Are free nucleotides found in the nucleoplasm..

JellyBellyBaby

.. or cytoplasm?
Thanks, any help much appreciated :smile:

Reply 1

Fluffy

Think about it logically.

Where would you want them to be in order to be able to use them?

nucleoplasm?

Nucleoplasm for DNA synthesis, but don't forget about molecules such as ATP and ADP and their function...

Reply 4

JellyBellyBaby

I am wanting to know for the replication of DNA, so would it be the nucleoplasm and also is it the enzyme helicase (in the same process) which binds to the DNA double helix?

Reply 5

Fluffy

Helicase unwinds the 2 DNA strands.

What level is this at? I'll try to give you a suitably pitched answer to the whole process :smile:

Reply 6

JellyBellyBaby

which makes the DNA unzip? (sorry should have added that) :smile:

Reply 7

JellyBellyBaby

This is for AS Level - I have a passage on DNA replication which I have to complete by filling in the spaces with the most appropriate word/words which I have attempted. I just need to make sure it is correct before completing it in pen (I find starting in pencil is best!)

Here is the passage:

During DNA replication the enzyme (1. helicase) binds to the DNA double (2. helix) This makes the DNA (3. unzip) and breaks the (4. hydrogen) bonds between the nucleotides. These nucleotides are bound together at (5. bases). The base adenine binds with (6. Thymine) and (7. Cytosine) binds with guanine. Free nucleotides found in the (8. nucleoplasm) bind with the exposed bases producing two strands of DNA. The process is said to be (9. semi-conservative) because in both of the two DNA strands produced, one sequence of nucleotides is new and the other is from the (10. original) DNA.

Reply 8

Fluffy

Assuming GCSE? Or start of AS.

This is probably as much detail as you need:

Unzipping enzyme = helicase, and the free bases are joined together by a polymerase.

the enzyme names usually tell you what they do...

There are other enzymes involved and the above is a heavily simplified version of the event. If you want more detail let me know...

Reply 9

JellyBellyBaby

Is the passage correct?

Reply 10

Fluffy

Looks OK - but without the full list of possible answers it's impossible to say with 100% certainty.

Reply 11

JellyBellyBaby

there wasn't any answers to choose from :/

Reply 12

Fluffy

Ok - well it makes sense at the level you're at. I'd go for it :biggrin:

I prefer unwind to unzip though :smile:

Reply 13

JellyBellyBaby

I then have a question 'When a sample of DNA was chemically analysed it was found that 36% of the bases were adenine. What were the percentages of the other bases?' I know that Thymine would also be 38% and Cytosine and Guanine would each be 14%.

However, I then have a question 'Is it possible to forecast the percentages of bases that would be present in the messenger RNA transcribed from this DNA? Explain your answer. (2 marks) which I am stuck with - any ideas?

Reply 14

Fluffy

JellyBellyBaby

A pairs with T so T = 36% too (not 38% - assuming that was a typo?).

Leaves you with 28% - so 28% of the DNA is either G or C, therefore each of these = 14%.

You can't really predict base percentage in eukaryotes as you have introns and exons in the DNA which are spliced out of pre-mRNA to give you mRNA as well as modifications that are made to the mRNA transcript (capping and poly A tails).

I'm not sure what detail you would need to go into for AS though...

Reply 15

JellyBellyBaby

Yes, sorry that was a typo! As for the rest, I am completley lost :frown:

perhaps I should ask my teacher on that one tomorrow.

Reply 16

Fluffy

Basically mammalian DNA contains sequences called Introns which are not expressed inthe final mRNA, and Exons which are (easiest way to remember which is which is EXons are EXpressed, INtrons are INactive).

Pre-mRNA (also called hnRNA in some books) is a straight transcript of the DNA sequence and contains the relevant complementary base [remembering that uracil replaces thymine in RNA].

However to make mRNA the introns are cut out and the exon sequences are all joined together - therefore you no longer have an exact template of the whole DNA strand.

I'll see if I can find a piccy online that shows this...

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Here we go - it's not a perfect piccy but should give you an idea...