show how a peptide bond forms between the two amino acids gylcine and valine. draw the structural formula for the reactants and the product. label the functional groups and linkages present

Expert Answers
mvcdc eNotes educator| Certified Educator

Glycine and valine are amino acids and when connected, the bond connecting them is called a peptide bond. Amino acids are so called because of the presence of a carboxylic acid group, COOH, and an amine group, NH2. Each amino acid is distinguished by the side chains attached to them. (I have included the structures of glycine, valine, and the glycine-valine dipeptide. As you can see, glycine has H as a side chain, while valine has a more complicated group, CH(CH3)CH3.) The peptide bond connects amino acids together via the carboxylic acid group of one, and the amine group of the other. Formation of a peptide bond is a type of a condensation reaction, one which produces water as a by-product.

Below is a simplified reaction of two amino acids with side chains R1 and R2:

H2N-CHR1-COOH + H2N-CHR2-COOH

R1 can be H if the first amino acid is glycine, and R2 is CH(CH3)CH3 if the second is valine. The peptide bond forms via condensation of the two amino acids, where water is formed from the OH group of the first amino acid and an H from the amine group of the second:

H2N-CHR1-CO-HN-CHR2-COOH (first amino acid in bold)

As can be seen in this simplified reaction and the attached image, the peptide bond is formed between the carbon of the carboxylic acid of amino acid 1 and the nitrogen of the amine group of amino acid 2. 

Functional groups present are, as already mentioned, carboxylic group (COOH) and amine group (NH2) from the amino acids. The resulting molecule from the formation of the peptide bond is an amide (RC(=O)NR, see attachment for other forms of amides).

By convention, polypeptides are written and drawn from the N-terminal (amine group of first amino acid) to the C-terminal (carboxylic group of the last amino acid).

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ankur16satya | Student
The peptide bond in terms of biology is formed when carboxyl group (=COOH) of one amino acid is chemically reacted to the amino group moiety (=NH2) of other amino acid and releasing the molecule of water (H2O) as the end product. between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O) thus resulting in formation of CO-NH bond which is called as a peptide bond. This process causes release of molecule from amino acids during formation so it is also called as dehydration synthesis reaction or condensation reaction. The glycine is the simplest amino acid having single hydrogen atom as its side chain whereas valine is having an isopropyl group as a side chain as shown in the picture given below. In the reaction of glycine+valine the structure of amino acid must be written in such a way that the NH2 terminal of amino acids should be come on left side and the COOH group should come on the right side with side chain in upper or lower side of the α- carbon as shown in the picture below. When glycine and valine joins chemically, the OH molecule of carboxyl group in glycine combines with the hydrogen molecule of amino group resulting in formation of peptide bond i.e. CO-NH bond between these two amino acids.
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malaikafernandes | Student

An amino Acid mainly has an amino group (NH2), a carboxyl group (COOH), HYDROGEN (H) and a 4th functional group that differs. All of the above found attached to a CARBON atom.

Thus, the 4th functional group for Glycine is a HYDROGEN (H) and the 4th functional group in Valine is Secondary propyl group. 

 

When Glycine and Valine come together, the peptide bond forms as Glycine looses its OH (Hydroxyl group) from its COOH functional group and Valine looses its H from the NH2 functional group. As a by-product, water is released out to form the peptide bond

(-CO-NH-) = PEPTIDE

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