2. SDS-PAGE can be used to determine:
a) whether subunits in a protein complex are identical or not.
b) the molecular mass of a native protein complex.
c) the overall charge on a polypeptide.
d) the molecular mass of denatured protein subunits.
e) none of the above.
3 . At the POI I active site, the primer 3′-OH is deprotonated and the incoming dNTP is bound as the pyrophosphate leaving group departs. This mechanism is carried out by:
a) side chains of the conserved asparagine residues present at the site.
b) two magnesium ions and does not include any protein side chains at all.
c) magnesium, together with conserved asparagine side chains.
d) a water molecule that is deprotonated.
e) None of the above.
12. Which of the following proteins does NOT contain enzymatic activity?
b) DNA ligase
c) Single-strand binding protein (SSB)
d) DNA helicase
12. A biochemist is purifying a new DNA helicase encoded by a pathogenic virus. The enzyme acti vity is readily detected after the first several purification steps that generate fractions a, b, and c, each with successively greater purity. The researcher then puts fraction c on an ionexchange column, and this process generates two new fractions, d and d’. The helicase acti vity cannot be detected in either of the new fractions. However, when fractions d and d are mixed, the activity reappears. The most likely explanation for this is:
a) The helicase is present in both fractions; however, the low concentration results in no activity. Mixing the fractions yields a higher helicase concentration and then acti vity can be observed.
b) The helicase is present one fraction; however, it has additional peptide sequences that must be removed in order for the helicase to assume an active form. An enzyme in the second fraction activates the helicase via proteolytic cleavage.
c) The helicase is present in one fraction and another protein or macromolecule required for helicase activity is present in the other fraction.
d) The helicase is present in one fraction; however, the helicase requires ATP, which is present in the other fraction. When the fractions are mixed, the helicase becomes catalytic again.
e) All of the above are equally likely.
13. The function of DNA ligase is to:
a) facilitate base pairing between single stranded molecules of DNA.
b) catalyze the formation of hydrogen bonds between adjacent nucleotides.
c) unwind the double-stranded DNA prior to replication.
d) catalyze the formation of covalent bonds between adjacent nucleotides.
e) keep the single strands of DNA apart during replication.
14. What is accomplished when ATP is hydrolyzed by DnaA?
a) Allows formation of the oriC/DnaA complex
b) Allows DnaA to unwind DNA
c) Inacti vates the DnaA for replication initiation
d) Removes DnaA at termination of replication
e) Helps bind DnaB helicase to the clamp
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