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Essential amino acids also have codons.Still they are needed by humans through diet?Will those codons do synthesize amino acids for some other purposes in humans or not?If so, what is the purpose?e.g?

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Codons are like 'put green ink here'. The amino acids themselves are like green ink. Humans can write things in green ink, we just need to go and get some first, because we cannot make the ink. Does that make sense? –  Resonating Jun 25 at 19:06

2 Answers 2

You are mixing things. First: Codons have nothing to do with the synthesis of amino acids.

A codon is the sequence of nucleotides on the DNA (or RNA) which code for a certain amino acid. For example UGU and UGC code for the amino acid Cysteine and given these codons it will appear in the protein being synthesized. The codons are basically a way to code the sequence of a protein with the smallest amount of information (simply by the sequence of the four nucleotides in DNA/RNA). For further information have a look at the Wikipedia page on Codons.

This look like this (image from the Wikipedia):

enter image description here

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Okay thanks.My question is codons also code for essential amino acids right?Could you please give me an example of an enzyme or any other protein produced by DNA sequence(mRNA--triplet codons--essential amino acid) with essential amino acids in it? –  Raghavakrishna Jun 25 at 18:38
    
They are the code for this amino acid on DNA/RNA, not more. Their synthesis is done by special enzymes (which are not all present in human, hence we have some essential amino acids) and "only" needs the right precursors. –  Chris Jun 25 at 18:41
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Try uniprot.org/uniprot/P02452 for the sequence of Collagen I alpha precursor. Scroll down(pretty far) for amino acid sequence. K stands for lysine, an essential amino acid. –  Resonating Jun 25 at 19:03

Answer to the comment

Could you please give me an example of an enzyme or any other protein produced by DNA sequence(mRNA--triplet codons--essential amino acid) with essential amino acids in it?


Partial Amino acid sequence of alpha amylase in Homo sapiens:

MKLFWLLFTIGF

Nucleotide sequence:

ATG AAG CTC TTT TGG TTG CTT TTC ACC ATT GGG TTC

Below s the amino acid single letter representation table that can be referred to understand the amino acid sequence

This amino acid single letter representation table can be referred to understand the amino acid sequence

Make sure you follow the reading frame scheme to read the nucleotide sequence. Each time frame should have a triplet codon without including the previous nucleotide. I've represented it for the first few codons. You can observe essential amino acids in this protein. All the amino acids in this partial sequence are essential except glycine. Hope this helps :)

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Can you shorten the example sequences? Just show something like 10 codons/aa. It just occupies more space and does not add to more information. –  WYSIWYG Jun 26 at 6:53
    
Perhaps worth adding that since most (all?) human initiation codons are AUG, most (all?) proteins contain an essential amino acid right there. –  Alan Boyd Jun 26 at 8:56

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