Lecture 43: Regulating Gene Expression and Introduction to Evolution

Overview of Gene Expression Regulation

• Key Terminology:
  • Transcription Factors: Proteins that help regulate the transcription of genes.
  • Activators and Repressors: Types of transcription factors; activators increase gene expression, repressors decrease it.

The Lac Operon in Prokaryotes

• Operon: A collection of genes transcribed together as a single mRNA.
  • Includes a single promoter and terminator, and multiple genes with their own start and stop codons.
  • Common in prokaryotes, absent in eukaryotes.
• Lac Operon: Operon related to lactose metabolism.
  • Involves three genes that encode proteins for breaking down lactose, a disaccharide.

Transcription Factors in Lac Operon

• Lac Repressor Protein:
  • Binds to the operator in the absence of lactose to block RNA polymerase, thus preventing transcription.
  • With lactose, it undergoes a shape change and cannot bind to DNA, allowing transcription.
• Catabolite Activator Protein (CAP):
  • Requires cyclic AMP (cAMP) to activate.
  • In low glucose conditions (high cAMP), CAP binds near the promoter to stabilize RNA polymerase, enhancing transcription.

Logical Scenarios

• Low glucose & lactose available: Strong expression due to absence of repressor and presence of activator.
• High glucose & lactose unavailable: No expression due to presence of repressor and absence of activator.
• Low glucose & lactose unavailable: No expression due to repressor's presence, despite activator's presence.
• High glucose & lactose available: Low expression due to absence of both repressor and activator.

Introduction to Evolution

• Key Terms Defined:
  • Hypothesis: A suggested explanation for an observation, testable.
  • Scientific Theory: A tested and confirmed explanation for observations, with broad scope and strong support.
  • Scientific Law: Similar support as a theory but with a narrow scope.
• Evolution Definition: Change in the genetic makeup of a population over time.
  • Population: All individuals of a species in a specific area.
  • Genetic Makeup: Refers to allele frequencies within a population.
  • Over Time: Changes occur over generations.