Metabolism 9

Question 1

The heart muscle is designed for which type of respiration?

Answer 1

Completely aerobic respiration

It can use free fatty acids, ketone bodies, and TCA cycle substrates

Question 2

What is gluconeogenesis?

Answer 2

Making glucose/glycogen from oxaloacetate

Requires ATP synthesis

DOES NOT PRODUCE ACETYL COA OR PYRUVATE

Question 3

Describe the reactions involved in gluconeogenesis.

Answer 3

1. Pyruvate conversion into oxaloacetate
2. Need enough oxaloacetate to produce phosphoenolpyruvate
3. Phosphoenolpyruvate allows you to convert back to glucose.

GLUCONEOGENESIS = -6ATP

Question 4

Describe protein metabolism

Answer 4

• Protein is excreted as urea
• AAs can be fed into glycolysis or TCA cycle in the form of pyruvate, acetyl CoA and other TCA substrates
• protein breakdown can be used to initiate gluconeogenesis

Question 5

What step is essential for gluconeogenesis to occur?

Answer 5

Pyruvate conversion to oxaloacetate

Question 6

Describe fat metabolism.

Answer 6

• fatty acids enter glycolysis/TCA in the form of acetyl-CoA
• ketone bodies also formed from fat metabolism, and some substrates can be used to generate AAs

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Question 7

What is not produced when fats are used in respiration?

Answer 7

Pyruvate

Question 8

Why can you not generate glucose via gluconeogenesis when using fats?

Answer 8

Pyruvate not produced, so no pyruvate conversion into oxaloacetate.

HOWEVER, FATTY ACIDS CAN BE BROKEN DOWN INTO SUBSTRATES FEEDING INTO THE GLUCONEOGENIC PATHWAY LATER ON

Question 9

How is an increased demand for glucose met?

Answer 9

More glucose transporters present in the plasma membrane

Question 10

What does adrenaline do?

Answer 10

1. Increase in muscle glycolysis - more ATP production
2. Increased gluconeogenesis - glucose produced in liver, which moves into blood and is transported to various tissues.
3. Increases the release of fatty acids - more fatty acids available for ATP generation

Question 11

What does insulin do?

Answer 11

Regulates movement of glucose transporters to membrane

Question 12

What happens in anaerobic respiration?

Answer 12

1. Muscle breaks down its glycogen stores
2. Increased rate of glycolysis causes pyruvate to accumulate, so more pyruvate converted to lactate.
3. Lactate transported out of muscle into liver, where it is fed into gluconeogenic pathway via conversion to pyruvate.
4. Moving lactate from blood prevents acidosis. Allows lactate to be used as an alternative fuel source for ATP generation.

Question 13

2 ways in which the metabolic pathway is controlled?

Answer 13

1. Product of reaction/pathways, end product is an activator/inhibitor
2. External signalling molecules relaying information from other pathways

Question 14

Which hexokinase does muscle have, which hexokinase does the liver have?

Answer 14

Muscle - Hexokinase 1

Liver - Hexokinase 4

Question 15

Describe Hexokinase 1

Answer 15

In muscle

1. High glucose affinity
2. Activity rises rapidly in response to rising glucose concentration
3. Reaches Vmax at relatively low glucose concs
4. Highly sensitive to G6P inhibition
5. If G6P accumulated, Hk1 is inhibited

Rate vs glucose conc graph is like steep start (almost vertical then starts to level off)

Question 16

Describe Hexokinase 4

Answer 16

In liver

1. Has low glucose affinity
2. Less sensitive to G6P
3. G6P can accumulate but Hk 4 will convert glucose to G6P.

Rate vs Glucose conc graph is meh at the start (approx 30 degrees from horizontal, but then starts to increase, reaches V1/2max at 4mM conc)

Question 17

What do glucocorticoids do?

Answer 17

Increase synthesis of metabolic enzymes concerned with glucose availability

Question 18

What are the complications arising from diabetes?

Answer 18

1. Hyperglycaemia - can cause progressive tissue damage
2. Cardiovascular implications due to increase in plasma fatty acids and lipoproteins
3. Increase in ketone bodies - potential acidosis
4. Hypoglycaemia - possible coma if insulin dosage incorrectly controlled
5. Glucose not taken up into muscle or liver as insulin not released or insulin signalling pathway is not activated.

Question 19

Explain regulation of hormone secrete in B cells in pancreas.

Answer 19

1. Glucose transported to B cell and metabolised to produce ATP.
2. ATP is also the signalling molecule within the cell
3. ATP binds to K ATP channel at cell surface and regulates function.
4. K ATP channels closed, cells become depolarised, causing Ca channels to open.
5. Ca enters from outside the cell.
6. Increased Ca conc in the cell causes insulin to be mobilised and released into bloodstream.
7. Cells also release zinc

Question 20

What does GLP 1 do?

Answer 20

Glucagon Like Peptide 1

Important drug in treatment of type 2 diabetes.

Works in conjunction with glucose, whereby mimetics of this drug don’t actually do anything in terms of insulin release.

However, if there is an increase in plasma glucose conc, GLP1 accentuates the amount of glucose, which leads to release of more insulin.

In type 2 diabetics, GLP1 can make their beta cells active

Question 21

How is glucagon regulated?

Answer 21

1. Glucose transported to alpha cells via glucose transporters.
2. Causes an increase in ATP via glucose metabolism
3. ATP signals to many ion channels, leading to inhibition of glucagon release.
4. GLP-1 inhibits glucagon release.