Question: What are the two main ways of controlling metabolism in bacterial cells?

Answer:

Question: What is a promoter?

Answer: a specific nucleotide sequence in the DNA of a gene that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place

Question: What is the operator, and what does it do?

Answer: in bacterial and phage DNA, is a sequence of nucleotides near the start of an operon to which an active repressor can attach. The binding of the repressor prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon

Question: What is an operon?

Answer: a unit of genetic function found in bacteria and phages, consisting of a promoter, and operator, and a coordinately regulated cluster of genes whose products function in a common pathway

Question: List the three components of an operon, and explain the role of each one.

Answer: 1. Operator: the segment of DNA that operates as the “switch”

2. Promoter: the site where RNA polymerase can bind with DNA to begin transcription

3. Genes: nucleotide sequences that specifically encode subunits of the enzyme

Question: How does a repressor protein work?

Answer: binds to the operator and blocks attachment of RNA polymerase to the promoter, preventing transcription. A repressor protein is specific for the operator of a particular operon

Question: What are regulatory genes?

Answer: a gene that codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes

Question: Distinguish inducible and repressible operons.

Answer: repressible: usually on, but can be inhibited (repressed) when a specific small molecule binds allosterically to a regulatory protein. An example is the trp operon

inducible: usually off but can be stimulated (induced) when a specific small molecules interacts with a regulatory protein. An example is the lac operon

Question: Fig 18.4

Answer: pg 354

Question: Compare and contrast the lac operon and the trp operon.

Answer: In both, the entire transcription unit is under the command of one main operator and promoter. The lac is an inducible operon, while the trp is repressible. In both, regulation involves negative control of genes, b/c operons are switched off by the active form of the repressor protein