Gene Control- Prokaryotic

Question 1

how do prokaryotic cells conserve energy and resources?

Answer 1

1. only transcribing genes when necessary
   a. don’t make mRNA for tryptophan producing enzymes if tryptophan can be absorbed from environment
2. only producing proteins when needed a. don’t need lactose digesting enzymes if no lactose is present

Question 2

prokaryotic gene control

Answer 2

Conserves Energy and Resources 
control enzymes already in cell 
control production of enzymes
negative and positive control 
operon models
regulatory genes

Question 3

how do prokaryotic cells control enzymes already in the cell

Answer 3

post translation control

1) allosteric enzymes (activated or inhibited)
2) feed back inhibition: end product of anabolic path is the inhibitor
3) adjustment to short term changes

Question 4

how do prokaryotic cells control of the production of enzymes

Answer 4

transcription control

1) control transcription of genes
2. slower/longer lasting effects: more stable environment

Question 5

how do they control transcription of genes

Answer 5

a. repressors bind to operators and stop transcription
b. enhancers bind to promotor to speed
transcription

Question 6

negative control

Answer 6

1) negative slows or stops function
2) feed back inhibition (allosteric enzymes)
3) repressors blocking transcription (gene control)

Question 7

positive control

Answer 7

1) SPEEDS up production
2) just allowing production does not count!!
3) Enhancers bound to promoter
4) allosteric activators

Question 8

operon model

Answer 8

clusters of functionally related genes controlled as a group (3 parts)

Question 9

three parts of operon model

Answer 9

1. DNA code for the genes
   2) promotor – stretch of DNA before genes
   a. attracts RNA polymerase
   b. needed to start transcription
   3) operator – DNA sequence near promotor
   a. binding site for repressor protein

Question 10

regulatory genes

Answer 10

make repressors found up stream from operon they regulate

Question 11

trp

Answer 11

tryptophan amino acid

Question 12

trp operon

Answer 12

1) Repressible operon bcs it is normally active

2) genes make trp

Question 13

low trp level in cell

Answer 13

operon active

a. repressor is inactive
b. promoter is open to RNA polymerase
c. genes to make trp are copied

Question 14

high trp level in cell

Answer 14

High trp level in cell : operon repressed

a. trp repressor is allosteric
1. binding to trp activates repressor
2. active repressor binds to operator
3. blocks RNA polymerase
4. genes not transcribed

Question 15

lactose

Answer 15

(galactose + glucose)

Question 16

lac operon

Answer 16

Inducible operon : usually off
a. repressor is active unless lactose bound to it
2. genes make
a. β-galactosidase cleaves lactose in 1/2
b. permiase membrane transport protein for lactose
c. third gene
unknown

Question 17

lac operon in the prescence of lactose

Answer 17

lactose binds to allosteric repressor

1) inactivates repressor
2) Repressor releases operator
3) RNA polymerase copies all 3 genes

Question 18

positive control of lac operon

Answer 18

1. lac operon is an inducible operon = can be activated
2. lac operon exhibits positive control = can be speeded up
3. If glucose is present E. coli prefer to use it

Question 19

If glucose is present E coli prefer to use it, process

Answer 19

a. lack of glucose causes E. coli to speed up use of lactose
b. lack of glucose causes build up of cAMP (cyclic AMP) = signal molecule
c. cAMP signals speed up operon translation
d. cAMP binds to regulatory protein CAP
e. build up in glucose in cell causes lack of cAMP so CAP becomes inactivated

Question 20

what happens when cAMP binds to regulatory protein cap

Answer 20

I. CAP becomes active
ii. CAP binds to start of promotor
iii. Makes promotor more attractive to RNA
polymerase

Question 21

repressible operons

Answer 21

a) repressor inactive w/o allosteric binding
b) normally on
c) usually anabolic

Question 22

inductible operons

Answer 22

a) repressor active unless bound
b) normally off
c) usually catabolic