Please Help?

[NAS]

Hey everybody, Im just stuck with a few A level biology Qz..I hate genetics!

If you could please list answerz to the following Qz..Id be very grateful!!

Explain y in a rat bone marrow cell, the amount of adenine is approx equal to the amount of thymine?


If DNA was taken from other tissues of this rat, explain why it would have the same base composition as that taken from the bone marrow cells?

Explain why the relative amounts of each base are different in all three organisms?

PLEASE HELP:cry: :cry:

[VikMcG]

Hi I have not had time to look this up in a book for you cause sitting exams at mo. But I think it is to do with base pairing that thymine and adenine pair together in a dna molecule so therefore the percentage of both will be similiar.In bone marrow, there are stem cells - these cells have the potential to make any different type of cell in the body. There fore the dna of stem cells will be similar to that of a mature cell which has been through the differentiation stages. For example Most mature cells exist in G0 phase of cell division i.e they are not dividing. dolly the sheep was cloned by placing a mature cell like a hepatocyte in to the cytoplasm of a stem cell (nucleus had been destory). Thus cytoplasmic factors induces the nucleus of the mature cell to start to divide and reverse of differentiation occurred . Thus a clone was made. I don't understand the last question which you have asked so cannot help there

[NAS]

Its ok bro, thanks for your reply!

A few members have kindly gave me a PM and shared their knowledge.

Thank you all:D

[elliottsimpson]

maybe you could post it here, so others will know, too.

[susanj]

Dear NAS,

>Explain why in a rat bone marrow cell, the amount of adenine is >approx equal to the amount of thymine?

VikMcG is right about the base-pairing. DNA is double-stranded (two molecules combine to form a helix) and wherever there's an adenine on one strand of DNA, it forms a hydrogen bond with a thymine on the other strand. (Similarly, cytosine pairs with guanine)

>If DNA was taken from other tissues of this rat, explain why it >would have the same base composition as that taken from the >bone marrow cells?

All of the nucleated cells of an individual organism (i.e. all the cells that contain a nucleus - which is everything except red blood cells and some skin cells) contain the exact same DNA. This is because all the organism's cells have arisen by successive rounds of cell division, and before a cell divides, it's DNA is copied exactly, so that each daughter cell gets an identical set of genes (=DNA).

What makes tissues different from one another is that different bits of the DNA (different genes) are "turned on" in the cells of each tissue. Scientists would say that "all nucleated cells have the same genome, but only a proportion of that genome is expressed in any one cell type".

Hope you followed that!

>Explain why the relative amounts of each base are different in >all three organisms?

I don't know which three organisms you're talking about, but it doesn't matter. I guess you are looking at some sort of table which shows different amounts of A/T and G/C pairs for each of 3 organisms?

The A/T and C/G content of an organism's DNA wil depend on the exact sequence of the DNA (genes) in that organism. Because it takes different DNA (=genes) to make a mouse, or an onion, or a human, we would expect their (genomic) DNA sequences to be different - and they are. The base composition could even be different between individuals of the same species, because of genetic variation/mutation, but the difference would be so small as to be virtually undetectable.

Hope this helps,

susanj

[Devlinator]

And susan should know, she has a phd in cell biology!!!!