S2 - Energy Storage And Lipid Transport

Question 1

What is the difference between oxidative phosphorylation and substrate level phosphorylation.

Answer 1

In oxidative phosphorylation, electrons are transferred from NADH or FADH2 to O2 - oxidation and phosphorylation are coupled.
In substrate level phosphorylation, ATP or GTP s formed by the direct transfer of a phosphorylation group to ADP or GDP - oxidation and phosphorylation are not linked.

Question 2

What is the normal plasma glucose level?

Answer 2

5mmol/L

Question 3

Where are the 2 main stores of glycogen in the body?

Answer 3

Liver

Muscle

Question 4

What is glycogenesis? Name the enzymes involved.

Answer 4

The synthesis of glycogen from glucose.
Hexokinase (or glucokinase in the liver)
Phosphoglucomutase
Glycogen synthase + branching enzyme

Question 5

What is glycogenolysis? Name the enzymes involved.

Answer 5

The breakdown of glycogen into glucose.
Glycogen phosphorylase + debranching enzyme
Phosphoglucomutase
Glucose-6-phosphatase (liver only)

Question 6

How does glycogenolysis differ in muscle and liver stores of glycogen?

Answer 6

In the liver, Glucose-6-phosphate is converted to glucose by the enzyme glucose-6-phosphatase. This glucose is released into the blood stream and transported to other tissues. Thus liver glycogen represents a store of glucose than can be made available to all tissues of the body.
In muscle, the enzyme glucose-6-phosphatase is absent, so glucose can’t be produced. Instead, the glucose-6-phosphate enters glycolysis and is used to provide energy for the exercising muscle. Thus, muscle glycogen represents a store of glucose-6-phosphate that can only be used by the muscle cells.

Question 7

Insulin and glucagon regulate glycogen metabolism. What are their effects?

Answer 7

Insulin - increases activity of glycogen synthase and decreases activity of glycogen phosphorylase - increases glycogenesis and decreases glycogenolysis.

Glucagon/adrenaline does the opposite.

Question 8

What are the possible substances that can be used in gluconeogenesis to make glucose?

Answer 8

Pyruvate, lactate and glycerol

Essential and non-essential amino acids whose metabolism involves pyruvate or intermediates of the TCA cycle

Question 9

What are the 3 main enzymes involved in gluconeogenesis?

Answer 9

PEPCK (early on)
Fructose 1,6 - biphosphatase - converts fructose 1,6-biphosphate to fructose 6-phosphate
Glucose 6-phosphatase - converts glucose 6-phosphate to glucose