Summary of chapter 14: Gene regulation in bacteria. Pay attention: there are figures and tables mentioned from the Genetics analysis & principles seventh edition. These are not put directly into the summary, so it is convenient to have the book ready to look at the figures when they are mentioned.
Gene regulation = the level of gene expression can vary under different conditions.
Constitutive genes = unregulated genes that have constant level of expression in all conditions over
time. They encode proteins that are continuously needed for survival of bacterium.
Gene regulation is important for cellular processes such as:
- Metabolism
- Response to environmental stress
- Cell division
- Differentiation and development
- Several other reasons (like cell fitness)
See figure 14.1 for common points where regulation of gene expression occurs in bacteria.
14.1
In bacteria, the most common way to regulate gene expression is by influencing the rate at which
transcription is initiated.
Repressor = a regulatory protein that binds to DNA and inhibits transcription, also called negative
control.
Activator = increases transcription, also called positive control.
Effector molecule = binds to a repressor or activator and influences whether the protein can bind to
the DNA.
Inducer = small effector molecule that causes transcription to increase. It can bind to a repressor
protein and prevent it from binding to the DNA, or it can bind to an activator protein and cause to
bind to the DNA.
Inducible genes = genes that are regulated by an inducer.
Corepressor = binds to a repressor protein and causes it to bind to DNA.
Inhibitor = binds to an activator protein and prevents it from binding to the DNA.
Repressible genes = genes regulated by a molecule that decreases transcription.
See figure 14.2 for binding sites on a genetic regulatory protein.
14.2
Enzymes are composed of proteins.
Enzyme adaption = the observation that a particular enzyme appears within a living cell only after the
cell has been exposed to a particular substance, it does not make the enzyme needed to metabolize
that substance.
Jacob and Manod
- The exposure of bacterial cells to lactose increased the levels of lactose-utilizing enzymes by
1000- to 10,000- fold.
- Antibody and labeling techniques revealed that the increase in the activity of these enzymes
was due to the increased synthesis of the proteins that form the enzymes.
- The removal of lactose from the environment caused an abrupt termination in the synthesis
of the enzymes.
- The analysis of mutations in the lac operon revealed that each protein involved with lactose
utilization is encoded by a separate gene.
Operon = a group of one or more genes that are transcribed from a single promotor.
Polycistronic mRNA = this is what an operon encodes, and the RNA contains the sequences of one or
more genes.
See figure 14.3a for organization of DNA sequences in the lac region of the E. coli chromosome.
-galactosidase = an enzyme that cleaves lactose into galactose and glucose. Encoded by lacZ.
Lactose permease = a membrane protein required for the active transport of lactose into the
cytoplasm of the bacterium. Encoded by lacY.
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