Post translational modification of proteins and protein targeting Flashcards
What is constitutive secretion?
constant maintain basal level
e.g albumin
What is regulated secretion?
only when stimulated
endo/ exo and neuro crine
How are proteins targeted?
contain intrinsic signals that govern their transport and localisation in the cell
Where are proteins destined for cytosol and post translational import to organelles translated?
free ribsosomes
Where are proteins destined for secretion or membrane translated?
ribosomes on rough endoplasmic reticulum
What are the requirements for protein sorting? explain each one.
signal - n terminal sequence
receptor to recognise signal - signal recognition particle SRP bind ribosome and protein stopping protein synthesis
translocation machinery- SRP bind SRP receptor on ER membrane pore open into ER
energy to transfer protein to new place- GTP hydrolysed and SRP released protein synthesis resumed
What enzyme may remove the signal sequence of the n terminal?
signal peptidase
Name the three main functions of the RER
n-linked glycosylation
formation of disulphide bonds
correct protein folding mediated by chaperones
Where aa side chain is n-linked glycosylated?
asparagine
What is glycosylation needed for?
folding
stability
interactions
What enzyme is responsible for formation of S-S bonds? Where do S-S bonds form?
protein disulphide isomerase
between cysteine residues
What diseases occur if there is a a deficiency in glycosylation?
congenital disorders of glycosylation
What happens if protein mis folds?
may degrade in cytosol
may accumulate in ER–> toxic level e.g. Fabry disease
Outline the structure of collagen
right handed triple helix made from three polypeptide chains - h bonds stabilise this formation
glycine every third residue- glycine R group small enough to fit helix formation
Other two residues likely to be proline or hydroxyproline
collagen triple gelix crosslink with each other to form fibrils
When does pre pro alpha chain become a pro alpha chain?
once signal sequence has been cleaved by signal peptidase
Which residues are hydroxylated and by which enzyme?
proline and lysine
prolyl hydroxylase
When are the N and C terminals removed form the propeptides? what is produced? which enzyme is involved?
extracellularly
tropcollagen
procollagen peptidases
Why are the terminals not cleaved within the cell?
After cleavage fibrils form if this occurred within the cell then the cell would explode
Which enzyme is responsible for the formation of crosslinks between the triple helices to form fibrils?
lysyl oxidase
Why is weakened connective tissue seen in scurvy?
weakened collagen structure due to reduced H bond formation
this is because H bond formation reliant on hydroxylation of alpha chains by proylyl hydroxylase
the enzyme proylyl hydroxylase requires vitamin C to function
What does Ehlers-Danlos syndrome result from?
lysyl oxidase deficiency so covalent bonds cannot form between triple helices
