Quiz 5

Question 1

Regulation of gene expression

Answer 1

Controlling any step (transcription and translation)

Question 2

How is regulation carried out in bacteria vs eukaryotes

Answer 2

Bacteria: primarily during transcription

Eukaryotes: more complex; transcription, translation, and post-translation

Question 3

Dynamic

Answer 3

Some genes switched off and some on; different genes can be expressed at different levels depending on need; the same gene can be expressed differently in different cells

Question 4

Constitutive genes

Answer 4

Always switched on

Question 5

Inducible genes

Answer 5

Normally switched off but can be expressed if stimulated by an inducer/positive regulator

Question 6

Repressible genes

Answer 6

Normally switched on; expression occurs unless a repressor/negative regulator switches off expression

Question 7

Positive regulation

Answer 7

Stimulates transcription; carried out by trans-acting factors called activators and occurs in both repressible and inducible genes

Question 8

Negative regulation

Answer 8

Inhibits or downregulates transcription; carried out by trans-acting factors called repressors and occurs in both repressible and inducible genes

Question 9

Operon

Answer 9

A group of adjacent genes that are transcribed from a shared promoter (mRNA for these genes is thus polycistronic)

Question 10

Proteins encoded by operon

Answer 10

Have related biological functions and the proteins work together; as such, the cell controls a specific biological function by regulating the shared promoter of the genes in said operon

Question 11

Components of an operon

Answer 11

A group of structural genes (encode proteins), regulatory region (cis-acting site) a.k.a. regulatory site that consists of a promoter and an operator, and regulatory genes (repressor gene that encodes for a repressor protein that controls expression of operon by binding to operator)

Question 12

Controlling the ability of RNA polymerase to initiate transcription from the shared promoter:

Answer 12

Controls expression of all the structural genes of the operon

Question 13

E. Coli’s preferred food and second best option

Answer 13

Glucose, then lactose and other sugars

Question 14

Function of lac operon

Answer 14

An inducible operon that can encode necessary proteins for using lactose as food

Question 15

Structure of lac operon

Answer 15

Three structural genes (Z for B-galactosidase, Y for permease, and A for transacetylase), regulatory site, and the regulatory gene (lacl, the repressor)

Question 16

Beta-galactosidase

Answer 16

Concerts lactose into glucose and galactose

Question 17

Permease

Answer 17

Involved in lactose impoet into the cell

Question 18

Transacetylase

Answer 18

Removes toxic byproducts

Question 19

Regulatory site of lac operon

Answer 19

RNA polymerase (trans-acting factor) binds to promoter (cis-acting site) and repressor protein (trans-acting factor) binds to operator (cis-acting site)

Question 20

Regulatory gene of lac operon

Answer 20

Called I, encodes the lac repressor protein

Question 21

Regulation of the lac operon involves:

Answer 21

Negative regulation by the repressor protein, induction by lactose, and positive regulation by cAMP-CAP

Question 22

Repression of lac operon

Answer 22

Repressor protein (I) bonds to operator in absence of lactose and blocks RNA polymerase from transcribing the structural genes

Question 23

Constitutive mutations

Answer 23

Cause the repressor protein to not bind to the operator for whatever reason so there is no negative regulator present and the lac operon is always expressed

Question 24

Induction of lac operon

Answer 24

Lactose binds to repressor protein and changes its 3D shape (an allosteric change), making it unable to bind to the operator; since RNA polymerase is no longer blocked it can transcribe the structural genes

Note: lactose inactivates all repressors within the fell; furthermore, if repressor protein is mutated so lactose can’t remove it or change it, it is permanently bound to the operator and the gene is permanently repressed

Question 25

Super repressed

Answer 25

Cannot be expressed at all

Question 26

If glucose and lactose are present at the same time

Answer 26

The lac operon is practically shit off with catabolite repression, which involves catabolite-activiating protein (CAP); the enzyme adenyl cyclase makes cAMP, and is shut off by glucose--if glucose levels are low, lots of cAMP is made to bind to CAP, a compound that can bind to the lac promoter at the CAP-binding site next to RNA polymerase

Question 27

Cooperative binding

Answer 27

cAMP-CAP bound to the promoter enhances RNA polymerase binding to the promoter, exerting positive control in expression

Question 28

Catabolite repression in the presence of glucose

Answer 28

Glucose shuts adenyl cyclase off so no cAMP is made and there no cAMP-CAP is formed to bind to the promoter and push RNA polymerase

Question 29

Tryptophan operon

Answer 29

Encodes enzymes to make tryptophan (amino acid); repressible operon

Question 30

Structure of the trp operon

Answer 30

Five structural genes that encode the enzymes that make tryptophan (E, D, C, B, and A), the regulatory region with the leader sequence and the attenuator, the promoter, and the operator, as well as the regulatory gene that encodes the repressor protein

Question 31

When trp operon is expressed:

Answer 31

The repressor protein is inactive

Question 32

Tryptophan regulation

Answer 32

IF levels become high, tryptophan binds to the inactive repressor protein causing an allosteric change that activates the repressor protein, switching off the trp operon

Question 33

Corepressor

Answer 33

Required for repressor protein to bind to operator; ex: tryptophan

Question 34

Trp operon expression

Answer 34

Low levels of tryptophan in a cell cause the repressor protein to be made; it cannot bind to the operator in its 3D shape, so the gene is expressed

Question 35

Trp operon repression

Answer 35

High levels of tryptophan in the cell means tryptophan binds to the repressor protein, changing its 3D shape so it can bind to the operator and thus repress the gene

Question 36

Trp operon attentuation

Answer 36

AN additional mechanism of repression of the trp operon in response to high levels of tryptophan in the cell by which the leader sequence is transcribed and THEN the trp operon is repressed; the trp opwron leader sequence contains a short coding sequence of 14 amino acids and two adjacent tryptophan codons in the first leader sequence Regions 2, 3, and 4 can participate in an RNA hairpin formation, as it contains a stretch of U nucleotides called the attenuator If tryptophan levels are low, regions 2 and 3 form antiterminator hairpin when the ribosome stalls at the tryptophan codons and transcription of the operon can take place; however, if levels are high then the ribosome doesn't stall, so regions 2 and 3 don't form a hairpin and regions 3 and 4 instead form a hairpin called a terminator hairpin that stops transcription