26.
(a)
Explain the process of DNA replication in prokaryotes.
(b)
Write the phase in cell cycle where DNA replication occurs in a
cell. What will happen if cell division fails to occur after DNA
replication in a cell ?
OR
5
State the hypothesis proposed by Oparin and Haldane. Describe how S.L.
Miller experimentally supported it.
5
27.
(a)
IVF is a very popular method these days that is helping childless
couples to bear a child. Describe the different steps that are carried
out in this technique.
(b)
Would you consider Gamete Intrafallopian Transfer (GIFT) as an
IVF ? Give a reason in support of your answer.
5
OR
(a)
Draw a sectional view of a human ovary and label primary follicle,
tertiary follicle, Graafian follicle and corpus luteum in it.
(b)
Name the gonadotropins and explain their role in oogenesis and
the release of ova.
5
Answers
Answer:
Eukaryotic DNA replication is regulated to ensure all chromosomes replicate once and only once per cell cycle. Replication begins at many origins scattered along each chromosome. Except for budding yeast, origins are not defined DNA sequences and probably are inherited by epigenetic mechanisms. Initiation at origins occurs throughout the S phase according to a temporal program that is important in regulating gene expression during development. Most replication proteins are conserved in evolution in eukaryotes and archaea, but not in bacteria. However, the mechanism of initiation is conserved and consists of origin recognition, assembly of pre-replication (pre-RC) initiative complexes, helicase activation, and replisome loading. Cell cycle regulation by protein phosphorylation ensures that pre-RC assembly can only occur in G1 phase, whereas helicase activation and loading can only occur in S phase. Checkpoint regulation maintains high fidelity by stabilizing replication forks and preventing cell cycle progression during replication stress or damage
Explanation:
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