Biochem ch 31

mikebewo's version from 2015-05-20 04:12


Question Answer
The primary driving force for folding is/are ____ and if crowding occurs then ____ is likely.
a. hydrogen bonding; dehydration
b. hydrogen bonding; non-specific bonding
c. hydrophobic interactions; aggregation
d. hydrophilic interactions; non-specific binding
e. none are true
Nascent (newly formed) proteins are often assisted in folding and ____ by a family of helper proteins known as ____.
a. unfolding; molecular principals
b. refolding; molecular principals
c. refolding; molecular chaperones
d. unfolding; molecular chaperones
e. unfolding; amyloids
In E. coli, ____ bound to large ribosomal subunits facilitates transfer to ____ to bind ____ residues, thus avoiding non-productive folding.
a. chaperonin; trigger factor; H-binding
b. trigger factor; DnaK; hydrophobic
c. DnaK; Hsp70; ionic
d. Hsp70; chaperonin; hydrophilic
e. all are true
Which of the following statements about protein folding is INCORRECT?
a. the Hsp70 proteins bind to hydrophilic regions of the protein, thus preventing aggregation
b. the Hsp60 proteins are also known as chaperonins
c. the GroEL protein provides an environment free from possibility of aggregation
d. the GroES protein serves as the cap for GroEL
e. all are correct
Characteristics of Hsp90 chaperones include all EXCEPT:
a. 1-2% of total cytosolic proteins in eukaryotes.
b. action depends on cyclic binding and hydrolysis of ATP.
c. major purpose is conformational regulation of signal transduction molecules.
d. directs proteins toward degradation pathways.
e. all are true.
The most common form of post-translational processing is:
a. carbohydrate addition.
b. lipid addition.
c. phosphorylation.
d. adding signal sequences.
e. proteolytic cleavage.
The primary function of Met-aminopeptidase is to:
a. cleave large inactive pro-proteins.
b. remove leader peptides after translocation.
c. transfer a Met to the C-terminal end for translocation.
d. remove invariable Met and introduce N-terminal diversity.
e. all are true.
Proteolytic cleavage has been shown to be involved in all of the following processes EXCEPT:
a. inactivation of regulatory enzymes.
b. elimination of the N-terminal Met residue.
c. activation of zymogens.
d. elimination of signal sequences after the protein has reached its proper location.
e. digestion of dietary proteins.
Characteristics of protein translocation systems include all EXCEPT:
a. proteins to be translocated are made as pre-proteins containing contiguous blocks of amino acid sequences that act as sorting signals.
b. membranes involved in translocation have specific protein receptors exposed on their cytosolic faces.
c. translocons catalyze movement of the proteins across the membrane and metabolic energy in the form of ATP, GTP, or membrane potential is essential.
d. pre-proteins are maintained in a loosely folded, translocation-competent conformation through interaction with molecular chaperones.
e. all are characteristics.
____ recognize the sorting signals as they emerge from the ribosome and together with ____ deliver the nascent protein chain to specific membrane complexes called ____ that mediate integration into and across the membrane.
a. Signal recognition particles; signal receptors; translocons
b. Signal receptors; translocons; signal recognition particles
c. Translocons; signal recognition particles; signal receptors
d. Signal receptors; signal recognition particles; translocons
e. Translocons; signal receptors; signal recognition particles
The ribosome and the ____ form a common conduit for transfer of the nascent protein through the ____ membrane.
a. translocon; endoplasmic reticulum
b. signal sequence; plasma
c. EF-G; endoplasmic reticulum
d. chaperonin; plasma
e. all are true
Characteristics of the mammalian translocon include all EXCEPT:
a. sec61 complex at the core.
b. transmembrane protein-conducting channel.
c. BiP carries out ATP-dependent protein folding.
d. composed of a single transmembrane spanning (TMS) protein.
e. all are true.
Proteins with ____ sequences remain embedded in the ER membrane with their ____-termini on the cytosolic face of the ER.
a. translocator; N
b. leader; C
c. translocational; N
d. stop-transfer; C
e. translocon; N
Mitochondrial presequences are ____ charged amphipathic sequences retained in the ____ stage through association with ____ molecular chaperones.
a. positively; folded; Hsp40
b. positively; unfolded; Hsp70
c. negatively; folded; Hsp70
d. neutral; unfolded; Hsp40
e. negatively; prefolded; Hsp90
Protein degradation is compartmentalized either in macromolecular structures known as ____ or in degradative organelles such as ____.
a. ribosomes; endoplasmic reticulum
b. ribosomes; Golgi
c. proteosomes; mitochondria
d. proteosomes; lysosomes
e. lysosomes; endoplasmic reticulum
A highly conserved protein that is involved in protein degradation is:
a. ricin
b. met-aminopeptidase
c. ubiquitin
d. degradase
e. peptidyl transferase
All are correct statements regarding the protein degradation process involving ubiquitin EXCEPT:
a. The modified protein is degraded by an ATP-dependent protease complex.
b. The ubiquitin binding to the protein to be degraded leads to a novel branched protein.
c. The ubiquitin is covalently attached to a cysteine residue in the protein to be degraded.
d. Three additional proteins (E1, E2, and E3) are involved in the ligation of ubiquitin to the protein.
e. Ubiquitin is a highly conserved protein.
In a protein targeted for destruction, ubiquitin is most commonly attached to a _____ residue, forming a/an ______ bond between ubiquitin and the targeted protein.
a. Ser; ester
b. Lys; amide
c. α-amine group of the N-terminal amino acid if the particular residue is Arg, Lys, His, Phe, Tyr, Trp, Leu, Asn, Gln, Asp or Glu; amide
d. Glu; acid anhydride
e. Cys; thioester
All are characteristics of HtrA proteases EXCEPT:
a. ATP-dependent.
b. chaperones at low temperatures.
c. proteases at high temperatures.
d. bind misfolded or unfolded proteins.
e. all are true.
What does Hsp (as in Hsp60) stand for?
a. helical stabilizing protein
b. hydrophobic sequestering protein
c. heat shock protein
d. high-histidine subunit protein
e. none of the above
Which of the following proteins would be commonly ubiquitinated and thus degraded by the proteasome?
a. proteins with Met as the N-terminal amino acid
b. proteins with short sequences rich in Pro, Glu, Ser and Thr
c. proteins with short sequences rich in Trp, Thr, and Phe
d. proteins having a C-terminal Cys for the formation of a thioester bond with ubiquitin
e. none of the above

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