Watson & Crick's DNA Model

DNA Structure

• DNA is composed of two right-handed polynucleotide chains that coil around each other to form a helical structure with an axis of symmetry.
• The chains are antiparallel, meaning they run in opposite directions.
• Purine and pyrimidine bases are hydrophobic and occupy the interior space, while deoxyribose sugar and phosphate backbone are hydrophilic and external.
• Base pairs are planar and almost perpendicular to the axis of the helix.

Hydrogen Bonding

• Hydrogen bonding occurs between purine base on one chain and pyrimidine base on the other, or vice versa.
• This specific interaction stabilizes the structure.

Grooves and Regulatory Proteins

• Major and minor grooves are formed in the DNA structure.
• These grooves provide access for binding of regulatory proteins.
• Anticancer drugs like actinomycin D (dactinomycin) intercalate into the minor groove, inhibiting DNA and RNA synthesis.

Denaturation and Renaturation

• The DNA double-helix can be reversibly melted and re-formed.
• DNA denaturation is the process of separating the two strands, and renaturation is the process of re-forming the double-helix.
• The melting temperature (Tm) depends on the GC content of the DNA.

Mitochondrial DNA

• Mitochondrial DNA is not contained in the nucleus.
• It has a light strand and heavy strand.
• It is maternally inherited and encodes for 22 tRNAs, 2 rRNAs, and 13 proteins involved in the electron transport chain.

Sugar Components

• Ribose is a monosaccharide with 5 carbon atoms (1', 2', 3', 4', and 5').
• 2'-deoxyribose is a sugar component of DNA.
• Ribose is a component of RNA.

Purine and Pyrimidine Bases

• Adenine (A) and guanine (G) are purine bases.
• Cytosine (C) and thymine (T) are pyrimidine bases.

Nucleotides and Nucleosides

• A nucleotide consists of a sugar, phosphate, and nitrogenous base.
• A nucleoside consists of a sugar and a nitrogenous base.

Physiological Functions of Nucleotides

• Nucleotides have various physiological functions in the body.

DNA Polymerization

• A sugar-phosphate chain is stabilized by 3'-5' phosphodiester bonds between 2-deoxyribose residues.

Chargaff's Rule

• The total amount of pyrimidines (T+C) always equals the total amount of purines (A+G).
• The amount of T always equals the amount of A, and the amount of C always equals the amount of G.

Telomere Replication

• Telomerase is an enzyme that helps to maintain telomere length.
• Without telomerase, telomeres may get shorter after each cell division.
• Telomerase has a possible role in 'Aging' and cancer.