How can a genetic code table be used to determine which codons correspond to specific amino acids?

Sourav PanNovember 8, 2024

Answered

The genetic code table is a crucial tool for translating the nucleotide sequences of mRNA into specific amino acids during protein synthesis. Here’s how it works:

Understanding Codons

1. Definition of Codons: Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids or stop signals. For example, the codon AUG codes for methionine and also serves as a start signal for translation .
2. Total Codons: There are 64 possible codons (4^3 combinations of the four nucleotides: adenine [A], uracil [U], cytosine [C], and guanine [G]). Out of these, 61 codons specify amino acids, while 3 are stop codons that signal the termination of protein synthesis .

Using the Genetic Code Table

1. Structure of the Table: The genetic code table typically displays codons in a grid format, where each row and column corresponds to specific nucleotide positions. The first two nucleotides determine the row and column, while the third nucleotide is found within that intersection .
2. Finding Corresponding Amino Acids:
   • To determine which amino acid a specific codon encodes, locate the first two nucleotides in the table to find the corresponding cell.
   • Within that cell, read the third nucleotide to identify the exact amino acid. For instance, if you have the mRNA sequence UUU, you would find UU in the table, which corresponds to phenylalanine .
3. Example Process:
   • Consider the mRNA codon ACG:
     • Locate A (first position) and C (second position) in the table.
     • Find G (third position) within that cell.
     • The result indicates that ACG codes for threonine .

Characteristics of the Genetic Code

1. Degeneracy: The genetic code is described as degenerate because multiple codons can specify the same amino acid. For example, both GAA and GAG code for glutamic acid. This redundancy helps protect against mutations since changes in DNA might not alter protein function .
2. Start and Stop Codons: The AUG codon not only specifies methionine but also marks the start of translation. Stop codons (UAA, UAG, UGA) signal the end of protein synthesis and do not correspond to any amino acid .
3. Universality: The genetic code is nearly universal across all organisms, which means that a codon will typically specify the same amino acid regardless of the organism from which it is derived . This universality provides strong evidence for a common evolutionary origin among all life forms.