bio18

What structural genes are included in lac?

lacZ lacY lacA

Is trp inducible or repressible?

repressible

LacY

codes for a permease to allow lactose to enter the cell.

Is trp anabolic or catabolic?

Anabolic Synthesizes tryptophan from precursors

What advantages are gained by having genes organized into operons?

As they are needed, both systems are set up to simultaneously turn on (or off) all of the genes required in a metabolic pathway. This is much more efficient than having each gene under independent control.

How are the lac and trp operons similar (in structure, function, or both)?

Both have regulatory genes that produce repressor proteins that can interact with the operator and shut down transcription of the structural genes.

Is lac anabolic or catabolic?

Catabolic Hydrolyzes or breaks down lactose(a disaccharide) into glucose and galactose (two sixcarbon surgars)

LacZ

codes for the -galactosidase enzyme, which digest lactose into glucose and galactose.

Under what circumstances would the trp operon be "on"versus "off"?

The trp operon would be off when excess tryptophan is readily available to the cell. It would be on at all other times.

LacA

codes for transacetylase. Its function is unclear

What regulatory genes are associated with the operon lac?

lacI promotor, CRP binding site operator

What are the key differences between the lac and trp operons

The lac operon is inducible; the presence of lactose induces production of the enzymes needed for lactose digestion. The trp operon is repressible; it is ordinarily on, producing tryptophan, which is needed for protein production by the cells. It is turned off or repressed only when an excess of tryptophan is available to the cell. The lac operon is controlled by both a regulatory protein, which interacts with the operator and blocks RNA polymerase action, and a CRP site. RNA polymerase does not attach effectively to the operator unless CRP (complexed with cAMP) is attached at the CRP site. Once attached, it enhances the interaction of RNA polymerase with the promoter region. cAMP levels in cells tend to be low when glucose is present. As a result, even if lactose is present at relatively high levels, this second control keeps production of the enzymes for digesting lactose at very low levels if glucose is also present in the cells.

Under what circumstances would the lac operon be "on" versus "off"?

The lac operon would be off when there is no lactose in the cell. The lac operon would be on when lactose is present and there is little or no glucose in the cell. However, the lac operon would be off (or operating at very low levels) even when lactose is present if sufficient glucose is simultaneously present

For lac, The repressor protein becomes active when it interacts with:

The repressor is active until it complexes with lactose (or allolactose). Then it becomes inactive.

For trp, The repressor protein becomes active when it interacts with:

The repressor is inactive until it complexes with excess tryptophan in the cell. Tryptophan changes the configuration of the repressor, and it is capable to binding to the operator and stopping transcription of the enzymes that synthesize or make tryptophan.

For lac, Is the repressor protein produced in active or inactive from

The repressor protein is produced in its active form. (The active form binds to the operator and stops transcription of the structural genes)

For trp,Is the repressor protein produced in active or inactive from

The repressor protein is produced in its inactive form.

tryA tryB tryC tryD tryE

These five genes code for the five enzymes required to convert a precursor molecule to tryptophan (one of the amino acids required for protein synthesis)

Is lac inducible or repressible?

inducible

what functions does each serve? for lac

lacI produces an active repressor protein that binds to the operator in the absence of lactose. The promotor is the site where RNA polymerase binds to the DNA. Binding of RNA polymerase is enhanced when cAMP interacts withCRP and the complex bind at the CRP site on the promotor region. As a result, the enzymes for lactose digestion are produced only when needed and only when glucose is not present.

what functions does each serve? for trp

trpR produces an inactive repressor protein that binds to the operator only when complexed with excess tryptophan. RNA polymerase binds at the promotor site and transcribes the genes for making tryptophan as long as tryptophan is not is excess

What regulatory genes are associated with the operon trp?

trpR promoter, operator

What structural genes are included in trp?

tryA tryB tryC tryD tryE