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MB351 > Lecture 33/34/35 Genetic Control > Flashcards

Lecture 33/34/35 Genetic Control Flashcards

1
Q

Why do bacterial cells need to regulate the expression of their genes?

A

enzymes are energetically expensive; most efficient when they adapt to their environment

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2
Q

Constitutive

A

always on, always needed, essential

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3
Q

Posttranslational control

A

control of enzyme activity; no product (ex. inhibited active site)

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4
Q

Translational control

A

translational control; no protein synthesis (folded into a different shape)

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5
Q

Transcriptional control

A

transcriptional control; no mRNA synthesis; most efficient (control at level of the DNA)

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6
Q

Operon

A

one gene cluster transcribed as a single unit and is controlled by the same elements

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7
Q

An operon functions at which level of genetic control?

A

transcriptional control

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8
Q

What are the three components of an operon?

A

promoter, operator, structural genes

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9
Q

What are most regulatory proteins?

A

DNA binding proteins

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10
Q

What do inverted repeats do?

A

bind strongly to regulatory molecules

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11
Q

Allosteric protin

A

protein which has an catalytic (active) site and regulatory (allosteric/effector) site

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12
Q

What are the two types of allosteric proteins?

A

repressor proteins and activator proteins

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13
Q

Repressor proteins

A

proteins that bind to the operator site; stop RNA polymerase binding and turn OFF transcription

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14
Q

Activator proteins

A

proteins that bind to the activator site (upstream of operon); increase RNA polymerase binding and turn ON transcription

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15
Q

Types of Effector Molecules

A

1) inducers
2) activators
3) corepressors

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16
Q

Inducers

A

molecules that bind to repressors and result in transcription being turned ON (during neg. induction)

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17
Q

Activators

A

molecules that bind to activator proteins and result in transcription being turned ON (during pos. control)

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18
Q

Corepressors

A

molecules that bind to repressors and result in transcription being turned OFF (during neg. repression)

19
Q

What is usually the product of repression?

A

enzymes that make an end product

20
Q

What is usually the product of induction?

A

enzymes that break down stuff

21
Q

Negative control

A

a regulatory mechanism that stops transcription through a repressor protein

22
Q

Positive control

A

a regulatory mechanism that starts transcription through a activator protein

23
Q

Purpose of global control systems

A

cells often need to coordinate the expression of multiple genes and operons in response to changing environmental conditions

24
Q

Common example of global control

A

Catabolite Repression

25
Q

Common example of negative repression

A

Tryptophan operon

26
Q

How does the tryptophan operon function when no tryptophan is present?

A

1) no tryptophan present
2) inactive repressor protein
3) RNA polymerase transcribes try biosynthesis genes
4) tryptophan synthesis occurs

27
Q

How does the tryptophan operon function when tryptophan is present?

A

1) tryptophan present
2) repressor protein is activated by tryptophan (corepressor)
3) RNA polymerase is blocked
4) tryptophan synthesis does not occur

28
Q

Common example of negative induction

A

Lac operon

29
Q

How does the lac operon function when no lactose is present?

A

1) no lactose present
2) repressor protein is active
3) repressor protein blocks RNA polymerase from transcribing
4) catabolic enzymes are not produced

30
Q

How does the lac operon function when lactose is present?

A

1) lactose present
2) allolactose (inducer) inactivates repressor protein
3) RNA polymerase catabolic transcribes enzymes

31
Q

How is microbial genetics helpful?

A
  • can make protein products such as insulin, hormones, and vaccines
  • can help us isolate genes for herbicide resistance, insect resistance, spoilage protection
32
Q

Why are the trp and lac operons both examples of negative control?

A

both operons are shut “off” by an active repressor

33
Q

Common example of positive control

A

maltose operon

34
Q

How does the maltose operon function when no maltose is present?

A

1) no maltose present
2) maltose activator protein is not active
3) no transcription occurs

35
Q

How does the maltose operon function when maltose is present?

A

1) maltose present
2) maltose (regulatory effector molecule/activator) binds to maltose activator protein
3) maltose activator protein binds to activator binding site on DNA; RNA polymerase binds to promoter
4) transcription proceeds

36
Q

Catabolic repression

A

when the synthesis of unrelated catabolic enzymes is repressed if glucose is present in a growth medium

37
Q

What is the point of catabolic repression?

A

ensures that the “best” carbon and energy source is used first

38
Q

Diauxic growth

A

two exponential growth phases

39
Q

Common example of catabolite repression

A

lac operon

40
Q

How is the lac operon regulated when glucose is present?

A

glucose inhibits the synthesis of cAMP and also stimulates cAMP transport out of the cell

41
Q

How is the lac operon regulates when glucose is not present?

A

1) cAMP binds to cyclic AMP receptor protein
2) CRP, once activated, binds to DNA at the DRP binding site
3) transcription of lac operon is activates

42
Q

What type of control does the lac operon showcase?

A

negative AND positive control

43
Q

What are the two conditions for lac genes to be transcribed?

A

1) levels of cAMP must be high enough that CRP binds to CRP binding site on DNA (positive control)
2) lactose must be present so that lactose repressor does not block transcription by binding to operator (negative control: induction)

MB351 (21 decks)

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