Gene Expression and Regulation in AP Biology

Gene expression and regulation are key processes in cellular function, guiding the conversion of genetic information into proteins. This lecture covers the principles of these processes and their implications in various fields.

Key Concepts

• Central Dogma of Molecular Biology: Describes the flow of genetic information from DNA to RNA to proteins.
• DNA: Blueprint for cellular processes, organized into genes coding for specific proteins.
• Transcription: Conversion of DNA to mRNA using RNA polymerase.
  • Occurs in the nucleus (eukaryotic) or cytoplasm (prokaryotic).
• Translation: Synthesis of proteins from mRNA, involving ribosomes and tRNA.
• Gene Expression Regulation: Ensures correct proteins are produced appropriately, regulated at transcription, post-transcription, and translation.
• Epigenetic Factors: DNA methylation and histone modifications affect gene expression without changing DNA sequence.

DNA Structure and Function

• DNA Composition: Double-stranded helix of nucleotides (sugar, phosphate, nitrogenous base).
• Base Pairing: A-T and G-C pairings stabilize the structure.
• DNA Organization: Coiled into chromosomes, forming a genetic code read in codons during protein synthesis.
• DNA Replication: Semi-conservative process ensuring genetic information is passed during cell division.

Transcription Process

• RNA Synthesis: Catalyzed by RNA polymerase starting at promoter sequence.
• Promoters: Upstream of genes, crucial for RNA polymerase binding.
• RNA Nucleotides: Include ATP, UTP, GTP, CTP; Uracil replaces Thymine.
• Termination and Processing: RNA released upon reaching termination sequence; mRNA processed by capping, tailing, splicing.

Translation and Protein Synthesis

• Ribosomes: Sites of protein synthesis, composed of rRNA and proteins.
• tRNA Role: Carries amino acids, matches anticodons to mRNA codons.
• Translation Stages: Initiation, Elongation, Termination.
• Post-translational Modifications: Folding, cleavage, functional group additions.

Gene Regulation in Prokaryotes

• Transcription Control: Via repressors/activators, e.g., lac operon (repressor), CAP system (activator).
• Operons: E.g., trp operon regulated by attenuation.

Gene Regulation in Eukaryotes

• Complex Regulation: At transcriptional, post-transcriptional, translational levels.
• Transcription Factors: Interact with DNA regulatory sequences.
• Chromatin Structure's Role: Euchromatin vs. heterochromatin, histone modifications.
• Post-transcriptional Regulation: Alternative splicing, RNA editing, miRNA.

Epigenetic Factors

• DNA Methylation: Affects gene silencing by interfering with transcription.
• Histone Modifications: Influence chromatin structure, gene expression.
• Environmental Influence: Diet, stress, toxins can affect epigenetic modifications.
• Reversibility and Role: Epigenetic changes reversible, crucial in cell differentiation, imprinting, chromosome inactivation.

Applications and Real-World Examples

• Medicine: Targeted therapies based on genetic profiles, epigenetic therapy.
• Agriculture: GMOs with enhanced traits (yield, resistance).
• Synthetic Biology: Designs biological systems for valuable compounds.
• Forensic Science: RNA sequencing for tissue origin analysis.
• Model Organism Research: Provides insights into human biology and diseases.