MCB Lecture 16 The Fasting State

Question 0

Wat is resting blood glucose levels?

Answer 0

5 mM

Question 1

What concentration of glucose in the blood constitutes fasting?

Answer 1

< 4.5 mM

Question 2

What does glucagon bring about?

Answer 2

Liver: gluconeogenesis, glycogenolysis
Muscle: glycolysis, glycogenolysis

Question 3

Which organs are prioritised in terms of glucose?

Answer 3

Brain
Retina
RBCs

Question 4

What is the ligand in the Glucagon signal transduction pathway in the liver?

Answer 4

Glucagon

Question 5

What is the receptor in the glucagon signal transduction pathway in the liver?

Answer 5

Glucagon receptor (GPCR)

Question 6

What is the G-Protein in the glucagon signal transduction pathway in the liver?

Answer 6

Guanyl nucleotide G protein

GDP replaced with GTP, which activates Adenyl cyclase

Question 7

What is the second messenger in the glucagon signal transduction pathway in the liver?
What happens from here?

Answer 7

Adenyl cyclase converts ATP to cAMP
cAMP activates PKA
PKA phosphorylates proteins, either switching them on or off

Question 8

What are the PKA targets in the liver hepatocyte? (5)

Answer 8

1. PFK-2/F-1,6-bP-2
2. Glycogen synthase
3. Pyruvate kinase
4. PEP carboxykinase
5. Glycogen phosphorylase

Question 9

Describe the overall signal-transduction pathway of glucagon in the liver

Answer 9

1. Glucagon binds to
2. Glucagon receptor
3. G-Protein activates, which activates
4. Adenyl cyclase which converts
5. ATP -> cAMP
6. PKA activates by cAMP
7. Proteins activated by PKA (phosphorylation)

Question 10

Describe the overall pathway of adrenaline signal-transduction in liver cells

Answer 10

1. Adrenaline binds to
2. Beta-adrenergenic receptor which activates
3. G protein (same as glucagon)

Question 11

How do the adrenaline and glucagon pathways differ?

Answer 11

The adrenalin pathway has a different ligand and receptor

Question 12

What is adrenaline synthesised from?

Answer 12

Tyrosine

Question 13

We’re is adrenaline released from?

When is it released?

Answer 13

It’s released from the adrenal cortex

It is released in response to stress

Question 14

From where is glucagon released?

Answer 14

Alpha cells of the pancreas

Question 15

What is the mechanism of activation of Glycogen Phosphorylase by PKA?

Answer 15

1. PKA phosphorylates and activates Phosphorylase Kinase

2. Phosphorylase Kinase phosphorylates and activates Glycogen Phosphorylase

Question 16

What is the mechanism of activation of PEP carboxykinase by PKA?

Which pathway is this involved with?

Answer 16

1. PKA phophorylates and activates CREB
2. CREB enters the nucleus and activates transcription of PEP carboxykinase

This is part of the glucagon and the adrenaline pathways

Question 17

To which hormone are hepatocytes more responsive in the fasting state?

Answer 17

Glucagon more than adrenaline

Question 18

Compare the structure of glucagon and adrenaline

Answer 18

Glucagon is a peptide hormone

Adrenaline is a steroid hormone

Question 19

From where is glucagon released?

When is it released?

Answer 19

The alpha cells of the pancreas

It is secreted in the fasting state, ie when blood glucose concentration is low (less than 4.5 mM)

Question 20

Which organs have glucagon receptors?

Answer 20

The liver