8.11.S: Regulation of Gene Expression (Summary)
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- Ying Liu
- City College of San Francisco
- Regulation of gene expression is essential to the normal development and efficient functioning of cells
- Gene expression may be regulated by many mechanisms, including those affecting transcript abundance, protein abundance, and post-translational modifications
- Regulation of transcript abundance may involve controlling the rate of initiation and elongation of transcription, as well as transcript splicing, stability, and turnover
- The rate of initiation of transcription is related to the presence of RNA polymerase and associated proteins at the promoter.
- RNApol may be blocked from the promoter by repressors, or may be recruited or stabilized at the promoter by other proteins including transcription factors
- The lac operon is a classic, fundamental paradigm demonstrating both positive and negative regulation through allosteric effects on trans -factors.
- In eukaryotes, cis -elements that are usually called enhancers bind to specific trans -factors to regulate transcriptional initiation.
- Enhancers may be modular, with each enhancer and its transcription factor regulating a distinct component of a gene’s expression pattern, as in the yellow gene.
- Sticklebacks provide examples of recent evolutionary events in which mutation of an enhancer produced a change in morphology and a selective advantage.
- Chromatin structure, including reversible modifications such as acetylation of histones, and methylation DNA CpG sites also regulates the initiation of transcription.
- Chromatin modifications or DNA methylation of some genes are heritable over many mitotic, and sometimes even meiotic divisions.
- Heritable changes in phenotype that do not result from a change in DNA sequence are called epigenetic. Many epigenetic phenomena involve regulation of gene expression by chromatin modification and/or DNA methylation.
Key Terms:
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gene expression transcriptional regulation operon lactose glucose lac operon lacZ lacY lacA galactosidase permease trans-acetylase P / promoter O / operator CBS CAP-binding site cis-elements trans-regulators lacI homotetramer repressor allosteric cAMP binding protein CAP CAP binding sequence CBS |
adenylate cyclase constitutive O c / I - / I s F-factor / episome GC boxes CAAT boxes TATA boxes GAL4-UAS Driver/responder transcription start site enhancers/silencers transcription factors hemoglobin/heme/globin pseudogene gene families stickleback primordium chromatin remodeling acetylation/deacetylation methylation/demethylation CpG sites epigenetics winter annual vernalization FLC |