Lecture 37

Question 1

Why does gene expression need regulation?

Answer 1

It is needed to ensure that only the necessary proteins are translated and resources are conserved.

Question 2

What are the ways in which genes are regulated?

Answer 2

1. gene copy number
2. level of mRNA transcription
3. level of mRNA transport/process
4. translation
5. control of rate of protein degradation

Question 3

What is the Lac Operon?

Answer 3

Encodes genes that are involved in metabolizing lactose as an alternative energy source for E. Coli when glucose levels are low

Question 4

Is the Lac Operon always on?

Answer 4

No. It is off because glucose is the preferred fuel source when it is present.

Question 5

What are the 3 genes encoded by the lac operon needed for lactose metabolism?

Answer 5

Lac Operon Z, Y,A

Question 6

What does Lac Z encode?

Answer 6

Beta-galactosidase

Question 7

What does Lac Z do?

Answer 7

Hydrolyzes lactose into sugar monomers, glucose and galactose, necessary such that they can enter into the glycolytic pathway

Question 8

What does Lac Y encode?

Answer 8

lactose transport protein

Question 9

What does Lac A encode?

Answer 9

transacetylase

Question 10

What does Lac A do?

Answer 10

Not known

Question 11

What happens when lactose is present in E Coli.?

Answer 11

a minor side reaction also occurs to produce allolactose

Question 12

What does allolactose do?

Answer 12

It signal the cell that lactose is present and the genes should be expressed.

Question 13

What is IPTG?

Answer 13

Like allolactose but artificial for lab use

Question 14

Where are the 3 genes located?

Answer 14

Adjacent to the promoter region near the LacO and CRP-binding site

Question 15

What does LacI do? Where is it located?

Answer 15

It is upstream and encodes the LacI repressor protein. When LacI is active, it binds to the operator region and blocks transcription

Question 16

What does cAMP repressor protein bind to? What does it do?

Answer 16

Binds upstream of the promoter and activates transcription by responding to cAMP levels

Question 17

Who proposed the original model of the Lac operon?

Answer 17

Francois Jacob and Jaques Monor

Question 18

What is the LacI operon?

Answer 18

It is the regulatory gene (or repressor) that binds to the operator to block transcription and now allow RNA Pol to bind

Question 19

What is the inducer in the lac operon?

Answer 19

It is the allolactose because it binds to the LacI(repressor) to allow transcription

Question 20

What is negative control?

Answer 20

The repressor keeping the RNA Pol away and blocking transcription

Question 21

How does binding and lac repressor protein regulate transcription?

Answer 21

They regulate transcription in a pos or neg way

Question 22

What are the domain of transcription factors?

Answer 22

One for DNA binding and the other for activation

Question 23

How do transcription factors bind?

Answer 23

They bind to DNA by recognizing base-pair sequence via major grooves. Happens through exposed bases

Question 24

What is the form of DNA binding?

Answer 24

Alpha-helix that sits on major groove.

Question 25

What are the motifs in DNA binding proteins?

Answer 25

helix-turn-helix, zinc finger, or leucine zipper

Question 26

What is the motif of the lac repressor protein?

Answer 26

It is a helix-turn-helix and has 2 alpha helices

Question 27

What is the structure of the lac repressor?

Answer 27

The recognition helix lies in the major groove of DNA making H-bonds with the bases recognizing a specific nucleotide sequence in the operator region

Question 28

What is positive control?

Answer 28

It is when glucose is low and cAMP is abundant. cAMP binds to CAP. Both bind to the promoter and CRP activates transcription. This happens from cAMP not low glucose

Question 29

What happens if there are high levels of glucose?

Answer 29

There is low cAMP and even if there is allolactose the alc operon is not turned on bc there is plenty of glucose. E coli uses this

Question 30

What is the CRP-DNA complex?

Answer 30

It is a structure that forms when CRP and DNA binds to turn on genes in the lac operon

Question 31

What is the structure of CRP-DNA complex?

Answer 31

It is a helix-turn-helix like the lac repressor

Question 32

What is true about CRP-DNA complex?

Answer 32

Binding of cAMP changes the conformation to allow specific binding of DNA and activate transcription

Question 33

What is a biosynthetic operon?

Answer 33

tryptophan

Question 34

How does tryptophan work?

Answer 34

It works by the genes making it. When it is low, it means the repressor is inactive, and RNA binds to make more tryptophan

Question 35

What happens when there is high tryptophan?

Answer 35

It acts as a corepressor and binds to repressor to activate and bind to operon. This block RNA pol and makes no more tryptophan

Question 36

What happens to the leader?

Answer 36

It forms a stem loop similar to rho independent. It also forms internal base pairing

Question 36

What is the structure of tryptophan?

Answer 36

helix turn helix

Question 37

How many genes are need for tryptophan?

Answer 37

5 genes

Question 37

What is true about 2-3 base pairing?

Answer 37

It is non terminating

Question 38

What does the leader gene do in tryptophan?

Answer 38

It regulates the gene expression through attenuation

Question 39

What is true about 3-4 pairing?

Answer 39

It is terminating

Question 40

What happens where is low levels of tryptophan? What do the ribosomes do?

Answer 40

They stall trp codons to prevent the formation of a loop and forms anti-terminating structures. This allows RNA Pol to keep going

Question 41

What happens where is high levels of tryptophan? What do the ribosomes do?

Answer 41

The ribosome allows for passing of codons and allows pin to form. This causes RNA Pol to stop and transcription ends

Question 42

What is true about lactose?

Answer 42

It is inducible to be turned on and off

Question 43

How does the lac repressor protein work?

Answer 43

It binds to the operator region, downstream and block transcription