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Bio 209 > Lecture 6 - Gene Expression > Flashcards

Lecture 6 - Gene Expression Flashcards

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1
Q

What type of gene control is present in prokaryotes?

A

Lac and Trp operons

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2
Q

What 6 kinds of gene control mechanisms are present in eukaryotes?

A
  • Chromatin remodeling and position effect variegation
  • Gene silencing (DNA methylation)
  • Dosage Compensation
  • Alternative mRNA splicing
  • mRNA stability
  • Regulatory RNAs (si and miRNAs)
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3
Q

What is an operon?

A

set of genes the share some sort of common function

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4
Q

What is the operator?

A

site on DNA where repressor binds - btw promoter and said genes

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5
Q

What is a repressor?

A

a regulator protein that represses transcription

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6
Q

What is negative control and what are the two types?

A

Repressors turn off transcription - inducible and repressible expression

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7
Q

What happens in inducible expression?

A

Basically no transcription is happening as their is a repressor bound to the operator. Inducer leads repressor to fall off and now transcription can occur. Usually apart of catabolic pathways (lac operons)

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8
Q

What is repressible expression?

A

So the transcription is going on. The way it stops is when the corepressor binds to repressor which then binds to operator. Usually is anabolic (trp operon)

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9
Q

What are the two effector molecules?

A

inducer or corepressor

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10
Q

What is the corepressor in Trp Operon?

A

Tryptophan. Genes here make this amino acid. Example of repressible control.

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11
Q

What happens in positive regulation?

A

The bound activator promotes transcription.

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12
Q

How many structural genes does the lac operon encode?

A

3

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13
Q

What does lac Z do?

A

cleaves lactose disaccharides into monosaccharides to begin their metabolism - glucose to galactose

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14
Q

What does lacY do?

A

transport protein (permease) gets lactose into the cell

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15
Q

What does lacA do

A

don’t know its full importance yet

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16
Q

What is gene I and its structure?

A

lac repressor that binds to operator - acts as a tetramer (4 same polypeptide chains that are noncovalently linked)

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17
Q

What is the inducer in lac operon?

A

Allolactose (sensor of lactose) - binds to repressor which releases from operator so transcription can start

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18
Q

How does glucose prevent expression of lac operon?

A

As it is the preferred carbon (energy) source for ecoli it will use that over lactose. So you need lactose and no glucose

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19
Q

What is catabolite repression?

A

when glucose is present it will act as a preventer of induction of lac operon - works by having secondary regulator protein CAP (an activator)

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20
Q

What does CAP do?

A

in response to cAMP it will act as an activator w lactose (inducer) to promote induction

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21
Q

What two things does the promoter site have?

A

CAP and RNA polymerase binding sites

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22
Q

What is glucose?

A

It is the inhibitor of the enzyme that makes cAMP (the effector molecule). When you have glucose you have low cAMP as glucose binds to adenylcyclase (preventing this prevents transcription)

23
Q

What does CAP/cAMP complex do?

A

binds to promoter and exerts positive control of lac operon on transcription

24
Q

What does DNA methylation do?

A

Changes structure of the base (cytosine methylation) and can alter the ability of certain binding proteins to recognize the base - in 2-7% of genome. Usually found in CpG island clusters.

25
Q

Does methylation repress transcription?

A

Yes represses transcription

26
Q

How does hypermethylation of CpG islands connect to cancer?

A

There are genes that inhibit cell division. Their hypermethylation can lead to silencing of their expression so now they can’t control cell division (cancer)

27
Q

Do histones undergo acetylation?

A

Yes

28
Q

What is the association btw H1 and chromatin structure?

A

H1 is associated w linker DNA so if you have less of it then u usually have less histone acetylation. Acetylation neutralizes pos charge on histones makes dna more heterochromatic (tightly bound so RNA polymerase activity is limited)

29
Q

How is methylation involved in imprinting?

A

Methylation is established in parental germ line. Somatic cells have same pattern, but germ line cells don’t. This pattern is reestablished if these germ line cells produce offspring. If og female was methylated eggs will be @end.

30
Q

What are the 3 ways that dosage compensation occurs?

A

Inactivation, hyperactivation, hypoactivation

31
Q

How does inactivation of X chromosome happen in mammalian female?

A

There is a gene called XIST on this long non coding RNA. Early in development, both X will express XIST. The, XIST will stabilize and cover one entire X chromosome and other will undergo degradation and will be repressed by methylation of promoter. This whole process is random but inactivation pattern continues. IF maternal inactivation, then progeny of that specific cell will do same.

32
Q

What is XIC?

A

X inactivation center - spreads in opposite directions towards ends of chromosome

33
Q

What is XIST gene stand for?

A

X inactive specific transcript

34
Q

What is a barr body?

A

A dense dark mass that is the inactivated X chromosome. This decondenses and is replicated after other chromosomes in the S phase. It will have low levels of acetylated H4 (lead to altered expression of certain genes on that specific chromosome)

35
Q

What is hyperactivation of X chromosome in male drosophila?

A

Single X will have more transcription to match that of the other two female X chromosomes. Male specific chromosomal genes turn on in males and result in increased transcription in males. Lots of these genes encode chromatin remodeling which is a likely cause of increase in transcription.

36
Q

What bind on the male X chromosome in fruit flies?

A

Complex of proteins and RNA bind to specific sites (30-40) - only expressed in males

37
Q

Why is it likely that these drosophila genes are involved in chromatin remodeling?

A

One encodes a helicase and other is a histone acetyl transferase

38
Q

What is hypoactivation of X chromosomes in C elegan females?

A

Don’t know exact stuff, but basically proteins binds to both the X chromosomes in the female and reduces transcription of them both

39
Q

What is the sex lethal gene important for?

A

Sex determination in fruit flies.

40
Q

How many exons at sex lethal gene?

A

8

41
Q

What happens when exon 3 is removed in Drosophila sex lethal gene?

A

protein that is translated will be full length and functional - ensures that various genes associated w female development are expressed

42
Q

What happens when exon 3 isn’t removed in the drosophila sex lethal gene?

A

There is a stop codon at the end of 3rd exon so if its not removed then mRNA will only translate exons 1 and 2 (not all 8 like when it was removed). Shorter segment activates genes needed for male development

43
Q

Which exon is important for drosophila sex determination?

A

exon 3

44
Q

Does mRNA half life vary?

A

Yes, diff ones have diff half lives

45
Q

What affects half live of mRNA?

A

Longer poly A tail is more stable. Metabolic state and regulatory mechanisms control poly A tail length

46
Q

What two mechanisms can be used to inhibit specific gene expression?

A

degradation of specific mRNAs or blocking their transcription

47
Q

What are micro RNAs?

A

genome has specific antisense RNA sequences that inhibit genes (sequences are miRNAs)

48
Q

What role do miRNAs play?

A

They form a hairpin loop in the nucleus

49
Q

What does Drosha do?

A

cleaves pri - miRNA

50
Q

What does exportin 5 do?

A

these released individual hairpin loops (pre - miRNA) are taken into cytoplasm from nucleus

51
Q

What does DIcer do?

A

It is a nucleus that takes double stranded RNA and processes them to make shorter sequences

52
Q

What does RISC do?

A

takes miRNA and carries it to certain mRNA transcripts. IF complementary, it’ll bind and then get degraded. If not fully complementary, translation is prevented bc ribosome fails to translate

53
Q

Where does double stranded RNA come from?

A

made in lab

54
Q

What does bantam do (fruitflies)?

A

suppresses HID (an apoptotic protein) which can prevent certain apoptosis of specific cells - basically controls certain cell fates

Bio 209 (1 decks)

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