Exam 3 Lecture 21

Question 1

Why is regulation important?

Answer 1

save energy; adapt to changing conditions in order to be competitive; activities of some gene products are detrimental

Question 2

What is a characteristic of a regulatory sequence?

Answer 2

symmetry involving inverted repeat sequences

Question 3

Binding of a _____ to a regulatory protein alters its binding to the regulatory sequence

Answer 3

Ligand

Question 4

cAMP is a _____

Answer 4

Inducer

Question 5

What is apo-CRP? What happens when cAMP binds?

Answer 5

apo-CRP = cAMP receptor protein but is not bound to cAMP, the ligand. When cAMP binds (2 cAMP per CRP since it is a dimer), there is 100-fold greater DNA binding affinity

Question 6

What is allosteric regulation?

Answer 6

function of a protein is altered by bindin to a small molecule, doesn’t interact with DNA but changes protein binding properties

Question 7

Ligand is a _____ or ______

Answer 7

Inducer or corepressor

Question 8

Repressors block ______

Answer 8

transcription

Question 9

Activators stimulate _______

Answer 9

transcription

Question 10

What happens when cAMP-CRP binds to DNA?

Answer 10

DNA bends to allow interaction between cAMP-CRP and RNA Pol. This physical interaction activates RNA Pol to begin transcription

Question 11

What are the components of the lac operon?

Answer 11

lacZ, lacY, lacA, lacI (has its own promoter)

Question 12

2 operator regions

Answer 12

lacO and lacOi. lacO is located upstream of lacZYA, and lacOi is located within lacI downstream of lacI promoter

Question 13

How is the lac operon kept off?

Answer 13

lacI repressor binds to lacO and lacOi to form a tetramer, engineering a DNA loop, preventiing transcription

Question 14

What is the role of allolactose?

Answer 14

Acts as inducer for lac operon; binds to LacI repessor to relieve repression and allow transcription of lac operon

Question 15

When is cAMP made?

Answer 15

Made by adenylate cyclase when the cell is starved for carbon (starved of glucose)

Question 16

2 things needed in order to transcribe lac operon:

Answer 16

Allolactose inducer binds to LacI repressor; cAMP binds to region 60 bp upstream of promoter

Question 17

What is catabolite repression?

Answer 17

when more favorable catabolite is present (glucose) that prevents expression of operon that enable catabolism of less preferred carbohydrate (lactose)

Question 18

Low level of B galactosidase means:

Answer 18

Some lactose in the cell will be converted to allolactose

Question 19

What is meant by inducer exclusion?

Answer 19

If lactose can’t even enter the cell, lac operon cannot be induced

Question 20

What happens when glucose is taken into the cell by protein IIC?

Answer 20

Immediately phosphorylated by protein IIB (which I believe is an adaptor protein as it is connected between IIC and IIA)

Question 21

When glucose is phosphorylated at its intake by IIC, which protein remains unphosphorylated? What is the downstream effect?

Answer 21

IIA is unphosphorylated –> this inhibits LacY and prevents lactose from being taken in

Question 22

What else does protein IIA do?

Answer 22

regulates adenylate cyclase to convert ATP to cAMP when glucose levels are low/absent

Question 23

How is amino acid biosynthesis controlled?

Answer 23

through transcriptional repression

Question 24

What is meant by transcriptional attenuation?

Answer 24

Lessens the amount of transcription