Topic 7 Flashcards
What are the 2 criteria needed in the gene regulation mechanism in bacteria?
- They must be able to recognize environmental conditions in which they should activate or repress the transcription of the relevant gene
- They must be able to toggle ON or OFF like a switch, the transcription of each specific gene or group of genes
What are constitutive genes?
Certain gene products (tRNA, rRNA, ribosomal proteins, RNA polymerase subunits) are essential components of almost all living cells
Genes that code products of this type are continuously expressed in most cells (no need to be strongly regulated)
What are inducible and repressible genes?
Inducible genes often associated with catabolic pathways
Catabolic pathways are activities of enzymes involved in lactose utilization
Repressible genes are often associated with anabolic pathways
Anabolic pathways are activities of tryptophan biosynthetic enzymes
Slide 8
What are activators and repressors?
Regulatory proteins that bind to sequence specific DNA regions
Most binding sites for repressors are termed operators
What is positive and negative regulation?
What are allosteric effectors?
Positive- an activator protein must bind to its target DNA site for transcription to begin
Negative- a repressor protein must be prevented from binding to its target DNA for transcription to begin
Allosteric effectors- bind to regulatory proteins (sensors)
Slide 9-12
What is the operon model?
Operons coordinately regulate units of gene expression
Operon- segment of DNA that encodes a multigenic mRNA as well as an adjacent common promoter and regulatory region
A single mRNA transcript carries the coding information of an entire operon
Operons containing more than one structural gene are multigenic
All structural genes in an operon are co transcribed and therefore coordinately expressed
Slide 14
What is the lactose operon in E. coli?
Related with lactose metabolism
“Lac operon”
2 enzymes required for lactose metabolism (a permease (Y) to transport lactose into cell and β-galactosidase to modify lactose into glucose and galactose
Third gene codify got another enzyme: transacetylase (not required for lactose metabolism)
All 3 genes transcribed into a single mRNA codon
Slides 15-21
What are the consequences of mutations in:
Structural genes of LacO
Inhibitor of LacO
Operator of LacO
Structural genes- disrupt the ability of cells to metabolize lactose, even when the operon is expresssed
Inhibitor- disrupts ability of cells to inhibit LacO expression (constitutively ON)
Operator- disrupts ability of cells to inhibit LacO expression (constitutively ON)
Slides 22-24
How does repression work?
Repressor binds to operator
For inhibitor and operator: Cis (strand specific) or trans (non strand specific)
Slide 25-28
How do you read genotypes from enzymatic assays?
Slides 30-31
How does operator control LacO?
Operator can only control (mediate repression) of structural genes in the same locus (in cis)
Slides 33-36
How does inhibitor (repressor) control LacO?
Inhibitor (repressor) can control (mediate repression) of structural genes in both locus (in cis and trans locus)
Inhibitor (repressor) (Is) is dominant to I+ (always repressed)
Repressor can not bind in mutated alleles
Slides 37-41
What is the role of the promoter in the LacO?
RNA polymerase contacts the promoter at specific sequences
Slides 42-43
What is catabolite repression of the LacO?
2 conditions for expressing the LacO should be met:
Lactose should be present (I-O regulation)
Glucose should be absent! For maximal metabolic and energetic efficiency
Repression of the lactose metabolizing genes in the presence of glucose is an example of catabolite repression
Works by a catabolite activation protein (CAP)
Slides 45-47
Study summary slides 48-52
Ok
