21. The melting of 40-45 bp at the oriC site of E. coli requires

A. DNA + ATP + HU
B. DNA + ATP + HU + DNAb
C. DNA+ ATP + HU + DNAb + DNAa
D. DNA + ATP + HU + DNAb + DNAa + Pol III holoenzyme

22. Overwinding or overtightening of DNA during replication is caused and removed by

A. DNAb, DNA polymerase
B. DNAa, gyrase
C. DNAb, gyrase
D. Single stranded protein, DNAa

23. How does ethidium bromide interact with DNA?

A. It binds to adenine
B. It binds to phosphate
C. It intercalates between bases
D. It does not interact

24. Number of times the two DNA strands are interwined in circular DNA and is known as

A. helix frequency
B. linking number
C. twisting number
D. none of these

25. The enzyme responsible for breaking the hydrogen bonds, and thus separating the DNA strands during DNA synthesis is

A. DNA polymerase
B. strandase
C. helicase
D. none of these