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eBMS1062 > TOPIC 4 - GENE REGULATION > Flashcards

TOPIC 4 - GENE REGULATION Flashcards

(45 cards)

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1
Q

Ground state of prokaryotes

A

ON
Transcribes normally

Negative regulation stops

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2
Q

Ground state of eukaryotes

A

OFF

regulatory sequences inaccesible

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3
Q

activator/repressor proteins regulate…

A

transcription

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4
Q

inducer molecules regulate…

A

activator/repressor proteins

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5
Q

Explain negative regulation using a repressor

A

repressor binds to the operator sequence, covering promoter sequence also, stopping RNA poly from starting translation

Inducer binding causes repressor inactivation by repressor coming off operator sequence

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6
Q

inducer molecules cause

A

the opposite effect of what the activator/repressor is doing initially

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7
Q

REPRESSOR

A

Causes:
negative regulation

By itself:
activated

With inducer:
inactivated

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8
Q

Explain positive regulation using an activator

A

Inducer molecules binds to activator, activator binds to promoter to guide RNA polymerase to start transcription

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9
Q

ACTIVATOR

A

Causes:
positive regulation

By itself:
inactivated

With inducer:
activated

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10
Q

Inducible and repressible refer to

A

if the presence of the effector induces or represses transcription

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11
Q

negative and positive regulation refer to

A

if transcription is blocked or activated by the protein binding

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12
Q

Explain lac operon regulation when lactose present

A

INDUCIBLE NEGATIVE REGULATION

lactose present = allo lactose also present

allo lactose is an inducer

inducer binds to repressor to allow transcription to occur

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13
Q

Explain lac operon regulation when glucose present

A

INDUCIBLE POSITIVE REGULATION

glucose present = inactivates adenylate cyclase = stops producing cAMP from ATP

cAMP inducer is not present and therefore CAP activator does not bind to lac operon. Repressor binds instead and Transcription of lac genes does not occur

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14
Q

glucose present, no lactose

A

decrease cAMP = CAP not induced = no transcription

decrease allo lactose = repressor not induced = repressor stays bound

NO LAC mRNA

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15
Q

glucose present, lactose present

A

decrease cAMP = CAP not induced = no transcription

allo lactose = repressor induced = transcription occurs

LITTLE BIT OF LAC mRNA

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16
Q

no glucose, lactose present

A

increase cAMP = CAP induced = transcription occurs

allo lactose = repressor induced = transcription occurs

HIGH LAC mRNA

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17
Q

Inducible genes:

A

genes where an inducer affects regulation and expression

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18
Q

repressible genes:

A

genes where repressor affects regulation and expression

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19
Q

What does ‘feedback’ mean in this context

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A

the concentration of a product of a pathway helps to regulate further gene expression

20
Q

what is feedback inhibition

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A

product of pathway INHIBITS an enzyme earlier in the pathway, stopping product being produced

21
Q

what is feedback repression

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A

product of pathway REPRESSES transcription

22
Q

Explain trp operon feedback inhibition

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A

if tryptophan is present, inhibits on of the 5 enzymes in the pathway to stop tryptophan being produced.

23
Q

Explain trp operon repressible negative regulation

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A

If tryptophan is present, binds to repressor causing transcription of trp operon to stop, enzyme aren’t produced, tryptophan is not produced

24
Q

What is a leader sequence

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A

sequence of DNA between the promoter and first exon of an operon.

mRNA form has intermolecular base bonding forming hairpins

25
What areas of leader sequence can bond
1 and 2 2 and 3 3 and 4
26
Explain trp operon transcriptional attenutation
2 trp codons in mRNA. high trp = lots of tRNA, codons translated, reaches stop codon between 1 and 2, ribosome blocks 1 and 2 from bonding, then stops 2 and 3 bonding also, so 3 and 4 bond forming hairpin = termination of transcription that was still occurring low trp = stalls at codons, does not block 2. 2 and 3 bond therefore 3 and 4 don't bond, no hairpin, transription continues
27
Explain trp operon transcriptional attenutation
2 trp codons in mRNA. high trp = lots of tRNA, codons translated, reaches stop codon between 1 and 2, ribosome blocks 1 and 2 from bonding, then stops 2 and 3 bonding also, so 3 and 4 bond forming hairpin = termination of transcription that was still occurring low trp = stalls at codons, does not block 2. 2 and 3 bond therefore 3 and 4 don't bond, no hairpin, transcription continues
28
Eukaryotes transcription initiation
TATA box sequence upstream from transcription start TBP binds to TATA, TFIID then binds, DNA bending acts as landmark for GTF to bind. Pre initiation complex forms and attracts RNA poly to start. CTD phosphorylated by one of the GTF is start of transcription
29
Explain gene repression by microRNA
microRNA sequence binds to argonaute protein and one strand of hairpin released. RISC complex generated if microRNA complimentary to mRNA, RISC cuts it causing degradation if microRNA partially complimentary to mRNA, complex as road block stopping translation
30
What does RISC stand for
RNA induced silencing complex
31
What are the 3 processing events that occur
7-methylguanosine cap generated at 5' polyA tail added to 3' splicing removes introns
32
What is CTD
Carboxyl Tail Domain regulated processing of pre mRNA, protrudes off RNA polymerase
33
5' cap generation
CTD recruits enzymes | adds a 7-methylguanosine residue to 5' triphosphate group
34
what do the cap and tail do
tells cell mRNA in intact protect from degradation attach here signal for ribosomes
35
poly A tail generation
CTD recruits CPSF protein which sits on CTD until AAUAAA sequence is transcribed Polymerase PAP adds 200 A resides to 3' end cleavage factors cleave mRNA from polymerase
36
Simply how does splicing occur
CTD recruits RNA splicing machinery occurs at same time as polyA tail sometimes exons excised as well changing cell type
37
Splicing mechanism
Small nuclear riboprotein, U1, recognises GU at 5' of introns U2 recognises A branch point of intron riboproteins join forming the splicesome A branch point and 5' site form phosphoester bond bond between exon and 5' intron broken cleaved exon forms bond at 3' of intron bond between exon and 3' intron broken intron has been cut out
38
What is self splicing
intron RNA catalyses own excision free OH of guanine nucleophilic attack on phosphate group. Splicesome still needed to bring A site closer to 5' site
39
What is an intercistronic region
mRNA sequence that separates genes, different to intron which is in the middle of 1 gene.
40
3 ways of chromatin remodelling
histone tail acetylation histone tail methylation DNA methylation
41
histone tail acetylation
amino acid tails sticking out acetylated stops bonding, stops condensation, favours transcription
42
DNA methylation
5' of cytosines get methylated methyl groups are recognition site for methyl cytosine binding protein (MeCP), recruits HDAC deacetylises histone tails, condensing, no transcription
43
Histone tail methylation
Lysines and Argines methylated by histone methyltransferase (HMTase). creates binding site for activators and repressors
44
What is the beta-INTERFERON ENHANCESOME
allows for regulation of chromatin enhancesome is a complex of factors, forms binding site between 2 nucleosomes for GCN5 complex. GCN5 binds to enhancesome and acetylated nearby tails. CBP lands on enhancesome, recruits RNAPII and SWI-SNF which use ATP to nudge nucleosome off TATA box.
45
Explain epigenetic inheritance
chromatin structure can be inherited. old histones are re used in DNA replication guiding modification of new histones Also methylation can be inherited causing methylation of daughter strand by DNA methyltransferase

eBMS1062 (7 decks)

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