Molecular Basis of Inheritance

Key Concepts

• DNA and RNA are types of nucleic acids, with DNA as the primary genetic material.
• DNA is composed of nucleotides, each consisting of a nitrogenous base, a pentose sugar, and a phosphate group.
• DNA structure was elucidated by Watson and Crick, showing a double helix with complementary base pairing.

Structure of DNA

• DNA is a long polymer of deoxyribonucleotides.
• DNA's length is measured in base pairs (bp).
• A nucleotide consists of:
  • Nitrogenous bases: Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Thymine in DNA, Uracil in RNA).
  • Pentose sugar: Deoxyribose in DNA, ribose in RNA.
  • Phosphate group.
• DNA strands are anti-parallel; one runs 5' to 3', the other 3' to 5'.
• Base pairing: Adenine pairs with Thymine (2 hydrogen bonds), Guanine pairs with Cytosine (3 hydrogen bonds).

DNA Replication

• Semiconservative process: each daughter DNA has one parental and one new strand.
• Enzymes involved include DNA polymerases.
• Replication occurs at replication forks, with continuous and discontinuous strands.

Transcription

• Transcription is the process of copying genetic information from DNA to RNA.
• Involves a transcription unit: promoter, structural gene, terminator.
• Only one DNA strand is transcribed into RNA.

Genetic Code

• Consists of sequences of three nucleotides (codons) that code for amino acids.
• 64 codons exist; 61 code for amino acids, 3 are stop codons.
• The code is universal but some exceptions in mitochondria and protozoa.

Translation

• Process of synthesizing proteins using mRNA as template.
• Involves tRNA as adapter molecules and ribosomes.
• Ribosomes facilitate the binding of tRNA and the formation of peptide bonds between amino acids.

Regulation of Gene Expression

• In prokaryotes, often regulated at transcriptional level.
• Operons (e.g., lac operon) control gene expression in response to environmental conditions.

Human Genome Project

• Aimed to sequence and map all the genes of the human genome.
• Key findings include the identification of about 20,000-25,000 genes and the understanding of genetic variability.

DNA Fingerprinting

• Technique used to identify differences in DNA sequences among individuals.
• Based on variations in repetitive DNA sequences.
• Applications include forensics and paternity testing.

Summary

• DNA is the primary storage of genetic information due to its stability.
• RNA acts as a messenger and adapter in protein synthesis.
• Transcription and translation processes highlight the central dogma of molecular biology: DNA -> RNA -> Protein.
• Advancements such as the Human Genome Project have expanded the understanding of genetic information and its applications.