Post translational protein targeting Flashcards
What is post translational protein modification?
All proteins adopt 3 dimensional structure to become active and some need additional processing
What examples of post translational protein modifications are there?
Proteolytic cleavage (collagen formation) and chemical modification eg glycosylation
What can proteolytic cleavage be used for?
To activate protein outside cell
What’s required for protein sorting?
Signal or address
Receptor that recognises signal
Translocation machinery
Energy to transfer protein
How are secretory proteins made across endoplasmic reticulum membrane?
Signal sequence coded for which then brings ribosome to signal receptor protein SRP and protein is then made inside the endoplasmic reticulum
Why do some proteins need to be secreted into endoplasmic reticulum?
It can insert them in membranes using stop transfer sequence
Proteolytic cleavage
Glycosylation
Disulphide bond formation for extracellular rote is
Folding assembly of multisubunits
Hydroxylation of certain residues
What is N linked glycosylation?
Sugars added to asparagine side chain
Encourages correct protein folding
Makes protein more stable
Allows to interact with other molecules
Glycosylation defects lead to serious disease
Happens in endoplasmic reticulum
What is the role of chaperones in the ER?
Encourage correct protein folding. Hold onto proteins in Er that have misfiled or not yet folded correctly
What happens with protein misfolding?
Protein can be returned to cytosol for degradation
If protein accumulates it will become toxic
Alzeihmers caused by protein disposal and osteogenesis i perfecta caused by it becoming toxic
What role does Golgi apparatus play in protein formation?
Phosphorylation and some sulfation.
Sorts proteins and packages them. Sends them to where they’re meant to be
Collagen structure
Tropocollagen basic unit. Three make collagen fibre and they’re alpha helixes. Glycine every third position on each chain. Triple helix structure.
Stabilised through hydrogen bonds
What is preprocollagen?
Procollagen with “pre” signal peptide which is chopped off by signal peptidase
Why does lack of vitamin C cause scurvy?
Vitamin C required as co-factor for prolyl hydroxylase which hydroxylates procollagen. Without H bonding get weak triple helix.
What is the difference between procollagen and tropocollagen?
Procollagen has disulphide bonds at ends which aren’t in triple helix formation. These stabilise molecule and are chopped off extracellularly and this allows collagen fibre to form from resulting tropocollagen. If happened in cell would tear it apart.
What is ehlors danlos syndrome?
Either a mutation in type 4 collagen or lysyl oxidase deficiency and results in weakened connective tissue
