Ch. 8 DNA Structure & Function Notes and Flashcards- Honey Ortiz

Chapter 8: DNA Replication

Semiconservative Model

• DNA replication is a key cellular process wherein a cell copies its DNA.

• In this model, each DNA molecule consists of 50% old (parental) DNA and 50% new (daughter) DNA.

• The two parental strands separate and act as templates for new strand synthesis.

• The base pairing rule (A-T and G-C) must be followed during this process.

Mechanism of DNA Replication

• The process involves:

  • Original Template Strands: Each of the original strands of the double helix serves as a template for the new strands.

  • Base Pairing: Nucleotides must adhere to the base pair rules, contributing to accurate replication of the DNA sequence.

  • Directionality: The strands run in an anti-parallel direction, with one strand oriented 5' to 3' and the other 3' to 5'.

Enzymes in DNA Replication

• DNA Helicase: “Unzips” the DNA helix by breaking hydrogen bonds between base pairs.

  • This unwinding separates the parental strands, preparing them for replication.

• DNA Polymerase: carries out synthesis of new DNA

  • Synthesizes new DNA strands based on the template strand.

  • Requires a primer (a short strand of nucleotides) to initiate synthesis.

  • Follows the base pairing rule during strand elongation.

  • Proofreads newly synthesized DNA to correct mismatched pairs and errors.

• The daughter strands that are made are IDENTICAL to the parent strands because its a REPLICATION.

Errors in DNA Replication

• Potential Mistakes: Can include wrong base addition, missed nucleotides, or extra nucleotides slipping into the sequence.

• Errors arise partly due to the rapid action of DNA polymerases.

• Replication errors can exacerbate if DNA has been previously damaged.

DNA Repair Mechanisms

• Most DNA polymerases have proofreading abilities to correct imperfections.

• other repair enzymes act by:

  • Detecting and repairing damaged sections of DNA.

  • For instance:

    • UV-induced damage is rectified by excising the damaged region; DNA polymerase then fills in the gaps with the correct nucleotides.

Mutations

• If errors in replication remain uncorrected, they become mutations
  if DNA polymerase or repair enzyme can’t “fix” the error, they become mutations:

  • Defined as permanent changes in the DNA sequence that can impact gene function.

  • Mutations affect diverse cell types and can be hereditary if they arise during gamete formation.

  • They can lead to harmful consequences, including the initiation of cancers.

  • While many mutations are detrimental, some contribute to genetic variation, acting as a basis for evolution.

Viruses and DNA

• Viruses can introduce new genetic material into cells. This is achieved when viral RNA or DNA integrates into the host cell's genetic framework.

• Viruses consist mainly of:

  • Genetic material (either DNA or RNA)

  • A protective protein coat

  • Occasionally, other components.

Types of Viruses

• Plant Viruses: Target only plant cells.

• Bacteriophages: Infect bacterial cells.

• Animal Viruses: Bind to various animal cell types.

Viral Replication Process

1. Attachment: Virus binds to cell surface receptors.

2. Penetration: Viral nucleic acid is released inside the host cell.

3. Synthesis: Host cellular machinery produces viral nucleic acids and proteins.

4. Assembly: Complete viruses are formed from synthesized components.

5. Release: New viruses exit the host cell to infect other cells.

Conclusion

• Understanding DNA replication and repair mechanisms is crucial for comprehending how genetic information is maintained, altered, and propagated across generations, as well as the implications of errors such as mutations in both health and disease contexts.