Atomic Guide: Molecular Basis of Inheritance

Handout Notes Integrated with NCERT Extracts

Basics

1. The Polynucleotide Chain

Handout Analysis:

Nucleic Acids (DNA/RNA) are polymers called Polynucleotides.
Nucleotide = Nucleoside + Phosphoric Acid.
Nucleoside = Sugar + Nitrogenous Base.
  • Sugar: Pentose sugar (5 Carbon).
  • Base: Nitrogenous heterocylic ring.
  • Acid: Phosphate group.
"A nucleotide has three components – a nitrogenous base, a pentose sugar (ribose in case of RNA, and deoxyribose for DNA), and a phosphate group."
[Source: NCERT Section 5.1.1]
Chemistry

2. Pentose Sugars

Handout Analysis:

Distinction based on 2' Carbon position:
1. Ribose: OH present at 2' position (Formula: C5H10O5).
2. Deoxyribose: H present at 2' position (One Oxygen less).
Ribose: 2'-OH Deoxyribose: 2'-H
"In RNA, every nucleotide residue has an additional –OH group present at 2'-position in the ribose."
[Source: NCERT Section 5.1.1]
Structure

3. Nitrogenous Bases

Purines: Double ring structure (Heterocyclic). Nitrogen at positions 1, 3, 7, 9.
Pyrimidines: Single ring structure. Nitrogen at positions 1, 3.
Type Bases Handout Detail
Purines Adenine (A)
Guanine (G)		 A: 6-amino purine
G: 2-amino 6-oxy purine
Pyrimidines Cytosine (C)
Thymine (T)
Uracil (U)		 C: 4-amino 2-oxy
T: 5-methyl uracil
U: 2,4-dioxy
"There are two types of nitrogenous bases – Purines (Adenine and Guanine), and Pyrimidines (Cytosine, Uracil and Thymine). Cytosine is common for both DNA and RNA and Thymine is present in DNA. Uracil is present in RNA at the place of Thymine."
Bonds

4. Chemical Linkages

1. N-Glycosidic Linkage:

Connects Sugar (1' Carbon) to the Nitrogenous Base.

2. Phosphoester Linkage:

Connects Phosphate to the Sugar (5' Carbon).

3. Phosphodiester Linkage:

Connects two nucleotides (3' of one sugar to 5' of the next).
"A nitrogenous base is linked to the OH of 1'C pentose sugar through a N-glycosidic linkage to form a nucleoside... When a phosphate group is linked to OH of 5'C of a nucleoside through phosphoester linkage, a corresponding nucleotide... is formed."
Naming

5. Nucleosides vs Nucleotides

Formula: Nucleoside + Phosphate = Nucleotide
Base: Adenine
Side: Adenosine
Tide: Adenylic Acid
Base: Cytosine
Side: Cytidine
Tide: Cytidylic Acid
"Nucleosides, such as adenosine or deoxyadenosine, guanosine or deoxyguanosine, cytidine or deoxycytidine and uridine or deoxythymidine."
RNA World

6. Roles of RNA

Handout Notes:

  • Genetic Material: In some viruses (e.g., TMV, QB bacteriophage).
  • Messenger: mRNA (carries info).
  • Adapter: tRNA (reads code, binds amino acid).
  • Structural: rRNA (Ribosome structure).
  • Catalytic: Ribozyme (acts as an enzyme).
"RNA though it also acts as a genetic material in some viruses, mostly functions as a messenger. RNA has additional roles as well. It functions as adapter, structural, and in some cases as a catalytic molecule."
History

7. Discovery & History

Friedrich Miescher (1869): Isolated substance from pus cells (nucleus). Named it "Nuclein".
Altman: Renamed it "Nucleic Acid" due to acidic nature.
Franklin & Wilkins: Produced X-ray diffraction data.
"DNA as an acidic substance present in nucleus was first identified by Friedrich Meischer in 1869. He named it as 'Nuclein'."

Interactive Review

Test your understanding of the Handout & NCERT contents