Glucose & Glycogen Metabolism

Question 1

How much glucose is present in the body and where?

Answer 1

10g in plasma

Question 2

How much glycogen is present in the body and where?

Answer 2

400g in tissue stores

Question 3

Why is there so little glucose in the body?

Answer 3

Immediate energy source

Osmotically active so stored as glycogen

Question 4

What bonds are present between glucose monomers in a glycogen molecule?

Answer 4

1,4-glycosidic bonds

1,6-glycosidic bonds at branches

Question 5

How much glycogen is stored in the liver?

Answer 5

100-120g

Question 6

What is the role of glycogen in the liver?

Answer 6

(Liver is sensitive to blood glucose concentration)

Acts to maintain blood glucose under influence of insulin and glucagon

Question 7

What is the role of glycogen in muscles?

Answer 7

Fuel for muscle contraction (used locally)

Question 8

What is muscle glycogen sensitive to? (5)

Answer 8

Needs of tissue

Calcium

Adrenaline

AMP

ATP

Question 9

Why is glycogen not converted all the way to glucose in muscle tissue?

Answer 9

Glucose-6-phosphate can enter glycolysis pathway directly

Question 10

What enzyme catalyses glycogen synthesis?

Answer 10

Glycogen synthase/synthetase

Question 11

What enzyme catalyses glycogen breakdown?

Answer 11

Glycogen phosphorylase

Question 12

What are the final products of glycogen degradation in the liver and muscles?

Answer 12

Liver: glucose

Muscle: glucose-6-phosphate

Question 13

Why are there two separate enzymes used to catalyse the synthesis/breakdown of glycogen?

Answer 13

Prevent a futile cycle

Question 14

What are the two general steps of glycogen synthesis?

Answer 14

1. Activation of glucose

2. Glycogen synthase reaction

Question 15

What occurs during the first step of glycogen synthesis?

Answer 15

Hexokinase/glucokinase phosphorylates glucose using ATP to form glucose-6-phosphate

Phosphoglucomutase converts glucose-6-phosphate to glucose-1-phosphate

UDP glucose pyrophorylase converts glucose-1-phosphate to UDP glucose using UTP (forms pyrophosphate/PPi)

Question 16

What occurs during the second step of glycogen synthesis?

Answer 16

UDP glucose and glycogen primer molecule joined by 1,4-glycosidic bond by glycogen synthase (forms glycogen and UDP)

Question 17

Describe the process of glycogen breakdown

Answer 17

Glycogen phosphorylase uses a phosphate to break glycogen into glycogen (n-1) and glucose-1-phosphate

Phosphoglucomutase converts glucose-1-phosphate to glucose-6-phosphate

Glucose-6-phosphatase catalyses hydrolysis of glucose-6-phosphate to glucose and Pi

Question 18

Where is glucokinase found?

Answer 18

Liver

Question 19

Where is hexokinase found?

Answer 19

All tissues except liver

Question 20

Where is glucose-6-phosphatase found?

Answer 20

Liver and kidney

Question 21

Where does glycolysis occur?

Answer 21

Cytosol of all cells in all organisms

Question 22

What is the purpose of glycolysis? (2)

Answer 22

Synthesise ATP using glucose as fuel

Forms intermediates for fat or amino acid synthesis

Question 23

Where can glucose be sourced from? (3)

Answer 23

Sugars and starch from diet

Glycogen stores in liver

Recycling from lactic acid, amino acids or glycerol

Question 24

How many reactions make up the glycolysis pathway?

Answer 24

10

Question 25

What are the four general stages of glycolysis?

Answer 25

1. Activation using ATP 2. Splitting of 6C sugar 3. Oxidation (removal of 2H) 4. Synthesis of ATP

Question 26

Describe the activation stage of glycolysis

Answer 26

1. Hexo/glucokinase uses ATP to phosphorylate D-glucose to glucose-6-phosphate 2. Phosphohexose isomerase converts glucose-6-phosphate to fructose-6-phosphate 3. Phosphofructokinase uses ATP to phosphorylate fructose-6-phosphate to fructose-1,6-bisphosphate

Question 27

Describe the splitting stage of glycolysis

Answer 27

4. Aldolase catalyses the splitting of fructose-1,6-bisphosphate into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate 5. Triose phosphate isomerase converts dihydroxyacetone phosphate to glyceraldehyde 3-phosphate

Question 28

Describe the oxidation stage of glycolysis

Answer 28

6. Glycerate 3-phosphate dehydrogenase converts glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate by adding a Pi NAD+ is reduced

Question 29

Describe the ATP synthesis stage of glycolysis

Answer 29

7. Phosphoglycerate kinase converts 1,3-bisphosphoglycerate to 3-phosphoglycerate; ATP formed 8. Phosphoglycerate mutase converts 3-phosphoglycerate to 2-phosphoglycerate 9. Enolase dehydrates 2-phosphoglycerate to phosphoenol pyruvate 10. Pyruvate kinase converts phosphoenolpyruvate to pyruvate; ATP formed

Question 30

What inhibits enolase?

Answer 30

Fluoride ions

Question 31

What are the three irreversible stages of glycolysis and their enzymes?

Answer 31

First (hexo/glucokinase) Third (phosphofructokinase) Last (pyruvate kinase)

Question 32

What is the net yield of ATP from glycolysis using one glucose?

Answer 32

2 ATP

Question 33

What is the reaction of anaerobic respiration?

Answer 33

Pyruvate + NADH + H+ --> lactate + NAD+

Question 34

What enzyme catalyses anaerobic respiration?

Answer 34

Lactate dehydrogenase

Question 35

Where is lactate converted back to pyruvate?

Answer 35

Liver

Question 36

What happens to pyruvate in micro-organisms?

Answer 36

Converted to ethanol (anaerobic respiration)

Question 37

What happens to pyruvate in aerobic conditions?

Answer 37

Converted to acetyl CoA then used in TCA cycle and oxidative phosphorylation to form carbon dioxide and water

Question 38

What happens to pyruvate in humans in anaerobic conditions?

Answer 38

Converted to lactate

Question 39

How does allosteric control of glycogen metabolism work?

Answer 39

Glucagon or adrenaline bind and activate cell surface receptor which activates an internal signalling pathway Protein kinase is activated Glycogen phosphorylase is phosphorylated = activated Glycogen synthase phosphorylated = deactivated

Question 40

Which allosteric regulators affect phosphofructokinase?

Answer 40

ATP and citrate = allosteric repressors/inhibitors AMP = allosteric activator

Question 41

What is the function of glycolysis in skeletal muscle? (2)

Answer 41

ATP production during intense exercise (lack of oxygen) Produce pyruvate to form acetyl CoA for aerobic respiration

Question 42

What is the function of glycolysis in red blood cells?

Answer 42

Only pathway for ATP production (no mitochondria)

Question 43

What is the function of glycolysis in the brain?

Answer 43

Major source of ATP (cannot use fat)