Unit 6: Gene Expression and Regulation Notes

Unit 6: Gene Expression and Regulation

• Nucleic Acids

  • Biological information molecules.
  • Monomers: Nucleotides, which consist of:
  • Sugar: Deoxyribose (in DNA) vs. Ribose (in RNA)
  • Phosphate Group
  • Nitrogenous Base:
    • DNA: A, T, C, G
    • RNA: A, U, C, G
  • DNA is typically double-stranded, while RNA is often single-stranded.

• Hydrogen Bonds and Base Pairing

  • Nucleic acids can form hydrogen bonds due to complementary base pairing of nitrogenous bases.

• History of DNA as Genetic Material

  • Key experiments:
  • Griffith Experiment: Demonstrated transformation in bacteria.
  • Avery-MacLeod-McCarty Experiment: Identified DNA as the transforming agent.
  • Hershey-Chase Experiment: Confirmed that DNA is the genetic material of viruses.
  • Franklin-Crick-Watson Model: Proposed the double helix structure of DNA.
  • Understand DNA roles in viruses and prokaryotes: transformation, conjugation, transduction, and unique characteristics of retroviruses.

• Central Dogma of Molecular Biology

  • Flow of genetic information:
    $$ ext{DNA}
    ightarrow ext{RNA}
    ightarrow ext{Protein} $$

• DNA Replication

  • Process of accurately copying genetic information.
  • Important enzymes:
  • Topoisomerase: Relieves tension in the DNA strand.
  • Helicase: Unwinds the DNA double helix.
  • Ligase: Joins Okazaki fragments.
  • Primase: Synthesizes RNA primers.
  • DNA Polymerase: Synthesizes new DNA strand in a 5’ to 3’ direction; works on antiparallel strands.
  • Leading vs. Lagging Strand:
  • Leading strand: Continuous synthesis.
  • Lagging strand: Discontinuous synthesis, forming Okazaki fragments.
  • Semi-Conservative Replication: Each new DNA contains one original and one new strand.
  • Proofreading Mechanism: Reduces mutation rates during replication.

• Transcription

  • Process of converting DNA into RNA, mainly performed by RNA polymerase.
  • Begins at the Promoter and ends at the Termination Site.
  • Pre-mRNA undergoes modification:
  • 5’ Cap and 3’ Poly-A Tail added for protection.
  • Introns (non-coding sequences) are removed, and Exons (coding sequences) are spliced together.

• Translation

  • mRNA is converted into a protein/polypeptide by ribosomes.
  • Codons (triplets of mRNA) correspond to specific amino acids (64 codons for 20 amino acids, indicating redundancy).
  • Ribosomes match codons with tRNA anticodons to build proteins.

• Mutations

  • Changes in the DNA sequence:
  • Point Mutations: Single nucleotide changes.
    • Sense/Silent Mutations: Same amino acid, usually harmless.
    • Missense Mutations: Different amino acid, potentially harmful or helpful.
    • Nonsense Mutations: Premature stop codon, always harmful.
    • Frameshift Mutations: Nucleotides added/removed, altering subsequent amino acids, always dangerous.

• Gene Regulation

  • Mechanisms by which cells control gene expression.
  • Prokaryotic regulation via Operons:
  • Types: Inducible and Repressible.
  • Eukaryotic regulation:
  • Transcription Factors: Proteins that modify gene expression, often related to signaling pathways.
  • Histone Modifications: Influence DNA packaging and gene expression.
  • Regulatory DNA Sequences (Enhancers): Recruit transcription factors to promote gene expression.
  • Alternative Splicing: Allows expression of different gene versions through selective splicing of exons.

• Biotechnology Techniques

  • Key techniques in genetic experimentation include:
  • Gel Electrophoresis: Separates DNA fragments based on size.
  • Polymerase Chain Reaction (PCR): Amplifies DNA sequences.
  • Bacterial Transformation: Inserts foreign DNA into bacteria.
  • DNA Sequencing: Determines the nucleotide sequence of DNA.