BGM1002/L24 Gluconeogenesis

Question 1

What are normal blood glucose levels?

Answer 1

4-6mmol/L

Question 2

What 2 hormones are involved in blood glucose homeostasis?

Answer 2

Insulin and glucagon

Question 3

Why must blood glucose levels be regulated? (3)

Answer 3

Glucose is preferred energy source of brain and CNS
Only fuel source of RBC
Breakdown in blood glucose homeostasis causes problems

Question 4

What is the only fuel source of RBCs?

Answer 4

Glucose

Question 5

Define blood glucose homeostasis.

Answer 5

Maintenance of blood sugar levels within narrow physiological limits

Question 6

What percentage of glucose does the brain use?

Answer 6

75% or 120g

Question 7

How much glucose is circulating the body at a given time?

Answer 7

20g

Question 8

How much glucose is readily available as glycogen at any given time?

Answer 8

190g

Question 9

How long would stored glucose last in the body?

Answer 9

1 day

Question 10

When does hypoglycaemia occur? (3)

Answer 10

Starvation
Insulin overdose
During and after exercise

Question 11

What results from hyperglycaemia? (3)

Answer 11

Low glucose levels inside cells
Hyperosmolar hyperglycaemic state
Long-term complications

Question 12

When does hyperglycaemia occur? (2)

Answer 12

Post-prandial (meal)
Inadequate insulin administration

Question 13

When is gluconeogenesis initiated?

Answer 13

2 hours post-prandially

Question 14

Give an advantage of gluconeogenesis.

Answer 14

Preserves glycogen for emergencies

Question 15

What is the maximum period that gluconeogenesis occurs for?

Answer 15

8-12 hours

Question 16

Where does gluconeogenesis occur?

Answer 16

High-intensity exercise principally in liver

Question 17

Name 3 sources for gluconeogenesis.

Answer 17

Pyruvate/lactate
Glycerol
Citric acid cycle intermediates
Amino acids

Question 18

When is lactate produced in cells? (2)

Answer 18

When pyruvate is not needed for Krebs cycle
When pyruvate cannot be fed into the cycle due to lack of oxygen

Question 19

What organ is responsible for most lactate production?

Answer 19

Skeletal muscle

Question 20

Why must lactate be transported to the liver?

Answer 20

It cannot be used for anything else
It is converted to glucose to be (re)used

Question 21

What can pyruvate be converted into in skeletal muscle?

Answer 21

Alanine

Question 22

How many pyruvate molecules are used to create a glucose molecule?

Answer 22

2

Question 23

Name 3 energy unfavourable reactions in glycolysis that must be overcome in gluconeogenesis.

Answer 23

Pyruvate -> PEP
F-1,6-bisphosphate -> F-6-P
G-6-P -> Glucose

Question 24

What is step 1 in gluconeogenesis?

Answer 24

Pyruvate -> phosphoenolpyruvate

Question 25

Name the intermediates in step 1 of gluconeogenesis.

Answer 25

Pyruvate -> oxaloacetate Oxaloacetate -> malate

Question 26

What enzyme converts pyruvate to oxaloacetate?

Answer 26

Pyruvate carboxylase

Question 27

What enzyme converts oxaloacetate to PEP?

Answer 27

PEP carboxykinase

Question 28

Why must oxaloacetate be converted to malate in step 1 of gluconeogenesis?

Answer 28

To exit mitochondria

Question 29

Name any additional molecules required to convert pyruvate to oxaloacetate.

Answer 29

CO2 + Biotin + ATP -> Biotin + ADP + Pi

Question 30

Name any additional molecules required to convert oxaloacetate to PEP.

Answer 30

GTP -> GDP + CO2

Question 31

What is step 2 of gluconeogenesis?

Answer 31

Fructose-1,6-bisphosphate -> Fructose-6-phosphate

Question 32

What enzyme is required to convert F-1,6-phosphate to F-6-phosphate?

Answer 32

Fructose-1,6-bisphosphatase

Question 33

What additional molecules are required in step 2 of gluconeogenesis?

Answer 33

H2O -> Pi

Question 34

Name step 3 of gluconeogenesis.

Answer 34

Glucose-6-phosphate -> glucose

Question 35

What enzyme is required for step 3 of gluconeogenesis?

Answer 35

Glucose-6-phosphatase

Question 36

What additional molecules are required for step 3 of gluconeogenesis?

Answer 36

H2O -> Pi

Question 37

What is the net cost of gluconeogenesis in the form of ATP and GTP?

Answer 37

4ATP and 2 GTP

Question 38

Where does the ATP for gluconeogenesis come from?

Answer 38

Lipid oxidation Amino acid catabolism

Question 39

What are the effects of overexpression of phosphoenolpyruvate carboxykinase in mice?

Answer 39

Enhanced exercise capacity (6k vs 0.2k) Ate 60% more than controls 1/2 body weight and 10% body fat of controls Increased mitochondria High triglyceride concentration Extended lifespan (+2yrs)

Question 40

What are the effects of a high-protein, carbohydrate-free diet in humans?

Answer 40

42% increase in energy expenditure Body uses amino acids as pre-cursors for gluconeogenesis

Question 41

How is gluconeogenesis regulated?

Answer 41

Allosterically of enzymes for irreversible steps in the liver

Question 42

When is gluconeogenesis activated?

Answer 42

When cells have a surplus of energy

Question 43

Why do AMP and ADP inhibit gluconeogenesis?

Answer 43

Low energy status Need to send pyruvate into TCA cycle to get energy

Question 44

Why do citrate and acetyl CoA activate gluconeogenesis?

Answer 44

Indicate high energy status Plenty of biosynthetic precursors Favours converstion of pyruvate into G6P for glycogen synthesis