cell biology course

Question

Why does it take up to a full cell cycle to observe the effects of a temperature-sensitive mutation? 

This is regarding to yeast strains (cdc13-1) in the CDC13 gene have temperature sensitive mutation where they grow fine at 23C but they experience G2 cell cycle arrest at 37C. and yeast cells take 60-90 minutes to go through 1 full cell cycle. so why does it take a full cell cycle to see those effects from temp mutations?

I need explanation ASAP pleaseee!

Answer 1

It depends on the context of your learning in class, but IN GENERAL, in a population of yeast cells, each cell is 'doing its own thing'--i.e. is at a random point in the cell cycle. So even if a cell stops IMMEDIATELY when it has a need for a given protein (say, cdc-13), many/most cells will be far away from executing that particular step, and so the lack of cdc-13 won't manifest until they get there.

You can think of it like a situation where everyone's watch is set to a different time. All of our watches have an alarm that will go off at 6:30, but if my watch says 4:00, it will be 2.5 hours before my alarm goes off, and if your watch says 11:00, you'll have to wait 7.5 hours before hearing the alarm.

This is why you'll see critical experiments on the cell cycle done with 'synchronized cells'--cells that have been brought to the exact same point in the cell cycle prior to initiating the experiment. the mating pheromone alpha factor is often used for this; cells of 'a' mating type go into cell cycle arrest in the presence of alpha factor.