Review of Prokaryotic Gene Expression

Question 1

List two examples of types of cells that can be created through undifferentiated stem cells.

Answer 1

Neuron and Red Blood Cells

Question 2

How is prokaryotic transcription regulated? What is the name of the enzyme?

Answer 2

It is controlled by a simple mechanism that controls transcription by RNA polymerase

Question 3

How many RNA polymerases are in eukaryotes?

Answer 3

Three

Question 4

What kinds of proteins recognize promoter elements (-10, -35)?

Answer 4

Sigma factors.

Question 5

What is the function of sigma factors when they recognize promoter elements?

Answer 5

They load RNA polymerase at the start site.

Question 6

Describe General Transcription Factors (Eukaryotes) and their function.

Answer 6

They are involved in a process of recognition of promoter elements and assembly of pre-initiation complex, then load the RNA polymerases.

Question 7

Name the two “things” responsible for the loading and release of RNA polymerase?

Answer 7

Activators and repressors

Question 8

The lac operon is a good example of a _____________?

Answer 8

Regulated prokaryotic promoter. The Lac operon and Trp operon are both promoters regulated by activators and repressors, specifically the lac operon repressed by lac I and activated by CAP.

Question 9

What activates the lac operon to bind it next to a promoter and recruit the RNA polymerase?

Answer 9

An activator protein (CAP) - Catabolite Activator Protein

Question 10

What is the lac operon repressed by?

Answer 10

A repressor protein (Lac Repressor)

Question 11

Describe the level of mRNA transcription with low lactose and high glucose (low cAMP).

Answer 11

No mRNA transcription. The lactose must fill in the spaces of the repressor in order to move it away.

Question 12

Describe the level of mRNA transcription with high lactose and high glucose (low cAMP).

Answer 12

There is low transcription

Question 13

Describe the level of mRNA transcription with high lactose and low glucose (high cAMP).

Answer 13

There is high transcription. cAMP activates cAMP and lactose represses the repressor so it does not sit on the DNA so that it can be transcribed to mRNA.

Question 14

Where does RNA polymerase bind too? What position?

Answer 14

-10 position relative to the transcription initiation site.

Question 15

RNA polymerase requires what kind of factor to initiate transcription? What position does this lay on?

Answer 15

Requires a sigma factor. The sigma factor associates with the -30 position. The -10 and the -30 DNA elements act as basal elements found in promoters.

Question 16

Is CAP an activator or repressor?

Answer 16

Activator. It binds to the CAP site.

Question 17

Where does the lac l repressor bind too?

Answer 17

The lac repressor binds to the “operator” binding site instead of lactose. It replaces the operator in the operator binding site.

Question 18

What happens when the lac repressor binds to the binding site?

Answer 18

The lac repressor takes the place of the operator and RNA polymerase cannot begin the transcription process and therefore no mRNA transcription occurs.

Question 19

Where does lactose bind do?

Answer 19

Lactose binds to the Lac repressor. Usually, Lac I will bind to DNA downstream of the transcription initiation site and prevent transcription by RNA polymerase.

Question 20

When there is (+) lactose and (+) glucose (low cAMP), describe the level of transcription.

Answer 20

Low (minimal) transcription when there is high lactose and high glucose (low cAMP).

Question 21

What is CAP activated by?

Answer 21

CAP is activated by cAMP.

Question 22

When is cAMP produced?

Answer 22

cAMP is produced in the absence of glucose and presence of lactose.

Question 23

Where does CAP bind to and what happens?

Answer 23

CAP binds to DNA upstream of the transcription initiation site and stimulates the recruitment of RNA polymerase.

Question 24

Describe the level of transcription when there is high cAMP.

Answer 24

High transcription.

Question 25

In the absence of glucose (high cAMP, CAP binds to the promoter) and the presence of lactose (Lac I does not bind to the promoter) the Lac operon is _______.

Answer 25

The lac operon is EXPRESSED.

Question 26

What is the TRP promoter regulated by?

Answer 26

Activators and repressors.

Question 27

If tryptophan is limiting in the cell, transcription proceeds to ____________. mRNA for the expression of enzymes for synthesis of tryptophan are produced.

Answer 27

Proceeds to the END OF THE OPERON.

Question 28

If the concentration of tryptophan is high, transcription is arrested (soon/far) __________ after initiation. Is mRNA produced?

Answer 28

Soon. No mRNA is produced.