Q.1. What are nucleoproteins?
Ans: Nucleoproteins are conjugated proteins, characterized by presence of non-protein prosthetic group nucleic acid attached to one or more molecules of a simple protein, a basic protein histone or protamine.
- Nucleoproteins →Nucleic acid + proteins (Histone or Protamine).
Q.2. What are purines and pyrimidines?
Ans: Purines and pyrimidines are heterocyclic compounds having “N” in their molecule. They are nitrogen bases present in nucleic acids.
In purines, there are four ‘N’ atoms while in pyrimidines, there are only two.
Q.3. Name the purine bases. Give their chemical names.
Ans: Purine bases are mainly two:
- Adenine: Chemically it is 6-amino purine.
- Guanine: Chemically it is 2-amino-6-oxy purine.
Note: Guanine can exist as “lactam” and “lactim” forms, adenine cannot.
Q.4. Name the pyrimidine bases. Give their chemical names.
Ans: Pyrimidines are mainly three:
- Cytosine: Chemically 2-deoxy-6-amino pyrimidine.
- Thymine: It is 5-methyl uracil. Chemically it is 2, 6-deoxy-5-methyl pyrimidine.
- Uracil: Chemically it is 2, 6-di-oxy pyrimidine.
Note: All the pyrimidine bases can occur both in “lactam”and “lactim” forms.
Q.5. Name the nucleic acids which are of biomedical importance.
Ans: Nucleic acids of biomedical importance are mainly two:
- DNA: Deoxyribonucleic acid—it constitutes the genetic material.
- RNA: Ribonucleic acid—involved in protein synthesis.
Q.6. Name the common nitrogen bases in DNA.
Ans: Adenine, guanine, cytosine and thymine
Note: Uracil is absent.
Q.7. Name the common bases in RNA.
Ans: Adenine, guanine, cytosine and uracil.
Note: Thymine is absent.
Q.8. What sugars are present in nucleic acids?
Ans: D-ribose and D-2-deoxy ribose are the only two pentose sugars found in nucleic acids.
Both sugars are present as the β-furanoside ring structures. D-ribose is present in RNA, while D-2-deoxy ribose is present in DNAs.
Q.9. Name same minor bases found in nucleic acids.
Ans: • Some minor bases found in nucleic acids are:
- 5-OH methyl cytosine in bacteriophages.
- Both bacterial and human DNA have been found to contain significant quantities of 5-methyl cytosine.
- Certain unusual bases found in m-RNA molecules of mammalian cells viz., N6-methyladenine, N7-methylguanine, N6-N6 dimethyl adenine.
Q.10. Name the methylated purines of plant origin which have pharmacologic properties.
Ans:
- Theophylline: found in tea. Chemically it is 1, 3-dimethylxanthine.
- Theobromine: found in cocoa. Chemically it is 3, 7-dimethyl xanthine.
- Caffeine: present in Coffee. It is Chemically 1, 3, 7-trimethyl xanthine.
Q.11. What is nucleoside? Give two examples.
Ans: The nucleosides are composed of purine or pyrimidine base + either D-ribose (as in RNA) or D-2-deoxy ribose (as in DNA).
Examples:
- Purine nucleoside; adenosine (purine base Adenine + D-ribose)
- Pyrimidine nucleoside: uridine (Pyrimidine base uracil + D-ribose)
Q.12. What is the linkage in purine nucleoside?
Ans: The linkage in purine nucleoside is at position 9 of purine base and carbon 1′ of D-ribose or D-2-deoxyribose (β-N-glycosidic linkage).
Q.13. What is the linkage in pyrimidine nucleoside?
Ans: The linkage in pyrimidine nucleoside is at position 3 of pyrimidine base and carbon-1′ of D-ribose or D-2-deoxyribose (β-N-glycosidic linkage).
Q.14. Name the nucleosides of adenine, guanine, cytosine and uracil with D-ribose.
Ans: Adenosine, guanosine, cytidine, uridine.
Q.15. Name the nucleosides of adenine, guanine, cytosine, and thymine with D-2-deoxy ribose.
Ans: Deoxy adenosine, Deoxy guanosine, Deoxy cytidine, and Thymidine.
Q.16. What is a nucleotide?
Ans: A nucleotide is a nucleoside to which a phosphoric acid group is attached to the sugar molecule by esterification of a definite -OH group.
Thus general composition will be: (purine or pyrimidine base-sugar-PO4)
Q.17. Name the synthetic nucleosides in which ribose is replaced by arabinose. What is the clinical importance?
Ans: They are:
- Cytabrine (arabinosyl cytosine or Ara c)
- Vidarabine (arabinosyl adenine or Ara a)
Both are synthetic nucleosides containing arabinose in place of ribose. They are used in chemotherapy of cancers and certain viral infections.
Q.18. What is the clinical importance of 5-iodo-deoxy uridine?
Ans: 5-iodo-deoxy uridine is a recent synthetic nucleoside analogue. It possesses anti-viral activities and found to be effective in treatment of herpetic keratitis.
Q.19. What is allopurinol? What is its clinical importance?
Ans:
- Allopurinol is a synthetic purine analogue. It is chemically 4-OH-pyrazolo pyrimidine.
- It is used as a drug in treatment of gout and hyperuricaemias. It inhibits the enzyme xanthine oxidase by competitive inhibition and thus lowers uric acid level in blood preventing uric acid formation.
Q.20. Classify and name the nucleotides found in tissues and cells which are biologically important.
Ans: Various nucleotides which can occur in tissues and cells and have diverse biochemical functions are:
- Adenosine nucleotides: ATP, ADP, AMP and cyclic AMP.
- Guanosine nucleotides: GTP, GDP, GMP and cyclic GMP.
- Uridine nucleotides: UTP, UDP, UMP and UDP-G
- Cytidine nucleotides: CTP, CDP, CMP