Lecture on Gene Expression and Regulation

Introduction

• Unit 6 focuses on gene expression and regulation.
• Resources available: Daily Review on Instagram, 374-page review guide on Weebly, and recorded FRQ Fridays.
• Practice questions included: 3 multiple choice questions and 2 free responses.

Central Dogma of Molecular Biology

• Central Dogma: DNA -> RNA -> Polypeptide (not necessarily a protein).
  • DNA replication makes a copy of DNA.
  • Transcription: DNA -> RNA.
  • Translation: RNA -> Polypeptide (multiple may form a protein, e.g., hemoglobin).
• Violations include retroviruses (e.g., HIV uses reverse transcriptase to convert RNA to DNA).

DNA Replication

• Occurs in nucleus (eukaryotes) or nucleoid region (prokaryotes).
• Structures differ: Eukaryotic DNA is linear, prokaryotic is circular.
• Key enzymes:
  • Helicase unzips DNA by breaking hydrogen bonds.
  • Topoisomerase prevents supercoiling by breaking and rejoining strands.
  • Primase synthesizes RNA primer.
  • DNA polymerase synthesizes DNA, replaces RNA primer, proofreads.
  • Ligase seals Okazaki fragments on lagging strand.
• Leading strand synthesized continuously; lagging strand synthesized in fragments (Okazaki fragments).

Transcription

• Produces mRNA from DNA in nucleus (eukaryotes); occurs in cytoplasm (prokaryotes).
• RNA polymerase synthesizes RNA, does not require helicase.
• Base pairing: A=U, C=G.
• Post-transcriptional modifications in eukaryotes:
  • 5’ cap added.
  • Poly-A tail added.
  • Introns spliced out.

Translation

• Converts mRNA to polypeptide.
• Occurs in the cytoplasm (eukaryotes: ribosomes in cytosol or rough ER; prokaryotes: cytosol).
• Involves rRNA, tRNA, and mRNA.
• Steps: Initiation (AUG start codon), Elongation, Termination (stop codon).
• tRNA anticodons pair with mRNA codons in ribosomal A, P, E sites.

Gene Mutations

• Point Mutations:
  • Silent: No change in amino acid.
  • Missense: Different amino acid.
  • Nonsense: Premature stop codon.
• Frameshift Mutations: Insertion/deletion shifts reading frame.
• Chromosomal mutations include duplications, deletions, inversions, and translocations.

Gene Regulation: Operons

• Exists in prokaryotes, e.g., lac operon (inducible, turns on with lactose) and trp operon (repressible, turns off with tryptophan).
• Components: Promoter, Operator, and Structural Genes.
• Operons regulate gene expression efficiently in prokaryotes.

Biotechnology Techniques

• Gel Electrophoresis: Separates DNA fragments by size.
• PCR (Polymerase Chain Reaction): Amplifies DNA.
• DNA Sequencing: Determines nucleotide sequence.
• Transformation: Uptake of foreign DNA by cells, often used with plasmids in bacteria.

Practice and Review

• Practice multiple choice and free-response questions were provided to enhance understanding and application of concepts.
• Emphasized understanding genetic mechanisms and regulatory processes.

Conclusion

• Unit 6 covers fundamental concepts in gene expression and regulation, essential for understanding biological processes.

Notes for Further Study

• Review specific case studies of operons (lac and trp) for deeper understanding.
• Practice gel electrophoresis and PCR interpretation.
• Explore additional resources and practice exams for comprehensive preparation.