Number 8 : A-E. Thank you! The following are observations from five experiments
ID: 97532 • Letter: N
Question
Number 8 : A-E. Thank you!
The following are observations from five experiments carried out to determine the mechanism of DNA replication in the hypothetical organism Fungus mungus. For each experiment, indicate whether the results support, refute, or have no bearing on the hypothesis that this fungus replicates its DNA by the same mechanism as that known for E coli. Explain your reasoning in each case. a. Neither of the two DNA polymerases of F. mungus appears to have an 5' rightarrow 3' exonuclease activity. b. Replicating DNA from F. mungus shows discontinuous synthesis on both strands of the replication fork. c. Some of the DNA sequences from F. mungus are present in multiple copies per genome, whereas other sequences are unique d. Short fragments of F. mungus DNA isolated during replication contain both ribose and deoxyribose. e. F. mungus cells are grown in the presence of the heavy isotopes 15N and 13C for several generations and then grown in normal (14N, 12C) medium. Subsequently, DNA is isolated from these cells and denatured after one, two, and three generations. For all three generations, the DNA molecules yield a single hand in a cesium chloride density gradient. For each of the following phrases decide whether it describes the synthesis of the leading strand, the lagging strand, or both strandsExplanation / Answer
Answer:
8.
a. Result supports as the E.coli DNA polymerase II and III have 3'-5' exonuclease activity rather than 5'-3' exonuclease activity.
b. Result refutes as in DNA replication in E. coli, all the DNA polymerase replicate DNA in 5'-3' direction. So, on the template strand (3'-5' orientation) new DNA is made in continuous pieces in normal 5'-3' direction. On the other strand (5'-3' orientation), DNA polymerase synthesises DNA in short pieces called okazaki fragments. Synthesis of DNA in this strand is discontinuous.
c. Result supports as small DNA repeat sequences are present in bacterial genomes. They are present in multiple copies.
d. Result supports as a RNA primer is synthesised by an RNA polymerase called Primase. This RNA primer is required for initiating DNA replication.
e. Result refutes the hypothesis as for all the three generations, the DNA molecules cannot yield a single band in Cesium chloride density gradient. DNA replication follows the semi conservative model. So, DNA isolated after first generation will produce a single band (intermediate between heavy and light DNA). In second generation two bands will be prooduced (one hybrid band and the other lighter band). In the third generation, the hybrid band gets fainter and the light band gets darker in conformity with the semi conservative model of DNA replication.
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