Module 8 Flashcards
Gene Regulation
The ability to alter the expression of genes
Gene regulation can occur at three distinct points in bacteria:
- Transcription
- Translation
- Posttranslation
Regulatory Proteins
Utilized in transcriptional regulation, includes repressors (bind to DNA and inhibit transcription) and activators (bind to DNA and increase transcription) and influenced by small effector molecules
Small Effector Molecules
Bind to regulatory proteins, influence whether or not they can bind (inducers and corepressors)
Inducers
Increase transcription by either binding to activators or binding to repressors and preventing them from binding
Genes regulated by these small effector molecules are “inducible”
Corepressors
Decrease transcription by either binding to repressors or binding to activators and preventing them from binding
Genes regulated by these small effector molecules are “repressible”
Enzyme Adaptation
A particular enzyme appears in the cell only after the cell has been exposed to the enzyme substrate
Operon
Regulatory unit consisting of a few protein-encoding genes under the control of a single promoter, encodes a polycystronic mRNA sequence
DNA elements that control lac operon transcription:
- Promoter (binds to RNA polymerase)
- Operator (binds to lac repressor)
- CAP site (binds the Catabolite Activator Protein)
lac Operon Structure
i promoter > lacI regulatory gene > CAP site > lac promoter > operator site > lacZ > lacY > lacA > lac terminator
lacZ Gene
Encodes B-galactosidase which enzymatically cleaves lactose, converting into allolactose
lacY Gene
Encodes lactose permease, allows for transport of lactose across cell membrane
lacA Gene
Encodes galactoside transacetylase which acetylates lactose to prevent buildup of toxins
After B-galactosidase breaks down lactose into allolactose, it acts as an ____ and binds to ____, preventing it from binding to the DNA
inducer, lac repressor
increases transcription
lacI Gene
Encodes the lac repressor, which binds to the operator when no lactose is present
Jacob, Monod, and Pardee Experiment Results
Determined that merozygote (lacI+ on chromosomal, lacI- on F’ factor) will remain inactive when lactose is absent and activate in presence of lactose
Due to presence of active repressor protein in chromosomal gene
Loss of function in lacI vs lacO
When negative with no lactose, both are at 100% expression. With lacI+ on F’ factor both will express 200% when lactose is present, when it is not present lacI will then cut its expression to 0% while lacO will still produce 100%
Catabolite Activator Protein (CAP)
In the presence of two sugars (diauxic growth), bacteria use glucose before lactose. Glucose inhibits cAMP production and leads to lack of small effector molecules needed to start lac operon
Results of lac operator research
Discovery that lac operon has three separate activators (O1 next to promoter, O2 downstream within lacZ gene, and O3 slightly upstream of promoter)
Found that DNA loops form from binding of lac repressors; if not all bound, O1 must bind to either O2 (stronger repression) or O3 (weaker repression)
Binding of lac operators (O1 to O2 or O1 to O3) forms a ____ since operators are far apart
loop
Riboswitches can regulate transcription and translation via the formation of a ____
stem loop (terminator/anti-terminator in RNA for transcription, inhibits translation of Shine-Dalgarno RNA sequence in translation)
Gene Regulation in Eukaryotes
Can occur at any point in the transcription, RNA processing, translation, posttranslational modification process
Combinatorial Control
Most eukaryotic genes regulated by many factors, such as activators and repressors
Activators and repressors in eukaryotes can be modulated by ____
small effector molecules, protein-protein interactions, covalent modifications, also via regulatory proteins, DNA methylation, and formation of heterochromatin