Gene Expression: The process through which genetic information leads to the production of proteins.
Genotype: Inherited alleles from parents.
Phenotype: Physical expression of traits.
Gene: Segment of DNA that codes for a protein.
Stages of Gene Expression
Transcription: DNA used as a template to make mRNA.
Promoters: Base sequences at the beginning of a gene where RNA polymerase begins transcription.
Transcription Factors: Proteins that bind to promoters; can act as enhancers or silencers.
Enhancers: Promote transcription.
Silencers: Inhibit transcription.
Translation: mRNA translated into an amino acid sequence.
Protein Function: Resulting proteins perform functions in the cell.
Regulation of Gene Expression
Transcription Factors and DNA Regions:
Silencers and enhancers are regions upstream of a gene where transcription factors bind.
Binding to enhancers increases transcription; binding to silencers decreases transcription.
Mature mRNA: Result of post-transcriptional modification includes splicing of exons, 5' cap, and poly-A tail.
Poly-A Tail: Length affects mRNA stability and translation frequency.
Cell Differentiation and Epigenesis
Cell Specialization: Stem cells differentiate into various cell types through gene expression regulation.
Epigenesis: Process of differentiation resulting in different tissues.
Epigenetic Tags: Chemical modifications that affect gene expression without altering DNA sequence.
Genomic Terminology
Genome: Complete genetic information in a cell.
Transcriptome: All mRNA sequences produced by a cell.
Proteome: All proteins produced by a cell.
Epigenetic Mechanisms
Methylation: Addition of methyl groups to DNA or histone proteins; silences genes.
Histone Modification: Methylation affects DNA availability for transcription.
Epigenome: Inherited epigenetic tags along with the genome during cell division.
Environmental and Inherited Influences
Environmental Factors: Can alter gene expression (e.g., air pollution affecting DNA methylation).
Genomic Imprinting: Silencing of specific alleles can affect inheritance patterns.
Case Studies and Examples
Imprinting in Lions: Different patterns in males and females affect litter sizes and offspring size.
Twin Studies: Monozygotic twins offer insights into nature vs. nurture.
Lactose Metabolism: Lactase gene expression regulated by lactose levels.
Hormonal Regulation
Hormones: Regulate gene expression by promoting or silencing it.
Estrogen: Binds to target genes, altering expression and making tissues responsive to other hormones (e.g., progesterone in the endometrium).
Conclusion
Gene expression is a complex process influenced by genetic, environmental, and epigenetic factors. Understanding these mechanisms is crucial for insights into development, differentiation, and disease.