BIOM-360 Lecture Notes - Lecture 25: Lac Operon, Trp Operon, Lac Repressor
2 May 2018
School
Department
Course
Professor
Which is true regarding translation in bacteria?
Translation begins with the formation of the 30S initiation complex.
Translation ends when the Shine-Dalgarno sequence is reached.
Shine-Dalgarno is at the start.
Anytime you see Shine, you’re at the start.
The 70S ribosome is composed of 20S and 50S subunits.
Should be 30S and a 50S.
All of the above.
Negative Control of Lactose (lac
) Operon
Inducible genes
3 structural genes coding for lactose uptake and metabolism
Remember that 3 is the magic number here. 3 shows up a lot.
Lac
repressor (lacl)
binds operator
Inhibits transcription
Everybody likes glucose because it’s easy to break down for energy. Lactose is another sugar that is
similar, another nice treat for your bacteria.
Enzymes normally not produced unless lactose present.
Remember: An operon consists of a structural gene, a promoter, and an operator.
Regulation of the lac
operon by the lac
repressor (p.327).
Positive Control of the lac
Operon
Regulated by catabolite activator protein (CAP).
Regulates in response to presence or absence of glucose.
Multiple levels of regulation.
The lac mechanism shows us multiple levels of regulation.
We want to conserve energy and conserve resources.
The Tryptophan (trp
) Operon
Consists of 5 structural genes which code for enzymes needed to synthesize tryptophan.
More strenuous than 3 structural genes.
Negative control of repressible genes by trp
repressor.
Remember that it goes by negative control!
Operon only functions in the absence of tryptophan.
The Arabinose (ara
) Operon
Transcriptional control by a protein (AraC) that acts both positively and negatively.
No transcription when arabinose is absent.
Document Summary
Translation begins with the formation of the 30s initiation complex. Translation ends when the shine-dalgarno sequence is reached. Anytime you see shine, you"re at the start. The 70s ribosome is composed of 20s and 50s subunits. 3 structural genes coding for lactose uptake and metabolism. Remember that 3 is the magic number here. Everybody likes glucose because it"s easy to break down for energy. Lactose is another sugar that is similar, another nice treat for your bacteria. Remember: an operon consists of a structural gene, a promoter, and an operator. Regulation of the lac operon by the lac repressor (p. 327). Regulates in response to presence or absence of glucose. The lac mechanism shows us multiple levels of regulation. We want to conserve energy and conserve resources. Consists of 5 structural genes which code for enzymes needed to synthesize tryptophan. Negative control of repressible genes by trp repressor. Operon only functions in the absence of tryptophan.
