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    What are peptides and peptide linkage? Explain with example.

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    What are peptides and peptide linkage? Explain with example.

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    Updated on : 2022-09-05

    The molecules having peptide linkage are known as peptides.

    Solution Verified by Toppr

    Peptide linkage is also known as peptide bond. it is an amide formed between −COOH and −NH

    2 ​

    group by elimination of a water molecule. It is represented as

    − O ∣∣ ​ C ​ −NH−.

    For example, following represents a dipeptide formed between two glycine molecules.

    H 2 ​ N−CH 2 ​ −COOH+H 2 ​ N−CH 2 ​ −COOH Δ −H 2 ​ O ​ H 2 ​ N−CH 2 ​ − O ∣∣ ​ C ​ −NH−CH 2 ​ −COOH.

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    Peptide Bond

    A peptide bond is a chemical bond by joining the carboxyl group of one amino acid to the amino group of another. A peptide bond is also sometimes called a eupeptide bond.

    JEEIIT JEE Study MaterialPeptide Bond

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    Peptide Bond

    A peptide bond also sometimes called eupeptide bond is a chemical bond that is formed by joining the carboxyl group of one amino acid to the amino group of another. A peptide bond is basically an amide-type of covalent chemical bond. This bond links two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another. This linkage is found along a peptide or protein chain.

    During the formation of this bond, there is a release of water (H2O) molecules. A peptide bond is usually a covalent bond (CO-NH bond) and since the water molecule is eliminated it is considered as a dehydration process. Generally, this process occurs mostly between amino groups.

    Meanwhile, a peptide is a Greek word that means “digested”. A peptide is a short polymer of amino acid monomers linked by an amide bond.

    Table of Content

    Peptide Bond Formation or Synthesis

    Characteristics of Peptide Bonds

    Different Forms of Peptide Bond

    Degradation of Peptide Bond

    Peptide Bond Structure

    Peptide Bond Features

    Important Questions

    Peptide Bond Formation or Synthesis

    A peptide bond is formed by a dehydration synthesis or reaction at a molecular level.  This reaction is also known as a condensation reaction which usually occurs between amino acids.

    As depicted in the figure given below, two amino acids bond together to form a peptide bond by the dehydration synthesis. During the reaction, one of the amino acids gives a carboxyl group to the reaction and loses a hydroxyl group (hydrogen and oxygen).

    The other amino acid loses hydrogen from the NH2 group. The hydroxyl group is substituted by nitrogen thus forming a peptide bond. This is one of the primary reasons for peptide bonds being referred to as substituted amide linkages. Both the amino acids are covalently bonded to each other.

    The newly formed amino acids are also called a dipeptide.

    Let’s have a look at a simpler diagram depicting the formation of the peptide bond.

    During the reactions that occur, the resulting CO-NH bond is the peptide bond, and the resulting molecule is an amide. The four-atom functional group -C(=O)NH- is called an amide group or a peptide group.

    Characteristics of Peptide Bonds

    1. Peptide bonds are strong with partial double bond character:

    They are not broken by heating or high salt concentration.

    They can be broken by exposing them to strong acid or base for a long time at elevated temperature. Also by some specific enzymes (digestive enzymes).

    2. Peptide bonds are rigid and planar bonds therefore they stabilize protein structure.

    3. Peptide bond contains partial positive charge groups (polar hydrogen atoms of amino groups) and partial negative charge groups (polar oxygen atoms of carboxyl groups).

    Different Forms of Peptide Bond

    Dipeptide = contains 2 amino acid units.Tripeptide = contains 3 amino acid units.Tetrapeptide = contains 4 amino acid units.Oligopeptide = contains not more than 10 amino acid units.Polypeptide = contains more than 10 amino acid units, up to 100 residues.Macropeptides = made up of more than 100 amino acids.

    Degradation of Peptide Bond

    Degradation of peptide bond involves a reaction in which breaking of the peptide bonds between the molecules occurs. Hydrolysis (addition of water) is the reaction used for the degradation of the peptide bond. During the reaction, they will emit Gibbs energy in an amount of 8-16 kJ/mol. But generally, this is a very slow process having a half-life of 350 to 600 years per bond at a temperature of 25oC. Enzymes like proteases are used as the catalysts for this process.

    Peptide Bond Structure

    A peptide bond is a planar, trans and rigid configuration. It also shows a partial double bond character. The coplanarity of the peptide bond denotes the resonance or partial sharing of two pairs of electrons between the amide nitrogen and carboxyl oxygen.

    The atoms C, H, N, O of the peptide bond lies in the same plane, like the hydrogen atom of the amide group and the oxygen atom of the carboxyl group are trans to each other.

    Linus Pauling and Robert Corey are the scientists who found that the peptide bonds are rigid and planar.

    Peptide Bond Features

    Some of the key features of this bond include;

    Writing Of The Peptide Bond Structure

    Generally, these bonds are written in a form where free amino acids are at the left and the free carboxyl on the right side. The left side is N-terminal residue and the right side is C-terminal residue. This amino acid sequence is read from the N-terminal to the C-terminal. And also the protein biosynthesis also starts in the same direction.

    Representation Of The Peptide Bond

    Rattlesnake moving representation is used for the peptide bond representation, from left to right of the page. The N-terminal residues to its rattle and C-terminal residues are considered as the fangs.

    स्रोत : byjus.com

    How is Peptide Linkage Formed?

    How is Peptide Linkage Formed?

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    How is peptide linkage formed?

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    SOLUTION

    1. α-Amino acids are bifunctional compounds containing a carboxylic acid group and an amino group on α-carbon.

    2. The reaction of the COOH group of one amino acid molecule and NH2 group of the neighbouring amino acid molecule forms peptide having -CO-NH-linkage by elimination of water.

    3. Above reaction repeats itself to give tri, tetra, penta and finally polypeptides

    (i.e.,protein).

    Concept: Proteins - Peptide

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