Session 2- Energy Storage And Lipid Transport

Question 1

Describe the energy stores in a 70kg man

Answer 1

Glycogen stored in skeletal muscle and liver- Alpha 1,4 glycosidic bonds and alpha 1,6 glycosidic bonds. Alpha 1,5 bonds are branch points. This allows it to be compact, branched allows many sites for addition/ removal hence rapid synthesis and degradation and osmotically inert
Triaglycerols
Muscle protein

Question 2

Describe, in outline, the reactions involved in glycogen synthesis

Answer 2

Starts from glucose+ ATP which forms glucose 6-P and ADP. Enzyme that does this is hexokinase but glucokinase in the liver.
Step 2: Glucose 6-P to glucose 1-P via phosphoglucomutase and is reversible
Step 3: Glucose 1-P+UTP+H20 to UDP-Glucose and 2pi (Pyrophosphate) Enzyme: G1P Uridyl transferase
Step 4: Glycogen ( n residues) + UDP-glucose to Glycogen (n+ 1 residues) + UDP
Enzymes: Glycogen synthase
Branching enzyme

Question 3

Which enzyme catalyses the reaction from glucose to glucose 6 phosphate?

Answer 3

Hexokinase

Liner: Glucokinase

Question 4

Which enzyme catalyses the reversible reaction Glucose 6-Phosphate to Glucose1-Phosphate?

Answer 4

Phosphoglucomutase

Question 5

What catalyses the reaction from Glucose1-Phosphate to UDP-glucose?

Answer 5

G1P-Uridyl transferase

Question 6

Which enzymes acts on the alpha 1,4 glycosidic bonds to create glycogen.

Answer 6

Glycogen synthase

Question 7

Which enzymes acts on the Alpha 1,6 glycosidic bonds to convert into glycogen?

Answer 7

Branching enzyme

Question 8

Describe the process of Glycogen degradation

Answer 8

Happens in skeletal muscle
Step 1:Glycogen (n residues)+ inorganic phosphate into glucose 1-phosphate + glycogen (n-1) via glycogen phosphorylase
Step 2: Glucose 1-phosphate converts into glucose 6-phosphate via phosphoglucomutase

Question 9

Function of glycogen store in the liver

Answer 9

Glucose 6-phosphate is converted into glucose via glucose 6-phosphotase. Glucose is released into blood stream.
It’s a buffer of blood glucose levels

Question 10

Function of glycogen stores in the muscle

Answer 10

G6P enters glycolysis.

Regulation of liver-glycogen metabolism

Question 11

What does the glycogen phosphorylase?

Answer 11

It targets the 1,4 glycosidic bonds but not the 1,6 glycosidic bonds
De-branching enzymes works on the 1,6 glycosidic bonds

Question 12

What’s the rate limiting enzyme for glycogen synthesis? (Regulation)

Answer 12

Glycogen synthase

Question 13

What’s the rate limiting enzyme for glycogen degradation? (Regulation)

Answer 13

Glycogen phosphorylase

Question 14

Function of glucagon hormone

Answer 14

Acts on the enzyme glycogen synthase
Mechanism phosphorylation
Decreases the enzyme activity

Question 15

Function of adrenaline

Answer 15

Acts on the enzyme glycogen phosphorylase
Mechanism phosphorylation
Increases the enzyme activity

Question 16

Function of insulin

Answer 16

Acts on the enzyme glycogen synthase
Mechanism de-phosphorylation
Increases the enzyme activity

Acts on the enzyme glycogen phosphorylase
Mechanism de-phosphorylation
Decreases the enzyme activity

Question 17

Does glucagon have an effect on muscle glycogen stores

Answer 17

No
The skeletal muscle doesn’t have glucagon receptors
The liver-glycogen storage function is to buffer the blood glucose levels
Whereas muscles are for energy and contraction

Question 18

Glycogen storage diseases

Answer 18

Inborn errors of metabolism (deficiency/ dysfunction of the enzymes in glucose metabolism)

Question 19

What is Von Gierke’s disease?

Answer 19

Glucose 6-phosphatase deficiency

Question 20

What is Mcardle disease?

Answer 20

Muscle glycogen phosphorylase deficiency

Question 21

When does Gluconeogenesis occur?

Answer 21

8-10 hours fasting

Liver

Question 22

What are the 3 major precursors of gluceoneogensis?

Answer 22

Lactate: From anaerobic glycolysis in exercising muscle and muscle blood cells (Cori cycle)
Glycerol: Released from adipose tissue breakdown of triglycerides
Amino acids: Mainly alanine

Question 23

What are the key enzymes in gluconeogensis?

Answer 23

PEPCK
Fructose 1,6-biphosphatase
Glucose-6-phosphatase

Question 24

Where does PEPCK act on?

Answer 24

It catalyses the reaction from oxaloacetate into phosphoenolpyruvate

Question 25

Where does Fructose 1,6bisphosphatase act on?

Answer 25

Converts Fructose 1,6busphosphate into Fructose 6-phosphate

Question 26

Where does Glucose-6-phosphates act on?

Answer 26

Glucose 6-phosphate into glucose

Question 27

What is the function of the hormone glucagon in gluceoneogensis?

Answer 27

Acts on PEPCK, increases the amount and stimulates the effects on gluconeogensis

Question 28

What is the function of the hormone cortisol in gluceoneogensis

Answer 28

Increases the amount and activity of Fructose 1,6 bisphosphatase and stimulates gluconeogensis

Question 29

What is the effects of the hormone insulin in gluconeogensis?

Answer 29

• Acts on PEPCK, decreases amount- inhibits gluceoneogensis

- Acts on Fructose 1,6 phosphatase- decreases amount and activity- inhibits

Question 30

What is the synthesis and hydrolysis of triacylglycerol What is the function of the hormone glucagon in

Answer 30

Synthesised from glycerol and fatty acids into triacylglycerol via esterification
Degradation- Lipolysis

Question 31

Benefits of triacylglycerol

Answer 31

Compact

Hydrophobic

Question 32

What are the two types of adipocytes

Answer 32

Unilocular (white)

Multinocular (brown)

Question 33

TAG metabolism process

Answer 33

TAG is hydrolysed by pancreatic lipase to fatty acids and glycerol
Which these two diffuse into intestinal epithelial cell
Converts back into TAG and binds to chylomicrons
Goes through lymph and blood
It has two places it can go: Storage or directly utilised as tissue (fatty acid oxidation)

Question 34

What effects are there on hormone sensitive lipase in adipose?

Answer 34

Glucagon and Adrenaline causes a positive effect on Hormone sensitive lipase which causes more mobilisation
Insulin causes a negative effects on Hormone sensitive lipase which causes less mobilisation