Hormone Synthesis And Action

Question 1

Synthesis of protein / peptide hormones by transcription

Answer 1

-transcription of dna to rna
-post transcriptional processing rna to mature rna with excision if introns , modification of 3’ and 5’ ends
-translation of mRNA into protein using tRNA to transfer amino acids
-post translational processing - cleavage of large pre pro hormone, folding of protein, addition of sugar

Question 2

What is the pre prohormone & pro hormone

Answer 2

Pre prohormone - signal sequence & prohormone

Pro hormone - hormone & peptide sequence

Question 3

Synthesis of insulin

Answer 3

• transcription to mRNA
  Excision of introns to messenger rna
  Removal of signal sequence
  Formation of disulphide bonds in RER
  Pre proinsulin forms proinsulin
  Transfer to Golgi apparatus
  Excision of c peptide and packing into secretory granules

Question 4

How is steroid synthesis controlled from cholesterol

Answer 4

• cholesterol Is bound to sterol carrier protein which is transported to the mitochondria
  -StAR protein transports cholesterol to inner mitochondrial membrane
  -cholesterol to progenolone by side chain cleavage and enzyme p450 scc
  -between mitochondria and SER steroids synthesised by hydroxylase enzymes

Question 5

Examples of steriod hormones

Answer 5

-androgen
-oestrogen
-progesterone
-cortisol
-aldosterone

Question 6

Synthesis of thyroid hormones

Answer 6

• active uptake of iodide to follicular cells
• transport across apical membrane
  -oxidation of iodine to iodinated intermediate by TPO which is activated by h2o2
  -iodination of tyrosine residues by thyroglobulin
  -coupling of iodinated tyrosine residues
  -storage of t3 & t4 on colloid
  -uptake of thyroglobulin droplet into follicles cells
  Release and secretion of t3 &t4

Question 7

Effects of steriod hormones in female

Answer 7

-oestrogen controls menstrual cycle , breast tissue development, fertility, reproductive organ development
Secondary sexual characteristics eg body hair

Question 8

Effect of steriod hormones in males

Answer 8

-testosterone controls reproductive and supportive organs , development of sexual characteristics in men eg deeping of voice , body hair

Question 9

What part of the structure of nuclear receptors is highly conserved

Answer 9

C domain , it is the dna binding region

Question 10

What domains of nuclear receptors have transcriptional activity

Answer 10

A/B and E/F domains

Question 11

Outline the structural organisation of nuclear receptors

Answer 11

A/B domain is the N terminal
C domain is the dna binding domain
D domain is the hinge domain
E- ligand binding domain
F-c terminal domain

Question 12

What are the key characteristics of a nuclear receptor and their roles

Answer 12

Ligand binding domain -binds specific steriod molecules with high affinity
DNA binding domain- bind specific dna sequences
Activation function domains - recruits gene activation machinery

Question 13

Describe the c domain of a nuclear receptor

Answer 13

• made of two zinc fingers which can slot into the helix of DNA

Question 14

Steroid hormone action

Answer 14

Hormone crosses cell membrane
Heat shock protein dissociates from receptor
Hormone binds to receptor and dimerization occurs
Dimerized receptors translocate to the nucleus
Binds to the hormone response element on the DNA
Along with other transcription factors transcription is initiated
Some receptors located within the nucleus not the cytoplasm

Question 15

Two types of diabetes

Answer 15

Type 1- autoimmune destruction of pancreatic islet - absolute insulin deficiency

Type 2 - insulin resistance , partial loss of insulin production

Question 16

How is atherosclerosis linked to obsesity

Answer 16

• obesity leads to insulin resistance which then causes
  Hyperglycaemia
  Hypertension
  Inflammation
  Endothelial dysfunction
  Impaired thrombolysis

Question 17

Aromatase deficiency in men

Answer 17

• Aromatase is responsible androgens into oestrogen
  This leads to decreased oestrogen levels and increased Androgen levels which is a hormonal imbalance that leads to
  -delayed or incomplete puberty
  -abnormal enlargement of breast tissue in men ( gynecomastia )
  Infertility
  Decreased bone density

Question 18

Aromatase deficiency in women

Answer 18

• lack of estrogen production
  Leads to infertility
  Delayed or absent puberty in females
  -increase facial hair growth , deepening of voice , male pattern baldness
  -decreased bone mineral density
  -menstrual irregularities

Question 19

What is androgen insensitivity

Answer 19

Lack of a functional receptor , so complete lack of response to testosterone, XY embryos develop as females , developmental anomalies , infertility

Question 20

What is androgen deficiency

Answer 20

Affects men of different ages
If occurs before puberty it can cause delayed puberty , developmental abnormalities,lack of secondary sexual characteristics eg no voice change, reduced muscle growth
In older men it leads to libido , impotence , loss of muscle mass

Question 21

What is a goitre and causes

Answer 21

• enlargement of thyroid gland
• lack of iodine in diet leads to t3 & t4 deficiency
  -Graves’ disease
  -thyroid adenoma

Question 22

How is Graves’ disease caused in terms of hormones

Answer 22

-auto antibodies to the tsh receptor act on thyroid gland which stimulates excess thyroid hormones and cause eye disease

Proptosis-bulging of eye