4. Glycogen & Fat

Question 1

By what mechanism do adrenaline and glucagon regulate the enzymes in glycogenesis/lysis?

Answer 1

Phosphorylation

Question 2

By what mechanism does insulin regulate the enzymes in glycogenesis/lysis?

Answer 2

Dephosphorylation

Question 3

How is the regulation of muscle glycogen stores different from liver stores?

Answer 3

Glucagon has no effect

AMP is an allosteric regulator

Question 4

What are 2 glycogen storage diseases?

Answer 4

McCardle

Von Gierke’s

Question 5

What enzyme is deficient in McCardle disease?

Answer 5

Muscle glycogen phosphorylase

Question 6

What symptoms would you expect to see in McCardle disease?

Answer 6

Exercise intolerance, exhaustion as cannot mobilise skeletal muscle glycogen stores.
Hypoglycaemic.

Question 7

What enzyme is deficient in Von Gierke’s disease?

Answer 7

Glucose - 6 -Phosphorylase

Question 8

What changes do you see in the liver in patients with Von Gierke’s disease and why?

Answer 8

Hepatomegaly as the liver cannot release it’s glycogen stores.
Hypoglycaemic

Question 9

What enzyme catalyses the conversion of Glucose -1P to UDP- glucose?

Answer 9

GTP- uridyltranferase

Question 10

Which enzyme does muscle lack?

Answer 10

Glucose-6- phosphorylase

Question 11

How long after eating do glycogen stores run out and gluconeogenesis begin?

Answer 11

8 hours

Question 12

Where does gluconeogenesis happen?

Answer 12

Liver and kidney cortex

Question 13

What are the 3 precursors used in gluconeogenesis?

Answer 13

Lactate (cori cycle)
Glycerol
Amino acids - alanine particularly

Question 14

Which 3 enzymes are needed in gluconeogenesis to bypass irreversible steps in glycolysis?

Answer 14

1. PEPCK
2. Fructose-1,6-bisphosphatase
3. Glucose-6-phosphatase

Question 15

What reaction does PEPCK catalyse?

Answer 15

Oxaloacetate -> phosphoenolpyruvate

Question 16

What reaction does fructose-1,6-bisphosphatase catalyse?

Answer 16

Fructose-1,6-bisphosphate -> Fructose-6-P

Question 17

What reaction does glucose - 6-phosphatase catalyse?

Answer 17

Glucose-6P -> Glucose

Question 18

Which 2 enzymes are more important for the regulation of gluconeogenesis?

Answer 18

PEPCK and Fructose-1,6-bisphosphatase

Question 19

What type of receptor is the glucagon receptor?

Answer 19

GPCR

Question 20

What type of receptor is the cortisol receptor?

Answer 20

Nuclear

Question 21

What type of receptor is the insulin receptor?

Answer 21

Tyrosine kinase

Question 22

Which 2 hormones increase gluconeogenesis?

Answer 22

Cortisol, Glucagon

Question 23

What effect does insulin have on gluconeogenesis?

Answer 23

Inhibits both PEPCK and F-1,6-BP

Question 24

What is the key regulatory enzyme in lipogenesis?

Answer 24

Acetyl CoA carboxylase

Question 25

How is AcetylCoA carboxylase regulated?

Answer 25

Stimulated by insulin and citrate | Inhibited by glucagon/adrenaline and AMP

Question 26

Why is Acetyl CoA carboxylase inhibited by AMP?

Answer 26

Low energy signal - process of lipogenesis requires ATP and NADPH so won't happen if no energy.

Question 27

Where does fatty acid synthesis occur?

Answer 27

Cytoplasm

Question 28

What are the major energy stores and when are they used?

Answer 28

Glycogen- overnight fast and as part of the response to stress and exercise. (1-10 hours) TAGs - starvation, prolonged exercise, stress Protein - emergency during starvation

Question 29

What happens to the fatty acids once they are taken up by adipose and muscle cells?

Answer 29

Re-esterified to triacylglycerols using glycerol phosphate derived from glucose metabolism.

Question 30

Why do individuals with a defect in the enzyme LCAT produce unstable lipoproteins of abnormal structure?

Answer 30

The spherical shape of lipoproteins is dependent on the ratio of core:surface lipids. As the core gets depleted, LCAT converts surface lipid cholesterol to cholesterol esters, a core lipid. This maintains stability.

Question 31

What is the clinical consequence of LCAT deficiency?

Answer 31

Lipid deposits occur in many tissues and atherosclerosis is a serious problem.