Problem 99 - A Complete Resource Book in Chemistry for JEE Main

Question

In the given polypeptideArg-Try-Ile-Asn-Gly C-terminus amino acid is (a) Arg (b) Try (c) Gly (d) Asn

Step-by-Step Solution

Answer

(c) Gly

Step 1: Understanding Peptide Sequence

A polypeptide is a chain of amino acids linked together in a specific sequence. The given polypeptide is Arg-Try-Ile-Asn-Gly. Each amino acid is represented by a three-letter code, meaning Arg is Arginine, Try is Tryptophan, Ile is Isoleucine, Asn is Asparagine, and Gly is Glycine.

Step 2: Identifying Terminal Ends

For a polypeptide chain, the amino-terminal (or N-terminus) is the beginning of the chain, and the carboxyl-terminal (or C-terminus) is the end of the chain. In the sequence Arg-Try-Ile-Asn-Gly, Arginine (Arg) is at the N-terminus, and Glycine (Gly) is at the C-terminus.

Step 3: Determining the C-Terminus Amino Acid

The C-terminus of the polypeptide refers to the last amino acid in the sequence. Thus, in the sequence Arg-Try-Ile-Asn-Gly, Glycine (Gly) is the last amino acid, making it the C-terminus amino acid.

Key Concepts

Amino Acids

Amino acids are the building blocks of proteins. They consist of a central carbon atom bonded to four distinct groups: an amine group, a carboxyl group, a hydrogen atom, and a distinctive R group or side chain. The side chain determines the characteristics and properties of each amino acid.

Amino acids are classified into essential and non-essential categories. Essential amino acids cannot be synthesized by the body and must be ingested through diet, whereas non-essential amino acids can be produced internally. These molecules are linked together by peptide bonds to form proteins and peptides.

• The peptide bonds are created through a dehydration reaction, which involves the removal of a water molecule.
• This binding occurs between the carboxyl group of one amino acid and the amino group of the next.

Understanding amino acids is crucial, as they are involved in various metabolic pathways and make up a significant portion of cells, tissues, and organs in the body.

Peptide Sequence

A peptide sequence is a specific order in which amino acids are arranged in a polypeptide chain. Each amino acid in the sequence is identified by its unique three-letter abbreviation, such as Arg for Arginine and Gly for Glycine.

The sequence of amino acids determines the protein's ultimate structure and function. The sequence is directional, with each chain having an N-terminus (amino end) and a C-terminus (carboxyl end), reflecting the order of synthesis from the ribosome.

• For example, in the peptide sequence Arg-Try-Ile-Asn-Gly, Arginine is the first amino acid (N-terminus) and Glycine is the last (C-terminus).
• The order and the composition of amino acids dictate the folding and 3D shape of the molecule, which in turn influences its biological activity.

Peptide sequences are critical as they carry the genetic instructions within proteins that define the functional roles in biological systems.

C-Terminus

The C-terminus is the end of an amino acid chain, terminated by a free carboxyl group. In a polypeptide chain, this is the last site that was added during synthesis and corresponds to the last amino acid in the sequence.

Identifying the C-terminus is vital for understanding the properties and function of the peptide. This terminal plays a significant role in determining how the peptide interacts with other molecules and the environment. Often, modifications such as lipidation or phosphorylation occur at the C-terminus to alter the peptide's function.

• In the polypeptide Arg-Try-Ile-Asn-Gly, Glycine is identified as the C-terminus, being the last amino acid in the sequence.
• Understanding and analyzing the C-terminal helps in studying protein interactions, stability, and function.

The C-terminus serves as a critical point for protein maturation, signaling pathways, and cellular localization.