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Biochemistry > Week 5: Gluconeogenesis > Flashcards

Week 5: Gluconeogenesis Flashcards

1
Q

What are primary pathways of anabolic carbohydrate metabolism?

A

Gluconeogenesis
Pentose Phosphate Pathway
Glycogen Degradation and Synthesis

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2
Q

What is gluconeogenesis

A

Making new glucose and the synthesis of glucose from non-carbohydrate precursors

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3
Q

What are the major precursors of gluconeogenesis?

A

Lactate, glucogenic amino acids, and glycerol

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4
Q

Is gluconeogenesis the reversal of glycolysis?

A

No

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5
Q

What is the site of gluconeogenesis?

A

Liver

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6
Q

What is the purpose for gluconeogenesis?

A

Used to maintain blood glucose levels in order to provide glucose to the brain and red blood cells

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7
Q

What are the differences between glycolysis and gluconeogenesis?

A
  1. Both thermodynamically favorable
  2. Exergonic
  3. Reversible reactions are used by both pathways
  4. Irreversible reactions of glycolysis must be bypassed in gluconeogenesis
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8
Q

What steps of glycolysis are irreversible?

A

1, 3, 10

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9
Q

What occurs when pyruvate is converted back to PEP?

A

1 . Pyruvate + HCO3 + ATP by pyruvate carboxylase and biotin to form oxaloacetate
2. Oxaloacetate is decarboxylated and phosphorylated by GTP and PEP carboxylkinase to produce PEP and CO2

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10
Q

How does oxaloacetate cross the mitochondrial membrane?

A

It is reduced to malate

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11
Q

What enzyme oxidizes malate back to oxaloacetate?

A

Malate dehydrogenase

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12
Q

Where in the body is lactic acid produced?

A

Muscle

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13
Q

How would glycerol enter gluconeogenesis and glycolysis?

A
  1. Glyceral fueled by ATP and glycerol kinase in converted to glycerol phosphate
  2. Glycerol phosphate is dehydrated by NAD+ and glycerol phosphate dehydrogenase to form dihydroxyacetone phosphate
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14
Q

How is F-1,6BP converted to F-6P

A

Through F-1,6 bisphosphatase

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15
Q

What are the important regulatory steps for the conversion of F-1,6BP to F-6P?

A
  1. Inhibited by AMP (energy-poor state)

2. Activated by high levels of ATP

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16
Q

What situations allow generation of glucose when glycogen stores are depleted?

A
  1. during fasting and starvation
  2. during vigorous exercise (cori cycle brings lactate from muscles)
  3. can generate glucose from amino acids, glycerol, and lactate
17
Q

What is reciprocal regulation?

A

Glycolysis will predominate when glucose is abundant, and gluconeogenesis will be highly active when glucose is low.

18
Q

Where does pentose phosphate pathway occur?

A

Cytoplasm

19
Q

What are the main products of Pentose Phosphate Pathway?

A

2 NADPH and ribose 5-phosphate

20
Q

What is NADPH used for in the Pentose Phosphate Pathway?

A
  1. Used for reductive biosynthesis of fatty acids and steroids
  2. Repairs oxidative damage
21
Q

What is ribose-5-phosphate used for in the Pentose Phosphate Pathway?

A
  1. Used in DNA and RNA synthesis

2. Synthesis of some coenzymes (NADH, FADH2, coenzyme A) and ATP

22
Q

What synthesis reactions would use NADPH?

A
  • Fatty acid biosynthesis
  • Cholesterol biosynthesis
  • Neurotransmitter biosynthesis
  • Nucleotide biosynthesis
23
Q

What detoxification reactions would use NADPH?

A
  1. Neutralizes reactive oxygen species

2. Reduction of glutathione

24
Q

What makes NADPH a strong reductant?

A
  1. Has the same reduction potential as NAD+ NADH redox pair
  2. Accepts 2e- in the form of a hydride ion (:H-) and releases a proton.
  3. Differs from NAD+ by phosphorylated ribose
25
Q

What does the oxidative phase of the Pentose Phosphate Pathway do?

A

Produces NADPH and Ribulose-5-phosphate

26
Q

What does the non-oxidative phase of the Pentose Phosphate Pathway do?

A
  1. Interconverts C3, C4, C5, C6, and C7 sugars in to sugar phosphates
  2. Reversible
27
Q

What 3 metabolic states must be met during the flux between the oxidative and reductive phases?

A
  1. If increased NADPH is required
  2. If nucleotide pools need to be replenished
  3. If ATP levels are low
28
Q

What occurs when NADPH levels are high?

A
  1. NAPDH competes with NADP+ for binding to G6PD resulting in lower enzyme activity
  2. Increased flux of Glucose-6-P through glycolysis

Biochemistry (16 decks)

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