Question

1. For cells to replicate properly, they must duplicate their genome. However, this must be done only once per cell cycle. Answer the following questions in detail.

A. During which cell cycle phase, does DNA undergo replication?

B. Which cyclin must accumulate within the cell to trigger DNA replication?

C. Explain the process by which cells replicate their DNA only once per cycle.

D. What consequences would there be if more than one round of replication occurred per cell cycle?

E. Identify the protein names/complexes that make up the pre-replicative complexes, explain how these are assembled onto the origins of replication, and how they are converted into pre-initiation complexes.

Answer 1

A.) DNA undergo replication in the S phase of the Interphase.During S phase the amount of DNA per cell doubles - like if initially there were 2 chromosomes, in S phase that will turn to 4C. Cell cycle occurs in 2 phhases- Interphase and M phase. Interphase is the phase of cycle in which all the preparatory steps take place before the cell division. G0, G1, S and G2 phase are in the Interphase. Cell spends approximately 95% time in Interphase and only 5% in the M phase.

B.) S cyclins trigger the replication of the DNA in cell. Cyclins bind to CDK molecule and this Cyclin-CDK protein complex controls the ability to phosphorylate traget proteins. S cyclins bind to CDK molecule to activate the replication process of DNA in cell.

C.) The process Replication licensing ensures that a cell undergoes replication only once per cell.Cyclin dependent kinases are the regulators of the cell cycle. CDK activity along with other protein complexes ensures that at the end of the mitosis these protein complexes are loaded on the chromosome and are activated till the chromosomes get doubled and once the replication is over CDK acticity drop down and restrict the licensed state.

D.) At the end of the cell cycle, after M phase the mother cell divides it's genetic material equally into 2 daughter cells. This is achieved once the replication of DNA is done precisely and correctly in the S phase. But if the cell enters in the M phase with doubled or over-replicated DNA there will be some genetic mutations and errors in the gentic material which can lead to the death of cell or cell might go in the resting phase permanently.