Glucose and Glycogen metabolism

Question 1

Give 3 structural differences between glucose and glycogen

Answer 1

Glucose is a monosaccharide and glycogen is a polysaccharide.
Glucose is osmotically active and glycogen is low osmolarity.
Glucose is an immediate energy store and glycogen is ` medium term energy store.

Question 2

What is the role of the liver in terms of glycogen?

Answer 2

It is a site of storage.

It acts to maintain blood glucose under the control of insulin and glucagon.

Question 3

What intermediate molecule can we use instead of glucose in the liver?

Answer 3

glucose - 6 - phosphate

Question 4

What is the name of the enzyme involved in glycogen synthesis?
What molecule is needed to
be an activated intermediate in this reaction?

Answer 4

Glycogen synthase

UDP glucose

Question 5

What enzyme is needed for glycogenolysis?

What ends as the final product in the liver? skeletal muscle?

Answer 5

Glycogen phosphorylase

glucose
glucose - 6 - phosphate

Question 6

What is the purpose of the synthesis and breakdown not being a direct reversal?

Answer 6

Independent regulation. Speeding up one process does not speed up the other.

Question 7

What are the 2 steps involved in glycogen synthesis?

Answer 7

1. Glucose is converted to UDP glucose.
   - add a phosphate to glucose forming glucose - 6 - phosphate
   - enzyme called phosphoglucomutase to form glucose - 1 - phosphate
   - Add UTP and make UDP glucose
2. Glycogen synthase enzyme used. It takes the UDP glucose and adds it to the glycogen chain.
   Different enzyme will be needed to add a branching glucose to position 6

Question 8

What is the 2 steps for glycogen breakdown?

Answer 8

1. Phosphorolysis - the phosphate bonds with the glucose leaving the glycogen chain and glucose - 1 - phosphate
   Phosphoglucomutase is then used to move the phosphate to position 6 making glucose - 6 - phosphate.
   Water and glucose - 6 - phosphatase (only found in liver and kidney) is added to remove the phosphate to form glucose.

Question 9

What are 3 sources of glucose to be used in glycolysis?

Answer 9

Sugars and starch from fat
Breakdown of stored glycogen from the liver
Recycled glucose from lactic acid or amino acids or glycerol

Question 10

What are the 4 ‘stages’ of glycolysis?

Answer 10

1 = activation (using up ATP)
2 = splitting the 6 sugar into half 
3 = oxidation (removing 2H atoms)
4 = synthesis of ATP

Question 11

Outline the first 3 reactions of the glycolytic pathway

Answer 11

1 = glucose to glucose - 6 - phosphate (done for diffusion purposes). Glucokinase enzyme catalyses this in the liver and hexakinase in the muscle
2 = glucose - 6 - phoshate to fructose - 6 - phosphate
3 = fructose - 6 phosphate to fructose 1,6 - bisphosphate

Question 12

What is the purpose of reactions 4 and 5?

Answer 12

Splitting the 6C sugar in 3C sugar

Question 13

Explain reactions 4 and 5

Answer 13

4 = aldolase is added to fructose 1, 6 - bisphopshate 
5 = This either froms glyceraldehyde 3 - phosphate or dyhydroxacetone phosphate. More of the first one gets used up so more of this is produced.

Question 14

What step is the oxidation step?

Answer 14

6

Question 15

What occurs in reaction 6?

Answer 15

Glyceraldehyde 3 - phosphate is converted to 1,3 - bisphosphoglycerate by the addition of phosphate and NAD+. Aldehyde is becoming a carboxylic acid

Question 16

Summarise reactions 7 - 10 which are the ATP synthesis stages

Answer 16

7 = substrate - level phosphorylation. Makes ATP from ADP and Pi.
3 - phosphoglycerate is made

8 = Movement of phosphate group to form 2 - phosphoglycerate

9 = Dehydration reaction as water is removed.
Forms phosphoenol pyruvate

10 = substrate level phosphorylation as pyruvate is formed. Removal of phosphate to turn ADP to ATP

Question 17

Explain the anaerobic process

Answer 17

Glycolysis occurs and pyravte is not converted to C02 and H20. It is converted into lactate in order to convert NADP to NAD+.
This is catalysed by lactate dehydrogenase.

Question 18

How are hormonal control and allosteric regulation relevant?

Answer 18

Hormonal control - hormone bind to cell surface receptor and activates internal signalling pathway. This activates kinase.
Allosteric regulation - alteration of the activity of an enzyme by means of a conformational change induced by a different molecule

Question 19

2. The metabolism of glucose to pyruvate:
   a) can only occur in anaerobic conditions.
   b) involves six irreversible reactions
   c) is the main source of ATP in red blood cells.
   d) occurs in the mitochondrial matrix.
   e) requires the cofactor FAD.

Answer 19

C

Question 20

4. When glycogen is broken down in skeletal muscle cells:
   A. glucose is produced by hydrolysis of glucose-1-phosphate.
   B. glucose is produced by hydrolysis of glucose-6-phosphate.
   C. glucose is produced by hydrolysis of glucose-1-6-bisphosphate
   D. glucose-1-phosphate is produced via glucose-6-phosphate.
   E. glucose-6-phosphate is produced via glucose-1-phosphate.

Answer 20

E