Metabolic stores

Question 1

Where are most carbohydrates stored and what as?

Answer 1

• Stored as glycogen

* Mainly in the liver and muscle

Question 2

How long would a typical glycogen store last for?

Answer 2

3-5 hours of moderate exercise

Question 3

Describe the two ways glycogen is broken down

Answer 3

1) 90% of the time: Pi is added forming Glucose-6-phosphate (no ATP required)
2) H20 is added forming glucose, transported out of the cell then phosphorylated in the destination using ATP

Question 4

Why are the two routes of breaking down glycogen needed?

Answer 4

• Glucose 6-phosphate cannot easily pass through the cell membrane
• Glucose can pass through the cell membrane

Question 5

What is the major form in which fuel is stored in the body and why?

Answer 5

Lipids

• Weight for weight they release about six times the amount of energy as glycogen

Question 6

What are triglycerides?

Answer 6

Esters of glycerol and fatty acids

Question 7

Describe lipolysis

Answer 7

1. Lipases digest triglycerides into glycerol and 3 fatty acids
2. Glycerol (from the triglyceride) becomes a glycolysis substrate producing pyruvate
3. Beta-oxidation chops 2 carbon acyl units off the fatty acids
4. Acyl units become acetyl CoA and can be used in the citric acid cycle

Question 8

Where are the majority of fatty acids and glycerol released by adipose tissue metabolised?

Answer 8

The liver

Question 9

What happens due to the process of fatty acids being linked to coenzyme A?

Answer 9

• Hydrogen and electrons are removed during fatty acid oxidation and are passed along the respiratory chain
• Indirectly produces ATP

Question 10

What does the breakdown of fatty acids lead to?

Answer 10

The formation of ketone bodies

Question 11

What are the main ketone bodies produced in the breakdown of fatty acids?

Answer 11

• Acetoacetate
• 3-hydroxybutyrate
• Acetone

Question 12

Why are ketone bodies made?

Answer 12

• Oxaloacetate becomes depleted because the liver converts it to pyruvate to produce glucose
• The acetyl group therefore cannot enter the cycle (can’t bind to anything)

Question 13

Why may someone’s breath smell fruity?

Answer 13

• If someone has been fasting for some time
• Lipids are being used as a fuel
• Ketone bodies smell fruity

Question 14

How can amino acids be used in metabolism?

Answer 14

• Amino acids can’t be stored so used as metabolic fuel
• Some amino acids can be deaminated, yielding NH4 and a keto acid which are intermediates of the glycolytic pathway or citric acid cycle
• Others that can’t undergo transamination, passing their amino acid on

Question 15

Describe transamination

Answer 15

• Pass amino group to a ketone acid (usually alpha-ketoglutarate)
• Resulting keto acid can be fed into glycolysis or the citric acid cycle
• Resulting amino acid can be deaminated and used similarly

Question 16

What is NH4 converted into and why?

Answer 16

• Urea

* Urea is less toxic

Question 17

What is gluconeogenesis?

Answer 17

Formation of glucose from non-carbohydrate sources

• Glycerol and the carbon backbone of amino acids can be fed into the pathway

Question 18

Where does the bulk of gluconeogenesis occur?

Answer 18

In the liver

Question 19

Describe lipid synthesis

Answer 19

1. Glycerol is made from glucose through glycolysis
2. Two carbon acyl units from acetyl CoA are linked together by fatty acid synthetase to form fatty acids
3. Glycerol plus 3 fatty acids make a triglyceride

Question 20

Where are the majority of triglycerides stored?

Answer 20

In adipose tissue

Question 21

Why would endurance athletes carbo load before an event?

Answer 21

• Lipids are not as effectively used as carbohydrate

* Energy production would therefore not be as high when we are using lipids as fuel rather than carbohydrate

Question 22

How can we get amino acids?

Answer 22

• Some provided in the diet

* Some made by transferring amino groups to keto acids

Question 23

What is the largest protein source?

Answer 23

Muscle

Question 24

What fuel sources can the brain use and why?

Answer 24

• Normally glucose (so needs a constant supply in the blood)
• In times of starvation: ketone bodies (mainly acetoacetate and 3-hydroxybutyrate) formed in other tissues
• Lipids cannot cross the blood brain barrier

Question 25

Which fuel sources can skeletal muscle use?

Answer 25

• Glucose
• Fatty acids
• Ketone bodies

Question 26

Which fuel does resting muscle use?

Answer 26

• Fatty acids

Question 27

Why can’t the brain or muscle transport glucose?

Answer 27

They can’t convert glucose-6-Phosphate or glycogen to glucose

Question 28

What happens when muscle is active?

Answer 28

• Rate of glycolysis outpaces the citric acid cycle
• Pyruvate is converted to lactate
• Lactate passes into the blood and to the liver where it is converted back to glucose

Question 29

How does the liver take some of the metabolic burden away from muscle?

Answer 29

• In transamination, many amino acids pass their amino group to pyruvate forming alanine
• Alanine is transported in the blood to the liver where it can be converted back to pyruvate which is used to synthesise glucose (gluconeogenesis)

Question 30

what makes up adipose tissue?

Answer 30

• Adipocytes, each of which has a fat droplet that occupies most of the cell

Question 31

What is the main function of adipose tissue?

Answer 31

• Synthesize and store triglycerides

* Release fatty acids and glycerol in times of need

Question 32

What determines the rate at which fatty acids are esterified?

Answer 32

The availability of glucose

Question 33

What hydrolyses triglycerides?

Answer 33

• Lipase (activity is hormone sensitive)

Question 34

What ensures the liver has ready access to nutrients absorbed by the gut?

Answer 34

Hepatic portal system

Question 35

What can the liver make new glucose from?

Answer 35

• lactate
• Alanine
• Glycerol

Question 36

When fuel supplies are available, what does the liver do?

Answer 36

• Synthesizes fatty acids
• Esterifies them
• Secretes them into the blood as very low density lipoprotein (VLDL)

Question 37

What does the liver do in fasting?

Answer 37

Generates ketone bodies for use in other tissues