Structure of DNA and RNA, replication, transcription, translation

1. Introduction

1. Genetics is the study of how traits are inherited from one generation to another.
2. The Molecular Basis of Inheritance focuses on DNA, RNA, and the processes of replication, transcription, and translation.
3. DNA (Deoxyribonucleic Acid) is the genetic material in most organisms.
4. RNA (Ribonucleic Acid) plays a crucial role in protein synthesis.

2. Structure of DNA

1. DNA is a double-stranded helical molecule discovered by James Watson and Francis Crick in 1953.
2. The structure is a double helix with two strands running in opposite directions (antiparallel).
3. Each strand is made up of nucleotides consisting of:
   • A phosphate group
   • A deoxyribose sugar
   • A nitrogenous base: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
4. Base pairing rule: A pairs with T (via two hydrogen bonds), and C pairs with G (via three hydrogen bonds).
5. DNA is packaged into chromosomes with the help of proteins called histones.

3. Structure of RNA

1. RNA is a single-stranded molecule.
2. Contains ribose sugar instead of deoxyribose.
3. Contains Uracil (U) instead of Thymine (T).
4. Types of RNA:
   • mRNA (Messenger RNA): Carries genetic information from DNA to ribosomes.
   • tRNA (Transfer RNA): Helps in assembling amino acids into proteins.
   • rRNA (Ribosomal RNA): A major component of ribosomes.

4. DNA Replication

1. DNA replication is the process of copying DNA to produce identical DNA molecules.
2. Occurs in the S-phase of the cell cycle.
3. It follows a semi-conservative model, where each new DNA has one original strand and one new strand.
4. Key enzymes in replication:
   • Helicase: Unwinds the DNA double helix.
   • DNA Polymerase: Adds new nucleotides to the growing strand.
   • Ligase: Seals gaps between fragments.

5. Transcription (DNA to RNA)

1. Transcription is the process of synthesizing mRNA from a DNA template.
2. Occurs in the nucleus of eukaryotic cells.
3. Key enzyme: RNA Polymerase.
4. Steps of transcription:
   • Initiation: RNA polymerase binds to the promoter region of DNA.
   • Elongation: RNA polymerase adds complementary RNA nucleotides.
   • Termination: RNA polymerase stops transcription when it reaches a termination signal.
5. The newly formed mRNA undergoes splicing to remove non-coding sequences (introns).

6. Translation (Protein Synthesis)

1. Translation is the process of converting mRNA into a protein.
2. Occurs in the ribosomes in the cytoplasm.
3. Requires mRNA, tRNA, and ribosomes.
4. Steps of translation:
   • Initiation: The ribosome assembles around mRNA.
   • Elongation: tRNA brings amino acids, which are linked to form a polypeptide chain.
   • Termination: The process stops when a stop codon is reached.
5. The polypeptide chain folds into a functional protein.

7. Differences Between DNA and RNA

8. Importance of Molecular Basis of Inheritance

1. Explains how genetic information is passed from parents to offspring.
2. Essential for genetic engineering and biotechnology.
3. Understanding mutations helps in studying genetic diseases.
4. Used in medical research, forensic science, and evolutionary biology.