Problem 19 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

A decapeptide (Mol. wt. 796) on complete hydrolysis gives glycine (Mol. wt. 75), alanine and phenylalanine. Glycine contributes \(47.0 \%\) to the total weight of the hydrolysed products. The number of glycine units present in the decapeptide is

Step-by-Step Solution

Answer

There are 5 glycine units in the decapeptide.

Step 1: Understand the Problem

We are given a decapeptide with a molecular weight of 796. Upon hydrolysis, it produces glycine, alanine, and phenylalanine. Glycine contributes 47% to the total weight of the hydrolyzed products. We need to find out how many glycine units are present in the decapeptide.

Step 2: Calculate the Weight Contribution of Glycine

The total weight contribution of glycine is given as 47% of the weight of the decapeptide (796). Thus, \[\text{Weight of Glycine} = 0.47 \times 796 = 374.12\].

Step 3: Find the Number of Glycine Units

Each glycine unit has a molecular weight of 75. To find the number of glycine units, we divide the total weight of glycine by the molecular weight of a single glycine:\[\text{Number of Glycine Units} = \frac{374.12}{75} \approx 4.99\].

Step 4: Interpret the Result

Since the number of glycine units must be an integer, we round 4.99 to the nearest whole number, which is 5. Therefore, there are 5 glycine units in the decapeptide.

Key Concepts

Decapeptide

A decapeptide is a peptide composed of ten amino acids linked together by peptide bonds. These chains are a class of peptides, which are short chains of amino acids, and are differentiated based on the number of amino acids they contain. Peptides are smaller and simpler than proteins.
Decapeptides play significant roles in biological processes and can be found naturally or synthesized in laboratories. They serve as hormones, neurotransmitters, and in numerous other biological functions.
Decapeptides are interesting due to their size, which allows them to function effectively without the complexity of larger protein structures.

Molecular Weight

Molecular weight, also known as molecular mass, is the sum of the atomic weights of all the atoms in a molecule. In the context of peptides, the molecular weight helps to identify the number of linked amino acids and their respective types.
To better understand, imagine each amino acid in a peptide as a block in a tower. Different blocks (amino acids) have different weights, and stacking 10 together gives us the molecular weight of the entire tower (the decapeptide).
For example, the molecular weight of the given decapeptide is 796, helping to calculate how much each component, including glycine, contributes to the overall structure.

Hydrolysis of Peptides

Hydrolysis is a chemical process where a water molecule is used to break down compounds. For peptides, this reaction breaks the peptide bonds that link amino acids together. It's akin to breaking a chain into individual links by adding a drop of water between them.
Upon hydrolysis, a decapeptide is broken into its constituent amino acids. This exercise involves calculating how much of the resulting amino acids come from glycine, post-hydrolysis.
Understanding peptide hydrolysis is crucial in biochemistry and molecular biology, particularly in the study of proteins and enzymes.

Glycine Computation

Glycine is the simplest amino acid and has a molecular weight of 75. In peptide chemistry, its contribution to the total molecular structure can be assessed through computation.
To compute the amount of glycine present in a peptide, one must know its proportion within the hydrolyzed product as well as its molecular weight. In this scenario, glycine contributes 47% of the total weight of the hydrolyzed peptide.
By calculating 47% of the decapeptide's molecular weight, we can determine how much glycine there is. Dividing this weight by the molecular weight of glycine gives the number of glycine molecules, reflecting its impact within the peptide structure.