where are proteins modified after translation
Endoplasmic reticulum or Golgi apparatus
what are the two main types of Post-translational modification
proteolysis and the covalent addition of molecules
what are the main functions of proteolysis ?
- Makes isoforms of proteins from single mRNA
- Convert protein to its active form
- Enhances proper protein folding
- Enhances insertion of protein to membrane or lumen of organelles
what are the main functions of the addition of covalent molecules to proteins?
- Enhance or disrupt interaction with other proteins
- Enhances stability or degradation
- Enhances transportation
Why is insulin produced in an inactive state ?
allows it to travel to its target tissue without having an immediate effect.
describe insulin matuaration
- From N term preproinsulin consists of a signal sequence, chain B, Chain C and chain A
- proinsulin is made when the signal sequence is removed from the N term
- Chain C is then removed to form active insulin, leaving chain B and A connected by di sulphite bridges.
what does the Acetylation of histones cause
causes relaxation of the nucleosome making DNA more accessible
what does the Methylation of histones cause
causes condensation of the nucleosome making DNA inaccessible
Phosphorylation
addition of phosphate group
what enzymes add phosphate groups
Kinases
what enzyme removes phosphate groups
phosphatase
Ubiquitylation
addition of Ubiquitin
what does ubiquitylation do
Tags protein for degradation, mostly uses to discard faulty proteins
Glycosylation
addition of sugar moiety side chains of amino acid
N-linked glycosylation
addition of sugar moiety to Nitrogen of Asparagine
what is N-linked glycosylation important for ?
protein folding
where does N-linked glycosylation occur
initially in the ER and is refined in the Golgi
O-linked glycosylation
addition of sugar moiety to the Oxygen atom of Serine and Threonine
what does O-linked glycosylation do
it is complimentary to phosphorylation and enhances protein-protein interaction
where does O-linked glycosylation occur
mostly in the cytoplasm
