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dna questions

1. The diagram shows a molecule of an enzyme called ribonuclease. Each amino acid in the protein is indicated by a 3-letter symbol e.g. Arg = arginine. How many nucleotides are there in the mRNA molecule that codes for this
enzyme? (1 mark)



2. The table below the mRNA code for the four amino acids in the part of the enzyme labelled X. Give the DNA code for the part of the enzyme labelled X (1 mark)



3 (i) Where does translation occur in a cell? (1 mark)
(ii) Describe what happens during translation (3 marks)

4. Explain how the structure of DNA is related to its function. (6 marks)
Reply 1
These are easy...

Think about it!
Reply 2
rahmed
These are easy...

Think about it!

I have never studied DNA before (ok.... only 1 lesson)
Reply 3
Number one is so easy that you shouldn't even have posted it. count.

Number two, I'm assuming that the part in the bracket is the bit labelled X.
GGUUUAAGUGAG

3. i. nucleus

look in a book for the rest :P

I haven't done DNA in a year.
Reply 4
of course it'lle be easy for you lots. :frown:
Reply 5
*Sparkle*

3. i. nucleus


That's incorrect. Transcription takes place in the nucleus but translation takes place within ribosomes typically outside the nucleus. Ribosomes in eukaryotes may be free floating or attached to the surface of the endoplasmic reticulum. In prokaryotes transcription and translation takes place more or less simultaneously due to the absence of a nuclear envelope.

*Sparkle*

Number two, I'm assuming that the part in the bracket is the bit labelled X.
GGUUUAAGUGAG


Your answer is here is incorrect, but the most obvious one in my view is that it specifically asks for the DNA code - DNA does not contain uracil but thymine so all your bases are muddled. The answer I get is CGT AAT TCA CTC - which looks nothing at all like your bases. The codes you are given at the mRNA codes so you need to work out the complementary DNA code to the mRNA code you have been given.

To the OP, for more information translation try reading this: http://en.wikipedia.org/wiki/Translation_%28genetics%29

The relationship between DNA structure and function is quite easy if you think about it. How is DNA copied? Why are complementary base pairings important to the structure and copying of DNA? Why is the double-helix important? Why is the DNA supercoiled? How is the DNA supercoiled? I'm not going to answer all those questions for you but those are the kind of answers you are seeking to break the question down for you a bit.
Reply 6
*Sparkle*
Number one is so easy that you shouldn't even have posted it. count.

Number two, I'm assuming that the part in the bracket is the bit labelled X.
GGUUUAAGUGAG


You have given the sequence of the mRNA (although made an error in the 2nd nucleotide - should be C not U) ... however the question asks for the DNA sequence so you need to give the complementary sequence and change any U's to T's. Also strictly you should write out the sequence "backwards" as the convention is to write it out 5' to 3' which would be the reverse of the mRNA sequence due to the antiparallel nature of DNA.

Also, question 1 is a bad question. I assume they want you to count the amino acids and multiply by 3 to get the number of nucleotides. However this is not the number of nucleotides in the mRNA, as there are also sequences at either end which are not translated but are still present in the mRNA (such as the polyA tail at the 3' end).
Reply 7
...and the 7-methyl guanosine cap at the other end! Damn I are clever.
Reply 8
the question asks for the "nucleotides in the mRNA that codes for the protein"

so you don't count the cap or the tail becuase these are removed from the sequence and do not code for amino acids in the protein...
Reply 9
Revenged
the question asks for the "nucleotides in the mRNA that codes for the protein"

so you don't count the cap or the tail becuase these are removed from the sequence and do not code for amino acids in the protein...


That means how many nucleotides are there in the mRNA molecule itself. So you have "the mRNA molecule that codes for the protein" and it wants to know how many nucleotides are in that molecule.

If it wanted to know the number of nucleotides that actually code for the protein (ie excluding non-coding nucleotides) then it should say "nucleotides in the mRNA that code for the protein" ie code not codes because "nucleotides" is a plural word whereas the mRNA is singular!
Reply 10
lol, ok... i'm sure it really doesn't matter though...
Reply 11
It doesn't. At A-level (which I assume this is for) you don't even discuss that level of knowledge.
Reply 12
What should i add up to get a definite answer?
Reply 13
124 amino acids, 3 nucleotides in each amino acid and so overall there are 372 nuclotides in mRNA
Reply 14
I was going to say the same but I got 123 amino acids
Reply 15
yes, you're right it's 123... so it's 369 nucleotides...
Reply 16
I wish my genetics exam was going to have questions like that :frown:

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