key term - N-terminus

Definition

The n-terminus, or amino terminus, refers to the end of a polypeptide chain that has a free amino group (-NH2). This end is critical for defining the primary structure of proteins, as it determines the directionality of the protein and influences its folding and function. The n-terminus is always at one end of the peptide chain, with the opposite end being the carboxyl terminus, which features a free carboxyl group (-COOH).

5 Must Know Facts For Your Next Test

1. The n-terminus is designated as the starting point during protein synthesis and dictates the sequence of amino acids that follow.
2. In proteins, the chemical properties of the n-terminus can influence how the protein interacts with other molecules and its overall stability.
3. The presence of specific modifications at the n-terminus can affect protein activity, localization, and degradation.
4. The n-terminus can be involved in signaling pathways, affecting how proteins are targeted to specific cellular locations.
5. During protein synthesis on ribosomes, the n-terminus is synthesized first, leading to a defined orientation for subsequent folding and function.

Review Questions

• How does the n-terminus contribute to the overall structure and function of proteins?
  • The n-terminus plays a vital role in determining the directionality of a protein, which affects its folding into secondary and tertiary structures. The properties of the amino acid present at the n-terminus can influence how the protein interacts with other molecules and its stability. Additionally, modifications at this terminus can affect functions such as enzyme activity and protein-protein interactions.
• Discuss the significance of the n-terminus in relation to peptide bonds and how this relates to protein synthesis.
  • During protein synthesis, peptide bonds form between amino acids as they are added to a growing polypeptide chain. The n-terminus marks where this process begins, with each new amino acid being attached to its carboxyl group. The orientation provided by the n-terminus not only establishes the sequence but also plays a role in how proteins achieve their three-dimensional shapes after synthesis through folding processes.
• Evaluate how changes or modifications at the n-terminus of a protein could impact its biological activity within a cell.
  • Modifications at the n-terminus can significantly impact a protein's biological activity by altering its stability, localization, or interaction with other molecules. For example, phosphorylation of an amino acid at the n-terminus can regulate enzyme activity or signal transduction pathways. These changes can have cascading effects on cellular processes, potentially leading to altered physiological responses or disease states if regulation goes awry.

Related terms

c-terminus:

The c-terminus, or carboxyl terminus, is the end of a polypeptide chain that has a free carboxyl group (-COOH), which is opposite the n-terminus.

peptide bond: A peptide bond is a covalent bond that links two amino acids together in a protein by connecting the carboxyl group of one amino acid to the amino group of another.

primary structure: The primary structure refers to the linear sequence of amino acids in a protein, which is determined by the genetic code and influences higher levels of protein structure.