Week 13

Question 1

gluconeogenesis

Answer 1

Synthesis of glucose from non-carbohydrate precursors (lactate, amino acids, glycerol)

Question 2

substrates of gluconeogenesis

Answer 2

• Lactate
• Alanine (amino acids)
• Glycerol
• Propionate (minor)

Question 3

location of gluconeogenesis

Answer 3

Organs: Liver (major), kidney cortex (minor)
Subcellular: Mitochondria, cytosol, and ER

Question 4

three bypass reactions in gluconeogenesis

Answer 4

1. Pyruvate → Oxaloacetate (pyruvate carboxylase)
2. Oxaloacetate → PEP (PEP carboxykinase)
3. Fructose-1,6-BP → Fructose-6-P (fructose-1,6-bisphosphatase)
4. Glucose-6-P → Glucose (glucose-6-phosphatase)

Question 5

energy requirement of gluconeogenesis

Answer 5

To make 1 glucose:
• 4 ATP
• 2 GTP
• 2 NADH

Question 6

futile cycle

Answer 6

Simultaneous operation of opposing metabolic pathways (e.g., glycolysis and gluconeogenesis) causing waste of ATP

Question 7

hormonal regulation of gluconeogenesis

Answer 7

↑ Glucagon, cortisol, epinephrine
↓ Insulin

Question 8

Cori cycle

Answer 8

Lactate from muscle → liver → converted to glucose → returned to muscle

Question 9

glucose-alanine cycle

Answer 9

Alanine from muscle → liver → converted to glucose + urea → glucose returned to muscle

Question 10

fructose-2,6-bisphosphate and its effect on gluconeogenesis

Answer 10

Regulatory molecule that:
• Inhibits fructose-1,6-bisphosphatase
• Decreases gluconeogenesis
• Stimulates glycolysis

Question 11

glycogen

Answer 11

Highly branched polymer of glucose used for energy storage

Question 12

where does glycogenesis occur

Answer 12

Cytosol of liver and skeletal muscle cells

Question 13

how long can glycogen sustain blood glucose in fasting

Answer 13

~12–24 hours

Question 14

difference between muscle and liver glycogen

Answer 14

Liver: maintains blood glucose
Muscle: used locally for contraction (no glucose export)

Question 15

function of glycogenin

Answer 15

Acts as primer for glycogen synthesis by attaching first glucose residues

Question 16

function of glycogen synthase

Answer 16

Forms α-1,4 glycosidic bonds in glycogen

Question 17

function of branching enzyme

Answer 17

Creates α-1,6 branches in glycogen

Question 18

benefits of branching in glycogen

Answer 18

• Increases solubility
• Allows rapid synthesis and breakdown
• Provides multiple ends for enzyme action

Question 19

rate-limiting enzyme of glycogenolysis

Answer 19

Glycogen phosphorylase

Question 20

product of glycogen phosphorylase

Answer 20

Glucose-1-phosphate

Question 21

two activities of the debranching enzyme

Answer 21

• Transferase (moves glucose residues)
• α-1,6-glucosidase (removes branch point)

Question 22

hormonal regulation of glycogenesis vs glycogenolysis

Answer 22

Insulin: ↑ glycogenesis, ↓ glycogenolysis
Glucagon & epinephrine: ↓ glycogenesis, ↑ glycogenolysis

Question 23

effect of AMP, ATP, Ca²⁺, glucose, G-6-P on glycogen metabolism

Answer 23

AMP & Ca²⁺: stimulate glycogenolysis
ATP & glucose: inhibit glycogenolysis
Glucose-6-P: stimulates glycogen synthesis

Question 24

what causes Von Gierke disease

Answer 24

Deficiency of glucose-6-phosphatase

Question 25

symptoms of Von Gierke disease

Answer 25

• Severe fasting hypoglycemia • Lactic acidosis • Hepatomegaly • Hyperuricemia • Hyperlipidemia

Question 26

diagnosis and treatment of Von Gierke disease

Answer 26

**Diagnosis:** hypoglycemia, ↑ lactate, genetic testing **Treatment:** frequent feeding, cornstarch, avoid fasting

Question 27

what causes McArdle disease

Answer 27

Deficiency of muscle glycogen phosphorylase

Question 28

symptoms of McArdle disease

Answer 28

• Exercise intolerance • Muscle cramps • Myoglobinuria • Fatigue

Question 29

diagnostic feature of McArdle disease

Answer 29

Second-wind phenomenon (symptoms improve after rest)

Question 30

management of McArdle disease

Answer 30

• Avoid strenuous exercise • Moderate aerobic exercise • High-protein diet • No cure