Constitutive Genes
i) Constant levels of expressions
c) Important for cellular processes such as
i) Metabolism
ii) Response to environmental stress
iii) Cell division
Regulation can occur at any point on the pathway to gene expression
Transcriptional level: whether or not to make the protein
Translational: can bind to message and prevent the process (physical blockage in RNA)
Post-translational
Transcriptional Regulation
Most common way to regulate gene expression in bacteria by influencing the initiation of transcription
Transcriptional regulation involves the action of two main types of regulatory proteins
(1) Repressor ? Bind to DNA and inhibit transcription
(2) Activator ? Bind to DNA and increase transcription
(a) Regulation via activator protein is termed positive control
ii) Small effecter molecules effect transcription
(1) Inducer: effecter molecule t
These molecules can also inhibit transcription in two ways
(1) Corepressor: small molecule that binds to a repressor protein, causing the protein to bind DNA
(2) Inhibitor: Binds to an activator protein and prevents the protein from binding to DNA
(3) Genes they regulate are termed repressible genes
The Phenomenon of Enzyme Adaptation Is Due to the Synthesis of Cellular Proteins
i) Enzyme adaptation refers to the observation that a particular enzyme appears within a living cell only after the cell has been exposed to the substrate for that enzyme. When a bacterium is not exposed to a substrate, it does not make the enzymes needed
Jacob and Monod focused on lactose in E. coli. Key observations:
(1) The exposure of bacterial cells to lactose increased the levels of lactose utilizing enzymes by 1,000 to 10,000
(2) Antibody labeling techniques revealed that the increase in the activity of these enzymes was due to the increased synthesis of the enzy
The lac Operon Encodes Proteins Involved in Lactose Metabolism
i) In Bacteria genes form together in a operon: group of two or more genes under the transcriptional control of a single promoter. An operon encodes a polycitronic RNA - RNA that contains the sequences for two or more genes.
(1) Operons occur in bacteria
The lac Operon Is regulated by a Repressor Protein
i) The action of a small effector molecule is called allosteric regulation, allosteric proteins have at least two binding sites. The effector molecule binds to the proteins allosteric site, which is a site other then the two active sites.
ii) Mechanism of
The Regulation of the Lac Operon Allows a Bacterium to Respond to Environmental Change
i) Small levels of proteins encoded by genes within the lac operon are continuously made, this along with the conditions where lactose in available in the environment and a leaky cytoplasm, allow for an increased concentration of lactose being transported
The LacI Gene Encodes a Diffusible Repressor Protein (EXP 14A)
i) Alternate hypothesis to explain how lacI- mutation could cause constitutive expression of the lac operon: correct explanation is the lac- mutation eliminates the function of the lac repressor protein, which prevents the protein from inhibiting the lac
Further Studies Have Revealed That the lac Operon Has _____ operator sites for the lack repressor
three
The trp operon is regulated by a repressor protein and also by attenuation
i) Attenuation can occur in bacteria because transcription and translation are coupled
ii) Bacterial ribosomes quickly attach to the 5' end of mRNA soon after it's synthesis begins via RNA polymerase. During attenuation transcription begins but is termina
Inducible Operons encode catabolic enzymes and repressible operon
anabolic enzymes.
Translation and Post-translational regulation
Refers to the functional control of proteins that are already present in the cell rather then regulation of transcription or translation.
Repressor Proteins and Antisense RNA can inhibit translation
i) A transitional regulatory protein recognizes sequences within the mRNA, in most cases translational proteins act to inhibit translation, these are termed translational repressors. When translational binds to mRNA it can inhibit translational initiation
b) Posttranslational regulation can occur via feedback inhibition and covalent modifications
i) A common mech to regulate the activity of metabolic enzymes is feedback inhibition
(1) Convert precursor molecules to a particular product, then the final product in a metabolic pathway then inhibits an enzyme that acts early in the pathway
ii) Alloste