Hormone synthesis Flashcards
What type of hormone is insulin?
Protein hormone
What are the steps of making insulin?
- Gene expresses the protein coding for insulin and is transcribed to make RNA
- Splicing of RNA = mRNA
- mRNA leaves the cell nucleus and goes to the ribosome
- In ribososme preproinsulin is formed
- Preproinsulin travels to the ER
- Here, preproinsulin is modified into proinsulin
- Proinsulin travels to the Golgi and is modified to form mature insulin
What is the structure of preproinsulin?
This is a preliminary protein
Composed of three chains: A, B and C
Contains signal sequence: makes the insulin inactive
What is the role of the signal sequence?
Direct the insulin from the ribosome to the ER
What happens when signal sequence is cleaved off?
Preproinsulin -> proinsulin
What modifications happen in the ER?
Signal sequence is cleaved off
Disulphide bridges form between A and B chains
Which enzymes cleave off the signal sequences?
Proteolytic enzymes
What are disulphide bridges?
Oxidation of thiol groups
What happens to the proinsulin when it enters the Golgi?
Modified to form mature insulin
Splice away the C chain
What is the process of synthesising peptide hormones?
- Gene codes for POMC
- This is transcribed and translated
- Split via proteolytic enzymes to form hormones
What does POMC stand for?
Proopiomelanocortin
What hormones are synthesised by the cleavage of POMC?
MSH
ACTH
Endorphins
How are steroid hormones synthesised?
Made from cholesterol
- Cholesterol makes pregnenolone precursor
- Modification of cholesterol can happen anywhere alonng the carbon chain to form the hormones
- Different enzymes catalyse these reactions
What are examples of enzymes that modify cholesterol?
11 hydroxylase - enzyme that hydroxylates (adds OH) to cholesterol on C-11
21 hydroxylase - enzyme that hydroxylates C-21 on cholesterol
What are examples of steroid hormones?
Glucocorticoids - further modified to make mineralocorticoids
GC : Cortisol
MC: Aldosterone
Androgens - further modified to make oestrogens
