gene control

Question 1

constitutive vs inducible genes

Answer 1

cons = transcribed at all times
induc = only transcribed under centrain conditions

Question 2

what is he role of the lac operon

Answer 2

contains genes that code protens for break down of lactose

Question 3

what proteins/enzymes does lac operon form and what genes are responsible

Answer 3

lacZ = beta=galactosidase
lacY = permease
lacA = transcetylase
lacI = repressor proteins (regulatory gene)

Question 4

role of each enzyme/protein n lac operon

Answer 4

b-gal - breaksdown/cleave lactose into its two monosaccharides (galactose and glucose)
permease = allows lactose into cell (permeability)
trans = transfers CoA to lactose
repressor = binds to operon and stops polymerase binding

Question 5

what is isoprpylthiogalactoside (IPTG)

Answer 5

a gratuitous inducer
- not metabolised

Question 6

how was beta galacotsidase measured in lab 4

Answer 6

• ONPG added to mixture, reacts with B-gal to form ONP which is directly proportional to B-gal, ONP is yellow so measured absorbance at 420nm

Question 7

what happens when no lactose or glucose is added

Answer 7

• no change
• repressor is able to bind to operator site so that RNA polymerase doesn’t bind and no transcription occurs
• cAMP- CAP complex forms but still doesnt work

Question 8

what happens when lactose is added?

Answer 8

• cAMP-CAP complex forms and polymerase is able to bind
• repressor protein is inactivated so will not block operator region and RNA polymerase binds

Question 9

Explain cAMP-CAP complex

Answer 9

in absence of glucose, ATP can become cAMP (catalysed by adenylcyclase).
- cAMP binds to CAP, forms CAP-cAMP complex, this complex bidns to CAP recognitions site near promotor region
- RNA more readily binds to promotor
- if glucose is present, ATP is used in glycolysis processes and adynyl cyclase is inhibited - catabolite repression

Question 10

Explainwhat happens when glucose is introduced with lactose

Answer 10

• glucose becomes primary carbon source of energy
• lactose will inacivate repressor
• however glucose inhiibits adynyl cyclase so cAMP cannot form and RNA pol can’t find promotor region
• very minimal transcription

Question 11

what does chlormaphenicol do

Answer 11

• binds to and inhibits the 50S subunit of ribosome so translation cannot occur and proteins are not made

Question 12

What does sodium azide do

Answer 12

• antibiotic
• kills the cells

Question 13

what is lactose

Answer 13

a disaccharide that is composed on two monosaccharides, galactose and glucose

Question 14

what is a regulatory gene

Answer 14

• encodes a protein that regulates gene expression

Question 15

what is a structural gene

Answer 15

• encodes protein that is not a regulatory gene

Question 16

what is the promotor region

Answer 16

where RNA polymerase binds

Question 17

what is the operator

Answer 17

regulatory protein binding site (repressor)

Question 18

what neg regulation occurs in lac operon? what pos reg occurs?

Answer 18

neg = lac repressor
pos = catabolite activator protein (CAP)

Question 19

what are the 5 stages of eukaryotic gene regulation WILL be in exam

Answer 19

1. genomic - changes in codensation of chromatin for transcription
2. transcriptional - enhancers and silencers of genes activated
3. post-transcriptional - RNA splicing removes introns
4. translational - binding of translational repressors to alter which mRNA genes are translated
5. post-translational - phosphylation or dephosphorylation (of proteins)