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Genetics Exam 3 > Lecture 16 > Flashcards

Lecture 16 Flashcards

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1
Q

constitutive

A

genes that are expressed at all times

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2
Q

Not all genes are constitutive because

A

Optimal energy efficiency

Gene products or pathways may be incompatible

In multicellular organisms → different cell types express unique gene combinations to achieve specific phenotypes

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3
Q

Some genes must be expressed at the same time to achieve

A

a given metabolic function

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4
Q

In bacteria, the protein RNA polymerase is a

A

multi-subunit holoenzyme

binds to DNA to initiate transcription

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5
Q

Regulation occurs through

A

protein-DNA interactions

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6
Q

RNA polymerase recognizes and binds

A

specific DNA sequences called promoters

consentual sequences (TATA, CAT) - nessary in promoter to have holoenzyme bind

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7
Q

DNA binding proteins tend to have

A

regulatory functions

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8
Q

DNA binding proteins regulatory functions binding

A
  • bind DNA via amino acid “domains”
  • Binding domains can be classified based on conserved structures called “motifs”
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9
Q

types of DNA binding proteins

A

1) helix -turn- helix → two helixes separated by flexible turn → can insert into DNA

2) Zinc fingers → two slim domains insert → contain zinc ions

3) Lucine Zipper → two slim motifs bind directly to DNA

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10
Q

DNA-protein interactions are conceptualized as

A

cis-acting elements & trans-acting factors

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11
Q

cis-acting element

A

a site on a DNA (RNA) molecule that functions as a binding site for a sequence-specific binding protein

cis-acting means that → protein binding to the site affects only DNA (RNA) on the same molecule

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12
Q

trans-acting factor

A

a diffusible regulatory protein that binds to a specific cis-acting element

Trans-acting factors (proteins) affect → any DNA molecules that are accessible

soluble proteins → can be expressed far away on genome

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13
Q

which is the trans-acting factor?
which is the cis-acting element?

A

RNA Pol → trans acting → binds to DNA

consensus sequences → cis acting → on same molecule as gene

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14
Q

Bacteria regulate transcription via

A

operons

→ multiple genes transcribed from a single promoter
→ Only ONE promoter; Only ONE transcript; but multiple genes
→ single transcript translated into multiple proteins

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15
Q

operon

A

set of regulatory sites and adjacent structural genes (ex. enzymes)

→ cis elements

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16
Q

structural genes

A

encode (non-regulatory) proteins

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17
Q

promoter drives production through

A

producing single mRNA

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18
Q

The lac operon model of gene control has____ genes

A

3 structural

B-galactosidase
permease
transacetylase

all transcribed from ONE promoter (i.e., single mRNA)

translated into separate proteins that function in lactose metabolism

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19
Q

coordinate induction

A

the simultaneous synthesis of several proteins stimulated by a specific molecule, the inducer

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20
Q

B-galactosidase (in lac operon)

A

cleaves lactose (lacZ)

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21
Q

permease (in lac operon)

A

transports lactose into cell (lacY)

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22
Q

transacetylase (in lac operon)

A

(lacA)

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23
Q

cis-acting elements comprise promoter region of lac operon

A

control transcription of structural genes

CAP binding DNA site → binds CAP-cAMP complex
promoter (P) DNA site → binds RNA polymerase
operator (O) DNA site →binds lac repressor encoded by lac i
lac i → repressor

24
Q

E. coli lac operon is an ____ system

A

inducible
no lactose present → turned off → not want to waste energy producing lactose

25
Q

Inducible systems are keyed to

A

substrates

26
Q

Inducible systems

tend to ___

repression released only if ____

release of repression allows _____

often encode ______

A

they tend to have metabolic functions (breakdown of sugars for energy)
under → negative control by a repressor protein

→ if inducer (substrate) present

→ allows transcription

→ encode enzymes that catabolize substrate (not needed if substrate absent)

27
Q

lac operon is best-studied inducible system

transcription keyed to substrate ____
by _____
for _____

inducer is _____

A

lactose,
metabolized by lac operon gene products (enzymes)
for energy

inducer is lactose (its derivative, allolactose)

28
Q

repressor protein has a ____ site

repressor protein also has a different, _____ site

A

DNA-binding → binds the operator → keeps RAN pol. from transcribing

allosteric site → binds the inducer (allolactose)

inducer → substrate/molecule nessary for releasing repressor (changes represor confotrmation)

29
Q

Presence of lactose

A

releases repression

when present, lactose (allolactose an inducer) →bindsrepressor → repressor fallsoff the DNA → allows transcription

30
Q

repression never completely shuts down transcription of the lac operon. Even with an active repressor bound to the operator

A

there is a low level of transcription,

31
Q

Mutations in regulatory DNA sites of operon uncovered _____

Mutations in repressor gene uncovered ___

A

Uncovered cis-acting operator and promoter (CIS ACTING)

Uncovered trans-acting repressor (encodes lac I)

32
Q

Mutations in structural genes of operon_____ and ____

uncovered _____

A

Missense mutations (amino acid replacement) → uncovered individual protein functions

Nonsense mutations (stop codon) → POLAR → eliminated multiple proteins; revealed polycistronic mRNA

33
Q

nonsense mutations affect

A

translation, not transcription

called polar → presence in one gene blocks translation of that gene and all downstream genes

BECAUSE → Normally → stop and then another start codon very close to each other → ribosome just “slides over”
nonsense mutation → stop codon → stops but far away from another start → ribosome disassociates from mRNA → no lac Y or A

34
Q

polycistronic mRNA

A

a mRNA that encodes several proteins and is characteristic of many bacterial and chloroplast mRNAs

35
Q

Other principles uncovered by analysis of mutations in partial diploids

A

F factor is an episome

able to replicate as a circular plasmid or integrate into the bacterial chromosome

Integration sites are variable
→ Hfr strains can have F in different positions
→ integrated F factor can excise and re-form as plasmid

36
Q

Episome

A

special type of plasmid, which remains as a part of the eukaryotic genome without integration.

37
Q

F factors can insert or excise from the bacterial chromosome by a → _____

Some bacterial chromosome can be removed during ____ can be _____

causing ____

A

single crossover event

excision → can be imprecise

Abnormal outlooping → creates F’ factors with bacterial chromosomal DNA
E.g., F’(lac) → can take some of lac operon w it

38
Q

F’(lac) factors (with lac mutations) can be transferred into E. coli cells (are WT) creating _____

A

partal diploid → merozygote → for lac

39
Q

merozygote

A

A bacterial cell having a second copy of a particular chromosomal region in the form of an exogenote.

40
Q

Partial diploid analysis shows repressor is

A

trans-acting

WT lac operon → makes repressor → is transfusable/trans/can move → binds to operator in both WT and mutant transcripts

→ WT rescues → making mutant “normal”

41
Q

Partial diploid analysis shows the repressor contains a ___ site

super mutant repressor mutation → version of repressor____

A

lactose-binding allosteric site

super mutant repressor mutation → version of repressor w/mutation at allosteric site → cannot bind to lactose (inducer) → lactose binds but is never released

→Transcription is permanently blocked from both DNA molecules, regardless of whether lactose is present

42
Q

Partial diploid analysis shows that operators are ____

A

cis-acting

O+ cannot rescue Oc (they are cis-acting DNA sites)

in WT → represor binds → expression blocked
in mutant → repressor cannot bind to altered operator → cannot block RNA pol from binding → always expresson of structural gene → always transcription

43
Q

If lactose and glucose are both present, cell prefers

A

glucose

glucose must be used up first →
only under low glucose is cyclic AMP formed

cAMP must complex with catabolite activator (CAP) to promote transcription of lac genes

44
Q

cAMP must complex with ____ to promote transcription of lac genes

A

catabolite activator (CAP)

45
Q

High Glucose / High Lactose
High Glucose / Low Lactose
Low Glucose / Low Lactose
Low Glucose / High Lactose

A
46
Q

Low Glucose / High Lactose
Low Glucose / Low Lactose
High Glucose / High Lactose
High Glucose / Low Lactose

A
47
Q

glucose is ABSENT

will active B-galactosidase protein be produced in the presence or absence of lactose?

I+P+O+Z+ / I+P+O+Z+

A

+ Lactose → Yes
- Lactose → No

48
Q

glucose is ABSENT

will active B-galactosidase protein be produced in the presence or absence of lactose?

I-P+OcZ+ / I+P+O+Z-

A

+ Lactose → Yes
- Lactose → Yes

49
Q

glucose is ABSENT

will active B-galactosidase protein be produced in the presence or absence of lactose?

I+P-OcZ- / I-P+OcZ+

A

+ Lactose → Yes
- Lactose → Yes

50
Q

glucose is ABSENT

will active B-galactosidase protein be produced in the presence or absence of lactose?

IsP+O+Z+ / I+P+O+Z-

A

+ Lactose → No
- Lactose → No

51
Q

glucose is ABSENT

will active B-galactosidase protein be produced in the presence or absence of lactose?

IsP+O+Z+ / I-P+O+Z+

A

+ Lactose → No
- Lactose → No

52
Q

glucose is ABSENT

will active B-galactosidase protein be produced in the presence or absence of lactose?

I-P+OcZ+ / I-P+O+Z-

A

+ Lactose → Yes
- Lactose → Yes

53
Q

glucose is ABSENT

will active B-galactosidase protein be produced in the presence or absence of lactose?

I-P-O+Z+ / I-P-OcZ+

A

+ Lactose → No
- Lactose → No

Look at P → if - → no promoter → always no

54
Q

glucose is ABSENT

will active B-galactosidase protein be produced in the presence or absence of lactose?

I+P+O+Z- / I-P+O+Z+

A

+ Lactose → Yes
- Lactose → No

55
Q

In which genotype(s) is B-galactosidase:

Constitutively expressed?
Regulated?
Uninducible?

A

Constitutively expressed → always expressed → 2, 3, 6

Regulated → normal so + lactose yes - lactose no → 1,8

Uninducible → never expressed → 4,5,7

Genetics Exam 3 (8 decks)

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