Protein Synthesis II Flashcards
What is the function of chaperones?
Mediate proper folding of proteins
Hsp70 family are ATP-dependent
Bind and cover hydrophobic patches
What is the function of protein disulfide isomerases?
Catalyzes the formation and cleavage of disulfide bonds
What is the function of peptidyl prolyl isomerase?
Catalyze the transition of proline residues between the cis and trans configurations
What are the three mechanisms of proteolytic processing?
- Removal of the initiator methionine at the N-terminus
- Cleavage of large precursors to form active enzymes or hormones
- N-terminal signal sequence cleavage
How is mature insulin formed?
Cleavage of a signal peptide and internal peptide
What is co-translational translocation?
The active translation of proteins into the ER lumen via the rough ER.
What is N-linked glycosylation?
Linkage of a carbohydrate to asparagine in the ER?
What is O-linked glycosylation?
Linkage of a carbohydrate to a serine or threonine residue in the golgi apparatus
What are calnexin and calreticulin?
Chaperone proteins that bind N-linked residue site when one glucose remains and stops binding when the last glucose is removed.
What is the role of the folding sensor protein?
Determines if the protein is correctly folded or not.
Adds glucose back if not properly folded
What is the role of glycosylphosphatidylinositol (GPI) anchors?
Attach proteins to the luminal side of the ER membrane.
Will eventually end up on the outside of the cell
What is N-myristoylation?
Attachment of myristic acid to an N-terminal glycine residue.
Glycine is exposed by the removal of the initiating met residue
What is palmitoylation?
Palmitic acid added to an internal cysteine residue
What is the role of serine/threonine and tyrosine kinases?
Phosphorylation of specified residues on proteins
What is the role of serine/threonine and tyrosine phosphatases?
Dephosphorylation of specifed residues on proteins
What is nitrolysation?
Addition of NO groups to internal cysteine residues
Catalyzed by (de)Nitrosylases
What is the unfolded protein response?
An excess of unfolded proteins leads to the expansion of the ER, production of more chaperones, and apoptosis in extreme cases.
What is the function of IRE1?
Receptor that recognizes unfolded proteins and activates XP1 transcription factors
What is the function of ATF6?
Receptor that recognizes ATF6, and cleaves, releasing ATF6 as a transcription factor
What is the function of PERK?
Recognizes unfolded proteins and phosphorylates eIF2, blocking translation
Leads to the activation of ATF4 TF
What is the function of XP1, ATF6, and ATF4?
TFs that target genes that encode chaperones, lipid synthesis enzymes, and ERAD proteins
How are proteins degraded?
Ubiquitinated by Ubiquitin ligase.
Degree of ubiquitination determines the likelihood of degradation
What are prion disorders?
infection with misfolded protein that stimulates other proteins to misfold.
Jakob-Crutzfeld, Kuru, Scrapie, Mad Cow
