Question

How many amino acids are common to all living systems?
a)20
b) 30
c) 100
d) 10

Answer 1

All living systems share 20 common amino acids that make up the building blocks of proteins, encoded by 64 possible codons in the genetic code.

Step-by-step explanation:

The number of amino acids common to all living systems is 20. These amino acids are the building blocks of proteins and are encoded by the genetic code. In addition to these 20, two more amino acids, Selenocysteine and Pyrrolysine, have been found in limited quantities in proteins but are not standard across all living organisms.

There are 64 codons in the genetic code, which are sequences of three nucleotides in RNA that specify which amino acid will be added next during protein synthesis. Despite there being 64 possible codons, they code for only 20 standard amino acids, plus one for a start signal and three for stop signals, showing that the genetic code is redundant or degenerate. This degeneracy allows for a certain level of protection against mutations within the genetic code.

Answer 2

Amino acids are the building blocks of proteins. In all living systems, there are 20 common amino acids that are used to build proteins. So, the answer is (a) 20.