Biosci 201 Flashcards
(43 cards)
What does the signal hypothesis state?
Proteins destined for secretion or membrane insertion are targeted to the ER during translation.
Who first proposed the signal hypothesis and in what year?
Blobel in 1971.
What is the pulse-chase labeling technique?
A method to track the movement of newly synthesized proteins using radioactive labeling.
What happens during the ‘pulse’ phase of pulse-chase labeling?
Cells are briefly exposed to a radioactively labeled molecule.
What occurs during the ‘chase’ phase of pulse-chase labeling?
The radioactive label is washed away and replaced with non-radioactive molecules.
What does autoradiography allow scientists to do?
Follow the movement of labeled molecules over time.
What is one piece of evidence for the signal hypothesis?
The relationship between larger precursor proteins and smaller mature proteins.
What happens to the signal peptide during protein maturation?
It is cleaved off, resulting in a smaller mature protein.
What is required for the production of mature secretory proteins?
The presence of microsomes.
What does the readout experiment prove about immunoglobulin G mRNA?
Proteins are translated into the ER lumen and the signal peptide is removed inside.
How does the presence of microsomes affect the length of the prolactin nascent chain?
It needs to be 130 codons long for the signal peptide to enter the ER lumen and be cleaved off.
What type of signal sequence do proteins destined for the ER contain?
An N terminus signal sequence or internal signal sequence.
What is the role of the signal recognition particle (SRP)?
It recognizes the signal sequence and pauses translation.
What occurs during post-translational translocation?
Proteins are targeted to the ER after translation.
What is the role of ATP in the translocation of proteins into the ER?
ATP hydrolysis from BiP helps pull the protein into the ER.
What is the nuclear localization signal (NLS)?
A C terminal sequence of 7 basic amino acids that targets proteins to the nucleus.
What is KDEL in the context of protein sorting?
A signal sequence that directs soluble cargo proteins back to the ER.
What is the process of cisternal maturation in the Golgi?
New vesicles from the ER fuse with the cis Golgi and mature into the trans Golgi.
What modifications occur in the Golgi?
Folding, disulfide bond formation, glycosylation, and specific proteolytic cleavages.
What is N-linked glycosylation?
The addition of sugars to asparagine residues on proteins occurring in the ER.
What is the function of clathrin-adapter protein coated vesicles?
Transport proteins from the trans-Golgi network to lysosomes or during endocytosis.
What is the role of dynamin in vesicle budding?
It hydrolyzes GTP to pinch the vesicle bud off.
What is a dominant negative mutant?
A non-functional protein that is still expressed and made.
What modification signals proteins to be targeted to the lysosome?
Mannose-6-phosphate modification in the cis-Golgi.
