Topic 10: Prokaryotic Gene Regulation- Lac Operon

Question 1

Transcriptional regulation in bacteria is relatively simple because it

Answer 1

involves a single activator or repressor protein

Question 2

Transcriptional regulation in eukaryotes is complex because (2)

Answer 2

• Multiple DNA sequences and proteins are involved
• DNA packaging with proteins in the nucleus (chromatin)

Question 3

Prokaryote have a —- of RNA polymerase

Answer 3

single type

Question 4

RNA polymerase

Structural

Answer 4

composed of a 5-subunit core plus a subunit called sigma factor.

Question 5

Sigma factor

Answer 5

Positions RNA polymerase corectly at the promotor and after transcription is initiated. sigma factor leaves. Some sigma factor recognize promotors of genes required for growth in high heat while others for nitrogen saturation

Question 6

Factor independent termination

Answer 6

GC rich DNA followed bu an A rich stretch causes RNA polymerase to release from the DNA template. Forms hairpin loop followed by bunch of UUUU mrna. Very unstable and polymerase try to stable by stoping but hairpin makes it fall off.

Question 7

Rho dependent termination

Answer 7

Rho factor recognize a C-rich sequence of RNA and climbs up to release RNA polymerase (stopped at terminator) from the DNA template.

Question 8

Promotor

Answer 8

DNA sequence where RNA polymerase binds to initate transcription

Question 9

Activator

What it is

Answer 9

Protein bringing the RNA polymerase closer to the promotor

Question 10

Repressor (2 types)

Answer 10

Protein blocking RNA polymerase from binding to the promotor or blocking it from moving along the DNA

Question 11

Allosteric effectors

Answer 11

Small molecules that bind to the allosteric site of regulatory proteins

Question 12

Effector binds which allows the activator to

Answer 12

Bind at the activator binding site

Question 13

Operon (4)

What it isx2+genes+product

Answer 13

• Linked genes under the control of a single promotor
• Functionally related genes (ex: all involved in lactose metabolism)
• Genes are transcribed onto a single mRNA molecule
• Either all or none of the gene products will be synthesized

Question 14

Lac Operon

Answer 14

Operon required for the transport and metabolism of lactose

Question 15

Permease (Y)

Answer 15

Transports lactose into the cell

Question 16

Beta-galactosidase (Z)

Answer 16

Modifies lactose into allolactose and cleaves lactose

Question 17

I gene

Answer 17

encodes the repressor (Protein that can then bind to the operator)

Question 18

Talk about the location of the I gene

Answer 18

it can be far away fro the lac operon or near, the location isnt important because only the protein that it encodes is important (free to float in cell)

Question 19

Trans-acting

Answer 19

Affect gene expression of distant genes (on DNA other than where the trans-acting factor is encodoes)- in addition to nearby genes

Far away gene, nearby gene, gene on same DNA, on different DNA

Question 20

Cis-acting

Answer 20

Affect gene expression of nearby genes (only genes on the sane piece of DNA as the cis-acting factor is found)

Affect nearby gene or gene on the same piece of DNA

Question 21

Lac operon expression is regulated by both

Answer 21

negative regulation and positive regulation

Question 22

Negative regulator

Answer 22

involves a repressor -> turning the lac operon ON/OFF

Question 23

Positive regulation

Answer 23

involves an activator -> fine tuning expression levels from the Lac operon

Question 24

Lactose is an

Answer 24

inducer(word for binding to repressors)

Question 25

P-

Answer 25

RNA plymerase cannot bind to the promotor

Question 26

Z-

Answer 26

Inactive Z

Question 27

Oc

Answer 27

Cannot bind to operator

Question 28

Constitutive mutation

Answer 28

operon is on wether the inducer is present or not

Question 29

In experiments, IPTG is

Answer 29

sometimes used as the inducer instead of Lactose

Question 30

F' plasmids

Answer 30

F plasmids carrying bacterial genomic DNA because exiting the genomic wasn't clean and pick up some surrounding dna

Question 31

Merozygote | +in terms of lac operon

Answer 31

partial diploid in which we have inserted a F' plasmid in a bacterial cell *2 copies of lac operon

Question 32

Z+ and Z-

Answer 32

Z+ is dominant over Z-

Question 33

O mutation is

Answer 33

cis acting

Question 34

I+ ad I-

Answer 34

I+ is dominant over I-

Question 35

Is and I+

Answer 35

Is is dominant over I+

Question 36

Oc is --- to Is

Answer 36

epistatic (mask the effect of Is)

Question 37

If glucose is present then expression from lac operon is

Answer 37

minimal

Question 38

If there is no glucose then expression from lac operon is

Answer 38

enhanced

Question 39

Glucose levels regulate ---- by

Answer 39

cAMP levels. Glucose inhibits conversion of ATP to cAMP

Question 40

cAMP is an ------ as it-----

Answer 40

Allosteric effector for CAP.cAMP binds to CAP, changing its shape and making it able to bind DNA and promote transcription

Question 41

CAP

Answer 41

Binds to the CAP-binding site in the promotor when bound to cAMP. CAP-cAMP complex enhances transcription by RNA polymerase

Question 42

CAP-

Answer 42

CAP cannot bind to the promotor

Question 43

CAP+ and CAP-

Answer 43

CAP+ is dominant over CAP-

Question 44

Tryptophan

Answer 44

An amino Acid

Question 45

TRP operon is turned on when

Answer 45

Turned on when tryptophan isnt avaliable from the environment

Question 46

Order of the structural genes in the trp operon | trpA/B

Answer 46

coressponds to the order that the proteins act in the biosynthetic pathway

Question 47

Trp operon expression is regulated by (2)

Answer 47

negative regulation and attenuation (regulation after transcription has been initated)

Question 48

tryptophan binding to TrpR repressor allows

Answer 48

TrpR to bind to trpO and inhibit transcription of the 5 structural genes

Question 49

in the abscene of tryptophan, TrpR

Answer 49

cannot bind to the TrpO and the genes are transcribed

Question 50

Leader peptide can

Answer 50

terminate transcripts before the RNA polymerase reaches the first structural gene of the operon by stalling ribosome - UGG codon for typtophan but its rare

Question 51

High tryptophan level in terms of attenuation

Answer 51

sufficient tRNAs charged with tryptophan to translate leader peptide which contains 2 Trp codons. Binding of ribosome in 4 and 3 causes mRNA conformation that favours transcription termination as there is a string of UUUU. so then the RNA pol gets stuck at the loop and unstable and falls of

Question 52

Low tryptophan level in terms of attenuation

Answer 52

Ribosome stalls at the Trp codons in the leader peptide (low tRNA). Cause region 2 and 3 to pair tgt as robsomes dont reach it. Favouts transcription.

Question 53

Factor- independent terminator +ex (2)

Answer 53

- a mechanism of transcription termination in which RNA poly transcribes a stem loop followed by a string of U's - - in Trp regulation, the 3-4 ste loop is followed by a string of U's