control of gene expression

Question 1

how does a cell determine which gene to transcribe

Answer 1

it’s controlled by sequence-specific DNA binding proteins called transcription regulators

Question 2

what do transcription regulators do

Answer 2

determine which genes to transcribe

Question 3

what do transcription regulators bind to

Answer 3

cis-regulatory sequences

Question 4

how long are cis-regulatory sequences

Answer 4

5-12 nucleotides in length

Question 5

T or F: many transcriptional regulators form dimers

Answer 5

true

Question 6

why do many transcriptional regulators form dimers

Answer 6

it helps to increase the specificity of their binding

Question 7

what protein is the trp operon regulated by

Answer 7

the tryptophan repressor protein

Question 8

what does the tryptophan repressor protein bind to

Answer 8

a cis-regulatory sequence called the tryptophan operator

Question 9

describe the trp operon when tryptophan levels are high

Answer 9

repressor binds to the operator of DNA which inhibits RNA pol from binding = no transcription = operon off

Question 10

describe the trp operator when tryptophan levels are low

Answer 10

repressor doesn’t bind to DNA, so RNA pol binds and transcription occurs = operon on

Question 11

when is the trp operon off

Answer 11

when trp levels are high

Question 12

when is the trp operon on

Answer 12

when trp levels are low

Question 13

what are the two types of transcription regulators

Answer 13

repressors and activators

Question 14

what two transcription regulators control the lac operon

Answer 14

CAP (catabolite activator protein)
Lac repressor

Question 15

what is the lac operon responsible for

Answer 15

it contains the genes involved in the metabolism of lactose

Question 16

what does Lac Z code for

Answer 16

B-galactosidase

Question 17

what does Lac Y code for

Answer 17

permease

Question 18

what does Lac A code for

Answer 18

no one knows yet

Question 19

describe what occurs when the lac operon is expressed

Answer 19

lactose can come into the cell to be broken down by B-gal

Question 20

describe the actions of the CAP for the lac operon

Answer 20

CAP binds to cAMP in order to bind to the cis-regulatory sequence of the operon

Question 21

when are cAMP levels high? when are they low?

Answer 21

high cAMP: low glucose
low cAMP: high glucose

Question 22

what glucose levels will allow CAP to bind to the lac operon

Answer 22

low glucose

Question 23

describe what happens when CAP binds to cAMP (in regards to lac operon)

Answer 23

CAP with cAMP bound will bind to RNA and help attract RNA pol to the promoter = transcription of the operon

Question 24

describe how the lac repressor works

Answer 24

when lactose is present, the repressor cannot bind to the operator = transcription occurs

Question 25

T or F: the lac repressor functions when lactose levels are low

Answer 25

true; low lactose levels = repressor functions

Question 26

we want to use some proteins therapeutically, but they’re produced in very low amounts in the eukaryotic cell. what is the solution?

Answer 26

use E coli as a factory for making them

Question 27

what is G-CSF

Answer 27

a protein we want to use therapeutically. It stimulates bone marrow to produce white blood cells and is often given to cancer patients

Question 28

describe how G-CSF is made using E coli

Answer 28

G-CSF cDNA is cloned to make a recombinant plasmid which is then transformed into E coli

Question 29

when making G-CSF using E coli, what does the plasmid contain + why

Answer 29

contains the lac promoter because we want transcription of the plasmid to occur

Question 30

when making G-CSF using E coli, why is IPTG added + what is it

Answer 30

it’s a molecular mimic of allolactose, and we add it because it inhibits the lac repressor = transcription can occur

Question 31

when making G-CSF using E coli, why do we use cDNA and not DNA

Answer 31

cDNA has no introns because it’s a copy of already processed mRNA

Question 32

when making G-CSF using E coli, describe what happens once the recombinate plasmid is in the IPTG E coli

Answer 32

proteins in E coli will come in and recognize the lac promoter, so that region will be transcribed, and eventually the protein will be made