E. coli is grown on a medium containing 15N for a long time. Cells were then transferred to medium containing only normal 14N. DNA samples were obtained for analysis after three rounds of replication
A. One with DNA containing both 15N and 14N
B. Two, one with DNA containing only 15N and one with DNA containing only 14N
C. Two, one with DNA containing both 15N and 14N and one with DNA containing only 14N
D. Three, one with DNA containing only 15N, one with DNA containing both 15N and 14N and one with DNA containing only 14N
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In E.coli, the RNA primer at the beginning of each Okazaki fragment is removed by（）
A. DNA polymerase I
B. DNA polymerase II
C. DNA polymerase III
DNA polymerase V
Which does not apply to most bacterial DNA（）
A. Circular
B. Relaxed
C. Not packed into nucleosomes
D. Supercoiled
The 3′ → 5′ exonuclease activity of E. coli DNA polymerase III accounts for the__ of polymerization（）
A. low error rate
B. high speed
C. directionality
D. All of the above
How might mitochondrial DNA be distinguished from eukaryotic nuclear DNA（）
A. Mitochondrial DNA is in the Z conformation, nuclear DNA is in the B conformation
B. Mitochondrial DNA is methylated, nuclear DNA is not
C. Nuclear DNA is linear, mitochondrial DNA are circular
D. They cannot be distinguished and must be clearly separate during purification
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