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Why does Glycine have two codons?

JellyBellyBaby

(as title) - nothing else to add really! :p:

Reply 1

Brutalyzer

I'm not sure in specific but from my biology I know that DNA code is degenerate i.e. one amino acid can be coded for by more than one codon. Glycine can be coded by four codons: GGU, GGC, GGA and GGG. Similarly, Alanine can be coded for GCU, GCC, GCA and GCG.

An advantage of this is if a substitution mutation occurs in our DNA, there are chances that the substituted base will result in the same amino acid so there won't be any harmful results (such as formation of a non-working protein).

Reply 2

JellyBellyBaby

Thankyou

Do you study A-Level Biology?

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Do you know the sequence of amino acids which would result from the DNA sequence: AGTCCCAAAT

Reply 3

Brutalyzer

Yep; sorry, I assumed that you did A-level Biology too. If you don't, that you probably won't understand what I meant by 'substitution mutation'. I'll try to explain it anyways as it could help other people: Primarily, there are 4 types of substitution (that I know of): Addition, deletion, substitution and inversion.

Addition and deletion mutation are considered the more harmful ones as they result in a frame shift i.e. a base is inserted or deleted causing the codons from the point of addition/deletion to move up or down to compensate for the free/lost space.

Substitution mutation occurs when one or more bases are substituted by one or more bases. For example, we have a codon of Glycine GGU. Say a substitution mutation occurs and U is replaced by C. The end product will be GGC, but as we know already, GGC codes for the same amino acid (Glycine) so this type of mutation won't have any effect on the polypeptide produced which eventually will fold itself into a tertiary structure of a protein.

Reply 4

Brutalyzer

JellyBellyBaby

Thankyou

Do you study A-Level Biology?

--------------

Do you know the sequence of amino acids which would result from the DNA sequence: AGTCCCAAAT

Yep, this is how to do it. Split them up in 3's. We have:

AGT CCC AAA T (bit confused about the T at the end, usually, you get whole numbers of 3)

Anyways, next step is convert them into the sequence that one would find in an mRNA strand by complementary base pairing:

UCA GGG UUU A

You must've been provided with a table of mRNA codons and the amino acids that they code for. So we have:

Serine Alanine Phenylalanine

Reply 5

JellyBellyBaby

I do AS Biology - what exam board are you on?

Reply 6

Brutalyzer

AQA Specification B. I'm doing A2 Biology.

Reply 7

JellyBellyBaby

cool - I'm on AQA Spec B also! May I ask what other subjects you do and what you got at AS? :smile:

Reply 8

Teehar

i read this post as "why does Glycine have two condoms?" :p:

Reply 9

stratomaster

I do AQA B but I don't know the particluar code for each amino acid :confused:

Do you have a data book or something with this in?

Reply 10

corkskrew

Remember to look at which DNA strand you're given....

If you're given the sequence of the *sense* strand, this is what the mRNA will look like (except Uracil every time there's a Thymine)
If you get the *anti-sense* strand (which you usually are), you have to go through the whole complementary base pairing malarkey.... basically:
A pairs U
T pairs A
C pairs G
G pairs C

stratomaster

I do AQA B but I don't know the particluar code for each amino acid :confused:

Do you have a data book or something with this in?

There's no way you'll be expected to know all 64 combinations at A Level. They'll give you the mRNA sequence table or DNA sequence which will look something like this:

http://psyche.uthct.edu/shaun/SBlack/geneticd.html

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