Gene Expression Regulation

• The unit covers gene expression regulation, biotechnology, and cell division.

Prokaryotic Gene Regulation

• Operons are gene clusters controlling protein production in response to environmental changes.
• The lac operon (E. coli) is an inducible system that regulates lactose breakdown.
• Lactose binds to a repressor protein, detaching it from the operator site, allowing transcription.
• The trp operon is a repressible operon that is activated by tryptophan which then prevents further tryptophan production.

Eukaryotic Gene Regulation

• Eukaryotic gene regulation is more complex due to larger genomes and diverse expression mechanisms.
• Gene expression is regulated at transcription, RNA processing, translation, and post-translation levels.
• Transcription factors bind to DNA to either promote or inhibit transcription.
• Enhancers and silencers are regulatory sequences that can enhance or repress transcription.
• The mediator complex facilitates the interaction between transcription factors and RNA polymerase.
• Chromatin remodeling regulates gene expression by exposing or hiding genes from transcriptional machinery.

Post-Transcriptional Regulation in Eukaryotes

• Alternative splicing allows a single gene to produce multiple mRNA transcripts, leading to different proteins.
• RNA interference (RNAi) involves small RNAs like microRNAs (miRNAs) and small interfering RNAs (siRNAs).
• miRNAs and siRNAs bind to mRNA to degrade them or inhibit translation.
• RNA stability is critical because mRNA degradation limits protein production.

Tumor Suppressor Gene p53

• p53 is a tumor suppressor gene crucial for maintaining genomic stability.
• p53 halts the cell cycle for DNA repair or triggers apoptosis if damage is severe.
• Mutated or inactive p53 can lead to cells with damaged DNA proliferating, causing tumors.

CRISPR-Cas9 Genome Editing

• CRISPR-Cas9 is a biotechnology tool for genome editing.
• CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) was discovered as a bacterial defense mechanism.
• Cas9 enzyme, guided by guide RNA, cuts DNA at a specific location.
• Cell repair mechanisms are then harnessed to disrupt a gene or insert new genetic material.
• CRISPR applications include gene therapy for genetic disorders like sickle cell anemia.
• Ethical concerns exist, particularly regarding germline editing.
• Germline editing has sparked debates about the moral implications of altering the human genome.

Cell Division: Mitosis and Meiosis

• Mitosis produces two genetically identical daughter cells, crucial for growth and tissue repair.
• The cell cycle regulates mitosis, with checkpoints ensuring cells divide only when ready.
• Cyclins and cyclin-dependent kinases (CDKs) regulate cell cycle progression.
• Meiosis produces gametes (sperm and egg cells) with half the chromosome number.
• Meiosis promotes genetic diversity through crossing over and independent assortment.

Cell Cycle Regulation

• Cell cycle regulation must ensure that cells divide only when appropriate.
• Checkpoints during the cell cycle assess DNA integrity and cell division progress.
• Failure of regulatory mechanisms can result in uncontrolled cell division (cancer).
• Proteins like p53, Rb, and CDKs are crucial for regulating the cell cycle.