Lecture Notes on Cell Differentiation and Gene Expression

Overview of Cellular Differentiation

Human Cells Variety: Bone, blood, muscle, nerve, fat cells, etc.
- Each type has different functions.
Origin of Cells: All cells originate from a single cell formed by the union of sperm and egg.
- Embryonic cells divide and differentiate, all containing the same DNA.
Role of DNA: Despite having identical DNA, cells differentiate to perform specific roles.

Gene Expression: Determines how cells with the same DNA take on different functions.
Energy Efficiency: Producing proteins is energy-intensive (ATP consumption).
- Cells avoid making unnecessary proteins to conserve energy (similar to not buying a winter coat when living in a warm climate).
Regulation of Gene Expression: Critical for cells to control protein production.
- Example: Nerve cells and muscle cells use different proteins despite having the same DNA set.

Bacteria Gene Expression: Simpler structure with fewer genes.
- Constitutive Expression: 60-80% of genes are always on for essential functions.
- Regulated Expression: 20-40% of genes are turned on/off as needed.
Operons in Bacteria:
- Operon Structure: Includes structural genes and regulatory DNA.
  - Structural Genes: Encode proteins required for related pathways.
  - Promoter Region: Site for RNA polymerase binding to begin transcription.
- mRNA Production: One mRNA can encode multiple proteins within an operon.
Types of Operons:
- Repressible Operons: Turned off when end product is abundant.
- Inducible Operons: Activated when a specific molecule is present.

Inducible Operon Example:
- Lac Operon: Activated in presence of lactose to digest and use lactose for energy.
- Functions only when lactose is present, demonstrating energy efficiency in gene expression.