Biomolecules

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Question
CBSEENCH12010351

Define the following as related to proteins:

(i) Peptide linkage

(ii) Primary structure

(iii) Denaturation

Solution

(i) Peptide linkage:

The amide formed between -COOH group of one molecule of an amino acid and –NH2 group of another molecule of the amino acid by the elimination of a water molecule is called a peptide linkage.

 

(ii) Primary structure:

The primary structure of a protein refers to the specific sequence in which various amino acids are present in it, i.e., the sequence of linkages between amino acids in a polypeptide chain. The sequence in which amino acids are arranged is different in each protein. A change in the sequence creates a different protein.

(iii) Denaturation:

In a biological system, a protein is found to have a unique 3-dimensional structure and a unique biological activity. In such a situation, the protein is called native protein. However, when the native protein is subjected to physical changes such as a change in temperature or chemical changes such as a change in pH, its H-bonds are disturbed. This disturbance unfolds the globules and uncoils the helix. As a result, the protein loses its biological activity. This loss of biological activity by the protein is called denaturation. During denaturation, the secondary and the tertiary structures of the protein get destroyed, but the primary structure remains unaltered.

One of the examples of denaturation of proteins is the coagulation of egg white when an egg is boiled.

Sponsor Area

Question
CBSEENCH12010377

(i) Write the name of two monosaccharides obtained on hydrolysis of lactose sugar.

(ii) Why Vitamin C cannot be stored in our body?

(iii) What is the difference between a nucleoside and nucleotide?

Solution

(i) Upon hydrolysis, lactose produces one molecule of D-glucose and one molecule of D-galactose..

(ii) Vitamin C is water-soluble in nature. It cannot be stored in the human body as it repeatedly gets eliminated through urine.

(iii)A nucleoside is formed by the attachment of purine or pyrimidine base to the 1- position of a pentose sugar.
On the other hand, a nucleotide is a unit formed by the attachment of nucleoside to phosphoric acid at the 5′-position of the sugar moiety.

Question
CBSEENCH12010396

i) Write the structural difference between starch and cellulose.
ii) What type of linkage is present in Nucleic acid ?
iii) Give one example each for fibrous protein and globular protein.

Solution

i) Cellulose is mostly linear chains of glucose molecules linked together by beta 1,4 glycosidic bonds whereas starch is found in both linear and branched chains.
ii) Phosphodiester linkage is present in the nucleic acid.
iii) Fibrous protein –  myosin
     protein          -   haemoglobin 

Question
CBSEENCH12010428

Write the main structural difference between DNA and RNA. Of the four bases, name those which are common to both DNA and RNA.

Solution

The structural differences between DNA and RNA are as follows:

DNA

RNA

1.

The sugar moiety in DNA molecules is b-D-2 deoxyribose.

1.

The sugar moiety in RNA molecules is b-D-ribose.

2.

DNA contains uracil (U). It does not contain thymine (T).

2.

RNA contains thymine (T). It does not contain uracil (U).

3.

The helical structure of DNA is double-stranded.

3.

The helical structure of RNA is single-stranded.