4.1.6 The Triplet Code

Key Features of the Triplet Code:

1. Definition:

• A triplet is a sequence of three DNA bases (or RNA bases during transcription) that codes for a specific amino acid.
• The triplet code is used to translate the genetic information into proteins.

2. Gene and Locus:

• A gene is a sequence of DNA bases that codes for a specific sequence of amino acids, forming a polypeptide.
• The location of a gene on a chromosome is known as its locus.

3. Coding and Non-Coding DNA:

• DNA is composed of exons (coding regions that specify amino acid sequences) and introns (non-coding regions that are removed during RNA processing).
• Not all DNA in the genome codes for proteins.

4. Amino Acids and Codons:

• There are 20 amino acids and only 4 nucleotide bases (adenine, thymine, cytosine, guanine).
• The genetic code is a triplet code because a group of three bases can create 64 possible codons ($4³ = 64$).
• This allows the code to be degenerate, meaning most amino acids are specified by more than one codon.

5. Characteristics of the Genetic Code:

• Universal: The same codons specify the same amino acids in almost all organisms.
• Non-overlapping: Each base is read only once, and codons do not share bases.
• Degenerate: Multiple codons can code for the same amino acid.

6. Formation of Proteins:

• Codons are translated into amino acids, which are joined by peptide bonds to form polypeptide chains. These chains fold into functional proteins.

Key Terms:

• Triplet Code: A sequence of three DNA bases coding for one amino acid.
• Codon: A triplet of bases on mRNA that codes for an amino acid.
• Exons: Coding regions of a gene.
• Introns: Non-coding regions of a gene.
• Degenerate Code: A characteristic of the genetic code where multiple codons code for the same amino acid.