Lab 4

Question 1

Bacteria have mechanisms in place that allow for certain genes to be expressed only when the conditions warrant their expression.

Answer 1

Most often this gene regulation is

Question 2

operon

Answer 2

consists of a set of structural genes and the regulatory sequences that control the expression of the genes.

Question 3

The set of genes in an operon are under the control of

Answer 3

a single promoter and are transcribed as a single mRNA.

Question 4

Operons can exhibit ______________, depending on whether their regulator is a repressor or activator, respectively.

Answer 4

negative or positive control

Question 5

Additionally, an operon can be _________, meaning that its structural genes are only transcribed in the presence of a certain molecule, or it can be _________, meaning its structural genes are only transcribed in the absence of a certain molecule

Answer 5

inducible, repressible

Question 6

lac operon, which contains structural genes that encode enzymes that play a role in

Answer 6

breaking down the sugar lactose.

Question 7

Z gene encodes the enzyme

Answer 7

β-galactosidase,

Question 8

Y gene codes for

Answer 8

Permease, transport protein that carries lactose into cell to be metabolized

Question 9

Like all genes, the Z and Y gene can only be transcribed when an ______________. This is accomplished when a ____________ binds to a regulatory sequence, called the _________, that overlaps with the promoter.

Answer 9

RNA polymerase binds to their promoter.

repressor protein,

operator

Question 10

What inactivates the repressor?

Answer 10

Lactose! Lactose binds to the repressor, causing it to change shape so that it can no longer bind to the operator. This allows RNA polymerase to bind to the promoter and transcribe the Z and Y genes.

Question 11

Note that the gene that encodes the repressor (the I gene) is not actually a part of the operon, although its protein product, the repressor, affects the operon.

Question 12

I represents the

Answer 12

repressor gene,

Question 13

P represents the

Answer 13

promoter of the Z and Y genes,

Question 14

O represents the

Answer 14

operator,

Question 15

If the repressor protein (the I gene) is mutated and unable to bind to the operator (I–P+O+Z+Y+),

Answer 15

RNA polymerase will bind to the promoter and turn the Z and Y genes on even if lactose is absent.

Question 16

There exists another repressor mutation, called a superrepressor (IS).

Answer 16

Unlike the previously mentioned mutant repressor, the protein product of the superrepressor still maintains the ability to bind to the operator; however, it is unable to be inactivated by lactose. Therefore, in the presence of lactose, a lac operon with the genotype ISP+O+Z+Y+, would not be able to transcribe the Z and Y genes because the superrepressor protein remains active and bound to the operator.

Question 17

Another possible mutation could exist in the operator sequence (Oc), and if all other sequences are normal,

Answer 17

the repressor protein, even though it is not mutated, will not be able to bind to the operator sequence because it can not recognize the mutant sequence