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1. What is the structure of chromosomes?

Ans. Chromosomes are complex fibres made of nucleoproteins with the following structure:

i) Each is made of two chromatids which appear spirally coiled fibres made at least of two chromonema.

ii) Dot like chromomeres remain arranged in rows on the chromonema.

iii) Each chromosome bears prominent centromere, on the basis of which chromosomes may be divided into different categories like Metacentric, Acrocentric, Telocentric etc.

iv) Inside each chromatid is DNA chain.

2. What is the chemical components of chromosomes?

Ans. Chemically the chromosome is made of the following components:

i) Nuclei Acids: 90 % of the Nucleic Acid moiety is constituted by DNA, while 10 % by RNA. DNA forms double helical chains and along with the proteins to constitute the body of the chromosome.

ii) Proteins- Mainly Histone proteins made of Histidine, Argenine, Lycine, Triptophan and Tyrosine are also present.

iii) Some carbohydrates, Lipids, Ca, Mg, Fe, etc.

3. What is DNA?

Ans. DNA ( Deoxyribonucleic acid) is the most remarkable nucleic acid, found in all the living organisms (excepting RNA viruses). It is the genetic material that is replicable, mutable and can transmit the genetic information through generations.

4. Where DNA can be found?

Ans. Except for the RNA viruses, DNA is found in all living organisms as their genetic material. Normally is is found in the chromosomes located within the nucleus. It is also found in Plasmids, Mitochondria and Centrioles. In Amoeba, Paramoecium, etc. DNA is also found in cytoplasm. The amount of DNA in every cell or species is fixed.

5. What is the biological significance of DNA?

Ans. i) During cell division it can produce its exact replica.

ii) It can keep the structure static although mutation can change it.

iii) Capable of controlling all biological processes.

iv) It is the most stable material in the Biosphere and in fact is immortal.

6. What are the important functions of DNA?

Ans. DNA plays the vital roles in maintaining life-processes and heredity. Its important functions are:

i) Acts in the maintenance and carriage of hereditary attributes through generations. i.e., Genetic Material.

ii) Controls all the matabolic functions directly or indirectly.

iii) It transcribes RNA for the synthesis of required proteins.

iv) It produces its own replica, which is transferred to the off springs.

7. What is the chemical structure of DNA?

Ans. i) Deoxyribose (Pentose) sugar.

ii) Phosphoric Acid.

iii) Nitrogen bases of two types: a) Pyrimidines: single ringed cytosine and thyamine, b) Purines: Double ringed Adenine or Guanine.

iv) All these three jointly form the units of DNA Nucleotides.

8. What are the constituent Deoxyribunucleosides and Deoxyribonucleotides of DNA?

Ans. The Deoxyribunucleosides are: a) De-oxy Adenosine; b)De-oxy Guanosine; c) De-oxy Cytosine and d) De-oxy Thyamidine.

The Deoxyribonucleotides are: a) De-oxy Adenilic Acid (dAMP); b) De-oxy Guanilic Acid (dGMP), c) De-oxy Cytidilic Acid (dCMP), d) De-Oxy Thymidilic Acid (dTMP).

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