Gene Expression Notes

Prokaryotic Cell Structure
- Capsule, Cell Wall, Cytoplasmic Membrane, Ribosomes, Pili, Cytoplasm, Nucleoid, Flagella
- Prokaryotes can adjust protein synthesis based on nutrients available, like food intake.
- Protein synthesis depends on whether specific DNA is expressed:
  - If a protein is needed, its DNA is expressed (transcribed/translated).
  - If not needed, the DNA for that protein is not expressed.

Definition: Organized clusters of genes contributing to a metabolic task (found only in prokaryotes).
- Types:
  - Inducible Operons: Typically 'off' but can be turned 'on'.
  - Repressible Operons: Typically 'on' but can be turned 'off'.

Components:
- Promoter (P): DNA region where transcription starts.
- Repressor (R): Prevents RNA polymerase from binding to the promoter.
- Operator (O): Functions as an "on/off" switch.
- Gene: Structural genes to be transcribed/translated (e.g., lacZ).
- Functional Examples:
  - When lactose is absent, the active repressor prevents transcription (Operon is off).
  - When lactose is present, it binds the repressor (inhibiting it), allowing transcription (Operon is on).

Function: Synthesizes tryptophan.
- When tryptophan is absent, the repressor is inactive and operon is 'on'.
- When tryptophan is present, it activates the repressor, and operon is 'off'.

Negative Control: Operons are switched off by the active form of the repressor.
Positive Control: Operons are switched on by inactive repressor and regulatory proteins enhancing transcription by facilitating RNA polymerase's binding to the promoter.

Transcription: Regulated by factors both inside (proteins inherited) and outside (signals from other cells) the cell.
Regulatory Mechanisms: At cellular levels include gene regulation, chromatin structure, and transcriptional controls.
Differential Gene Expression: Key to how cells become specialized despite having the same DNA.

Euchromatin vs Heterochromatin:
- Euchromatin: Loosely packed and actively transcribed.
- Heterochromatin: Tightly packed and not transcribed.
- Acetylation: Increases transcriptional activity; methylation decreases it.

RNA Processing: Involves splicing out introns, adding 5' cap and poly-A tail.
RNA Interference: MicroRNA can reduce gene expression by degrading mRNA.

Differentiation: Process by which cells develop different structures/functions despite having the same genetic material.
Cytoplasmic Determinants: Unevenly distributed substances influencing gene expression in early development.
Induction: Signals from surrounding cells that guide genetic development.

Role of Morphogens: Proteins that direct the development of body plans and structures through concentration gradients (e.g., Bicoid).
Homeotic Genes: Genes dictating body parts, highly conserved across species, influencing the placement of structures.

The genetic regulation determining cellular function and specialization is complex, relying on a network of interactions and modifications impacting transcription, translation, and cellular behavior.