Chapter 14 Biomolecules Solutions
Question - 21 : - What type of bonding helps in stabilising the ∝-helix structure of proteins?
Answer - 21 : -
The H-bonds formed between the −NH group of each aminoacid residue and
the
group of the adjacentturns of the ∝-helix help in stabilising the helix.
Question - 22 : - Differentiate between globular and fibrous proteins.
Answer - 22 : -
S.No | Fibrous protein | Globular protein |
1 | These proteins are held together by strong hydrogen and disulphide bonds. | The polypeptide chain in this protein is folded around itself, giving rise to a spherical structure. |
2 | It is usually insoluble in water | It is usually soluble in water. |
3 | Fibrous proteins are usually used for structural purposes. For example, keratin is present in nails and hair; collagen in tendons; and myosin in muscles. | All enzymes are globular proteins. Some hormones such as insulin are also globular proteins. |
Question - 23 : - How do you explain the amphoteric behaviour of aminoacids?
Answer - 23 : -
In aqueous solution, the carboxyl group of an amino acidcan lose a proton and the amino group can accept a proton to give a dipolar ionknown as zwitter ion.
Therefore, in zwitter ionic form, the amino acid can actboth as an acid and as a base.
Thus, amino acids show amphoteric behaviour.
Question - 24 : - What are enzymes?
Answer - 24 : -
Enzymes are proteins that catalyse biological reactions.They are very specific in nature and catalyse only a particular reaction for aparticular substrate. Enzymes are usually named after the particular substrateor class of substrate and some times after the particular reaction.
For example, the enzyme used to catalyse the hydrolysis ofmaltose into glucose is named as maltase.
Again, the enzymes used to catalyse the oxidation of onesubstrate with the simultaneous reduction of another substrate are named asoxidoreductase enzymes.
The name of an enzyme ends with ‘− ase’.
Question - 25 : - What is the effect of denaturation on the structure ofproteins?
Answer - 25 : -
As a result of denaturation, globules get unfolded andhelixes get uncoiled. Secondary and tertiary structures of protein aredestroyed, but the primary structures remain unaltered. It can be said thatduring denaturation, secondary and tertiary-structured proteins get convertedinto primary-structured proteins. Also, as the secondary and tertiarystructures of a protein are destroyed, the enzyme loses its activity.
Question - 26 : - How are vitamins classified? Name the vitamin responsiblefor the coagulation of blood.
Answer - 26 : -
On the basis of their solubility in water or fat, vitaminsare classified into two groups.
(i) Fat-solublevitamins: Vitamins that are soluble in fat and oils, but not inwater, belong to this group. For example: Vitamins A, D, E, and K
(ii) Water-solublevitamins: Vitamins that are soluble in water belong to this group.For example: B group vitamins (B1, B2, B6, B12,etc.) and vitamin C
However, biotin or vitamin H is neither soluble in waternor in fat.
Vitamin K is responsible for the coagulation of blood.
Question - 27 : - Why are vitamin A and vitamin C essential to us? Givetheir important sources.
Answer - 27 : -
The deficiency of vitamin A leads to xerophthalmia(hardening of the cornea of the eye) and night blindness. The deficiency ofvitamin C leads to scurvy (bleeding gums).
The sources of vitamin A are fish liver oil,carrots, butter, and milk. The sources of vitamin C are citrus fruits, amla,and green leafy vegetables.
Question - 28 : - What are nucleic acids? Mention their two important functions.
Answer - 28 : -
Nucleic acids are biomolecules found in the nuclei of allliving cells, as one of the constituents of chromosomes. There are mainly twotypes of nucleic acids − deoxyribonucleic acid (DNA) and ribonucleic acid(RNA). Nucleic acids are also known as polynucleotides as they are long-chainpolymers of nucleotides.
Two main functions of nucleic acids are:
(i) DNAis responsible for the transmission of inherent characters from one generationto the next. This process of transmission is called heredity.
(ii) Nucleicacids (both DNA and RNA) are responsible for protein synthesis in a cell. Eventhough the proteins are actually synthesised by the various RNA molecules in acell, the message for the synthesis of a particular protein is present in DNA.
Question - 29 : - What is the difference between a nucleoside and anucleotide?
Answer - 29 : -
A nucleoside is formed by the attachment of a base to
position of sugar.
Nucleoside = Sugar + Base
On the other hand, all the three basic components ofnucleic acids (i.e., pentose sugar, phosphoric acid, and base) are present in anucleotide.
Nucleotide = Sugar + Base + Phosphoric acid
Question - 30 : - The two strands in DNA are not identical but arecomplementary. Explain.
Answer - 30 : -
In the helical structure of DNA, the two strands are heldtogether by hydrogen bonds between specific pairs of bases. Cytosine formshydrogen bond with guanine, while adenine forms hydrogen bond with thymine. Asa result, the two strands are complementary to each other.