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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

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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

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A

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

25
Inducible systems are keyed to
substrates
26
Inducible systems tend to ___ repression released only if ____ release of repression allows _____ often encode ______
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
lac operon is best-studied inducible system transcription keyed to substrate ____ by _____ for _____ inducer is _____
lactose, metabolized by lac operon gene products (enzymes) for energy inducer is lactose (its derivative, allolactose)
28
repressor protein has a ____ site repressor protein also has a different, _____ site
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
Presence of lactose
releases repression when present, lactose (allolactose an inducer) → binds repressor → repressor falls off the DNA → allows transcription
30
repression never completely shuts down transcription of the lac operon. Even with an active repressor bound to the operator
there is a low level of transcription,
31
Mutations in regulatory DNA sites of operon uncovered _____ Mutations in repressor gene uncovered ___
Uncovered cis-acting operator and promoter (CIS ACTING) Uncovered trans-acting repressor (encodes lac I)
32
Mutations in structural genes of operon_____ and ____ uncovered _____
Missense mutations (amino acid replacement) → uncovered individual protein functions Nonsense mutations (stop codon) → POLAR → eliminated *multiple* proteins; revealed polycistronic mRNA
33
nonsense mutations affect
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
polycistronic mRNA
a mRNA that encodes several proteins and is characteristic of many bacterial and chloroplast mRNAs
35
Other principles uncovered by analysis of mutations in partial diploids
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
Episome
special type of plasmid, which remains as a part of the eukaryotic genome without integration.
37
F factors can insert or excise from the bacterial chromosome by a → _____ Some bacterial chromosome can be removed during ____ can be _____ causing ____
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
F’(lac) factors (with lac mutations) can be transferred into E. coli cells (are WT) creating _____
partal diploid → merozygote → for lac
39
merozygote
A bacterial cell having a second copy of a particular chromosomal region in the form of an exogenote.
40
Partial diploid analysis shows repressor is
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
Partial diploid analysis shows the repressor contains a ___ site super mutant repressor mutation → version of repressor____
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
Partial diploid analysis shows that operators are ____
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
If lactose and glucose are both present, cell prefers
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
cAMP must complex with ____ to promote transcription of lac genes
catabolite activator (CAP)
45
High Glucose / High Lactose High Glucose / Low Lactose Low Glucose / Low Lactose Low Glucose / High Lactose
46
Low Glucose / High Lactose Low Glucose / Low Lactose High Glucose / High Lactose High Glucose / Low Lactose
47
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+
+ Lactose → Yes - Lactose → No
48
glucose is ABSENT will active B-galactosidase protein be produced in the presence or absence of lactose? I-P+OcZ+ / I+P+O+Z-
+ Lactose → Yes - Lactose → Yes
49
glucose is ABSENT will active B-galactosidase protein be produced in the presence or absence of lactose? I+P-OcZ- / I-P+OcZ+
+ Lactose → Yes - Lactose → Yes
50
glucose is ABSENT will active B-galactosidase protein be produced in the presence or absence of lactose? IsP+O+Z+ / I+P+O+Z-
+ Lactose → No - Lactose → No
51
glucose is ABSENT will active B-galactosidase protein be produced in the presence or absence of lactose? IsP+O+Z+ / I-P+O+Z+
+ Lactose → No - Lactose → No
52
glucose is ABSENT will active B-galactosidase protein be produced in the presence or absence of lactose? I-P+OcZ+ / I-P+O+Z-
+ Lactose → Yes - Lactose → Yes
53
glucose is ABSENT will active B-galactosidase protein be produced in the presence or absence of lactose? I-P-O+Z+ / I-P-OcZ+
+ Lactose → No - Lactose → No Look at P → if - → no promoter → always no
54
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+
+ Lactose → Yes - Lactose → No
55
In which genotype(s) is B-galactosidase: Constitutively expressed? Regulated? Uninducible?
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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