Replication, Transcription, and Translation

Overview

This lecture focuses on the molecular biology processes of DNA replication, RNA transcription, and protein translation, which are essential for cellular function and gene expression.

DNA Replication

• Purpose: To duplicate the cell's DNA before cell division.
• Key Enzymes:
  • DNA Helicase: Unwinds the DNA double helix.
  • DNA Polymerase: Synthesizes new DNA strands by adding nucleotides complementary to the template strand.
  • DNA Ligase: Joins Okazaki fragments on the lagging strand.
• Process:
  • Initiation at origins of replication.
  • Elongation with leading and lagging strands.
  • Termination leading to two identical DNA molecules.

Transcription

• Purpose: To convert DNA sequences into mRNA.
• Key Enzymes:
  • RNA Polymerase: Synthesizes mRNA from the DNA template.
• Process:
  • Initiation: RNA polymerase binds to promoter regions.
  • Elongation: RNA strand is synthesized using DNA as a template.
  • Termination: RNA polymerase detaches after the transcript is synthesized.
• Product: Messenger RNA (mRNA) that carries genetic information from DNA to the ribosome.

Translation

• Purpose: To synthesize proteins using mRNA as a template.
• Components:
  • Ribosomes: Site of protein synthesis.
  • tRNA: Transports the correct amino acids to the ribosome.
• Process:
  • Initiation: Ribosome assembles around the mRNA.
  • Elongation: tRNA brings amino acids, and peptide bonds form.
  • Termination: Stop codon is reached, and the polypeptide chain is released.
• Outcome: A polypeptide chain that folds into a functional protein.

Key Concepts

• Central Dogma of Molecular Biology: Describes the flow of genetic information from DNA to RNA to protein.
• Gene Expression: The process by which information from a gene is used in the synthesis of a functional gene product (often protein).
• Mutations: Changes in the DNA sequence can lead to changes in protein structure and function.

Applications

• Understanding these processes helps in fields such as genetic engineering, biotechnology, and medicine, particularly in understanding diseases and developing genetic therapies.