Session 4-Energy Storage (Glycogen And Fat)

Question 1

Which tissues have an absolute requirement for glucose as an energy source? (4)

Answer 1

1) red blood cells
2) neutrophils
3) innermost cells of kidney medulla
4) lens of eye

Question 2

Define glycation

Answer 2

Addition of glucose to protein without enzymatic regulation

Question 3

What is the normal blood glucose concentration?

Answer 3

~5mmol/L

Question 4

What are the consequences of the following blood glucose concentrations:
A) 2.8 mmol/L
B) 1.7 mmol/L
C) 1.1 mmol/L
D) 0.6 mmol/L

Answer 4

A) confusion
B) weakness, nausea
C) muscle cramps
D) brain damage, death

Question 5

What is glycogen stored as?

Answer 5

Granules

Question 6

Glycogen is a polymer consisting of chains of which residues?

Answer 6

Glucose

Question 7

The chains of glycogen are branched and originate from a dimer of which protein?

Answer 7

Glycogenin

Question 8

Which reactions in glycogenesis require energy and which enzymes catalyse these reactions? (2)

Answer 8

1) glucose + ATP -> glucose-6-phosphate + ADP
Catalysed by hexokinase (glucokinase in liver)
2) glucose-1-phosphate + UTP + water -> UDP-glucose + PPi
Catalysed by G1P uridylyltransferase

Question 9

Which enzyme catalyses the reversible reaction between glucose-6-phosphate and glucose-1-phosphate?

Answer 9

Phosphoglucomutase

Question 10

Which enzyme/s catalyse the following reaction:

Glycogen + UDP-glucose -> glycogen + UDP

Answer 10

Glycogen synthase
Or
Branching enzyme

Question 11

What is glycogenolysis?

Answer 11

Glycogen degradation

Question 12

Which enzyme catalyses the following reaction:

Glycogen (n residues) + Pi -> glucose-1-phosphate + glycogen (n-1 residues)

Answer 12

Glycogen phosphorylase
OR
De-branching enzyme

Question 13

True or false: glycogenolysis is a simple reversal of glycogenesis

Answer 13

FALSE - different enzymes allow inhibition of one pathway and stimulation of another

Question 14

How is glucose-6-phosphate used in muscle?

Answer 14

Used in glycolysis for energy production

Question 15

How is glucose-6-phosphate used in the liver?

Answer 15

Converted to glucose which is released into the blood for use by other tissues

Question 16

True or false: liver glycogen is a buffer of blood glucose levels

Answer 16

TRUE

Question 17

Which enzyme does muscle lack?

Answer 17

Glucose-6-phosphatase

Question 18

What is the rate limiting enzyme for glycogen synthesis?

Answer 18

Glycogen synthase

Question 19

What is the rate limiting enzyme for glycogen degradation?

Answer 19

Glycogen phosphorylase

Question 20

What effect does glucagon and adrenaline have on:

1) glycogen synthase
2) glycogen phosphorylase

Answer 20

1) decreases enzyme activity

2) increases enzyme activity

Question 21

What effect does insulin have on:

1) glycogen synthase
2) glycogen phosphorylase

Answer 21

1) increases enzyme activity

2) decreases enzyme activity

Question 22

True or false: glucagon has no effect in the muscle

Answer 22

TRUE - no glucagon receptors in muscle

Question 23

What is an allosteric activator of muscle glycogen phosphorylase but not of the liver form of the enzyme?

Answer 23

AMP

Question 24

What can diminished glycogen stores lead to?

Answer 24

Hypoglycaemia and poor exercise tolerance

Question 25

What is von Gierke's disease?

Answer 25

Glucose-6-phosphatase deficiency

Question 26

What happens to the liver in von Gierke's disease?

Answer 26

Hepatomegaly

Question 27

What is McArdle disease?

Answer 27

Muscle glycogen phosphorylase deficiency

Question 28

Where does gluconeogenesis occur?

Answer 28

In liver and to lesser extent in kidney cortex

Question 29

What are the three major precursors for gluconeogenesis?

Answer 29

1) lactate 2) glycerol 3) amino acids (mainly alanine)

Question 30

Why is there no net synthesis of glucose from acetyl-CoA?

Answer 30

Acetyl-CoA cannot be converted into pyruvate because the pyruvate dehydrogenase reaction is irreversible

Question 31

Which enzyme converts glucose-6-phosphate to glucose in gluconeogenesis?

Answer 31

Glucose-6-phosphatase

Question 32

Which enzyme converts fructose 1,6-bisphosphate to fructose 6-phosphate in gluconeogenesis?

Answer 32

Fructose 1,6-bisphosphatase

Question 33

Which enzyme converts oxaloacetate to phosphoenolpyruvate in gluconeogenesis?

Answer 33

PEPCK

Question 34

Which two key enzymes are regulated by hormones in response to starvation/fasting, prolonged exercise and stress?

Answer 34

Fructose 1,6-bisphosphatase PEPCK

Question 35

What effect does glucagon and cortisol have on: 1) PEPCK 2) Fructose 1,6-bisphosphatase 3) gluconeogenesis

Answer 35

1) increases amount 2) increases amount and activity 3) stimulates

Question 36

What effect does insulin have on: 1) PEPCK 2) Fructose 1,6-bisphosphatase 3) gluconeogenesis

Answer 36

1) decreases amount 2) decreases amount and activity 3) inhibits

Question 37

Which receptor does insulin act through?

Answer 37

Tyrosine kinase receptor

Question 38

Which receptor does glucagon act through?

Answer 38

GPCR

Question 39

Which receptor does cortisol act through?

Answer 39

Steroid hormone nuclear receptor

Question 40

How many hours after feeding does gluconeogenesis occur?

Answer 40

8-10 hours

Question 41

What is excess energy intake converted to for storage?

Answer 41

Triacylglycerol (TAG)

Question 42

True or false: TAGs are hydrophilic and stored in hydrous form in adipose tissue

Answer 42

FALSE - hydrophobic so stored in anhydrous form

Question 43

True or false: TAG has an energy content that is twice that of carbohydrate or protein

Answer 43

TRUE

Question 44

When is TAG utilised?

Answer 44

Prolonged exercise Stress Starvation During pregnancy

Question 45

Why does fatty acid oxidation not occur in the brain?

Answer 45

Fatty acids don't easily pass blood-brain barrier

Question 46

Where does lipogenesis occur?

Answer 46

Mainly in liver

Question 47

Which two molecules does lipogenesis require?

Answer 47

ATP | NADPH

Question 48

What is the key regulatory enzyme in liver lipogenesis?

Answer 48

Acetyl-CoA carboxylase

Question 49

Describe the steps involved in lipogenesis (50

Answer 49

1) glucose -> pyruvate (glycolysis) 2) pyruvate enters mitochondria and forms acetyl-CoA and oxaloacetate which condense to form citrate 3) citrate -> cytoplasm and cleaved back to acetyl-CoA and oxaloacetate 4) acetyl-CoA carboxylate produces malonyl-CoA from acetyl-CoA 5) fatty acid synthase complex builds fatty acids by addition of 2 carbon units from malonyl-CoA

Question 50

What does insulin and citrate do to acetyl-CoA carboxylase?

Answer 50

Increases activity

Question 51

What does glucagon/adrenaline and AMP do to acetyl-CoA activity?

Answer 51

Decreases activity

Question 52

Where does fatty acid oxidation occur?

Answer 52

Mitochondria

Question 53

Where does fatty acid synthesis occur?

Answer 53

Cytoplasm

Question 54

True or false: fatty acid oxidation is reductive

Answer 54

FALSE - oxidative, fatty acid synthesis is reductive

Question 55

What is the term given to fat mobilisation?

Answer 55

Lipolysis

Question 56

What do glucagon and adrenaline do to hormone sensitive lipase (HSL)?

Answer 56

Lead to phosphorylation and activates HSL

Question 57

What does insulin do to hormone sensitive lipase (HSL)?

Answer 57

Leads to de-phosphorylation and inhibits HSL

Question 58

Which protein transports fatty acids to muscle and other tissues?

Answer 58

Albumin