Metabolic Pathways and ATP Production 2 (Cholesterol/Hormonal control)

Question 1

Recall four examples of blood-borne hormones which act as metabolic regulators

Answer 1

• Glucagon
• Adrenaline
• Glucocorticoids
• Insulin

Question 2

Explain glucagon’s mode of action

Answer 2

Stimulates production of glucose:

• Glycogenolysis
• Lipolysis
• Gluconeogenesis

Question 3

Explain adrenaline’s mode of action

Answer 3

Makes more glucose available to body for ‘fight or flight’ response
Similar mechanisms to glucagon

Question 4

Explain glucocorticoids’ mode of action

Answer 4

Steroid hormones

• Increase synthesis of enzymes concerned with glucose availability.
• Increases glucose available since rate of glucose-providing mechanisms increases

Question 5

Explain insulin’s mode of action

Answer 5

Stimulates uptake and use of glucose

Promotes storage of glucose as glycogen and fat

Question 6

List the mechanisms of action for metabolic hormones

Answer 6

• Product inhibition
• Enzyme phosphorylation
• Allosteric effectors
• Change in enzyme levels

Question 7

Explain the metabolic abnormalities in diabetes types 1 and 2 and describe the overall effect on the body’s metabolism

Answer 7

Type 1 = Make insufficient insulin
Type 2 = Reduced responsiveness to insulin
Overall effect is that body metabolism becomes primed as if for starvation, regardless of dietary intake.

Question 8

Summarise the synthesis of cholesterol from acetyl-CoA

Answer 8

1) Acetyl CoA (2C) -> Mevalonate (6C)
2) Mevalonate (6C)-> Isopentenyl-PP (5C)
3) Isopentenyl-PP (5C) elongated to squalene (30C)
4) Squalene undergoes cyclisation and demethylation to form Cholesterol.

Question 9

Summarise the synthesis of steroid hormones

Answer 9

• Synthesised from pregnenolone (cholesterol)
• Pregnenolone generated by cholesterol desmolase
• Levels of steroid hormones are controlled by rate of synthesis and hence the rate of pregnenolone production

Question 10

Summarise the synthesis of bile salts and acids

Answer 10

• Synthesised in the liver
• Regulated step is the conversion of cholesterol into 7-alpha-hydroxycholesterol involving cytochrome P450 monooxygenase
• Further reactions occur to form conjugated bile salts, excreted in aqueous form into GI tract

Question 11

Explain the mechanism for transport of cholesterol around the body

Answer 11

Packaged inside a phospholipid monolayer with cholesterol and hydrophilic proteins making the hydrophilic inside. Cholesterol and other uncharged insoluble lipids travel around the body in the hydrophobic core of these packages.

Question 12

What is the mechanism for cholesterol uptake in the body?

Answer 12

Endocytosis - LDL receptor trafficking

Question 13

What is the role of cholesterol in atherosclerosis?

Answer 13

Excessively high cholesterol levels result in increased low-density lipoprotein in the blood. This damages artery walls and once damaged enough, begin to enter and build up within the walls, forming plaques.