Lecture 3 - Energy Storage

Question 1

Give two cells that have an absolute requirement for glucose

Answer 1

RBC’s/neutrophils/innermost cells of kidney medulla/lens of the eye

Question 2

What is the ideal blood glucose concentration?

Answer 2

5mM

Question 3

Give some symptoms of someone with low blood glucose (hypoglycaemia)

Answer 3

Confusion/weakness/nausea/muscle cramps/ brain damage and death at 0.6mM/L and below

Question 4

Why does brain damage occur below 0.6mMol/L blood glucose?

Answer 4

Because although the brain can use ketone bodies for metabolism it still needs a sufficient level of glucose

Question 5

Hyperglycaemia can be dangerous too, give two symptoms of hyperglycaemia?

Answer 5

Retinopathy/uropathy/nephropathy/poor wound healing

Question 6

Why is a high level of glucose harmful in the body?

Answer 6

It can react with proteins and disruptive their function. This is called glycation of proteins (addition of glucose)

Question 7

The two main stores of glycogen are the muscle and the liver, how do their functions differ?

Answer 7

Liver - used to replenish plasma glucose levels -> delivered to where it’s needed

Muscle - can only be used by the muscle for contraction, can’t exit the muscle

Question 8

Glycogen is a polymer of glucose arranged in a tree like structure. What binds link the individual monomers of glucose and what bonds form the branch points every 8-10 residues?

Answer 8

Monomers - alpha 1-4 glycosidic bonds

Branch points - alpha 1-6 glycosidic bonds

Question 9

Give a reason why glycogen a hugely branched structure is favourable

Answer 9

There are several points from which a glucose molecule can be cleaved, so more than one can be cleaved at once

Being stored as a large macromolecule it doesn’t bring water in

Question 10

Starting from the first enzyme in glycogen SYNTHESIS name the enzymes involved

Answer 10

1) hexokinase/glucokinase in liver
2) phosphoglucomutase
3) G1P uridyltransferase
4) glycogen synthase/branching enzyme

Question 11

Glycogenolysis can’t use all the same enzymes in reverse. What enzymes are different?

Answer 11

Debranching enzyme/glycogen phosphorylase depending on branch point or end point

Glucose-6P to change it back to glucose in the liver

Question 12

What is missing in the muscle glycogen to mean that it can’t contribute to buffering blood glucose levels

Answer 12

The glucose-6-phosphatase enzyme

Question 13

What is the rate limiting enzyme in

a) glycogenesis
b) glycogenolysis

Answer 13

a) Glycogen synthase

b) Glycogen phosphorylase

Question 14

Glucagon phosphorylates and insulin dephosphorylates the rate limiting enzymes, would insulin increase or decrease the following enzyme activity

a) glycogen synthase
b) glycogen phosphorylase

Answer 14

A) increase

B) decrease

Question 15

What hormone mirrors the actions of glucagon in regards to glucose mobilisation?

Answer 15

Adrenaline

Question 16

Von Gierkes disease is a deficiency of glucose 6-phosphatase, what are the symptoms of this?

Answer 16

Hepatomegaly (enlarged liver)

Explanation - this enzyme mobilises glucose so it can be transported in the bloodstream. Without the glycogen builds up in the liver and enlarges it

Question 17

McArdle’s disease results in the muscle not being able to mobilise glucose for muscle contraction. This results in the patient having severe tired ness on excercise, which enzyme is deficient in this?

Answer 17

Muscle glycogen phosphorylase

Question 18

After how many hours post feeding is new glucose required via gluconeogenesis

Answer 18

8 hours

Explanation - because the lovers glycogen stores are by this point depleted

Question 19

Where does gluconeogenesis occur?

Answer 19

Liver

A little bit in the kidney

Question 20

Give the three main precursors which can feed into gluconeogenesis

Answer 20

Lactate
Glycerol
Amino acids (mainly alanine)

Question 21

How is lactate produced in the muscle converted back into glucose for the muscle?

Answer 21

Via the cori cycle - lactate carries to the liver in blood -> converted back to glucose in liver -> back to muscle

Question 22

Name the three main regulatory enzymes in gluconeogenesis, which two are the major two control points?

Answer 22

PEPCK
Fructose 1,6-bisphosphatase
Glucose-6-phosphatase

Top two are major control points

Question 23

Glucagon and insulin again are the regulatory hormones of gluconeogenesis. Does glucagon increase or decrease activity of

a) PEPCK
b) fructose 1,6 bisphosphatase

Answer 23

a) increase
b) increase

Explanation - think in terms of increasing levels of circulating glucose

Question 24

Triglycerides are a storied form of lipid made up of glycerol and fatty acids. What type of tissue are they stored in?

Answer 24

Adipose tissue

Explanation - TAGs are hydrophobic and need to be stored thus is this anhydrous form

Question 25

What’s the key regulatory enzyme in fatty acid synthesis?

Answer 25

Acetyl-CoA carboxylase

Question 26

Name two things that increase the activity of acetyl-CoA carboxylase and two things which decrease its activity

Answer 26

Increase - insulin/citrate

Decrease - glucagon/adrenaline/AMP

Question 27

beta oxidation occurs in the mitochondria, where does fatty acid synthesis occur?

Answer 27

The cytoplasm

Question 28

The mobilisation of fatty acids and glycerol from adipose tissue is controlled by what enzyme?

Answer 28

Hormone sensitive lipase

Question 29

Does glucagon inhibit or stimulate hormone sensitive lipase?

Answer 29

Stimulates

Explanation - glucagon wants to increase blood glucose levels, HSL breaks TAGs down to glycerol and FA’s. The glycerol can go into gluconeogenesis

Question 30

In what form is most energy stored in a human, the proportion of energy stored as this increases in obesity

Answer 30

TAG’s/adipose tissue

Question 31

Name three differences between Beta oxidation (fatty acid oxidation) and fatty acid synthesis

Answer 31

B oxidation occurs in mitochondria, fatty acid synthesis in the cytoplasm
B oxidation is oxidative (produces reducing power), fatty acid synthesis is reductive (uses reducing power)
Insulin inhibits beta oxdation, insulin stimulates fatty acid synthesis
B oxidation requires little ATP, fatty acid synthesis needs a lot of ATP

Question 32

Give the key regulatory enzymes in:

a) glycolysis
b) gluconeogenesis
c) lipogenesis
d) beta-oxidation
e) glycogenesis
f) glycogenolysis

Answer 32

glycolysis - pyruvate kinase, phosphofructokinase (main) , hexokinase
gluconeogenesis - PEPCK, Fructose-1,6 bisphosphatase
glycogenesis - glycogen synthase
glycogenolysis - glycogen phosphorylase
lipogenesis - acetyl-CoA carboxylase
beta oxidation - CAT1