Why there are only 20 amino acids, although a amino acid is coded by a single codon with three bases. That means by permutation, 3*3*3=27 amino acids must exist ???

Question

anonymous · Answer

In nature there are many more variations amino acids than the simple 20 found in humans. However, when analyzing the human genome sequence, there is a code for all 64 permutations (4^3), only some of them share amino acids. This is a safe-guard against mutations of one or two nucleotides. For example, the amino acid Alanine is coded with four different nucleotide sequences: GCA, GCC, GCG, GCU. 
Also some amino acids code the same like UUU &UUC

anonymous · Answer

@BiomedStudent how is the possibility of 64 permutations ?

anonymous · Answer

Some codes will sequence the same amino acid.
The attached chart should help

anonymous · Answer

Humans only need 20 of them. Why waste ATP on something that can be substituted?

anonymous · Answer

while there are possible 64 codons. fidelity is higher in the first two nucleotides. the most redundancies occur at the third - lo-fi , this is commonly known as "wobble".
aside of codons for AA u need also stop codons (3 or 4 if i remember correctly. UAG UGA as an example.

anonymous · Answer

The degeneracy within the coding system allows for errors to occur without too many damaging effects. It is a clever safety measure created by the biological system

anonymous · Answer

Human biology only uses the most common amino acids, that is, 20 amino acids. You have 4 letters (ATGC) in the genetic code. If you have to code for the 20 amino acids, you need to combine these for letters in a way that can be achievable. If you start with a code that is established in a 2 letter way, there is not enough combinations that can code for the whole 20 amino acids. But if you have a code that is based in a 3 letter way, you have 64 possible combinations, which is actually the way the genetic code works. It's important to remark, that not all codons code for a amino acids, there a certain codons that work like the grammar of the genetic code (points, commas, etc), and other several codons can code for the same amino acid.