lecture 22 - prokaryote gene regulation

• How do prokaryotes coordinate the expression of functionally relevant genes?

  Through gene regulation mechanisms that vary under different conditions.
• What does a recombination frequency of 50% indicate?

  The two genes are likely to be located on different chromosomes.
• In Drosophila, what is the relationship between the slo and bw alleles?

  Both slo and bw alleles are recessive to their respective wild type alleles.
• What role does keratin play in the body?

  It helps form the tissues of hair, nails, and the outer layer of the skin.
• In which cells would you expect to find the keratin gene?


  In the hair, nails, and outer layer of the skin.
• In which cells would you expect to find the keratin protein?


  In the hair, nails, and outer layer of the skin.
• What is gene regulation?

  It is the phenomenon in which the level of gene expression can vary under different conditions.

  
• What are the important processes that gene regulation affects in bacteria?

  • Metabolism
  • Response to environmental stress
  • Cell division
• What is a repressor in gene regulation?

  A regulatory protein that binds to DNA and inhibits transcription.

  
• What is an activator in gene regulation?

  A regulatory protein that binds to DNA and increases the rate of transcription.

  
• What is negative regulation in transcription?

  Transcriptional regulation by a repressor.
• What is positive regulation in transcription?

  Transcriptional regulation by an activator.
• What is an inducer?

  A small molecule that causes the rate of transcription to increase.
• What are inducible genes?

  Genes that are regulated by inducers.
• What is a co-repressor?

  A small effector molecule that binds to a repressor, causing it to bind to DNA.
• What is an inhibitor in gene regulation?

  A molecule that binds to an activator protein and prevents it from binding to DNA.
• What is the function of the trp operon?

  It encodes enzymes involved in tryptophan biosynthesis.

  
• What happens to the trp operon when tryptophan levels are low?

  The trp operon is active and transcription occurs.

  
• What happens to the trp operon when tryptophan levels are high?

  The trp operon is repressed and transcription is inhibited.

  
• What are the components of the lac operon?

  • Promoter: signals the beginning of transcription
  • CAP site: positive regulation site of catabolite activator protein
  • Operator: negative regulation when bound by repressor protein
  • lac Z, lac Y, & lac A: protein coding genes for lactose metabolism

  
• What occurs in the absence of lactose in the lac operon?

  The repressor binds tightly to the operator, inhibiting transcription.

  
• What occurs in the presence of lactose in the lac operon?

  The repressor is inactivated by the binding of allolactose, altering the conformation of the repressor protein, and preventing it from binding to the operator site. This allows transcription to occur.

  
• What is the function of the CAP site in the lac operon?

  It is a positive regulation site for the cyclic-AMP receptor protein (CRP).

  
• How does cAMP affect the lac operon?

  cAMP binds to CRP, increasing the affinity of RNA polymerase and accelerating transcription.

  
• How does glucose affect the lac operon?

  Glucose inhibits adenylyl cyclase, preventing the production of cAMP and inhibiting CRP binding.
• What are the conditions for the lac operon to be active?

  • Lactose present
  • Glucose absent
• What are the conditions for the lac operon to be inactive?

  • Lactose absent, glucose present
  • Lactose & glucose both present
  • Lactose & glucose both absent
• Expression refers to how much a gene is transcribed (into mRNA) and translated (into protein)
• When can gene regulation occur?


  Regulation can happen at any point on the way to gene expression.
• What is an operon?


  A group of genes that are regulated together and function as a single unit, regulated by a single promoter
• Operons have three main components: operator, promoter, structural genes
• Inducer 


  A small molecule that causes the rate of transcription to increase
• What is a repressible gene?


  Gene regulated by a co-repressor or inhibitor
• Repressible operons and inducible operons are 2 types of negative gene regulation as they use repressors to regulate transcription.
• Repressible operon is one that is usually on and active, but can be switched off by the binding of a repressor to the operator as this can shift transcription off
• An inducible operon is one that is usually off, and an inducer can inactivate the repressor and turn on transcription
• Trp operon


  A repressible operon that encodes enzymes involved in tryptophan biosynthesis
• The lac operon is an example of an inducible operon