Transcription & RNA Processing Flashcards

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1
Q

3 steps of transcription

A

initiation, elongation, termination

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2
Q

define promoter

A

sequence of double stranded DNA where RNA polymerase binds

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3
Q

when does initiation occur

A

when RNA polymerase binds to the promoter

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4
Q

what helps RNA polymerase bind to the promoter in eukaryotes?

A

transcription factors

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5
Q

transcription factors + RNA polymerase + promoter = ?

A

pre-initiation complex

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6
Q

How much of your genome is replicated right before your cells divide?

A

all of it

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7
Q

How much of your genome is converted to protein (transcribed, then translated)?

A

<2%

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8
Q

How much of your genome is converted to RNA (transcribed)?

A

80%

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9
Q

What are transcription factors?

A

proteins that bind to the promoter first and allow RNA polymerase to bind

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10
Q

What sort of sequence does a promoter usually contain? Why is this helpful?

A

T-A rich sequences called TATA boxes; easier to seaparate because they have fewer hydrogen bonds

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11
Q

What happens during elongation?

A

RNA polymerase starts moving along DNA strand and synthesizes the pre-mRNA transcript

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12
Q

Where do transcription factors go during elongation?

A

stay at the promoter

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13
Q

Why do transcription factors stay at the promoter? What does this allow?

A

allows another RNA polymerase to bind at the promoter and start transcribing another pre-mRNA transcript; this makes transcription faster and more efficient

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14
Q

How fast does RNA polymerase add nucleotides?

A

10-100 nucleotides / sec

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15
Q

What is the “sense” strand?

A

strand of DNA that is the same sequence as the pre-mRNA transcript

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16
Q

What is the “antisense” or “template” strand?

A

the strand of DNA that serves as the template for RNA polymerase

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17
Q

Which strand is “read” by RNA polymerase?

A

“antisense” strand

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18
Q

all “sense” strands are…

A

5’ —> 3’

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19
Q

What happens during elongation?

A

RNA polymerase untwists DNA and synthesizes mRNA by connecting free ribonucleotides to elongating strand

20
Q

Does RNA polymerase have proofreading activity?

A

no

21
Q

Does RNA polymerase need a primer to start synthesizing?

A

no

22
Q

What happens during termination?

A

RNA polymerase, DNA and RNA transcript dissociate

23
Q

How does RNA polymerase know when to stop in bacteria?

A

stops at “termination sequence” by itself

24
Q

How does RNA polymerase know when to stop in eukaryotes?

A

proteins/enzymes are needed to recognize DNA sequences and make RNA stop in the right place

25
Q

Does RNA polymerase need topoisomerase?

A

no, the double stranded DNA quickly rewinds into the double helix after being read by RNA polymerase

26
Q

When a single pre-mRNA molecule is made in one of our cells, how much information does it contain?

A

the genetic code for one allele from one chromosome

27
Q

What nucleotide does RNA use that is different from DNA?

A

uracil instead of thymidine

28
Q

what do most RNA transcripts code for?

A

some for protein, others for rRNA, tRNA, some mysterious

29
Q

transcripts that encode protein

A

pre-mRNA

30
Q

average human pre-mRNA transcript length

A

27,000 nucleotides

31
Q

average human protein length

A

400 amino acids (requires only 1200 nucleotides)

32
Q

exons

A

blocks of pre-mRNA transcripts or “primary transcripts” that are kept and encode for proteins and some regulatory sequences

33
Q

introns

A

intervening sequences that get cut out of pre-mRNA

34
Q

what are “UTRs”

A

untranslated regions at the 5’ and 3’ ends that are part of exons and are not translated into proteins

35
Q

purpose of the 5’UTR and 3’UTR sequences

A

regulate the lifespan of the mRNA, translation rate, and where in the cytoplasm the mRNA is placed

36
Q

what is splicing and what does it result in?

A

process of removing introns and ligating exons together to make mature mRNA (messenger RNA)

37
Q

what enzyme performs splicing and what is its structure?

A

spliceosome; made of several “small nuclear RNAs” or “snRNAs”

38
Q

how does the spliceosome accurately remove introns?

A

recognizes the “splice donor” and “splice acceptor” sites at the 5’ and 3’ ends of each intron

39
Q

what consequence might mutating the DNA sequences encoding the splice donor or splice acceptor have?

A

prevents splicing

40
Q

how might we make different splice forms of the same gene? what is this process called?

A

by removing exons; called alternative splicing

41
Q

what does alternative splicing allow?

A

allows a single gene to code for several mRNAs, and thus make several different proteins

42
Q

after splicing, what two modifications are made to the ends of mRNA?

A

5’ cap and poly-A tail

43
Q

what is the 5’ cap? how is it accomplished? purpose?

A

a modified guanine nucleotide added to the 5’ end by capping enzymes; needed for stabilization and ribosome binding

44
Q

what is the poly-A tail? purpose?

A

50-250 adenine nucleotides are added to the 3’ end; needed for stabilization and ribosome binding

45
Q

how is the poly-A tail added to the transcript?

A

ribonuclease recognizes the AAUAAA (polyadenylation signal) in the primary transcript and cleaves 11-30 nucleotides 3’ to that sequence; then poly(A) polymerase can add As

46
Q

how long does it take to make a single 10,000 nucleotide primary transcript?

A

2 minutes