02.16- Protein Processing Flashcards
What are the three basic post-translation processes?
Cleaving
Altering
Degrading
Which of the following is incorrect?
a. Trypsinogen is a zymogen of trypsin.
b. The inactive form of chymotrypsin is chymotrypsinogen.
c. Proinsulin is activated by altering.
d. Caspases are activated by cleavage of procaspases
c. Proinsulin is activated by altering. (The formation of insulin from proinsulin is due to cleavage.)
What type of post-translational modification is characterised by covalent attachment of chemical groups to proteins?
Altering
An example of protein altering that is characterised by the addition of carbohydrates is called?
Glycosylation
What sugar is attached to proteins targeted by lysosomal digestion?
Mannose-6-phosphate
What Vitamin C-dependent protein altering mechanism is important in modifying proline and lysine residues in collagen?
Hydroxylation
The formation of gamma-carboxyglutamate from glumatate residues is due to what type of covalent modification?
Carboxylation
Attachment of lipids for anchoring proteins to membranes is called:
Farnesylation
What regulatory protein tags aberrant proteins for proteasomal digestion?
Ubiquitin
What structure destroys ubiquitin-tagged proteins?
Proteasome
True or False: Procollagen may undergo multiple modifications before becoming collagen.
True (hydroxylation, oxidation, cleavage, etc.)
True or False: There is no structural difference between ribosomes found in the cytosol and ribosomes found in the RER.
True
What are the two protein sorting pathways in the cell?
Cytosolic pathway
Rough ER pathway
Enumerate the cellular components that acquire proteins via the cytosolic pathway.
Nucleus
Peroxisome
Mitochondria
Cytosol
Enumerate the cellular components that acquire proteins via the RER pathway.
Membranes
Lysosomic enzymes
Secretory protein
True or False: It is hypothesised that all protein synthesis begins in free ribosomes, unless that ribosome is directed to the rough ER.
True
Arrange the steps of the signal hypothesis in order (no choices):
I - Release of SRP
II - Attachment of SRP to the signal sequence
III - Translocation of polypeptide chain into the ER lumen
IV - Synthesis of the signal sequence
V - Binding of SRP-bound signal sequence to SRP receptor
VI - Cleavage of signal sequence by signal peptidases
IV-II-V-I-III-VI
What amino acid sequence directs the protein to further translation in the nucleus?
Nuclear Localization Proteins
What amino acid sequence directs the protein to further translation in the peroxisome?
Peroxisomal-matrix targeting sequences
The targeting proteins to the matrix signals the protein to undergo further translation in which organelle?
Mitochondria
After cleavage of the signal sequence by signal peptidases in the ER lumen, the polypeptide then proceeds to which organelle?
Golgi apparatus (for further modification and export)
Which of the following does not use receptor-mediated endocytosis?
a. LDL uptake
b. Waste disposal of haemoglobin complexes
c. Digestion of defective mitochondria
d. Mucosal transfer/transcytosis of IgA
c. Digestion of defective mitochondria (This is macroautophagy.)
What proteins are responsible for receptor-mediated endocytosis?
Clathrin and adaptin
What protein is responsible for phagoycytosis?
Actin
