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BIO 2317 Topic 5
| Question | Answer |
|---|---|
| How is gene expression controlled | Transcriptional control is the most common because it is slower and uses less energy |
| Negative control: Repressor protein | Binding of the repressor blocks transcription by negative regulation |
| What do repressor proteins contain | Allosteric domain and DNA binding domain |
| Negative control: Inducers | Binding of an inducer molecule to repressor protein allows transcription |
| Where does the inducer bind | To the allosteric domain in the repressor protein |
| Positive control: activator proteins | Binds to the promoter site |
| What happens when the inhibitor binds to the activator protein | Activator binding and transcription is prevented |
| What happens when there is no inhibitor binding to the activator | Activator can bind and transcription happens |
| Positive control of the lac operon | Occurs at the CAP binding region of the activator which attracts activator call the CAP-cAMP complex |
| What does the CAP-cAMP facilitate | strong RNA pol binding to lac promoter |
| Regulation of CAP-cAMP glucose levels | Almost no CAP-cAMP complex forms, no activator |
| Regulation of CAP-cAMP without an activator bound to lac | lac gene transcription is very inefficient |
| Operon | Cluster of genes under a shared regulatory region, coordinated transcriptional regulation, genes usually act in the same metabolic pathway |
| What helps bacterial cells respond rapidly to environmental changes | Coordinated regulation |
| What do genes in the lac operon encode | Proteins needed for lactose metabolism |
| Lac operon structure contains.. | 1. Promoter that binds RNA polymerase 2. Operator (lacO) that binds lac repressor protein 3. CAP-cAMP binding region |
| lac Z | encode beta-galactosidase |
| lac Y | Encodes enzyme permease |
| lac A | encodes transacetylase |
| lac L | encodes repressor protein |
| Permease | Enzyme that allows lactose to enter the cell at the membrane |
| B-galactosidase | Enzyme needed to break B-galactoside linkage |
| Allolactose | Breakdown intermediate, acts as the inducer compound |
| Lactose metabolism in E.coli | Glucose is the preferred energy source, lactose serves as an alternative carbon source if glucose is not present |
| Lac operon function when lactose is unavailable | lac repressor protein binds to operator sequence and inhibits transcription |
| Lac operon function when lactose is available | With repressor protein inactivated by allolactose binding, RNA pol carries out transcription, inducers make repressors inactive |
| When glucose is present but lactose is absent, what happens? | Transcription is inhibited, repressor binds to the lacO, lac operon is not expressed |
| When glucose is absent but lactose is present, what happens? | Allolactase restricts repressor so transcription can be carried out and RNA pol can be placed on the lacO, there is little transcription unless it binds with an activator |
| When both glucose and lactose is present, what happens | Small amount of lac operon is expressed, repressor is inactive but no activator is present |
| What does the activator depend on | Glucose availability |
| Transcriptional regulatory elements in eukaryotes | Cis-regulatory elements consist of single binding sites, located to the 5' of the gene |
| What does the SHH (sonic hedgehog) gene direct | Limb formation in humans |
| Enhancer | Regulatory sequence that binds activator proteins |
| How did snakes lose their limbs | SHH was present in the snake genome but was limitedly expressed, Mutations to the enhancer region but the activators did not bind so the process was stopped |
| Chromatin | Compact packing of chromosomes with protein into chromatin |
| Heterochromatin | Chromosomes that contain densely compacted chromatin and few expressed genes |
| Effects on RNA from heterochromatin | Harder for RNA pol to find and bind promoters |
| How much transcription in heterochromatin | Less or no transcription |
| Methylation and acetylation in heterochromatin | More methylation on DNA and less acetylation on histones |
| Euchromatin | Contains chromatin that is not densely compacted |
| Are genes expressed in euchromatin | yes |
| Transcription in euchromatin | Gets transcription |
| Methylation and acetylation in euchromatin | Less methylation on DNA and histones and more acetylation on histones |
| Epigenetics | Heritable patterns or changes in gene expression that are not associated with any change in DNA sequence |
| Modifications of epigenetics | Chemical modification or DNA or associated histone proteins that alter chromatin structure and influence transcription |
| Environmental epigenetics | Parental nutrition and diet may lead to epigenetically controlled modification of gene expression that is passed on to offspring |
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