# How many amino acids are coded for by this section of DNA? GCSE Biology question HELPWatch

This discussion is closed.
#1
Well on a past paper i was just doing, I came across this question:

"Look at the sequence of bases for a section of DNA.

GTACTCTGA

1) How many amino acids are coded for by this section of DNA?
2) Write down the complementary DNA base code for this section of DNA. "

I know the answer from the marks scheme now, but i don't have a clue how you get to the answer...

can somebody help me, please? and explain to me how you find the answers to these two question? THANK YOU SO MUCH!!!
0
7 years ago
#2
1) Three bases code for each amino acid - so you have 9 bases -> they code for 3 amino acids

2) C and G are complimentary and A and T are complimentary - so the answer is CATGAGACT
0
7 years ago
#3
1) 3 amino acids

2)CATGAGACT

Three bases (ie letters) code for an amino acid. So, there are 9 letters here meaning 3 amino acids.

The base code is the other side of the double helix. 'G' bases always pair with 'C' bases. Similarly, 'T' bases always pair with 'A' bases. So, you can see how I got answer 2 from that =]
0
7 years ago
#4
Three bases code for one amino acid

The base pairing rules are A-T G-C
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7 years ago
#5
wait till you do A level biology and you have to learn about mRNA and tRNA.....
0
#6
thanks!
so, ALWAYS, 3 bases code for 1 amino acid? but i don't get the second bit; i know that AT-GC are the complementary base pairs but the answer is CATGAGACT, how does C and A pair together and then T and G and so on? or am i wrong, please explain? thanks so much!
(Original post by oli_G)
1) 3 amino acids

2)CATGAGACT

Three bases (ie letters) code for an amino acid. So, there are 9 letters here meaning 3 amino acids.

The base code is the other side of the double helix. 'G' bases always pair with 'C' bases. Similarly, 'T' bases always pair with 'A' bases. So, you can see how I got answer 2 from that =]
0
7 years ago
#7
(Original post by SenFer)
thanks!
so, ALWAYS, 3 bases code for 1 amino acid? but i don't get the second bit; i know that AT-GC are the complementary base pairs but the answer is CATGAGACT, how does C and A pair together and then T and G and so on? or am i wrong, please explain? thanks so much!
Ok, imagine a DNA molecule like a long rectangle. On one side are the bases 'A' 'C' 'G' and 'T'. These stand for the chemicals stand for 'Adenine' , 'Thymine', 'Guanine' and 'Cytosine', if you're interested. There needs to be bases on the RHS also. The way that these chemical pair is that 'A' always pairs with 'T' and 'C' with 'G'. So you can imagine that if you know one side of a DNA structure, you can work out the other.

There are more complications such as tRNA, RNA, mRNA and loads of them which are more complicated. DNA is the form that this genetic material takes inside the nucleus of a body cell =]
0
7 years ago
#8
(Original post by cheekymon999)
wait till you do A level biology and you have to learn about mRNA and tRNA.....
wait until you have to do all of the other RNAs... what difference does it even make?
0
7 years ago
#9
(Original post by oli_G)
Ok, imagine a DNA molecule like a long rectangle. On one side are the bases 'A' 'C' 'G' and 'T'. These stand for the chemicals stand for 'Adenine' , 'Thymine', 'Guanine' and 'Cytosine', if you're interested. There needs to be bases on the RHS also. The way that these chemical pair is that 'A' always pairs with 'T' and 'C' with 'G'. So you can imagine that if you know one side of a DNA structure, you can work out the other.

There are more complications such as tRNA, RNA, mRNA and loads of them which are more complicated. DNA is the form that this genetic material takes inside the nucleus of a body cell =]
Ah, tRNA and mRNA. They're not that complicated though. Just switch Thymine for Uracil and you're all set, not too brain-twisting. Bit tricker than DNA but not by a lot. Or maybe that's just my forte. Cos plant biology always screws me up. It's the bloody cambiums that I hate.
0
7 years ago
#10
(Original post by NaturalDisaster)
Ah, tRNA and mRNA. They're not that complicated though. Just switch Thymine for Uracil and you're all set, not too brain-twisting. Bit tricker than DNA but not by a lot. Or maybe that's just my forte. Cos plant biology always screws me up. It's the bloody cambiums that I hate.
Yeah, personally I'm fine with the variations on 'RNA', although it is complicated understanding the role each of these take. Some uni dude came and gave us a lesson at my school and there are literally 20 or 30 different ones in reality
0
7 years ago
#11
(Original post by cheekymon999)
wait till you do A level biology and you have to learn about mRNA and tRNA.....
Easy stuff lol.
0
7 years ago
#12
Triplet code !
0
7 years ago
#13
(Original post by oli_G)
Yeah, personally I'm fine with the variations on 'RNA', although it is complicated understanding the role each of these take. Some uni dude came and gave us a lesson at my school and there are literally 20 or 30 different ones in reality
Oh lord help us all. Yeah, mRNA and tRNA are cool. But those damn plants...grrr. Wish my school did Human Biology but oh well, at least they do some kind of Biology.
0
7 years ago
#14
(Original post by cheekymon999)
wait till you do A level biology and you have to learn about mRNA and tRNA.....
We did it for GCSE
0
7 years ago
#15
right if you still cant understand it:
this is how the pairing works.

A - T
C - G

the 4 base pairs always pair like that so say you had a sequence of DNA that read:

ACCGTAGCA

A T
C G
C G
G C
T A
A T
G G
C C
A T

hope this helps
0
7 years ago
#16
(Original post by SenFer)
thanks!
so, ALWAYS, 3 bases code for 1 amino acid? but i don't get the second bit; i know that AT-GC are the complementary base pairs but the answer is CATGAGACT, how does C and A pair together and then T and G and so on? or am i wrong, please explain? thanks so much!
If it helps, adenine and guanine (A and G) are purines, and thymine and cytosine (T and C) are pyramidines [as is uracil in RNA].

The purines have two rings of carbon and nitrogen atoms, and the pyramidines have one ring of carbon and nitrogen atoms.

They pair together so the DNA double helix has a constant width:
A and T = 2 + 1 rings
G and C = 2 + 1 rings

Therefore DNA is always 3 rings wide for each pair of bases (for instance, A and G would be 4 and T and C would be 2, which would mess up the helix).

Don't know if you really wanted all that, but it might make it more clear. It helped me anyway because I have to do an exam on it next week...
0
7 years ago
#17
(Original post by NaturalDisaster)
Oh lord help us all. Yeah, mRNA and tRNA are cool. But those damn plants...grrr. Wish my school did Human Biology but oh well, at least they do some kind of Biology.
I'm in Year 11 now and did this human health gcse instead of triple science (so have science and add sciene at a* already plus a human health gcse). Human biology is very interesting compared to plants etc. =]
0
#18
thanks everyone! I understand it now- how silly, i know this stuff but i though it in a complicated way... thanks anyways, really helped- especially with the 1st question
1
3 years ago
#19
How did you get that for answer 2? If C Goes With G and T with A then why is C with A to start and so on? I have the same problem but mine is TATATGTAAAAACAA
0
3 years ago
#20
(Original post by Treybc123)
How did you get that for answer 2? If C Goes With G and T with A then why is C with A to start and so on? I have the same problem but mine is TATATGTAAAAACAA
You had it right. Guanine always matches with cytosine, while adenine always matches with thymine. If you have the sequence TATATG on one of the strands, the complementary strand should be ATATAC. I'm sure you'll be able to do the rest of your sequence knowing this

This is quite an old thread so I will be closing it. If you have any further queries or need any help, please make a new thread
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