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Biol 265 > Control of Gene Expression in Prokaryotes > Flashcards

Control of Gene Expression in Prokaryotes Flashcards

1
Q

What are Structural Genes

A

Encode proteins involved in metabolism/biosynthesis or have structural or defense role

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2
Q

Regulatory Genes

A

Encode proteins or RNA that interact with other DNA or RNA sequences and affect their transcription/translation

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3
Q

Constitutive Genes

A

Structural genes that are expressed continuously (always switched on)

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4
Q

Regulatory Elements

A

DNA sequences that are not transcribed but affect the expression of DNA to which they are physically linked (promoter, enhancer)

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5
Q

What are the levels of DNA condensation in prokaryotes and eukaryotes? What are the processes that can be done at each level?

A
  1. Compact DNA
  2. Relaxed DNA (can then be transcribed)
  3. Pre-mRNA (needs mRNA processing) (Eukaryotes only)
  4. Processed mRNA (stability- way of regulating expression and translated)
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6
Q

What are post-translational modifications of proteins?

A

Modifications done to a protein after translation putting that protein in an active state

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7
Q

What is an operon?

A

A set of structural genes (encode products that are all involved in a single cellular pathway), a single promoter that transcribed all the structural genes into one mRNA, and other regulatory elements that control their transcription.

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8
Q

How many mRNA strands result from the transcription of one operon?

A

One mRNA strand results.

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9
Q

How many proteins are produced from a single operon?

A

The number of proteins produced from a single operon are dependent on the number of genes included in the operon

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10
Q

What is an operator sequence?

A

Affects whether transcription can take place or not and is located beside the promoter, and beside the first gene of the operon

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11
Q

What is negative control?

A

The regulator protein is a depressor that inhibits transcription.

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12
Q

What is positive control

A

Regulator protein is an activator that enhances transcription.

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13
Q

What is an inducible operon?

A

Transcription of operon normally switched off but something must happen for transcription to be switched on

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14
Q

What is a repressible operon?

A

Transcription of operon normally switched on but something must happen to repress transcription

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15
Q

What is a negative inducible operon?

A

Operon is normally switched off and the regulatory gene encodes an active repressor that behinds to the operator and prevents transcription (RNA pol. Cannot bind promoter)

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16
Q

What is an allosteric protein?

A

A protein that changes their shape upon binding to another molecule

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17
Q

How are negative inducible operons turned on?

A

The inducer binds repressor and alters it’s shape and repressor can no longer bind to the operator and transcription is then turned on

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18
Q

What is a negative repressible operon?

A

Transcription is normally switched on and the regulatory gene encodes a repressor that is synthesized in an inactive form that cannot bind to operator by itself and requires a co-repressor to do so and thus inactivates the operon

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19
Q

How is a co-repressor of a negative repressible operon produced?

A

The co-repressor is an end product of a biochemical pathway that requires structural gene products of the operon. When enough enzymes are produced from the operon, co-repressor is one of the produced products and shuts off the operon

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20
Q

What is a positive inducible operon?

A

Transcription is turned off in default state and encodes an inactive activator that only becomes active on binding to a substrate. The activator undergoes a conformational change when the substrate binds to it.

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21
Q

What is a positive inducible operon

A

The regulator gene encodes and active activator that normally stimulates transcription by RNA pol. But a substance (end product of pathway regulated by operon) can bind to activator altering its conformation and rendering it unable to bind to the regulatory element so transcription is switched off

22
Q

What is the lac operon?

A

Set of structural genes required for utilization of lactose as an energy source in absence of glucose (since glucose is preferred energy source).

23
Q

What type of operon is the lac operon?

A

An example of both a negative inducible and positive inducible operon.

24
Q

How does a lac operon work?

A

Permease actively transports lactose into the cell where the enzyme beta-galactosidase breaks it into galactose and glucose. Beta-galactosidase also converts lactose into the compound allolactose and then converts allolactose into galactose and glucose.

25
Q

What are the structural genes of a lac operon?

A

Lac Z: beta galactosidase
Lac Y: permease
Lac A: transacetylase (function in lactose metabolism not yet clear)

26
Q

How does the lac operon function as a negative inducible operon?

A

In the absence of lactose the regulator protein (repressor) binds to the operator therefore inhibiting transcription since no lactose utilization is needed.

27
Q

What gene produced the repressor protein when the lac operon is functioning in a negative inducible fashion?

A

The regulator Gene (lacl) produced the repressor through transcription and translation. The repressor then binds to the operator (lacO) which blocks RNA pol. From binding.

28
Q

What happens if the repressor falls off the operator momentarily when the lac operon is functioning in a negative inducible way?

A

Low level of transcription of lac operon which is known as the basal level of transcription allowing some lactose to enter.

29
Q

What happens after some lactose enters the cell due to the basal level of transcription of the lac operon?

A

When lactose is present, some of it is converted into allolactose which then binds to the regulator making it inactive and unable to being to the operator. This results on the structural genes being transcribed and translated.

30
Q

What did Jacob and Monod use in place of lactose/allolactose as an inducer?

A

IPTG a molecular mimic of allolactose that can inactive lacI (repressor) and switches on transcription of lac operon but is not a substrate of the operon.

31
Q

What is cis-acting?

A

Those elements can control transcription of lac operon genes only when they are on the same piece of DNA as the operon (eg. Regulatory elements)

32
Q

What are trans-acting elements?

A

Elements that can control transcription of lac operon genes when they are not on the same DNA molecule as the operon since they make a diffusible product (eg. Regulatory proteins)

33
Q

How did Jacob and Monod produce partial diploid strains of E. Coli?

A

They took a bacterial chromosome with its lac operon and regulator genes and died a circular piece of DNA (plasmid) engineered to carry the lac operon and regulator genes.

34
Q

What happened in mutations found in lac Z?

A

No functional beta galactosidase was produced.

35
Q

What happened in mutations found in lac Y?

A

No functional permease produced

36
Q

What did Jacob and Monod find out about mutations in the lac structural genes?

A

Mutation affects the structure of genes rather than the regulation of their synthesis (proteins made but not functional)

37
Q

Are mutant lac alleles recessive or dominant to the wild type alleles?

A

Mutant lac alleles are recessive with respect to wild type alleles.

38
Q

What happens if there is a mutation in the repressor protein? (LacI -) is the mutant allele dominant or recessive in respect to the wild type?

A

Mutant repressor cannot bind to the operator. The mutant repressor functions in a recessive way to the wild type.

39
Q

What happens to the expression of LacZ and LacY if IPTG is not present?

A

The resulting proteins are not created.

40
Q

What is the super-repressor mutation of LacI? (LacIs)

A

Repressor is unable to bind to the inducer. Therefore is doesn’t respond to the inducer but can bind to operator. It functions in a dominant manner.

41
Q

What does an operator mutation do? (LacOc)

A

Mutation is sequence of DNA of operator such that the repressor cannot bind to the operator which causes constitutive synthesis of functional beta-galactosidase in the presence of IPTG or not.

42
Q

Is LacO cis or trans acting?

A

LacO gene is a cis acting gene and can only affect genes on the same DNA molecule as itself.

43
Q

Is LacP a cis acting or trans acting gene?

A

LacP is a cis acting gene meaning that if the chromosomal mutation is present, no functional beta-galactosidase will be made

44
Q

Do bacteria metabolize glucose preferentially over lactose or vice versa?

A

Glucose is metabolized preferentially over lactose

45
Q

What does catabolite repression refer to?

A

When glucose is present inside a bacterial cell, genes involved in metabolizing other sugars are repressed.

46
Q

What is a scenario when the lac operon is being expressed higher than the basal level of transcription but less than when glucose is absent and lactose is present?

A

This scenario would occur when both glucose and lactose are present since some lactose will be metabolized

47
Q

What is the positive inducible control of the lack operon depended on?

A

The positive inducible control of the lac operon is dependent on the absence of glucose

48
Q

What is the catabolite activator protein (CAP) and where does it bind?

A

CAP binds to the CAP site which is just upstream of lac promoter. CAP causes DNA to bend which facilitates stable/efficient binding of RNA pol. To the promoter causing efficient transcription.

49
Q

What does CAP need to be complexed to in order to bind to the CAP site?

A

Cap can only bind to the CAP site when complexed to cyclic adenosine monophosphate (cAMP).

50
Q

Which type of proportionality does cAMP have to glucose?

A

cAMP levels are inversely proportional to the level of glucose. (Low glucose, high cAMP; vice versa)

Biol 265 (2 decks)

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