Question

Please if anyone understands this can they explain it to me because I'm lost.
How many amino acids could be specified if codons consisted of two nucleotides instead of three? What problem would this present for an organism making proteins using all 20 amino acids?

Answer 1

normally you have 64 codons in a cell ( 4 nucleotides in combinations of 3 ie 4 raised to the power of 3 or 4 cube gives you 64.) and 20 amino acids . There are more codons than amino acids and thus all the 20 amino acids can be easily encoded for by the 64 codons. in fact there are a few amino acids which are coded by multiple codons and a few coded by a single codon.

Now if the same 4 nucleotides are arranged in combinations of 2 ( 4 raised to the power of 2 or 4 square) you get only 16 codons which means you have less codons and more amino acids. Even if we assume that each of the 16 codons code for one amino acid , there would be 4 amino acids which would be left out . In other words if a cell used codons made up of two nucleotides instead of three , it would not be able to incorporate all of the 20 aa in its proteins.

effect on the organism : greater the number of amino acids present , greater are the different combinations in which they can be assembled to give rise to different proteins and thus greater the spectrum of functions which a cell will be able to carry out. If the cell codes for 16 instead of 20 amino acids , the repertoire of proteins which it produces will be less and thus the number of functions it will be able to perform also decrease. In other words a cell might not be able to produce all the proteins necessary for its survival if it had 16 codons and thus would not have survived/existed at all.