L36 - Cell Signalling: Insulin

balance for adrenalin

Insulin Signalling

uses:

Enzyme-coupled Receptors = binding of signal molecule turns on receptors enzyme domain

→ contains receptor tyrosine kinases (RTKs) : phosphorylate the receptors own tyrosines when signal binds → phosphorylates target proteins too

Insulin Signalling: Purpose

1. makes digestive enzyme for gut

2. releases glucagon proteins when blood [glucose] is low

via: alpha islet cells

mech: alpha cells release glucagon → signals liver cell to release glucose into blood

3. releases insulin proteins when blood [glucose] is high

via: beta islet cells

mech: beta islet cells release insulin → signals fat/muscle cells to uptake glucose from blood

note: fat & muscle cells display insulin receptors → import glucose

which cells have the most glucagon receptors?

liver cells

Insulin Signalling: Activation

1. insulin is released via regulated exocytosis

   

2. insulin binds to insulin receptors (homodimers) on fat/muscle cells

3. insulin receptors phosphorylate itself → results in phosphorylation of target proteins → activated

active target protein: responses

1. GLUT to plasma membrane

2. increased glycogen synthesis (store glucose)

3. decreased glycogen breakdown

Insulin Signalling: Responses

1. import glucose (brings GLUT out to plasma memb for glucose to enter cell)

via: kinase cascade

2. store glucose

via: activation of glycogen synthase + inhibits glycogen breakdown

Insulin Signalling: Deactivation

1. remove insulin

2. dephosphorylate target cells (via phosphates)

3. pinocytosis brings GLUTs back into cell from plasma membrane

→ thus, glucose cant enter cell

Insulin Signalling: Medical Significance

Diabetes Mellitus = inability to regulate blood glucose → high blood sugar

→ Type 1 = WBCs kill insulin producing beta islet cells

→ Type 2 = fat cells have fewer insulin receptors → CANT take in more glucose

• from overeating

• can use kidney cell SGLT to treat : acts as inhibitor to stop reuptake of glucose by kidneys → pee out extra glucose

  

treatments:

• insulin

• monitor blood glucose

• healthy diet

Edmonton protocol to treat DM 1

• take beta islets from donor → inject into liver instead of pancreas so WBCs cant kill them

Examinable Content