A dividing animal cell is injected with radioactivedeoxythymidine triphosphate (

Question

A dividing animal cell is injected with radioactivedeoxythymidine triphosphate (dTTP). The dTTP will be incorporatedinto the DNA if replication takes place anytime during the courseof the experiment. After varying periods of time, cell division isstopped and the DNA assayed to see if it has becomeradioactive. The DNA will become radioactive if: a.) you inject during G2 and stop cell division during thefirst metaphase that follows, True or False? b.) you inject while the chromosomes are condensing and stopcell division during the first G2 that follows, True orFalse? c.) you inject just after the chromosomes have been duplicatedand stop cell division during the first G1 that follows, True orFalse? d.) you inject during G1 and stop cell division during thefirst cytokinesis that follows, True or False? e.) you inject during anaphase and stop cell division duringthe first prophase that follow, True or False? Some explaination would be much appreciated! Thanks inadvance. A dividing animal cell is injected with radioactivedeoxythymidine triphosphate (dTTP). The dTTP will be incorporatedinto the DNA if replication takes place anytime during the courseof the experiment. After varying periods of time, cell division isstopped and the DNA assayed to see if it has becomeradioactive. The DNA will become radioactive if: a.) you inject during G2 and stop cell division during thefirst metaphase that follows, True or False? b.) you inject while the chromosomes are condensing and stopcell division during the first G2 that follows, True orFalse? c.) you inject just after the chromosomes have been duplicatedand stop cell division during the first G1 that follows, True orFalse? d.) you inject during G1 and stop cell division during thefirst cytokinesis that follows, True or False? e.) you inject during anaphase and stop cell division duringthe first prophase that follow, True or False? Some explaination would be much appreciated! Thanks inadvance.

Explanation / Answer

The cell cycle goes in this way: G1--S--G2--M---new cells The synthesis and duplication of DNA only occurs in the Sphase. so only in the S phase the radioactive dTTP can beincorporated into the DNA. Therfore: a.It is FALSE. you inject during G2 and stop cell division during the firstmetaphase that follows. G2 is followed by M phase which has metaphase in it. Here noDNA synthesis occurs, so it is false b.It is FALSE. you inject while the chromosomes are condensing and stop celldivision during the first G2 that follows, The chromosomes condense at the end of S phase. and S phase isfollowed by G2 phase. So no synthesis. so false c.It is FALSE. you inject just after the chromosomes have been duplicated andstop cell division during the first G1 that follows In S phase the chromosomes will be duplicated. It isfollowed by G2 and M phase and next by G1. So if we stop in G1there is no synthesis of DNA and so it is false d. It is TRUE. you inject during G1 and stop cell division during the firstcytokinesis that follows After G1 the S phase follows during which synthesis of DNAoccurs. So the radioactive dTTP can be incorporated. The firstcytokinesis is seen in M phase. so it is true e. It is TRUE. you inject during anaphase and stop cell division during thefirst prophase that follows Anaphase comes in M phase. but after that G1 phase comeswhich is followed by S phase. Here synthesis of DNA occurs and theradioctive dTTP can be incorporated. It is stopped only in thefollowing prophase which is in M phase. hence it is true

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