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Biochemistry > Chapter 10- gluconeogenisis > Flashcards

Chapter 10- gluconeogenisis Flashcards

1
Q

What are the three primary pathways for anabolic carbohydrate metabolism?

A

Gluconeogenisis
Pentose phosphate pathway
Glycogen degredation and synthesis

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2
Q

What does glycolysis do?

A

Convert glucose to pyruvate

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3
Q

What is gluconeogenesis?

A

Synthesis of glucose from non-carbohydrate precursors

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4
Q

TF: Gluconeogenesis is a reversal of glycolysis

A

False

There were 3 irreversible reactions in glycolysis so we cannot reverse the reactions

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5
Q

What are the major precursors for gluconeogenesis?

A

Lactate
Glucogenic amino acids
Glycerol

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6
Q

Where are the major sites of gluconeogenisis?

A

liver and kidney

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7
Q

What is gluconeogenesis used to do?

A

Maintain blood glucose levels in order to provide glucose to the BRAIN and red blood cells

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8
Q

What kind of reactions are used in both glycolysis and gluconeogenesis?

A

The reversible reactions

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9
Q

TF: ATP is made in gluconeogenesis?

A

FALSE

no ATP is generated

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10
Q

Why is gluconeogenesis and glycolysis differentially regulated?

A

To prevent a futile cycle

SO anabolic and catabolic reactions do not happen at same time

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11
Q

What steps in glycolysis must be bypassed in gluconeogenesis?

A

Reactions 1,3 and 10

the irreversible steps

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12
Q

Where do the first gluconeogenic steps travel through

A

the mitochondria

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13
Q

After glycolysis where does pyruvate go?

A

Into the mitochondria

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14
Q

What cannot escape out of the membrane of mitochondria?

A

Oxaloacetate

Can be converted to PEP or malate to allow for transport to cytosol for gluconeogenesis

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15
Q

What is needed for gluconeogenesis to occur?

A

Increased cytosolic levels of NADH

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16
Q

What does pyruvate carboxylase do and what is its prosthetic group?

A

Converts pyruvate to oxaloacetate

Biotin is the prosthetic groups (carries activated CO2)

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17
Q

What does pyruvate carboxylase use to convert pyruvate to oxaloacetate?

A

ATP and HCO3-

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18
Q

Why is pyruvate converted to oxaloacetate?

A

To keep it from leaving the mitochondria

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19
Q

What does phosphoenolpytuvate carboxykinase do?

A

Coverts oxaloacetate to PEP
CO2 is removed/ phosphate is added
Oxaloacetate is decarboxylated and phosphorylated

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20
Q

What is the phosphoryl donor for Phosphoenolpyruvate carboxykinase?

A

GTP

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21
Q

How is Oxaloacetate moved outside of the mitochondria?

A

It is reduced to malate which exits the mitochondria into the cytosol
Remember oxaloacetate cannot cross mitochondrial membrane

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22
Q

How is Oxaloacetate moved outside of the mitochondria?

A

It is reduced to malate which exits the mitochondria into the cytosol
Remember oxaloacetate cannot cross mitochondrial membrane

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23
Q

When would oxaloacetate be utilized?

A

In the Kreb’s cycle

Gluconeogenesis but needs to be converted to PEP to go to cytosol

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24
Q

What needs to happen for Glyceraldehyde 3 P production?

A

NADH equivalents need to move from inner mitochondrial matrix to the cytosol

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25
Q

How is NADH produced for gluconeogenesis?

A

Malate is oxidized back to oxaloacetate by malate dehydrogenase and then NADH is produced in the cytosol

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26
Q

Where is lactic acid produced from anaerobic metabolism?

A

In muscle cells and from cells lacking a mitochondria

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27
Q

TF: When lactate is the precursor for gluconeogenesis and pyruvate is the precursor, both use the same PEP carboxykinase from oxaloacetate

A

FALSE

Each pathway uses a different PEP carboxykinase (mitochondrial for lactate pathway and cytosolic for pyruvate pathway)

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28
Q

What does the cori cycle do?

A

Provides glucose to muscle cells during exercise

Converts lactate to glucose

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29
Q

Where is lactate produced by anaerobic glycolysis?

A

In muscle cells

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30
Q

Where is lactate converted back into glucose?

A

Liver by gluconeogenesis

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31
Q

What is produced in gluconeogenesis?

A

NADH

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32
Q

What does gluconeogenesis use?

A

4 ATP and 2GTP

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33
Q

What does anaerobic glycolysis produce?

A

2 ATP and NAD+ for glycolysis

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34
Q

How is glycerol generated?

A

From the hydrolysis of triacylglycerols in adipose tissue (storage form of fat)

35
Q

How is glycerol transported to the liver for gluconeogenesis?

A

By the blood from the adipocytes

Adipocytes lack glycerol kinase

36
Q

What does glycerol kinase do and where does the energy come from?

A

Adds a phosphate group to glycerol to make glycerol phosphate and uses ATP as the phosphate source and energy source

Kinase = phosphate

37
Q

How is glycerol phosphate oxidized into dihydroxyacetone phosphate?

A

Glycerol phosphate dehydrogenase oxidizes glycerol phosphate and reduces NAD+ to NADH and H+

38
Q

What reactions in gluconeogenesis use the same enzymes as glycolysis?

A

Step 3-8

39
Q

Why is an enzyme other than phosphofructokinase 1 needed in gluconeogenesis?

A

PFK-1 is a committed step in glycolysis and is highly regulated

40
Q

What does frucose-1,6-bisphosphatase do?

A

Dephosphorylates Carbon 1 of Fructose 1,6 - bisphosphate to make fructose -6- phosphate
Uses water to create a hydroxyl group in place of a phosphate

Hydrolysis/does not generate ATP

41
Q

How is this step regulated in gluconeogenesis?

A

By an allosteric enzyme
Inhibited by AMP (poor energy state)
Activated by high levels of ATP (high energy state)

42
Q

What does phosphohexose isomerase do?

A

Converts fructose 6-p to glucose 6-p (furanose to a pyranose)

43
Q

What is the final step of gluconeogenesis?

A

Conversion of glucose 6 phosphate to glucose

44
Q

Why is hexokinase kept in a separate cellular compartment from glucose 6 phosphotase?

A

To prevent a futile cycle (hexokinase adds a phosphate group to glucose while glucose 6 phosphotase takes off a phosphate group from glucose 6 p

45
Q

Where is glucose 6P dephosphorylated to free glucose?

A

In the smooth ER of the liver and kidney cells

NONE IN MUSCLE CELLS

46
Q

What can export free glucose to the blood?

A

GLUT 2

47
Q

Why is gluconeogenesis expensive?

A

Costs 4 ATP, 2 GTP and 2NADH

48
Q

Why is gluconeogenesis necessary even though it is so expensive?

A

To supply glucose to Brain, nervous system, and red blood cells that can use glucose to make ATP

49
Q

What does gluconeogenesis allow for when glycogen stores are depleted?

A

Generation of glucose during fasting and starvation, vigorous exercise (cori cycle brings lactate from muscles), can generate glucose from AAs, glycerol, and lactate

50
Q

How are gluconeogenesis and glycolysis reciprocally regulated?

A

Regulated so that within a cell one pathway is inactive while the other is active

51
Q

When will glycolysis predominate over gluconeogenesis?

A

When glucose is abundant

52
Q

When will gluconeogenesis be highly active?

A

When glucose is low

53
Q

Where are glycolysis and gluconeogenesis reciprocally regulated?

A

The interconversion of fructose 1,6-bisphosphate and fructose 6 phosphate
Interconversion of PEP and pyruvate

54
Q

Where does the pentose phosphate pathway occur?

A

In the cytoplasm

55
Q

What is the initial substrate for PPP?

A

Glucose 6P

56
Q

What are the main products of the PPP?

A

2 NADPH and ribose 5 phosphate

57
Q

What is NADPH used for?

A

It is an electron donor
Reductive biosynthesis of fatty acids and steroids
Repairs oxidative damage

58
Q

What is Ribose 5 phosphate and what is it used for?

A

Biosynthetic precursor of nucleotides and is used for DNA and RNA synthesis
Used for synthesis of coenzymes and ATP

59
Q

What kind of pathways use NADP+ instead of NAD+?

A

Anabolic (building up) pathways use NADP+ while catabolic pathways use NAD+

60
Q

What kind of synthesis is NADPH used for?

A

Fatty acid
Cholesterol
Neurotransmitter
Nucleotide

61
Q

How is NADPH used for detoxification?

A

TO neutralize reactive oxygen species

Reduction of glutathione

62
Q

How does NADP+ differ from NAD+?

A

It has a phosphorylated ribose

63
Q

What are the two phases of PPP?`

A

Oxidative (steps 1-3) that produces NADPH and Ribulose 5 phosphate
Nonoxidative (remaining reactions) Converts sugars into sugar phosphates and is reversible

64
Q

When would PPP be used?

A

If increased NADPH is required
If nucleotide pools need to be replenished
If ATP levels are low

65
Q

What enzyme is used in the regulating step of the oxidative phase of PPP?

A

Glucose 6 phosphate dehydrogenase

66
Q

What enzyme in the oxidative phase of PPP is used to release carbon from glucose as CO2?

A

6Phosphogluconate dehydrogenase

67
Q

What is ribulose 5 phosphate used for?

A

DNA/RNA biosynthesis

68
Q

Where is NADPH needed for fatty acid biosynthesis?

A

Liver
Lactating mammary glands
Adipose tissue

69
Q

Where is NADPH needed for the biosynthesis of steroid hormones?

A

Testes, ovaries, placenta

70
Q

What does the nonoxidative phase of PPP do?

A

Regenerates glucose 6 p from ribose 5 p

71
Q

Where does the nonoxidative phase of PPP occur?

A

in all cells synthesizing nuclotides

72
Q

How much ATP is used in the nonoxidative phase of PPP?

A

None

73
Q

What can the intermediates of nonoxidative phase of PPP do?

A

Feed into glycolysis

Make ribose 5 phosphate

74
Q

When will glucose 6 P be pushed into the PPP?

A

When NADP+ levels are high

75
Q

What allosterically activates Glucose 6 phosphate dehydrogenase in PPP?

A

NADP+

76
Q

How is PPP down regulated?

A

When NADPH levels are high NADPH and NADP+ compete for binding with G6PD which causes lower enzyme activity

77
Q

What is a reactive oxygen species ROS that is a byproduct of aerobic metabolism and from drugs and environmental toxins?

A

H2O2

78
Q

What is glutathione reductase dependent upon?

A

NADPH (it needs to be oxidized in order for Glutathione to be reduces on the cysteine residue

79
Q

What does glutathione peroxidase do?

A

Oxidizes glutathione and neutralizes H2O2 into 2 H2O

80
Q

What happens in G6P dehydrogenase deficiency?

A

NADPH production is diminished
Glutathione levels are deplete
THis inhibits H2O2 detoxification and results in higher levels of ROS

81
Q

What does G6P dehydrogenase deficiency lead to?

A

Oxidative damage to lipids, proteins and DNA

Lysis of RBC (jaundice)

82
Q

What do monooxygenases do?

A

Incorporate one atom from O2 into a substrate to create a hydroxyl group

83
Q

What does cytochrome P450 monooxygenase do in the inner mitochondrial membrane?

A

Synthesizes steroid hormones in steroidogenic tissues and in bile acid synthesis in liver

84
Q

What is cytochrome P450 monooxygenase system used for in the smooth ER?

A

Detoxification

Biochemistry (10 decks)

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