Integration of Metabolism

Question 1

What is the link between Pyruvate/TCA cycle intermediates and amino acids?

Answer 1

Pyruvate and the TCA cycle intermediates can be converted into amino acids and vice versa.

Question 2

What glycolysis product (not pyruvate) can be used to form nucleotides and how?

Answer 2

Glucose-6-phosphate via the pentose phosphate pathway.

Question 3

The pentose phosphate pathway generates a lot of what?

Answer 3

NADPH needed for anabolic pathways (e.g. cholesterol synthesis).

Question 4

Describe the metabolic requirements of the brain.

Answer 4

Requires a continuous supply of glucose.

It cannot metabolize anything but glucose though it can use ketone bodies as a partial substitute.

Question 5

What can hypoglycaemia result in?

Answer 5

Faintness and coma.

Question 6

What can hyperglycaemia result in (in the brain)?

Answer 6

Irreversible damage.

Question 7

Although only making up 2% of total body weight, what percentage of the body’s metabolism is due to the brain and nervous tissue?

Answer 7

20%

Question 8

Describe the metabolic requirements of skeletal muscles.

Answer 8

It can use fat and carbohydrates mainly but can also use ketone bodies.
ATP requirements vary depending on the exercise undertaken.

Question 9

For light contractions, how are skeletal muscle energy requirements met?

Answer 9

Oxidative phosphorylation, using glucose and other substrates as fuels.

Question 10

Why do muscles need ATP?

Answer 10

For muscle actomyosin ATPase and cation balance.

Question 11

How do muscles meet increased demands for glucose?

Answer 11

An increase in the number of glucose transporters on the membranes of muscle cells.

Question 12

How does adrenalin help muscles meet the demands for ATP?

Answer 12

Increases the rate of glycolysis in muscle, increases the rate of gluconeogenesis by the liver, increases the release of fatty acids from adipocytes.

Question 13

For vigorous contractions, how are skeletal muscle energy requirements met?

Answer 13

O2 becomes a limiting factor leading to the abandoning of the TCA cycle/OP and instead lactate is formed and sent to the liver.

Glycogen is also broken down as glucose supply can no longer meet demands.

Question 14

What is the breakdown of glycogen known as?

Answer 14

Glycogenolysis.

Question 15

What does the liver do to pyruvate?

Answer 15

Pyruvate is converted to lactate by LDH (lactate dehydrogenase) and can be later used to generate glucose via gluconeogenesis.

Question 16

Describe the metabolic requirements of the heart.

Answer 16

The heart must constantly beat and so is very flexible with the types of energy sources it can use (fats, ketones, carbohydrates).
It is especially designed for aerobic metabolism and so is rich in mitochondria.

Question 17

What happens when the heart receives a lack of oxygen?

Answer 17

Unlike other cells, anaerobic conditions are particularly devastating. It results in cell death and myocardial infarction which is made worse by the fact that most heart cells do not grow back.

Question 18

Describe the metabolic features of the liver.

Answer 18

Highly metabolically active and undertakes a wide repertoire of metabolic processes.
It can interconvert nutrient types.
Mainly uses fatty acids for energy but can use glucose. too.
Cannot use ketone bodies for energy.
Plays a central role in maintaining blood glucose.
Involved in lipoprotein metabolism and transport of triglycerides and cholesterol.

Question 19

What happens to excess glucose-6-phosphate in the liver?

Answer 19

Used to generate glycogen.

Question 20

Deamination of all 20 amino acids gives rise to how many molecules?

Answer 20

Seven.

Question 21

What are the molecules formed from the deamination of amino acids?

Answer 21

Pyruvate
Acetyl CoA
Acetoacetyl CoA
Alpha-ketoglutarate
Fumarate
Oxaloacetate
Succinyl CoA
(Acronym: Proteins And Amino Acids Follow Our Sugars)

Question 22

What are glucogenic amino acids?

Answer 22

Amino acids whose skeletons can give rise to glucose via gluconeogenesis.

Question 23

What are ketogenic amino acids?

Answer 23

Amino acids whose skeletons cannot enter gluconeogenesis but can be used to synthesis fatty acids and ketone bodies.

Question 24

What are triglycerides broken into?

Answer 24

Fatty acids and glycerol.

Question 25

What is glycerol converted to before entering the gluconeogenic pathway?

Answer 25

DHAP

Question 26

Why can’t fatty acids be converted into glucose?

Answer 26

Fatty acids end up as acetyl CoA through beta-oxidation (2 carbons). It combines with pre-existing oxaloacetate to form citrate and as the cycle progresses it loses two carbon atoms as CO2 before re-forming oxaloacetate. This regenerates the oxaloacetate we used at the start and the loss of the CO2 in the cycle means there is no net gain of carbon and so no net synthesis of oxaloacetate or pyruvate is possible from acetyl CoA.