Chapter 11: How Genes are Controlled

Overview

• Focus on the regulation and control of gene expression.
• Regulation of transcription is the most important step in gene regulation.

Gene Regulation Concepts

• Gene Regulation: Turning on and off of genes to respond to environmental changes.
• Gene Expression: Process where genetic information flows from genes to proteins, affecting phenotype.
• Cells produce specific proteins as needed for function.
• Example: E. coli in the intestine breaks down lactose when abundant.

Transcription Control

• Promoter: Site where RNA polymerase attaches to start transcription.
• Operator: Acts as a switch; regulates RNA polymerase's access to the promoter.
• Operon: Cluster of genes with related functions, including promoter, operator.
• Transcription is inhibited when a repressor protein binds to the operator, blocking RNA polymerase.
• Regulatory Gene: Codes for repressor proteins, maintaining a supply of repressors.
  • Ex: Excess tryptophan in E. coli binds to the repressor, switching off the trp operon.
• Activators: Proteins that turn operons on by stimulating gene transcription.

DNA and Chromatin Modifications

• Histones: Proteins crucial for DNA packing.
• Methylation: Adding CH3 groups makes DNA compact, reducing transcription.
• Acetylation: Adding COCH3 groups opens structure, promoting transcription.
• Methylation patterns are inherited during cell division, known as epigenetic inheritance.
• X Inactivation: One X chromosome in female mammals is inactivated randomly, creating epigenetic inheritance.

Eukaryotic Gene Expression

• RNA polymerase requires transcription factors to function.
• Enhancers: DNA sequences far from the gene; activators bind to them to initiate transcription.
• DNA-Bending Proteins: Bring enhancers closer to promoters.
• Complex Protein Assembly: Required for RNA polymerase to start transcription.
• Alternative RNA Splicing: Allows multiple polypeptides from one gene.

Additional Gene Expression Regulation

• mRNA Lifespan: Longer-lived mRNA can produce more proteins.
• Protein Processing: Further modifies gene expression.
• Non-Coding RNAs:
  • miRNAs: Bind to mRNA to regulate expression.
  • siRNAs: Involved in RNA interference, silencing specific genes.

Signal Transduction Pathways

• Converts surface signals to internal responses.

1. Signaling molecule secreted.
2. Binds to receptor on target cell.
3. Activates relay proteins inside the cell.
4. Triggers transcription of specific genes.

Cloning and Genetic Potential

• Totipotent Cells: Capable of producing any cell type.
• Nuclear Transplantation: Replacing zygote nucleus with somatic cell nucleus, used in cloning.
• Cloning can lead to health issues due to methylation.

Cancer Genetics

• Oncogenes: Cancer-causing genes inserted by viruses.
• Proto-oncogenes: Normal genes that can become oncogenes.
• Tumor-Suppressor Genes: Inhibit cell growth to prevent uncontrolled proliferation.