5 Energy Storage (glycogen and fat)

Question 1

Tissues with absolute requirement for glucose

Answer 1

-RBCs - no mitochondria
-lens of eye
-neutrophils - located in areas of low O2
-innermost cells of kidney medulla - low O2 environment

Question 2

Outline glycogen storage

Answer 2

Stored as granules
- muscles - 300mg only be used by muscles, no glucose 6 phosphate
-liver 100mg used to buffer plasma glucose

Question 3

Glycogenesis definition

Answer 3

Synthesis of glycogen
Anabolic-reducing

Question 4

Is glycogenesis reducing or oxidative?

Answer 4

Anabolic so reducing

Question 5

Glycogenolysis definition

Answer 5

Breaking down glycogen to glucose

Question 6

Two examples of glycogen storage disease

Answer 6

1- Von Gierke’s disease: glucose 6 phosphate deficiency
2- McArdle disease: muscle glycogen phosphorylase deficiency

Question 7

Consequence of increased glycogen storage

Answer 7

Tissue damage

Question 8

Consequence of decreased glycogen storage

Answer 8

Hypoglycaemia
Poor exercise tolerance

Question 9

Gluconeogenesis definition

Answer 9

Production of new glucose from an originally non glucose source
After 8 hours of fasting

Question 10

Where and when does gluconeogensis occur?

Answer 10

Mainly liver
Partially in kidney cortex

~ 8 hours of fasting

Question 11

What are the non glucose sources in gluconeogensis?

Answer 11

• amino acids: mainly alanine
• glycerol: release from adipose tissue-breakdown of triglycerides
• lactate: from anaerobic respiration

Question 12

What is the cori cycle?

Answer 12

Lactate being used as a non glucose source in gluconeogensis

1- muscles used up glucose
2- lactate is produced in anaerobic respiration
3- lactate transported to liver in blood
4- glucose made in liver via gluconeogensis

Question 13

3 key enzymes involved in gluconeogenesis

Answer 13

PEPCK
Fructose 1,6 phosphatase
Glucose 6 phosphatase

Question 14

Which enzymes are regulated in gluconeogensis and how?

Answer 14

PEPCK and fructose 1,6 phosphatase

Stimulated by glucagon and adrenaline - glucose needed in times of starvation and stress

Inhibited by insulin - glucose not needed

Question 15

When are lipids used as an energy source?

Answer 15

-prolonged exercise
-stress
-starvation
-during pregnancy

Question 16

How are TAGs stored?

Answer 16

-hydrophobic
-stored in anhydrous form - no osmotic effect
-in adipose tissue

Question 17

How can you identify adipose in a H&E stain?

Answer 17

-white fat broken down during fixation
-nucleus and cytoplasm pushed to side

Question 18

Lipogenesis definition

Answer 18

Fatty acid synthesis

Question 19

Where are fatty acids synthesised?

Answer 19

Liver

Question 20

What is the regulator enzyme in lipogenesis?
Describe the regulation

Answer 20

-acetyl CoA carboxylase

• inhibited by glucagon,adrenaline and AMP: acetyl CoA needed for respiration
• stimulated by insulin+citrate

Question 21

What does the fatty acid synthase complex do?

Answer 21

Additions of 2C units from malonyl CoA (from beta oxidation) to make fatty acids

Question 22

Lipolysis definition

Answer 22

Fat mobilisation

Question 23

How are fatty aids transported to muscle?

Answer 23

In the blood
Albumin complex

Question 24

Weight and energy content of TAG in healthy 70kg man

Answer 24

15kg
600,000kJ

Question 25

Weight and energy content of TAG in obses 135kg man

Answer 25

80kg 3,000,000kJ

Question 26

Glucose synthase function

Answer 26

Adds glucose molecules onto existing branches on glycogen making a1-4 glycosidic bonds

Question 27

Branching enzyme function

Answer 27

Creates new branches off of glycogen from the formation of a1-6 glycosidic bonds

Question 28

Hexokinase/glucokinase function

Answer 28

-kinase: adds a phosphate group Glucose > glucose 6 phosphate Glucokinase in liver

Question 29

Phosphoglucomutase function

Answer 29

Reversible reaction of G6P to G1P

Question 30

G1P uridyl transferase function

Answer 30

Transfers phosphate group on G1P to UDP G1P > UDP glucose

Question 31

Glycogen phosphorylase function

Answer 31

Breaks a1-4 glycosidic bonds in the chains of glycogen

Question 32

De-branching enzyme

Answer 32

Breaks a1-6 glycosidic bonds on glycogen branches

Question 33

Why does insulin stimulate fatty acid production?

Answer 33

Lots of glucose > lots of glycolysis > lots of acetyl CoA > acetyl CoA made into malonyl CoA to make fatty acids

Question 34

Why can’t glycogen stored in muscles be used to raise blood sugar?

Answer 34

They don’t have glucose 6 phosphatase

Question 35

Signs and symptoms of baby with Von Gierke’s Disease

Answer 35

- **protuberant abdomen** (looks like a potato) from heptaomegaly as glycogen is deposited in liver and not broken down fully - **sweating** and **pallor** from hypoglycaemia - **high blood fatty acids** from gluconeogensis to compensate for low blood glucose

Question 36

Normal blood glucose range

Answer 36

4-6 mmol/L

Question 37

What is the role of insulin on lipogenesis?

Answer 37

Stimulates fatty acids synthesis via dephosphylation of acetyl CoA carboxylase

Question 38

What is the renal threshold for glucose?

Answer 38

10mmol/L

Question 39

Describe the molecular structure of glycogen

Answer 39

a 1-4 glycosidic chain bonds a 1-6 glycosidic branch bonds

Question 40

Outline the steps in glycogenesis

Answer 40

Glucose + ATP > glucose 6 phosphate + ATP *hexokinase/glucokinase* Glucose 6 phosphate > glucose 1 phosphate *phosphoglucomutase* Glucose 1 P + UTP + H2O > UDP-glucose + Pi *uridyl transferase* Glycogen (n residues) + UDP-glucose > glycogen (n+1 residues) + UDP *glycogen synthase / branching enzyme*

Question 41

Outline glycogenolysis

Answer 41

Glycogen (n residues) + Pi > glycogen (n-1 residues) + glucose 1 P *glycogen phosphorylase / debranching enzyme) Glucose 1 P > glucose 6 P *phosphoglucomutase* Glucose 6 P > released into blood as glucose (liver) > used for glycolysis (muscle)

Question 42

What is the rate limiting enzyme for glycogenolysis?

Answer 42

Glycogen phosphorylase

Question 43

What is the rate limiting enzyme in glycogenesis?

Answer 43

Glycogen synthase

Question 44

What effect does glucagon + adrenaline have on the rate limiting enzymes in glycogen metabolism?

Answer 44

**Mechanism**: phosphorylation Decreases glycogen synthase Increases glycogen phosphorylase

Question 45

What effect does insulin have on the rate limiting enzymes in glycogen metabolism?

Answer 45

**Mechanism** - dephosphorylation Increases glycogen synthase Decreases glycogen phosphorylase

Question 46

How do glycogen storage diseases occur?

Answer 46

Arise from deficiency or dysfunction of enzymes or glycogen metabolism

Question 47

Why can glucose not be made from acetyl CoA?

Answer 47

Acetyl CoA can’t be converted to pyruvate PDH reaction is irreversible

Question 48

Outline lipogenesis

Answer 48

In liver +oxaloacetate Glucose > pyruvate > acetyl coA > citrate Citrate > acetyl coA + oxaloacetate in cytoplasm Acetyl coA > malonyl coA *acetyl coA carboxylase* Malonyl coA + 2C units > fatty acids *fatty acid synthase complex*

Question 49

Outline lipolysis

Answer 49

Triacylglycerol > glycerol + fatty acids *hormone sensitive lipase*

Question 50

What is the regulation of lipolysis

Answer 50

**inhibited by insulin** > phosphorylation **stimulated by glucagon + adrenaline** > dephosphorylation