controlling gene expression and genetic engineering

Gene Regulation and Metabolic Pathways

Enzyme Regulation in Metabolic Pathways

  • Feedback Inhibition:

    • Final product of a metabolic pathway binds to an earlier enzyme in the pathway.
    • Acts as an allosteric inhibitor, changing enzyme shape and reducing activity.
    • This process conserves energy and resources as it prevents unnecessary production of intermediates.

  • Gene Expression Regulation:

    • Cells control the amount of enzyme produced by regulating transcription of its gene.
    • Allows for increased enzyme production when substrate is present and turning off when it is not needed.
    • Example: The lac operon in prokaryotes.

Constitutive Gene Expression

  • Definition: Genes expressed constitutively are always transcribed and translated.
  • Limits:
    • This can lead to energy waste as resources are spent producing proteins continuously.
  • Comparison:
    • Negative Gene Control: A repressor protein binds to DNA to block transcription, thus can be switched off.
    • Regulated Genes: Controlled on demand, conserving energy by only being active when necessary.
    • Inducible Genes: Off until induced.
    • Repressible Genes: On until repressed.

Gene Control in Prokaryotes

  • Gene control in prokaryotes is generally viewed as occurring at the transcriptional level because:
    • Transcription and translation are coupled (occur simultaneously) in prokaryotes.
    • This process is more efficient, as prokaryotes lack a nucleus.

Lac Operon Structure and Function

  • Components:
    • Structural genes (e.g., lacZ, lacY) for metabolizing lactose.
    • Regulatory gene (lacI) produces repressor protein.
  • Function:
    • When lactose is present, it binds to the repressor, inactivating it, allowing transcription of the operon.
    • Conserves energy by ensuring enzymes for lactose metabolism are only produced when lactose is available.

Comparison of Inducible vs. Repressible Operons

  • Similarities:
    • Both involve regulation of gene expression to conserve resources.
  • Differences:
    • Inducible Operons: Typically off until required (e.g., lac operon).
    • Repressible Operons: Typically on until turned off by a repressor (e.g., trp operon).

Post-Translational Control Mechanisms

  • Post-translational modifications include:
    • Glycosylation: Adding sugars to proteins.
    • Phosphorylation: Adding phosphate groups, affecting enzyme activity.
    • Proteolytic cleavage: Cutting proteins to activate or deactivate them.

Structural vs. Regulatory Genes

  • Structural Genes:
    • Code for proteins that have functional roles (e.g., enzymes).
  • Regulatory Genes:
    • Control expression of structural genes by producing regulatory proteins (e.g., repressors that control operons).

Gene Regulation in Prokaryotes vs. Eukaryotes

  • Prokaryotes:
    • Regulation primarily at transcription and translation levels (2 levels).
  • Eukaryotes:
    • More complex regulation with 6 levels of control including:
    1. DNA unpackaging/unwinding.
    2. Transcriptional control with transcription factors.
    3. Transcript processing (splicing).
    4. RNA export from the nucleus.
    5. Translation control with UTR.
    6. Post-translational modification.

Structure of Eukaryotic DNA

  • Eukaryotic DNA is tightly packed, impacting gene expression.
    • Closed DNA = genes off.
    • Open DNA = genes on, allowing access for transcription.

CRISPR and Genetic Engineering

  • Restriction Endonucleases:

    • Enzymes that cut DNA at specific sequences for protection against phage infections.
    • Highly specific defense mechanism for bacteria.

  • DNA Ligase: Enzyme that covalently bonds DNA strands together.

  • Importance of Bacteria in Genetic Engineering:

    • Simple, fast-growing, and easy to manipulate.
    • Ideal for producing large amounts of proteins from engineered genes.
    • Use of plasmids facilitates gene transfer.

CRISPR Overview

  • Function of CRISPR: Enables precise gene editing by targeting and modifying specific DNA sequences.

    • Originated from bacteria as a natural defense mechanism.

  • Genetic Disease Example - Cystic Fibrosis:

    • Mutation in CFTR gene leads to respiratory and digestive issues.
    • CRISPR could target and correct this mutation by delivering a corrected DNA template to epithelial cells.

  • Ethical Considerations: Risks of unintended mutations and designer babies, which raises concerns about consent and genetic discrimination.

  • Strategy for Infectious Disease Eradication: Utilizing CRISPR to target and modify bacterial DNA to eliminate infection; however, feasibility would depend on specific pathogens and conditions.