Lecture 14a

Question 1

What do regulatory transcription factors do?

Answer 1

They influence the level of gene expression by enhancing or inhibiting it.

Question 1

What is transcriptional regulation?

Answer 1

When regulatory transcription factors influence the level of gene expression by inhibiting or enhancing expression.

Question 2

In both bacteria and eukaryotes, how many ways are there to control protein activity level?

Answer 2

There are 3 ways in which the activity level of a protein is controlled.

Question 3

What are the 3 ways in which protein activity level is controlled?

Answer 3

1) Transcriptional control
2) Translational control
3) Posttranslational control

Question 4

What is transcriptional control? Name two examples.

Answer 4

This refers to how much RNA is being made.

The Lac Operon and the Trp operon are examples.

Question 5

What is translational control? Name an example.

Answer 5

This refers to how heavily the mRNA is being translated.

The use of the antisense RNA to inhibit translation.

Question 6

What are operons?

Answer 6

In bacteria, there are clusters of genes dedicated to the same biochemical pathway.

Question 7

T/F: In an operon, the polycistronic mRNA shares regulation for all of these genes in the operon.

Answer 7

True!

Question 8

What is polycistronic mRNA?

Answer 8

One mRNA that encodes for multiple genes/proteins.

Question 9

In an operon, where do Shine-Delgarno sequences exist?

Answer 9

They precede the start codons of genes.

Question 10

What are Shine-Delgarno sequences?

Answer 10

These are located on operons in bacteria and are where the ribosomes will load to translate the mRNA.

Question 11

Does eukaryotic mRNA have Shine-Delgarno sequences? What are the exceptions?

Answer 11

Eukaryotic mRNA does NOT have Shine-Delgarno sequences EXCEPT in mitochondrial DNA/mRNA and Chloroplast DNA/mRNA.

Question 12

What is catabolism?

Answer 12

The breakdown of a substance.

Question 13

What do we mean when we say catabolism is inducible?

Answer 13

We only breakdown a substance for use when we need to. This is for efficiency.

Question 14

In E. coli and other bacteria, what does the Lac Operon do?

Answer 14

It encodes 3 enzymes that catabolize lactose.

Question 15

When Lactose is not available to be metabolized, what happens?

Answer 15

The lac operon is shut down by the lac repressor binding to the lac Operator and blocking transcriptional activation.

Question 16

What encodes the lac repressor protein?

Answer 16

lacI

Question 17

What does lacI do?

Answer 17

Encodes a repressor protein that binds to the operator.

Question 18

What type of protein is the lacI protein?

Answer 18

A diffusible protein that binds to the lacO site.

Question 19

What is the lacO site?

Answer 19

This is the lac operon operator site.

Question 20

If a repressor protein is bound to lacO, what does this say about the presence of lactose?

Answer 20

There is NOT lactose available to be metabolized.

Question 21

Generally speaking, when is the Lac operon on?

Answer 21

The Lac operon is only on when Lactose is the most efficient carbon source available.

Question 22

What is typically the most efficient carbon source? What effect does its presence have on the Lac operon?

Answer 22

Glucose is the most efficient carbon source.

If Glucose is available, the Lac operon will be turned off.

Question 23

What happens when both lactose and glucose are available?

Answer 23

A small portion of Lactose is spontaneously converted to allolactose, which binds to the lac repressor, inactivating the repressor so it cannot bind to the operator.

Question 24

Describe the level of transcription when lactose and glucose are available.

Answer 24

There is a basal or low-level of transcription of the lac operon taking place.

Question 25

Why is there a low-level of lac operon transcription when lactose and glucose are both present?

Answer 25

The glucose is used first. The lac operon is transcribed only slightly because the CAP protein needed for high levels of transcription is inactive when CAP is by itself.

Question 26

If there is a lack of CAP binding, what does this say about glucose and lactose levels?

Answer 26

Glucose and lactose must both be present.

Question 27

What happens when there is no glucose but there is lactose?

Answer 27

The absence of glucose causes cyclic AMP (cAMP) to accumulate. cAMP binds to the CAP protein, which forms a complex that will activate the Lac Operon as long as the Lac repressor is also absent.

Question 28

What does the cAMP-CAP complex do?

Answer 28

CAP binding enhances the binding of RNA polymerase to the promoter.

Question 29

What is the binding site for the cAMP-CAP complex called?

Answer 29

The CAP site.

Question 30

When there is a high rate of transcription, what does this say about glucose and lactose levels?

Answer 30

Glucose is absent and lactose must be present.

Question 31

What is Anabolism? Is it inducible or repressible?

Answer 31

The biosynthesis of a substance. It is repressible meaning that the cell will keep making components unless it has enough, then it will be repressed.

Question 32

What happens when the amino acid tryptophan level is low?

Answer 32

The entire Trp operon is transcribed in order to synthesize tryptophan.

Question 33

How many enzymes does the trp operon have?

Answer 33

It includes 5 enzymes.

Question 34

What happens when the amino acid tryptophan levels are high?

Answer 34

The Trp operon will be repressed.

Question 35

Describe the mechanism for Trp operon repression.

Answer 35

The trpR gene produces a repressor trpR protein. This will bind to tryptophan to form an active complex which binds to the operator to repress it.

Question 36

What acts as the repressor and co-repressor in tryptophan repression?

Answer 36

The trpR protein is the repressor. Tryptophan is the co-repressor.

Question 37

What is a co-repressor?

Answer 37

A small molecule that binds to a repressor, which is usually a protein.

Question 38

When will tryptophan act as a repressor?

Answer 38

Only when we have sufficient tryptophan that we don't need to produce anymore.

Question 39

T/F: The trpR protein is active by itself.

Answer 39

False! It is inactive unless it is bound by its co-repressor, tryptophan.

Question 40

What is the most common method of genetic regulation in bacteria?

Answer 40

Predominantly at the level of transcription.

Question 41

T/F: Translational control is more common than transcriptional control.

Answer 41

False! Transcriptional control is more common than translational control.

Question 42

Describe the action of a translational regulatory protein.

Answer 42

A protein can bind outside the start codon and act as a translational repressor to prevent it from being translated.

Question 43

T/F: A translational regulatory protein can only bind to one place on the mRNA.

Answer 43

False. The protein can bind on multiple places, such as the 5' end and start codon, to prevent translation.

Question 44

What is the Antisense RNA?

Answer 44

It is another RNA that can bind to the mRNA to prevent translation by preventing the ribosome from assembling and binding to the 5' of the mRNA.

Question 45

What is an example of using Antisense RNA to inhibit translation?

Answer 45

Regulating the amount of water in a bacterial cell (osmoregulation).

Question 46

What produces the Antisense RNA?

Answer 46

The micF gene produces the antisense RNA.

Question 47

What does micF do?

Answer 47

Binds to the ompF RNA to prevent translation and reduce pores that bring water into the cell.

Question 48

What is an example of posttranslational regulation?

Answer 48

A common mechanism to regulate the activity of allosteric enzymes is feedback inhibition.

Question 49

What are allosteric enzymes?

Answer 49

Enzymes that can exist in different shapes to be either active or inactive.

Question 50

What is feedback inhibition?

Answer 50

This is when the final product will go back and inhibit the first enzyme by binding to the regulatory site.

Question 51

What are the sites in an allosteric enzyme? What enzyme in the feedback loop would this be?

Answer 51

It has a catalytic and regulatory site to be either active or inactive. Enzyme 1 is an allosteric enzyme.