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Question 1

`What is feedback inhibition?

Answer 1

A regulatory mechanism where the end product of a metabolic pathway inhibits an enzyme involved earlier in the pathway.

Question 2

Which type of regulation occurs immediately after translation?

Answer 2

Feedback inhibition.

Question 3

What molecule usually acts as an allosteric inhibitor in feedback inhibition?

Answer 3

The end product of the biosynthetic pathway.

Question 4

What is enzyme induction?

Answer 4

The increased synthesis of an enzyme in response to the presence of its substrate.

Question 5

Which classic example illustrates enzyme induction?

Answer 5

The lac operon in E. coli.

Question 6

What induces the lac operon?

Answer 6

Lactose or an analog like IPTG.

Question 7

What is the role of the lac repressor?

Answer 7

It binds to the operator region to inhibit transcription when lactose is absent.

Question 8

How is the lac repressor inactivated?

Answer 8

By binding to allolactose (or IPTG)

Question 9

What is enzyme repression?

Answer 9

Downregulation of enzyme synthesis when an end product is abundant.

Question 10

What is an example of enzyme repression?

Answer 10

The trp operon in E. coli.

Question 11

When is the trp operon repressed?

Answer 11

When tryptophan is abundant

binding the repressor protein to the operator sequence via a corepressor which blocks RNA polymerase from transcribing the trp-related genes

Question 12

What is the corepressor in the trp operon?

Answer 12

Tryptophan.

Question 13

What is positive control in gene expression?

Answer 13

Activation of transcription by a regulatory protein.

Question 14

What protein mediates positive control in the lac operon?

Answer 14

CAP (catabolite activator protein).

Question 15

When does CAP activate transcription?

Answer 15

When bound to cAMP under low glucose conditions.

Question 16

What is the effect of glucose on cAMP levels?

Answer 16

High glucose leads to low cAMP

Question 17

What is catabolite repression?

Answer 17

A global regulatory mechanism that inhibits the expression of catabolic operons when a preferred carbon source (like glucose) is available.

Catabolite repression allows microorganisms to adapt quickly to a preferred (rapidly metabolizable) carbon and energy source first

Question 18

Which operons are affected by catabolite repression?

Answer 18

Lac

Question 19

How is the lac operon affected by catabolite repression?

Answer 19

It is repressed when glucose is present

Question 20

What is attenuation?

Answer 20

A regulatory mechanism that uses transcription termination to control gene expression

Question 21

What operon is a classic example of attenuation?

Answer 21

The trp operon in E. coli.

Question 22

What causes attenuation in the trp operon?

Answer 22

High tryptophan levels lead to fast translation of the leader peptide

Question 23

How does low tryptophan affect attenuation?

Answer 23

Ribosome stalls at tryptophan codons

Question 24

What is the leader sequence in attenuation?

Answer 24

An upstream mRNA region with tryptophan codons and secondary structure potential.

Question 25

Why is the leader peptide important in attenuation?

Answer 25

Its translation speed influences RNA secondary structure formation.

Question 26

How do ribosomes affect attenuation?

Answer 26

Their position on the mRNA determines whether a terminator or anti-terminator hairpin forms.

Question 27

What is an operator?

Answer 27

A DNA segment where repressors bind to regulate gene expression.

Question 28

What is a promoter?

Answer 28

A DNA region where RNA polymerase binds to initiate transcription.

Question 29

What happens to lac operon expression when both lactose and glucose are present?

Answer 29

It is low due to catabolite repression.

Question 30

What is IPTG?

Answer 30

A non-metabolizable analog of allolactose that induces the lac operon. | Synthetic

Question 31

What is allolactose?

Answer 31

An isomer of lactose that binds to the lac repressor to induce expression.

Question 32

How does cAMP interact with CAP?

Answer 32

It binds to CAP

Question 33

What is the role of glucose in lac operon regulation?

Answer 33

It represses expression by lowering cAMP levels.

Question 34

Why is the trp operon a repressible operon?

Answer 34

It is turned off when tryptophan is abundant.

Question 35

How do repressors function?

Answer 35

They bind to operators to block transcription.

Question 36

How do inducers work?

Answer 36

They bind to repressors and prevent them from binding to operators.

Question 37

What is a corepressor?

Answer 37

A molecule that activates a repressor by binding to it.

Question 38

What kind of feedback is enzyme repression?

Answer 38

Negative feedback at the transcriptional level.

Question 39

How is enzyme induction different from repression?

Answer 39

Induction increases transcription in response to substrate; repression decreases it in response to product. | Induction: absence of substrate Repression: presence of product

Question 40

How does attenuation respond to amino acid availability?

Answer 40

It alters transcription termination based on translation of the leader peptide.

Question 41

What is the consequence of a terminator hairpin?

Answer 41

RNA polymerase stops transcription prematurely.

Question 42

What structural features are required for attenuation?

Answer 42

Leader sequence with codons and potential for alternative stem-loop structures.

Question 43

Can attenuation occur in eukaryotes?

Answer 43

No

Question 44

What determines whether attenuation will occur?

Answer 44

The speed of ribosome movement on the leader peptide.

Question 45

What is the function of CAP in the lac operon?

Answer 45

It enhances transcription in low glucose conditions.

Question 46

How does glucose inhibit CAP binding?

Answer 46

By reducing cAMP levels.

Question 47

Why does E. coli prefer glucose?

Answer 47

It yields more energy and is easier to metabolize.

Question 48

What is diauxic growth?

Answer 48

A biphasic growth pattern when E. coli uses glucose first

Question 49

How does the cell know glucose is present?

Answer 49

Through the phosphotransferase system that affects cAMP synthesis.

Question 50

What is the lac operon an example of?

Answer 50

An inducible operon under both negative and positive control.

Question 51

What is the trp operon an example of?

Answer 51

A repressible operon regulated by both repression and attenuation.

Question 52

How does RNA structure regulate transcription in attenuation?

Answer 52

Alternative hairpin loops determine continuation or termination.

Question 53

Why is simultaneous transcription and translation important for attenuation?

Answer 53

It allows ribosome position to influence RNA structure.

Question 54

What does the presence of an inducer mean for enzyme synthesis?

Answer 54

It signals the need for the enzyme and starts transcription.

Question 55

What is global regulation?

Answer 55

A regulatory mechanism that controls many operons simultaneously

Question 56

What does a repressor do?

Answer 56

binds to operators and prevents gene expression --> decreases transcription

Question 57

What does a inducer do?

Answer 57

binds to the repressor and inhibits its activity (think double negative) --> increases transcription

Question 58

What does an activator do

Answer 58

enhances interaction between RNA pol and promoters --> increases transcription

Question 59

Does attenuation occur in prokaryotes?

Answer 59

Yes | Eg. E.Coli