Post Transational Modifications Flashcards
What is post-translational modification?
Additional processing after a protein is made
What is proteolytic cleavage?
Breaking peptide binds to remove part of the protein
What is chemical modification?
Addition of functional groups to amino acid residues
What kind of proteins are synthesised on free ribosomes?
Proteins for cytosol or posttranlational import into organelles
What kind of proteins are synthesised by ribosomes on the RER?
Proteins for membrane or secretory pathway
What is required for protein sorting?
Signal
Receptor
Translocation machinery
Energy
What must proteins targeting peroxisomes have?
Must have the peroxisomes targeting sequence -Serine, lysine, leucine at c terminus usually
This is recognised by the pex5 which binds to cargo protein
This binds to the 13 per protein channel across peroxisomal membrane
ATP hydrolysis recycles PTS receptor
What disorders are caused if peroxisomes targeting goes wrong?
Peroxisomes biogenesis disorders
Zellweger syndrome
Rhizomelic chondroysplasia punctata
What is constitutive secretion?
All the time/continuous secretion
What do endocrine cells secrete?
Hormones
What do exocrine cells secrete?
Digestive juices
What do neurocrine cells secrete?
Neurotransmitters
What is a signal sequence?
At the n terminus
5-30 amino acids in length
Form alpha helix
Central region hydrophobic
What is the signal recognition particle?
Receptor needed to bind the signal peptide on proteins destined for the ER
6 proteins and a short piece of RNA
Recognises signal peptide and ribosome
What are the functions of the endoplasmic reticulum?
Insert proteins into membranes Specific proteolytic cleavage Glycosylation Forms S-S bonds Folds proteins Assembles multisubunit proteins Hydroxylation of selected lys and pro residues
What is glycosylation?
Addition of sugars
Why is glycosylation of proteins important?
Correct protein folding
Protein stability
Facilitates interactions with other molecules
Deficiencies in n linked glycosylation leads to CDG
What protein helps from disulphide bonds?
Disulphide isomerise
What happens if there are folding problems with a protein?
May be trapped in misfolded conformation
Mutation
Incorrectly associate with another sub unit
What do ER chaperones do?
Retain unfolded proteins in ER
Act as sensor to monitor extent of protein mis folding
What happens if misfolding of proteins cannot be corrected?
Degradationin cytosol
Accumulate to toxic levels and cause disease
Where does o linked glycosylation occur and what happens?
In Golgi
Sugar attach to hydroxyl group of serine and threonine
What is proteolytic cleavage?
Breaking of a peptide bond to remove part of the protein
What is chemical modification?
Addition of functional groups to amino acid residues
