Modulating Transcription

Question 1

What is needed for prokaryotic growth?

Answer 1

• Nutrient rich environment containing amino acids and carbohydrates
• Favourable temperatures
• Conditions can be replicated in the lab

Question 2

Housekeeping Genes

Answer 2

Genes required all the time for normal functions

• Constantly expressed for maintenance of general cellular activity
• Always being transcribed and translated!

Includes:

• Structural proteins
• Ribosomal proteins

Question 3

Regulated Genes

Answer 3

Genes that can be turned on and off on an as-needed basis

• Expressed only when needed
• Altered in a changing environment by producing enzymes/proteins that bring change in growth/division
• E.g. enzymes

Question 4

Regulating Expression of Enzymes

significance? an example?

Answer 4

• Enzymes required to metabolize nutrients
• Cells must metabolize macromolecules (carbohydrates –> ATP) when they are present in the environment
• This can be done by the regulation of gene expression of enzymes
• Example: Metabolizing lactose using beta-galactosidase requires regulating it’s gene expression

Question 5

The Glucose Effect in E.Coli Cells

Answer 5

• E.coli grown in environment w/ glucose and lactose
• Bacteria metabolize all glucose before switching to utilize lactose as a fuel source
  * Presence of glucose represses expression of lactose-metabolizing genese
• Bacteria upregulate expression of genes that produce lactose-metabolizing enzymes in presence of lac, absence of glu
  * Not synthesized when lac absent as that’s a waste of resources

Question 6

Glucose Metabolism through Lactose at Cellular Level

Answer 6

• Cell can metabolize lactose (glucose + galactose)
• β-Galactosidase: Enzyme that metabolizes lactose to produce glucose and galactose
• That glucose is used in metabolism by cell!
• β-Galactosidase produced by TURNING ON β-galactosidase gene… only when lac present and glu absent

Question 7

Francois Jacob and Jacques Monode on E.Coli and β-Galactosidase

Answer 7

How are E.Coli able to produce β-Galactosidase needed for lac metabolism?

• Observation: Production of enzyme dependent on present of lactose in environment
• Method: Measuring amt of β-galactosidase produced as (1) E.Coli grown in lactose-free medium, (2) Lactose added to medium, (3) Lactose removed from medium
• (1) constant, (2) growth, (3) constant
• Conclusion: Lactose induced expression of β-galactosidase gene

Question 8

Gene Expression

Answer 8

• Functional product of the gene is made, modified, and activated
• Controlled at 3 levels: transcriptional , translational , post-translational
• Disruption in one of these steps results in NO activated protein
• Variation of expression of genes may depend on one level of regulation

Question 9

Transcriptional Regulation

Relative to other mechanisms?

Answer 9

Controls amount of mRNA produced in the cell

• Proteins must bind to region near the beginning of gene, promoter, to increase binding of RNA polymerase
• Control of binding of proteins to promoter can ACTIVATE or INHIBIT transcription

Slowest Mechanism of Regulation

• Cell creating protein from scratch
• More prevalent with more drastic environmental changes
• β-galactosidase gene transcription controlled in E.coli…
• Results in delay of production in response to the initial exposure of bacterial cells to lactose

Most Efficient Mechanism of Regulation

• Cell does not waste energy/resources making mRNA or PPT unless it really needs to!
• E.coli cells only increase gene expression of β-galactosidase gene in presence of lac

Question 10

Translational Control

Answer 10

Initiation may or may not start…

• EUK translation initiation occurs by binding of ribosome to 5’CAP
• PROK translation initiation occurs by ribosome binding at Shine-Dalgarno sequences

Rate at which translation occurs affect amt of protein produced –> depends on stability of mRNA (mRNA degraded quickly –> little protein made)

Question 11

Post-Translational Control

Relative to other mechanisms?

Answer 11

• PPT chain folded into functional 3D structure + further chemical modifications for activation
• Regulate ability of protein to be active/inactive
• Binding substrates, driving assembly into complexes, unmasking of enzymatic domains

Fastest Mechanism of Regulation

• Allows cell to have many inactive proteins
• Once signal recieved, modification can TURN ON all inactive proteins
• Results in quick cellular response to changes in environment

Question 12

What are the Slowest, Fastest, and Most Efficient Mechanisms of Regulation?

Answer 12

Transcriptional, post-translational, transcriptional

Question 13

A change in the environment….

Answer 13

Elicits a response within the organism

• Gene regulation (of regulated genes, of course) helps prokaryotes respond and adapt