Gene Regulation

Question 1

Do prokaryotic genomes contain introns?

Answer 1

No

Question 2

Can transcription and translation occur simultaneously in prokaryotes?

Answer 2

Yes.

Question 3

What mechanism allows prokaryotes to translate multiple genes from the same mRNA transcript?

Answer 3

Operons: clusters of genes under the control of a single promoter.

Question 4

What is the lac operon?

Answer 4

A collection of genes that regulate the metabolism of lactose in E. coli.

Question 5

What is the role of lacI?

Answer 5

lacI is a repressor gene that regulates binding of RNA polymerase to lacO (the operator).

Question 6

How does the addition of lactose result in the subsequent metabolism of lactose?

Answer 6

A small amount of added lactose becomes transformed into allolactose, which is an inducer that prevents the binding of the repressor to lacO.

Question 7

What is polycistronic mRNA?

Answer 7

mRNA that encodes multiple genes.

Question 8

What is bacterial conjugation?

Answer 8

A mechanism of horizontal gene transfer in bacteria.

Question 9

What are cis-acting elements?

Answer 9

Elements encoded on the same chromosome as the gene they regulate (promoters, enhancers)

Question 10

What are trans-acting factors?

Answer 10

Factors that may be encoded on different chromosomes from the genes they influence (transcription factors, polymerases)

Question 11

What is the lacI s mutation? (superrepressor)

Answer 11

A mutation of the repressor that cannot bind the inducer, thus lacZ (which produces b-galactosidase) is always repressed.

Question 12

What is the dominance relationship between lacI alleles?

Answer 12

lacI s > lacI + > lacI -

Question 13

What does it mean if a gene is constitutive?

Answer 13

The gene is always expressed.

Question 14

What does it mean if a gene is inducible?

Answer 14

The gene can either be expressed or repressed.

Question 15

Do nucleosomes inhibit transcription?

Answer 15

Yes, it is more difficult for polymerases to bind promoters when genetic information is tightly wrapped in nucleosomes.

Question 16

What is heterochromatin?

Answer 16

Chromatin that is not transcriptionally active.

Question 17

What is euchromatin?

Answer 17

Chromatin that contains sites of transcriptional activity.

Question 18

What is a promoter?

Answer 18

It is where basal transcription factors and RNA polymerase II binds, defining the site of transcription initiation.

Question 19

Do genes typically have more than one promoter?

Answer 19

No.

Question 20

Where is the promoter located?

Answer 20

Upstream, very close to the coding region.

Question 21

What is one example of a promoter sequence?

Answer 21

A TATA box.

Question 22

What is an enhancer?

Answer 22

A region containing binding sites for many different transcription factors allowing for finely tuned transcription.

Question 23

Where are enhancers located?

Answer 23

Either upstream or downstream of the gene, sometimes thousands of kb away.

Question 24

Can one enhancer influence the expression of more than one gene?

Answer 24

Yes.

Question 25

What is the enhanceosome?

Answer 25

The complex of promoter, mediator, enhancer, and transcription factors that collectively recruit transcriptional machinery to begin gene expression.

Question 26

What are insulator elements?

Answer 26

DNA sequences which bind specialized proteins, thereby limiting the promoters that a given enhancer can influence.

Question 27

What is positive gene regulation?

Answer 27

Regulation that results in increased expression of genes.

Question 28

What is negative gene regulation?

Answer 28

Regulation that results in decreased expression of genes.