms of FAD?

A

FAD (oxidized), FADH2 (reduced)

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9
Q

What are the goals of the citric acid cycle?

A
  • Produce electron carriers (NADH, FADH2)
  • Produce GTP
  • Generate metabolic intermediates
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10
Q

What is the role of coenzyme A in the citric acid cycle?

A

Serves as a cofactor for acyl transfer reactions

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11
Q

What is the mnemonic for the citric acid cycle?

A

Citrate Is Kreb’s Starting Substrate For Making Oxaloacetate

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12
Q

True or False: The citric acid cycle produces ATP directly.

A

False

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13
Q

What is the only step in the citric acid cycle where energy in the form of ATP/GTP is generated?

A

Formation of succinate and GTP

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14
Q

What happens during the reaction catalyzed by citrate synthase?

A

Condensation reaction of acetyl-CoA and oxaloacetate to form citrate

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15
Q

What type of reaction is catalyzed by isocitrate dehydrogenase?

A

Oxidative-decarboxylation reaction

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16
Q

What is produced during the oxidative-decarboxylation reaction catalyzed by α-ketoglutarate dehydrogenase?

A

NADH and CO2

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17
Q

What vitamin deficiency is associated with a lack of NAD+?

A

Pellagra (niacin deficiency)

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18
Q

What is the role of manganese in the citric acid cycle?

A

Helps stabilize negative charges of reaction intermediates

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19
Q

Fill in the blank: The citric acid cycle is also known as the _______.

A

Kreb’s cycle

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20
Q

What is the fate of the six carbon atoms from glucose in the citric acid cycle?

A

They are released as CO2

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21
Q

How many turns of the citric acid cycle occur for each glucose molecule?

A

Two turns

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22
Q

What are the main products generated from one cycle of the citric acid cycle?

A

3 NADH, 1 FADH2, 1 GTP, 2 CO2

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23
Q

What is the energy yield from 1 NADH and 1 FADH2 during oxidative phosphorylation?

A
  • 1 NADH = 2.5 ATP
  • 1 FADH2 = 1.5 ATP
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24
Q

What regulates the citric acid cycle?

A

Regulation occurs at the three irreversible steps

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25
Q

What is a potential consequence of mutations in citric acid cycle enzymes?

A

Linked to cancer

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26
Q

What is the energy yield of 1 NADH?

A

2.5 ATP

NADH is a key electron carrier in cellular respiration, contributing to the production of ATP during oxidative phosphorylation.

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27
Q

What is the energy yield of 1 QH2?

A

1.5 ATP

QH2 represents ubiquinol, which is part of the electron transport chain.

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28
Q

How many ATP are generated from the citric acid cycle?

A

32 ATP

This total includes ATP produced from all cycles and associated processes.

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29
Q

What regulates the citric acid cycle?

A

Three irreversible steps

These steps are critical control points in the cycle.

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30
Q

What is the effect of a high ATP/ADP ratio on the citric acid cycle?

A

Inhibits the cycle

A high ATP/ADP ratio indicates sufficient energy, leading to reduced cycle activity.

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31
Q

What is the effect of a low NADH/NAD+ ratio on the citric acid cycle?

A

Activates the cycle

A low NADH/NAD+ ratio suggests a need for energy production.

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32
Q

What is the mnemonic for the citric acid cycle?

A

Citrate is Krebs’ starting substrate for making oxaloacetate

This mnemonic helps remember the order of substrates in the cycle.

33
Q

What are the main substrates in the citric acid cycle in order?

A
  • Citrate
  • Isocitrate
  • α-Ketoglutarate
  • Succinyl-CoA
  • Succinate
  • Fumarate
  • Malate
  • Oxaloacetate

Understanding the flow of substrates is essential for grasping the cycle’s function.

34
Q

What is the impact of a high NADH/NAD+ ratio on the citric acid cycle?

A

Inhibits the cycle

A high NADH/NAD+ ratio indicates that the cell has sufficient reducing power, leading to decreased cycle activity.

35
Q

What characterizes cells in a resting metabolic state regarding the citric acid cycle?

A
  • Use little energy
  • High ATP/ADP ratio
  • High NADH/NAD+ ratio

These conditions lead to decreased activity of the cycle.

36
Q

What characterizes cells in an active metabolic state regarding the citric acid cycle?

A
  • Use more energy than resting cells
  • Low ATP/ADP ratio
  • Low NADH/NAD+ ratio

Active cells need to produce more ATP, thus activating the cycle.

37
Q

Where are NADH, GTP, FADH2, CO2, and coenzyme A produced in the TCA cycle?

A

Various points in the cycle

Each of these molecules is generated at specific steps within the cycle.

38
Q

Where are ATP and O2 found in the TCA cycle?

A

ATP is produced in the cycle, O2 is not directly produced

Oxygen is used in the electron transport chain, not in the cycle itself.

39
Q

What is the Citric Acid Cycle also known as?

A

TCA Cycle

TCA stands for Tricarboxylic Acid.

40
Q

What are the three types of high-energy products generated in the Citric Acid Cycle?

A
  • 1 GTP
  • 3 NADH
  • 1 FADH2
41
Q

Which steps in the Citric Acid Cycle are highly regulated?

A

Steps 0, 1, 3, and 4

42
Q

What is the significance of hydroxylation of collagen?

A

Cofactor: Ascorbic acid (Vitamin C)

Deficiency leads to Scurvy.

43
Q

Define activation in metabolic pathways.

A

Formation of a more reactive, higher energy substance

44
Q

What is Coenzyme A’s role in metabolic pathways?

A

Key co-enzyme for attaching molecules to the sulfhydryl end (-SH) for subsequent release

45
Q

What happens during thioester hydrolysis?

A

Releases a large amount of free energy

46
Q

What does the term ‘amphibolic’ mean in relation to the Citric Acid Cycle?

A

Functions in both anabolic and catabolic reactions

47
Q

What is the consequence of reaction 8 being endergonic in the Citric Acid Cycle?

A

Oxaloacetate is harder to form

48
Q

What happens to pyruvate during exercise?

A

Some pyruvate is converted to α-ketoglutarate

49
Q

What are anaplerotic reactions?

A

Reactions that replenish citric acid cycle intermediates

50
Q

What is the role of acetyl-CoA in lipid anabolism?

A

Starts lipid synthesis in the cytosol

51
Q

Fill in the blank: The Citric Acid Cycle is a source of starting materials for the biosynthesis of _______.

A

[lipids, proteins, carbohydrates]

52
Q

True or False: Glycogen is converted to glucose during caloric restriction.

53
Q

What is the primary function of transaminases?

A

Interconversion of amino acids

54
Q

What is the result of low oxaloacetate levels?

A

Elevated acetyl-CoA levels

55
Q

What is the biochemical function of Biotin (Vitamin B7)?

A

Cofactor for carboxylation reactions

56
Q

What are the main components that feed into the Citric Acid Cycle during catabolism?

A
  • Proteins
  • Carbohydrates
  • Fatty acids
57
Q

What are the consequences of insufficient oxaloacetate in the Citric Acid Cycle?

A

Elevated levels of Acetyl-CoA and activation of pyruvate carboxylase

58
Q

What is the function of NADPH produced during lipid anabolism?

A

Used in fatty acid synthesis

59
Q

What happens to citric acid cycle intermediates diverted to other pathways?

A

They can be replenished

60
Q

What is the role of glutamate in amino acid formation?

A

Precursor of glutamine, arginine, and proline

61
Q

How does exercise affect the Citric Acid Cycle?

A

Boosts activity up to 100-fold

62
Q

What is the main difference between catabolic and anabolic pathways in the context of the Citric Acid Cycle?

A

Catabolic pathways degrade while anabolic pathways synthesize

63
Q

Fill in the blank: The hydrolysis of a thioester is more exergonic than the hydrolysis of an ordinary _______.

A

[oxygen ester]

64
Q

What are the two types of regions found in lipids?

A

Positive or negative regions and nonpolar regions

65
Q

List the forms of lipids with extended chains.

A
  • Fatty acids
  • Triacylglycerols
  • Sphingolipids
  • Phosphoacylglycerols
66
Q

What are the cyclic forms of lipids?

A
  • Cholesterol
  • Steroid hormones
67
Q

Define a lipid.

A

A lipid is a group of organic compounds that are insoluble in water but soluble in organic solvents.

68
Q

What is a fatty acid?

A

An unbranched-chain carboxylic acid (with COO-), most commonly with 12 - 20 carbons.

69
Q

What is a saturated fatty acid?

A

A fully hydrogenated fatty acid with no C=C double bonds or alkenes.

70
Q

What does the ‘acyl’ nomenclature refer to?

A

It refers to the naming convention used for fatty acids and their derivatives.

71
Q

What are the common saturated fatty acids with 12 carbons?

A
  • Lauric acid (Dodecanoic acid)
  • Structure: CH3(CH2)10COOH
72
Q

Identify the common saturated fatty acid with 14 carbons.

A
  • Myristic acid (Tetradecanoic acid)
  • Structure: CH3(CH2)12COOH
73
Q

What is the common name for a saturated fatty acid with 16 carbons?

A

Palmitic acid (Hexadecanoic acid)

74
Q

What is the structure of stearic acid?

A

CH3(CH2)16COOH

75
Q

What is the common name for a saturated fatty acid with 20 carbons?

A

Arachidic acid (Eicosanoic acid)

76
Q

What is the structure of behenic acid?

A

CH3(CH2)20COOH

77
Q

Fill in the blank: Fatty acids usually contain ______ numbers of carbons.

78
Q

What is the relationship between chain length and melting temperature in fatty acids?

A

The longer the chain, the higher the melting temperature.

Biochemistry 3630 (21 decks)

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