Difference Between Unambiguous and Degenerate Code

The key difference between unambiguous and degenerate code is that genetic code is an unambiguous code since a particular codon always codes for the same amino acid, while genetic code is a degenerate code since one amino acid may be specified by more than one codon.

Genes are the structural units of heredity. There is a precise nucleotide sequence in a gene, which is known as the genetic code. It is responsible for the correct order of the amino acid sequence of a protein. There are four types of bases in DNA. When genetic code is divided into the groups of three bases (triplets), one triplet is known as a codon. There are 64 different triplets or codons. Out of the 64 codons, three codons are stop codons that do not code for amino acids. The remaining 61 codons code for 20 different amino acids. Each codon always specifies one specific amino acid. Hence, we say that the genetic code is unambiguous. Moreover, a particular amino acid can be coded by more than one codon. For example, the amino acid serine is coded by six codons: UCU, UCC, UCA, UCG, AGU and AGC. Therefore, we say that the genetic code is degenerate.

CONTENTS

1. Overview and Key Difference
2. What is Unambiguous Code
3. What is Degenerate Code
4. Similarities Between Unambiguous and Degenerate Code
5. Side by Side Comparison – Unambiguous vs Degenerate Code in Tabular Form
6. Summary

What is an Unambiguous Code?

The genetic code is unambiguous since a particular triplet or a codon always codes for a specific amino acid. It does not code for another amino acid. For example, codon GGA only codes for glycine. It does not code for any other amino acids. Similarly, all the other codons code only for its’ specific amino acid.

One codon does not code for two or more amino acids. A difference in single base or nucleotide (a point mutation) in a codon can result in a different amino acid. It can give rise to a deleterious effect, or it can produce a non-functional protein.

What is a Degenerate Code?

The genetic code is degenerate. More than one codon can code for a specific amino acid. In other words, a specific amino acid could be encoded by more than one nucleotide triplet. As an example, the six different codons UCU, UCC, UCA, UCG, AGU and AGC code for a single amino acid called serine.

Another example is phenylalanine, which has two codons. They are UUU and UUC. Moreover, glycine is coded by four codons and lysine is coded by two codons. Generally, one amino acid may be encoded by 1 to 6 different triplet codes. Since the genetic code has this ability, we say that the genetic code is degenerate.

What are the Similarities Between Unambiguous and Degenerate Code?

• The genetic code is unambiguous and degenerate.
• A codon has a specific order of three nucleotides.
• There are 64 codons and 20 amino acids.

What is the Difference Between Unambiguous and Degenerate Code?

In unambiguous code, one codon codes for only one amino acid. In degenerate code, more than one codon can be coded for a specific amino acid. So, this is the key difference between unambiguous and degenerate code. The genetic code of all organisms is unambiguous and degenerate.

Below is a summary of the difference between unambiguous and degenerate code.

Summary – Unambiguous vs Degenerate Code

Three nucleotides specify each amino acid. Generally, the genetic code of each gene is unambiguous and degenerate. In unambiguous code, each codon specifies only one amino acid. In degenerate code, one amino acid may be specified by more than one codon. Therefore, a given amino acid could be encoded by more than one nucleotide triplet. Thus, this summarizes the difference between unambiguous and degenerate code.

Reference:

1.“Reading: Codons” Lumen, Available here.
2.“Codon.” Nature News, Nature Publishing Group, Available here.

Image Courtesy:

1. “Codons aminoacids table” (CC BY-SA 3.0) via Commons Wikimedia
2. “06 chart pu3” By NIH –  (Public Domain) via Commons Wikimedia