Lac / mal operons and gene regulation

Question 1

Induction

Answer 1

genes are expressed bc of a signal molecule

Question 2

Repression

Answer 2

gene repressed bc of a signal molecule

Question 3

when can gene expression be regulated

Answer 3

transcription, translation, and post translationally

Question 4

constitutively expressed genes

Answer 4

genes which are expressed all the time no matter what ex. polymerase subunits, ribosome components, amino acyl tRNA synthetases

level of expression CAN change, but always transcribed to some extent

Question 5

constitutively expressed genes

Answer 5

genes which are expressed all the time no matter what ex. polymerase subunits, ribosome components, amino acyl tRNA synthetases

level of expression CAN change, but always transcribed to some extent

Question 6

environmentally regulated genes

Answer 6

genes expressed at high levels only under certain environmental conditions

Question 7

inducer

Answer 7

signal molecules which causes expression to occur

Question 8

catabolic genes

Answer 8

produces enzymes necessary to break down a food source, logically would be positively controlled by the food source it needs to break down

ex. the lac operon

Question 9

anabolic genes

Answer 9

needed to synthesize a specific compound, logically negatively controlled by the compound it’s synthesizing

Question 10

operon

Answer 10

a region of bacterial DNA that contains a series of functionally related genes, transcribed from a single promoter into polycistronic mRNA

Question 11

polycistronic mRNA

Answer 11

mRNA which encodes 2 or more proteins

Question 12

components necessary to gene regulation

Answer 12

DNA regulatory region

regulatory protein

signal molecule

Question 13

DNA regulatory region

Answer 13

nucleotide sequence near or partially overlapping the promotor, ex an operator

Question 14

operator

Answer 14

a type of DNA regulatory region where the regulatory protein may bind

Question 15

where would gene coding for regulatory protein be found? how is it expressed?

Answer 15

NOT on the operon, but likely close by. usually constitutively expressed at low levels

Question 16

allosteric proteins

Answer 16

proteins which change shape/function based on whether a signal molecule (in the case of regulatory proteins) is bound to them

Question 17

positive regulation

Answer 17

regulatory protein activates gene expression by binding to the DNA regulatory region

Question 18

negative regulation

Answer 18

regulatory protein prevents gene expression by binding to the DNA regulatory region

Question 19

how does an inducer interact with a regulatory protein??

Answer 19

generally the regulatory protein would negatively control gene expression, so an inducer would bind to this and change it’s shape so that it couldn’t bind to the regulatory site and therefore the gene could be expressed

Question 20

what type of regulation occurs with the lac operon

Answer 20

expression of proteins which break lactose down are negatively controlled by a regulatory protein, but a derivative of lactose binds to this and prevents it from binding therefore induces the expression of the operon

Question 21

lacz

Answer 21

conding sequence for B galactosidase, cleaves lactose into glucose and galactose, lacZ+ is funcitonal non mutant form of the gene

Question 22

lacY

Answer 22

codes for lactose permease, transports lactose from external medium into the cell, func non mutant denoted as lacY+

Question 23

inducer of lac operon

Answer 23

allolactose

Question 24

inducer of lac operon

Answer 24

allolactose

Question 25

CRP-cAMP complex

Answer 25

positive regulator of lactose operon, bc when other sources of energy are available not necessary to use lactose, crp-camp is sensitive to this, lots of smth else not much cAMP so doesnt bind to regulatory region and rna polym doesnt blind either

cAMP binds to CRP, which bins to site near operator

therefore CRP is a positive regulator, and cAMP is an alosteric activator of CRP binding

Question 26

two ways a bacterophages can infect a cell/ processes

Answer 26

Both:
phage reaches cell and releases it’s dna inside, dna circularizes
Lytic pathway:
1. phage dna is replicated and phage proteins are synthesized, bacterial dna is fragmented
2. more phages are assembled then the cell breaks and mature phages are released

Lysogeny:
1. recombination occurs between the phage dna and bacterial dna
phage dna replicated along with bacterial dna

Question 27

when would lysogeny often occur?

Answer 27

under poor conditions, only gene from phage dna that would be expressed is that that represses transcription of other phage genes therefore entry into lytic pathway

under stress, recombination is reveresed, freeing phage dna and initiating lytic pathway

Question 28

what determines if lytic pathway or lysogeny will occur?

Answer 28

presency of the protein cro an cI

<cro, lytic pathway

<cI, lysogenic pathway

Question 29

components of an operon

Answer 29

regulator, promoter, operator, structural genes

Question 30

components of an operon

Answer 30

regulator, promoter, operator, structural genes

Question 31

the mal operon (general)

• genes
• purpose
• structure
  -regulatory protein
• what type of regulation?
  -signal molecule

Answer 31

codes for malP and malQ, enzymes which modify and break down maltose

maltose is a disaccharide/ source of energy and carbon which must be broken down by enzymes

operator upstream an close to promotor region

Regulatory protein: MalT

**positive regulation

Signal molecule: Maltose

Question 32

regulation of the mal operon

Answer 32

on their own, RNA polymerase and malT bind weakly (low/basal)

in precense of maltose - high levels of transcription of malP and malQ

Question 33

transcription of malP and malQ absence of maltose

Answer 33

low/basal

Question 34

transcription of malP and malQ in presence of maltose

Answer 34

high

Question 35

transcription of lacY and lacZ in the absence of lactose

Answer 35

low/basal

Question 36

transcription of lacY and lacZ in the presence of lactose

Answer 36

high

Question 37

summary of lac and mal

Answer 37

lac is negatively regulated by lacI, binds tightly to operator and prevents expression UNTIL signal molecule/activator allolactose is present, prevents lacI from binding thus lacY,Z,A are expressed

mal is positively regulated by malT, but this binds weakly by itself. when signal molecule maltose is present (activator), allosteric changes occur allowing malT to bind to the operator and malP,Q to be expressed