peptide hormones

Question 1

general physiochemical properties

peptide hormones

Answer 1

hydrophilic
transported unbound in blood plasma > no blood carrier proteins
very short biological half-lives
bind to membrane bound receptors
secreted by; pituitary gland, parathyroid gland, the heart, stomach, liver and kidneys

Question 2

angiotensin II structure

Answer 2

a linear chain

Question 3

somatostatin structure

Answer 3

a ring structure due to disulfide bonds

Question 4

insulin structure

Answer 4

2 chains held together by disulfide bonds

Question 5

insulin maturation

Answer 5

mature mRNA is translated into preproinsulin containing a ‘leader’ sequence and A,B and C domains
the leader sequence is cleaved in the lumen of the endoplasmic reticulum to produce proinsulin
proteases cleave proinsulin at 2 sites to remove the C peptide. the A and B chains remain connected by disulfide bonds
mature insulin is stored in secretory vesicles, being released via exocytosis due to an increase in intracellular Ca2+ concntrations after a signalling response

Question 6

insulin secretion

Answer 6

insulin is secreted by pancreatic beta-cells
increase in blood glucose increases diffusion of glucose into the beta-cell by GLUT2 facilitated transport, glucose is phosphorylated by glucokinase resulting in glycolysis of glucose-6-phosphate to generate ATP in the mitochondria. increase in ATP/ADP ratio in the cell causes closure of ATP sensitive K+ channels resulting in membrane depolarisation and the opening of voltage-activated Ca2+ channels which increases intracellular ca2+ concnentration triggering insulin secretion

Question 7

type two diabetes

Answer 7

insulin receptors are down-regulated due to high levels or sustained secretion of insulin
chemical signalling error
insulin is present
obesity is a cause, so can be reversed
1. insulin receptor has lost function
2. this is due to overstimulation due to high blood glucose levels in the blood over a long time, the receptor is desensitised
3. glucose is not removed from the blood
4. patients have a high blood glucose level

Question 8

end hormones

peptide hormones

Answer 8

different end hormones can be made by cleaving a common precursor with a different enzyme