Biology 30 - Central Dogma Mutations and Meiosis (Reyda)

Unit 3 Genetics and Biotechnology: DNA Processes

Overview

• Focus: Investigation of how genetic information is stored, transmitted, and expressed at the molecular level.

Important Scientists

• Frederick Griffith (1928)

  • Conducted the first major experiment leading to DNA discovery by using bacterial strains.

  • Conclusion: A disease-causing factor is transferable from dead to live strains.

• Oswald Avery (1944)

  • Identified DNA as the transforming molecule. Initially not widely accepted; proteins were thought to be the genetic material.

• Alfred Hershey and Martha Chase (1952)

  • Provided definitive evidence for DNA as the transforming agent using bacteriophages.

• Erwin Chargaff (1950)

  • Analyzed DNA composition:

    • Chargaff's Rules: Amount of Adenine (A) = Thymine (T)

    • Amount of Guanine (G) = Cytosine (C)

• Maurice Wilkins and Rosalind Franklin

  • Utilized X-ray diffraction to reveal the double helix structure of DNA (1952).

• James Watson and Francis Crick (1953)

  • Developed the double helix model based on Chargaff and Franklin's work. Awarded Nobel Prize in 1963.

Central Dogma of Molecular Genetics

• Process:

  • DNA resides in the nucleus.

  • RNA is produced in the nucleus, travels to the cytoplasm.

  • Proteins are synthesized at ribosomes or the endoplasmic reticulum.

DNA Processes Discussed

1. DNA Replication

2. Protein Synthesis (includes transcription and translation)

3. Meiosis

   • Videos:

     • Amoeba Sisters - DNA Replication

     • Crash Course DNA Structure and Replication

DNA Replication

• Purpose: To create identical DNA copies for nuclear division.

• Occurs: During S phase of interphase, requiring ATP

• Key Features:

  • Semi-conservative replication: Each new double-stranded DNA helix contains one original and one new nucleotide strand.

  • Enzymes involved: Helicase, DNA polymerase, DNA ligase.

DNA Replication Process

1. Helicase enzyme unwinds the DNA strands at hydrogen bonds.

2. RNA Primer attaches to the exposed DNA.

3. DNA Polymerase synthesizes new DNA strand from 5' to 3'.

   • The leading strand is continuous.

   • The lagging strand is made in Okazaki fragments.

4. DNA Ligase seals sugar-phosphate sections together.

Transcription

• Process:

  • mRNA synthesis occurs in the nucleus where RNA polymerase creates mRNA based on the DNA template.

  • Each mRNA corresponds to a specific protein coding (1 gene = 1 protein).

Translation

• Process:

  • mRNA travels to the ribosome, where codons are read in groups of 3 to synthesize proteins.

  • tRNA brings corresponding amino acids, which are joined to form polypeptides.

  • The cycle continues until a stop codon is reached.

Mutations

• Types of Mutations:

  • Deletion: Loss of a base; may lead to frameshift.

  • Insertion: Addition of a base; may also lead to frameshift.

  • Point Mutation: Substitution of one base for another.

    • Missense Mutation: New amino acid.

    • Nonsense Mutation: Early stop codon.

    • Silent Mutation: No change in amino acid sequence.

Meiosis and Genetic Variation

• Purpose: Create haploid gametes, reducing chromosome number for sexual reproduction.

• Key Processes:

  • Crossing Over: Exchange of genetic material between homologous chromosomes.

  • Random Assortment: Each daughter cell receives a random mix of maternal and paternal chromosomes.

Important Differences Between Mitosis and Meiosis

Formation of Human Gametes

• Spermatogenesis: Continuous sperm production.

• Oogenesis: Egg formation begins before birth, pauses until puberty, leading to unequal resource allocation in gametes.

Conclusion

• Understanding DNA processes is crucial for insights into genetics, molecular biology, and applications in biotechnology.