What is the Difference Between N-terminus and C-terminus

The main difference between N-terminus and C-terminus is that N-terminus is the end of the peptide with a free amine group (-NH2), whereas C-terminus is the end of the peptide with a free carboxyl group (-COOH).

N-terminus and C-terminus are the two termini of a peptide. Peptides contain a free amine group end and a free carboxyl group end.   

Key Areas Covered

1. What is N-terminus
     – Definition, Structure, Function
2. What is C-terminus
     – Definition, Structure, Function
3. Similarities Between N-terminus and C-terminus
     – Outline of Common Features
4. Difference Between N-terminus and C-terminus
     – Comparison of Key Differences

Key Terms

C-terminus, N-terminus

What is N-terminus

N terminus is the starting end of the peptide. It also contains a free amine group. Generally, an amino acid is the building block of the protein or a peptide chain. A protein is made up of a sequence of amino acids. The N terminus is the starting end of the above-mentioned amino acid sequence. Therefore, it contains the first amino acid of the protein, which is methionine. In the amino acid sequence, methionine contains a free amine group.

Figure 1: Tetrapeptide Structure

Furthermore, the N terminus contains the first amino acid of the amino acid sequence of a protein. Since it is the starting end of the protein, the naming of the amino acids of the polypeptide chain also starts from the N terminus. In addition, protein sequencing determines the sequence of the amino acids in a protein. One of the methods of protein sequencing is N terminal sequencing, which is also known as gas phase sequencing, Edman sequencing, or Edman degradation. It starts from the N terminus.

What is C-terminus

C terminus is the final end of the peptide. It also contains a free carboxylic group. A protein is made up of an amino acid sequence. In general, amino acids link to the amino acid sequence from the N terminus to the C terminus. Therefore, the incoming amino acid links to the peptide chain from the amine group. The bond that forms between the two amino acids is the peptide bond. Hence, the carboxylic end of the amino acid is always free in the growing protein chain.

Figure 2: Primary Structure of Protein

Moreover, the C terminus contains the final amino acid of the peptide chain, which contains a free carboxylic acid group. Therefore, it is the ending of the amino acid sequence of the protein. In protein naming, the C terminus contains the final amino acid. Moreover, in protein sequencing, sequencing a protein from the C terminus uses the carboxypeptidase digestion and/or mass-spectrometric mapping strategies.

Similarities Between N-terminus and C-terminus

• N-terminus and C-terminus are two ends of the peptide molecule.
• Peptides are named from the N-terminal end to the C-terminal end.
• Both ends are important in protein sequencing.

Difference Between N-terminus and C-terminus

Definition

N terminus refers to the front end of a polypeptide chain, which has a free (unattached) amine (NH2) group, while the C terminus refers to the end of a polypeptide chain that consists of an amino acid with a free carboxyl group.

Type

N terminus is the amino terminus of the peptide while C terminus is the carboxylic terminus of the peptide.

Contains

N terminus contains a free amine group while C terminus contains a free carboxyl group.

End

Moreover, N terminus is the start of the peptide while C terminus is the end of the peptide.

Translation

The ribosome starts the translation of messenger RNA to produce the N terminus of the peptide while the ribosome ends the translation of messenger RNA to produce C terminus.

Function

The N terminus of a protein contains signal peptides that target a protein to a secretory pathway while the C terminus of the protein contains retention signals for protein sorting.

Conclusion

In brief, N terminus and C terminus are the two ends of a peptide. N terminus is the starting end of the peptide where the ribosome starts the synthesis of amino acids. Generally, it contains a free amine group in the first amino acid of the peptide. On the other hand, in the peptide naming, the N terminus contains the first amino acid. However, the C terminus ends the peptide where the ribosome stops the synthesis of amino acids. Therefore, it contains a free carboxylic group at the final amino acid. In peptide naming, the C terminus contains the final amino acid of the peptide. The main difference between N terminus and C terminus is the position of the peptide.

References:

1. “Biomolecules:Protein 1.” Protein Sequences (Primary Structure), 

Image Courtesy:

1. “Tetrapeptide structural formulae v.1” By Ju – Own work (Public Domain) via Commons Wikimedia
2. “Protein structure (full)” By Thomas Shafee – Own Work (CC BY 4.0) via Commons Wikimedia