L18 Control of gene expression

Introduction to Gene Regulation

Overview: Discussion on the process from DNA to protein through transcription and translation. Importance of understanding gene expression control.

Gene Expression: Refers to the activation of a gene resulting in the production of protein.
Example in Cancer: Yellow staining observed in cancer cells indicates gene expression upregulation in response to methotrexate treatment.
Focus: Emphasis on transcription control in eukaryotes with examples of regulatory mechanisms.

Differential Gene Expression: Explanation of how different cell types have distinct gene expression patterns leading to their unique functions (e.g., neurons vs liver cells).
Evidence of the Same Genetic Material: Cloning experiments demonstrate that differentiated cells retain the same DNA as stem cells (e.g., adult frog cells transferred to fertilized eggs leading to normal embryos).

Transcription Factors: Proteins that determine if a gene is switched on or off; they bind to specific DNA sequences and influence transcription frequency.
Eukaryotic vs. Prokaryotic Regulation: Detailed differences between eukaryotic complexity and prokaryotic simplicity in transcription regulation.
- Prokaryotic: Rapid and efficient due to coupled transcription and translation processes. Use of simple activator and repressor mechanisms.
- Eukaryotic: Multiple levels of control with transcription factors, enhancers, and chromatin structure.

Constitutively Expressed vs. Regulated Genes: Discussion of genes always on for basic functions (e.g., respiration) versus those regulated depending on cellular need.
Transcriptional Control: Highlighting transcription as the primary regulation point for gene expression, with approximately 73% of proteins regulated at this level.

Complexity: Overview of eukaryotic transcription factors having DNA binding domains and activation domains to interact with other proteins.
Types of Eukaryotic Transcription Factors:
- Homeodomain: Regulates developmental genes.
- Zinc Finger Domains: Most common form of eukaryotic transcription factor.
- Leucine Zipper: Structure allowing protein interactions.
Regulatory Sequences: Discussion on multiple enhancers and silencers influencing transcription.

Enhancers: Potential thousands of base pairs from their target; regulate gene transcription.
Experimental Tools: Using reporter constructs (e.g., GFP) to visualize gene activation patterns in living organisms (e.g., zebrafish).

Chromatin Remodeling: DNA and histone proteins interplay affecting gene accessibility; euchromatin (active) and heterochromatin (inactive).
Histone Modifications: Reversible nodulation influencing transcription (e.g., acetylation activates, methylation silences).
Epigenetics: Inheritable changes in DNA activity without altering the sequence itself, influencing traits such as metabolism.

Alternative Splicing: Process generating different protein isoforms from a single gene (e.g., auditory perception channels).
MicroRNAs: Non-coding RNAs regulating target mRNA, influencing stability and translation.
Proteasome Function: Role in protein degradation through ubiquitination, influencing cell cycle and dynamics.

Drug Targeting: Most drugs target proteins; e.g., chemotherapy like doxorubicin interacts with DNA, while tamoxifen inhibits transcription factors.
Emerging Therapies: mRNA therapies (e.g., COVID vaccines) represent a new horizon in gene expression manipulation.

Pluripotency: Early embryonic cells have the potential to become any cell type; gene expression patterns are critical in development.
Induced Pluripotent Stem Cells (iPSCs): Specialized cells can be reprogrammed to stem cells using specific transcription factors, holding promise for regenerative medicine.

Key Takeaways: Emphasis on the intricate regulation of gene expression and how understanding these processes allows for advancements in biology and medicine.