Question

RECALL A genetic code in which two bases encode a single amino acid is not adequate for protein synthesis. Give a reason why.

Short answer

A two-base codon system can only make 16 combinations, which is not enough to encode all 20 amino acids.

Step-by-step solution

Understand Codons

In genetics, codons are sequences of three nucleotides (triplets) in DNA or RNA that correspond to a specific amino acid.

Calculate Combinations with Two Bases

If only two bases encoded a single amino acid, the possible combinations would be: Number of combinations = 4 bases (A, U, G, C) ^ 2 = 16 different combinations.

Compare to Actual Number of Amino Acids

There are 20 standard amino acids that need to be encoded. With only 16 combinations, we would not have enough codons to represent all 20 amino acids uniquely.

Conclusion

This inadequacy means that a genetic code with only two bases per codon cannot encode the 20 different amino acids required for protein synthesis.

Key concepts

Codons

In genetics, a codon is a sequence of three nucleotides found in DNA or RNA. These sequences act as the basic language of genetic instruction. Each codon specifies a particular amino acid, or a start or stop signal in the synthesis of proteins.
Codons play a crucial role in translating genetic information from DNA into proteins, which are the building blocks of life.
The genetic code is thus made up of a set of codons. With four different nucleotide bases (adenine [A], thymine [T], guanine [G], and cytosine [C] in DNA; uracil [U] replaces thymine in RNA), a triplet code (three bases) creates 64 possible codon combinations (4^3). This number is more than sufficient to encode the 20 standard amino acids, as well as start and stop signals for protein synthesis.
This triplet nature is essential because shorter sequences (like two nucleotide sequences) would not provide enough combinations to code for all amino acids needed for life processes.

Amino Acids

Amino acids are the building blocks of proteins. There are 20 standard amino acids that combine in various sequences to form proteins.
Each amino acid has a unique structure, consisting of an amino group, a carboxyl group, and a side chain that distinguishes each from the others.
When codons are read during the process of protein synthesis, they determine the sequence in which amino acids are assembled. This sequence dictates the structure and function of the resulting protein.
Because there are 20 amino acids and only one or two bases per codon would create insufficient combinations, the triplet code (three bases per codon) is necessary for specifying each amino acid uniquely.

Protein Synthesis

Protein synthesis is the process by which cells generate proteins. This process involves two main stages: transcription and translation.
During transcription, the DNA sequence of a gene is transcribed into mRNA. This mRNA then carries genetic instructions from the DNA to the ribosome, where translation occurs.
Translation is the actual process of decoding the information in mRNA to assemble amino acids in the correct order to form a protein. During translation, each codon in the mRNA sequence is read and matched with the corresponding amino acid, which is then added to a growing polypeptide chain.
This intricate process ensures that proteins are synthesized accurately and efficiently, allowing cells to perform various essential functions.
Ensuring the correct sequence of amino acids in a protein is vital because it directly impacts the protein's structure and function in the body.