This diagram shows an early stage of DNA replication. Can you name the protein r
ID: 165399 • Letter: T
Question
This diagram shows an early stage of DNA replication.
Can you name the protein represented by each icon in the diagram? Then, for each protein, can you identify how DNA replication would be affected if that protein were nonfunctional?
Explanation / Answer
Ans. Sequence- (From left to right)
I. Single strand binding (SSB) protein: Several copies (see large number of this protein) bind throughout the ssDNA strands of both leading and lagging strand. It prevents single strand DNA from nuclease activity as well prevents non-desirable annealing during replication.
If nonfunctional: DNA strands would not remain separated; single strands would reanneal to forms dsDNA.
II. Primase: It synthesizes RNA primer to both the leading and lagging strands. DNA polymerase III only extends these primers to synthesize complementary strands. Note that no DNA polymerase can initiate DNA synthesis without an RNA primer.
If nonfunctional: RNA primers would not form; DNA polymerase III could not synthesize DNA.
III. Helicase. It is DnaB helicase, characteristically identified by the “hexameric” form. It unwinds DNA at origin of replication- to which rest other replication machinery is loaded for replication.
If nonfunctional: DNA strand would not separate.
IV. Topoisomerase: It removes strains in DNA by cutting and re-ligating one or both the strands of DNA during replication.
If nonfunctional: DNA would become tangled downstream of the replication fork; replication may start, but would stop when it reaches the tangled DNA.