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04:01A biochemist isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture?
a. DNA polymerase
b. DNA ligase
c. Okazaki fragments
d. Primase
E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment?
a. One high-density and one low-density band
b. One intermediate-density band
c. One high-density and one intermediate-density band
d. One low-density and one intermediate-density band
What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?
a. The origins of replication occur only at the 5′ end.
b. Helicases and single-strand binding proteins work at the 5′ end.
c. DNA polymerase can join new nucleotides only to the 3′ end of a pre-existing strand, and the strands are antiparallel.
d. DNA ligase works only in the 3′→5′ direction.
The elongation of the leading strand during DNA synthesis
a. Progresses away from the replication fork
b. Occurs in the 3′→5′ direction
c. Produces Okazaki fragments
d. Depends on the action of DNA polymerase
The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage?
a. Nuclease, DNA polymerase, DNA ligase
b. Telomerase, primase, DNA polymerase
c. Telomerase, helicase, single-strand binding protein
d. DNA ligase, replication fork proteins, adenylyl cyclase
In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules?
a. A=G
b. A+G=C+T
c. A+T=G+C
d. A=C
