BMS07-1026 Glucose & Glycogen Metabolism

Question 1

Draw the structure of glucose

Answer 1

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Question 2

Draw the structure of glycogen

Answer 2

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Question 3

What is the difference between glucose and glycogen?

Answer 3

Glycogen is a polysaccharide of glucose

Question 4

What is gluconeogenesis?

Answer 4

Glucose from AA or FA

Question 5

How is glycogen used in the liver?

Answer 5

It’s converted to glucose-6-phosphate and then looses a Pi to form glucose

Question 6

How is glucose-6-phosphate converted to glucose?

Answer 6

hydrolyses glucose-6-phopshate so a Pi is released, forming glucose

Question 7

Why do the final products of glycogenolysis differ in the liver and muscle?

Answer 7

In the muscle the end product is glucose-6-phosphate not just glucose as it has to enter the glycolysis pathway

Question 8

What is glycogenolysis?

Answer 8

Glucose from glycogen

Question 9

Describe glycogen breakdown in the liver and kidney

Answer 9

Glycogen is converted to glucose-1-phosphate using the enzyme glycogen phosphorylase (stimulated by insulin) and a debranching enzyme, by adding a Pi

Glucose-1-phosphate is converted to glucose-6-phosphate using the enzyme phosphoglucomutase

Glucose-6-phosphate is then converted to glucose using the enzyme glucose-6-phosphatase and adding a water

Question 10

Describe the osmolarity of glucose and glycogen

Answer 10

Glucose is osmotically active while glycogen has a low osmolarity

Question 11

What stimulates glycogenolysis in the muscle and liver?

Answer 11

in the liver insulin and glucagon stimulate it while in the muscle AMP, ATP, Ca and adrenaline stimulate it

Question 12

Describe the activation of glucose

Answer 12

Glucose is converted to glucose-6-phosphate by converting ATP to ADP

Glucose-6-phosphate is converted to glucose-1-phosphate by the enzyme phosphoglucomutase

Glucose-1-phosphate is converted to UDP glucose through the conversion of UTP to PPi and the use of the UDP glucose pyrophosphorylase enzyme

Question 13

How does glucose activation differ in the liver and muscle?

Answer 13

In the muscle hexokinase is the protein kinase at work while in the muscle it’s glucokinase

Question 14

What is UDP glucose?

Answer 14

This is the active form of glucose

Question 15

Why do we activate glucose?

Answer 15

This allows us to reform glycogen

Question 16

How is glycogen reformed?

Answer 16

UDP glucose and a glycogen primer join using the enzyme glycogen synthase (which is activated by insulin) to and a branching enzyme to form glycogen

Question 17

What are the 4 stages of the glycolysis pathway?

Answer 17

Activation- using ATP
Splitting the 6C sugar in half
Oxidation (removing 2H)
ATP synthesis

Question 18

Which reactions are involved in the activation stage?

Answer 18

Reactions 1, 2 and 3

Question 19

Describe reaction 1

Answer 19

D glucose is converted to glucose-6-phosphate
ATP is converted to ADP
Hexokinase or glucokinase catalyses this

Question 20

Describe reaction 2

Answer 20

Glucose-6-phosphate is converted to fructose-6-phosphate

It is catalysed by phosphohexose isomerase

Question 21

Describe reaction 3

Answer 21

Fructose-6-phosphate is converted to fructose-1,6-bisphophate using the enzyme phosphofructokinase
ATP is converted to ADP

Question 22

Describe reaction 6

Answer 22

Glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate
The enzyme glyceraldehyde-3-phosphate dehydrogenase is used
NAD + Pi is converted to NADH + H

Question 23

Which step is the oxidation step?

Answer 23

Reaction 6

Question 24

Which step is the activation step?

Answer 24

Reaction 1, 2 and 3

Question 25

Which step is the splitting step?

Answer 25

Reaction 4 and 5

Question 26

Describe reaction 4

Answer 26

Fructose-1,6-bisphosphate is converted to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate

Question 27

Which product from reaction 4 is taken forwards in the reaction chain?

Answer 27

Glyceraldehyde-3-phosphate

Question 28

Describe reaction 5

Answer 28

The conversion of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate using the triose phosphate isomerase enzyme

Question 29

What is significant about reaction 6?

Answer 29

It swaps a H on glyceraldehyde-3-phosphate to OP which is a high energy bond

Question 30

Which reactions are in the ATP synthesis stage?

Answer 30

Reaction 7, 8, 9 and 10

Question 31

What kind of reaction is reaction 7?

Answer 31

Substrate level phosphorylation

Question 32

Describe reaction 7

Answer 32

1,3-bisphosphoglycerate to 3-phosphohlycerate This is catalysed by phophoglycerate kinase ADP is converted to ATP

Question 33

What kind of reaction is reaction 8?

Answer 33

Isomerisation

Question 34

Describe reaction 8

Answer 34

3-phosphoglycerate is converted to 2-phosphoglycerate using the enzyme phosphoglycerate mutase

Question 35

What changes during reaction 8?

Answer 35

The OP group swaps places with the OH group from the reactant to the product

Question 36

Describe reaction 9

Answer 36

2-phosphoglycerate is converted to phosphoenol pyruvate Enolase catalyses this Water is released

Question 37

What is significant about reaction 9?

Answer 37

A high energy phosphate bond is formed

Question 38

What kind of reaction is reaction 10?

Answer 38

Substrate level phosphorylation

Question 39

Describe reaction 10

Answer 39

Phosphoenolpyruvate is converted to pyruvate Pyruvate kinase catalyses this ADP is converted to ATP

Question 40

What is the ATP yield from glycolysis?

Answer 40

The early stages use 2 ATP but the later ones make 4 ATP so there is a net yield of 2 ATP

Question 41

What happens during anaerobic glycolysis?

Answer 41

Instead of pyruvate being metabolised to carbon dioxide it's converted to lactate to regenerate NAD from NADH + H

Question 42

Describe the conversion of pyruvate to lactate in the liver and muscle

Answer 42

In the muscle lactate dehydrogenase catalyses the conversion forming NAD from NADH + H In the liver the reverse of this reaction occurs

Question 43

How do microorganisms use pyruvate?

Answer 43

To form ethanol in fermentation regenerating NAD for glycolysis

Question 44

Other than forming lactate and ethanol, what is another metabolic fate of pyruvate? (4)

Answer 44

Form acetyl coenzyme A which is converted to fatty acids when there is an excessive calorie intake Form acetyl coenzyme A which is used in the citric acid cycle to form carbon dioxide Form alanine by transamination To oxaloacetate and then glucose 6 phosphate which can be converted back to pyruvate

Question 45

How is glycolysis used in the body?

Answer 45

In skeletal muscle during intense exercise In RBC In the brain

Question 46

Where does glycolysis occur

Answer 46

In the cytosol

Question 47

Why isn't the synthesis and breakdown of glycogen direct reversals of eachother?

Answer 47

So independent regulation can occur and there isn't a futile cycle

Question 48

What is special about glycolysis?

Answer 48

It can occur in aerobic and anaerobic conditions

Question 49

How is glycolysis linked to the citric acid cycle?

Answer 49

Pyruvate can enter it

Question 50

How is glycogen adapted for glycolysis?

Answer 50

Has many branches so it breaks down quickly

Question 51

What is special about muscle cells?

Answer 51

They can use glucose-6-phosphate directly it doesn't need to be converted to glucose

Question 52

Why is UTP energetically favourable?

Answer 52

UTP breaks down leaving PPI, PPI instantly breaks down into 2 Pi so the reaction is pulled forwards

Question 53

What is present in most tissues glucokinase or hexokinase?

Answer 53

Hexokinase

Question 54

What's the difference between bis and bi in chemical names?

Answer 54

Bi means they are attached while bis means they aren't

Question 55

Discuss the speed of reaction 5?

Answer 55

It happens quickly as glyceraldehyde-3-phosphate is removed very quickly pushing the reaction forwards

Question 56

What is substrate level phosphorylation?

Answer 56

Adding a Pi to ADP to form ATP

Question 57

What are the 2 fates of lactate?

Answer 57

Converted straight to glucose or put back into the blood stream

Question 58

What is allosteric inhibition?

Answer 58

Covalent alteration

Question 59

Which reactions are irreversible?

Answer 59

Reaction 1, 10 and 3

Question 60

How is reaction 3 regulated?

Answer 60

Phosphofructokinase needs ATP to bind at one site, but when it binds at the other the reaction is slowed. Insulin activates phosphatase to remove to Pi making it inactive

Question 61

How is reaction 1 regulated? (5)

Answer 61

Glucagon activates the GPCR, the alpha units runs off as GDP turns to GTP, this activates adenylyl cyclase, this increases cAMP, this activates protein kinase A, this adds a Pi to glycogen phosphorylase, activating it Insulin activates phosphodiesterase, converting cAMP to AMP and activates protein phosphatase which dephosphorlyses glycogen phosphorylase Hexokinase is inhibited by it's product Glucagon stops the synthesis of glucokinase Insulin causes the synthesis of glucokinase

Question 62

How is reaction 10 regulated?

Answer 62

A Pi is added to glycogen synthase turning it off

Question 63

How does glycogen regulate glycolysis?

Answer 63

It binds to the GPCR causing a conformational change so the alpha subunit is released and converts ATP to cAMP and Pi, cAMP activates hexo/glucokinase which phosphorylyses glycogen phosphorylase to turn the enzyme on

Question 64

What's the difference between hexokinase and glucokinase?

Answer 64

Glucokinase has a higher km so can catalyse the reaction at a faster rate

Question 65

How can pyruvate be formed?

Answer 65

From many amino acids

Question 66

How is the irreversible reaction of glycolysis bypassed?

Answer 66

Oxloacetate is converted to phosphoenolpyruvate

Question 67

How is the synthesis of oxaloacetate enhanced?

Answer 67

Acetyl coenzyme A activates pyruvate carboxylase so more is made

Question 68

What chemicals regulate glycogen phosphorylase?

Answer 68

ATP and glucose-6-phosphate

Question 69

How is pyruvate kinase regulated? (3)

Answer 69

Fructose 1,6-bisphosphate and ATP activates it Glucagon phosphorylates it making it inactive by a cAMP dependant protein kinase Insulin activates phosphatase removes a Pi activating it