Central Dogma of Molecular Biology

• Explanation of Genetic Information Flow: Occurs within a cell in three stages:
  1. Replication: DNA is duplicated.
  2. Transcription: Information from DNA is transferred to RNA.
  3. Translation: Information in mRNA is used to build polypeptides, forming proteins.

DNA Structure in Prokaryotic Cells

• DNA Characteristics:
  • Usually a single, circular molecule.
  • Right-handed helix structure.
  • 10.5 bases per turn in a relaxed state.
  • Does not fit in the cell without compaction.

Supercoiling in DNA

• Purpose: Allows DNA to fit within a prokaryotic cell.
• Types of Supercoiling:
  • Negative Supercoiling:
    • Occurs when DNA is twisted in the opposite direction of its helix.
    • Results in fewer than 10.5 bases per turn.
    • Relieves stress during replication and transcription, facilitating strand separation.
  • Positive Supercoiling:
    • Important for thermophilic archaea living in high heat conditions.
    • DNA is overwound, with more than 10.5 bases per turn.
    • Helps resist heat-induced denaturation.

Role of Topoisomerases

• Function: Enzymes that introduce supercoiling in DNA.
• Type II Topoisomerases:
  • Example: DNA Gyrase
  • Uses ATP to break both DNA strands, reconfigure, and reseal them, introducing negative supercoils.
  • Mechanism:
    1. DNA gyrase binds to DNA, breaking both strands.
    2. ATP usage allows passage of one strand through the break.
    3. DNA strands are re-sealed, adding a negative coil.
• Type I Topoisomerases:
  • ATP-independent.
  • Break only one strand, allowing DNA to relax.
  • Reseal to maintain DNA integrity.

Importance

• Supercoiling: Critical for DNA stability and function, especially in varying environmental conditions.
• Topoisomerases: Essential for managing DNA topology during genetic processes.

These notes provide a summary of the concepts of DNA structure, supercoiling, and the role of topoisomerases in molecular biology, as discussed in the lecture.