Question

1. the genetic code specifies 20 amino acids, but there are 64 different codons. what are the \extra\ 44 combinations?
2. what is the purpose of mrna/why it is necessary?

Explanation:

1. Among the 64 codons, 61 codons code for amino acids (with some amino acids having multiple codons - degeneracy of the genetic code). The remaining 3 codons (UAA, UAG, UGA) are stop codons. They do not code for any amino acid but signal the termination of protein synthesis.
2. mRNA (messenger RNA) is necessary because it carries the genetic information (the "message") from DNA (where the genetic code is stored in the nucleus) to the ribosomes (in the cytoplasm). The ribosomes then use this information (the sequence of codons on mRNA) to assemble amino acids in the correct order to form a polypeptide chain (protein).

Answer:

1. 61 codons code for amino acids (with some amino - acid redundancy) and 3 are stop codons.
2. mRNA carries genetic information from DNA to ribosomes for protein synthesis.