Hormones and Blood Glucose

Question 1

What hormones are involved in glucose homeostasis?

Answer 1

• Insulin
• Glucagon
• Adrenaline
• Glucocorticoids

Question 2

When is adrenaline secreted in response to blood glucose?

Answer 2

When blood glucose is low

Question 3

What is the effect of adrenaline on blood glucose?

Answer 3

It increases it by stimulating fuel metabolism in muscle and adipose tissue

Question 4

What type of cells is glucagon secreted by?

Answer 4

α pancreatic cells

Question 5

When are glucocorticoids secreted?

Answer 5

In reponse to stress and starvation

Question 6

What type of receptor does glucagon bind to?

Answer 6

G-protein coupled receptor

Question 7

What is PKA activated by?

Answer 7

cAMP

Question 8

Outline how glucagon exerts its effects within a cell

Answer 8

• Binds and causes a change in shape so GPCR can interact with G protein
• Activated G_sα moves to adenyl cyclase and activates it
• Adenyl cyclase catalyses cAMP formation which activates PKA
• PKA phosphorylates cellular proteins

Question 9

What reverses the activation of PKA?

Answer 9

Degradation of cAMP

Question 10

How does cAMP activate PKA?

Answer 10

• Regulatory subunits act in an inhibitory fashion
• cAMP binds to regulatory subunits causing the catalytic subunits to be released

Question 11

How can PKA alter gene expression?

Answer 11

• PKA can activate CREB which is a transcription factor

Question 12

How is the GPCR signal turned off?

Answer 12

• Phosphodiesterase hydrolyses cAMP to AMP
• intrinsic GTPase activity of α subunit
• Receptor is phosphorylated and inactivated

Question 13

How can a GPCR be inactivated?

Answer 13

• Activated GPCR stimulates GPCR kinase to phosphorylate the GPCR at multiple sites
• Arrestin binds to the phosphorylated sites

Question 14

How does cholera toxin lock GPCRs in the active form?

Answer 14

It blocks the GTPase activity of the α_s subunit

Question 15

What are the cellular consequences of the cholera toxin?

Answer 15

• continual activation of adenyl cyclase leads to high PKA activity
• Activation of PKA means activation of CFTR Cl^- channel and Na⁺/H⁺ opening them both

Question 16

How does the cholera toxin cause diarrhoe?

Answer 16

• opening of CTRF Cl- and Na+/H+ channels causes abnormally high [ions] into the surrounding of the gut
• Water moves with the ions so water is lost from cells

Question 17

What channel does the cholera toxin affect?

Answer 17

CFTR Cl^- channel

Question 18

What is the relationship of caffeine to adenosine receptors?

Answer 18

It acts as an antagonist

Question 19

What is the effect of caffeine on PKA activity in cells?

Answer 19

It increases it

Question 20

What enzyme does caffeine inhibit?

Answer 20

Phosphodiesterase

Question 21

What processes does glucagon activate?

Answer 21

• glycogen breakdown
• triglyceride breakdown
• gluconeogenesis

Question 22

What processes does glucagon inhibit?

Answer 22

• fatty acid synthesis
• glycogen synthesis
• glycolysis

Question 23

How does glucagon activate glycogen breakdown?

Question 24

How does glucagon activate triglyceride breakdown?

Answer 24

Activates and phosphorylates of hormone sensitive lipase

Question 25

How does glucagon activate gluconeogenesis?

Answer 25

Inactivates and phosphorylates PFK2

Question 26

How does glucagon inhibit fatty acid synthesis?

Answer 26

Phosphorylates and inactivates acetyl-CoA carboxylase

Question 27

How does glucagon inhibit glycogen synthesis?

Answer 27

Phosphorylation and inactivation of glycogen synthase

Question 28

How does glucagon inhibit glycolysis?

Answer 28

Phophorylates and inactivates pyruvate kinase

Question 29

What kind of receptor are adrenergic receptors?

Answer 29

GPCRs linked to hetertrimeric G proteins

Question 30

What is the effect of adrenaline on adipose?

Answer 30

Activates tricglyceride mobilisation

Question 31

What are the effects of adrenaline in muscle?

Answer 31

* Activates glycogen breakdown * Inhibits glycogen synthesis

Question 32

What is the effect of adrenaline in the liver?

Answer 32

Activates glycogen breakdown

Question 33

How does adrenaline activate glycogen breakdown in the liver?

Answer 33

Ca²⁺ activates phosphorylase kinase

Question 34

Give examples of signalling molecules which can act as transcription regulators

Answer 34

* Cortisol * Testosterone * Vitamin D₃

Question 35

Outline how a signalling molecule can alter gene expression

Answer 35

* Binds to its specific receptor on the nucleus * This causes confomational change of the receptor which binds to specific regulatory regions called hormone response elements in DNA * Receptor attracts coactivator or corepressor proteins and regulates transcription of the adjacent genes

Question 36

What are glucocorticoids?

Answer 36

Steroid hormones derived from cholesterol that are involved in the long term regulation of fuel metabolism and the immune system

Question 37

How many domains does the glucocortcoid receptor have?

Answer 37

3

Question 38

What are the 3 domains on the glucocorticoid receptor?

Answer 38

* Transactivation domain * DNA binding domain * Hormone binding domain

Question 39

What are the effects of glucocorticoids?

Answer 39

* Activate triglyceride mobilisation * Activates gluconeogenesis * Enhances protein catabolism * Has anti-inflammatory effects