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Cell and Molecular Biology > RNA synthesis > Flashcards

RNA synthesis Flashcards

1
Q

What is transcription?

A

Process of RNA synthesis from a DNA template

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2
Q

What is the central dogma?

A

DNA -> RNA -> Protein

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3
Q

What are the four RNA types?

A

mRNA
tRNA
rRNA
Noncoding RNAs

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4
Q

What is mRNA?

A

Codes for proteins, makes uo 3 to 5% total RNA

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5
Q

What is tRNA?

A

participates in translation, there are 49 families, each carries an amino acid and has a specific anticodon loop

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6
Q

What is rRNA?

A

ribosomal RNA, major constituent of ribosomes, There are 4 main types

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7
Q

What are noncoding RNAs?

A

Serve as structural and enzymatic functions

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8
Q

What are the four major differences between RNA and DNA?

A

1) Contains ribose instead of deoxyribose
2) Contains U instead of T
3) Synthesised as a new strand
4) RNA is very unstable

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9
Q

What is the structural difference between deoxy-ribose and ribose?

A

Deoxyribose does not have an OH group at C3, just has a H

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10
Q

Which bases pair up in RNA?

A 
U = A
G = C
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11
Q

What is non Watson Crick pairing and can it occur in RNA

A

Where the pairs do not pair according to the watson crick rule ie G = U
Yes it can occur

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12
Q

What is the secondary structure of RNA like?

A

It forms stem-loop secondary structures

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13
Q

What is RNA tertiary structure?

A

Where the RNA folds into a three dimensional shape

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14
Q

What are RNA polymerases?

A

The enzymes which perform RNA synthesis

There are 3 types in eukaryotes

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15
Q

What are the 3 types of RNA polymerases?

A

RNA polymerase I, II and III

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16
Q

What is RNA polymerase I?

A

only transcribes ribosomal RNA

Accounts for 50% of RNA polymerases

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17
Q

What is RNA polymerase II?

A

Protein encoding genes

Transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA

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18
Q

What is RNA polymerase III?

A

The genes transcribed are”housekeeping” genes
Regulation primarily tied to the regulation of cell growth and the cell cycle
eg tRNA, small nuclear RNA and 5S rRNA

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19
Q

Which rRNA does RNA polymerase I not transcribe?

A

5s rRNA

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20
Q

True or false - only one RNA polymerase molecule can bind to a gene at anyone time

A

False - multiple RNA polymerases can bind on the same gene

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21
Q

Is a primer needed for RNA synthesis?

A

No

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22
Q

How many strands are used as a template for RNA synthesis?

A

Only one strand is used

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23
Q

Does the RNA transcript remain bound to the DNA template?

A

No

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24
Q

Describe an issue with RNA synthesis compared to DNA synthesis

A

There is a much higher error rate

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25
Q

How does RNA polymerase act on the DNA double helix?

A

It unwinds it

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26
Q

Give 5 differences between DNA replication and RNA synthesis

A

1) No primer needed
2) Only one strand of DNA is used as the template
3) Transcript does not remain bound to template
4) Higher error rate
5) Multiple RNA Pol bind on the same gene

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27
Q

What are the two directions RNA polymerase can run?

A

Left to right - 5’ to 3’

Right to left - 3’ to 5’

28
Q

Why does RNA polymerase run in both directons?

A

Genes can be on either strand of the DNA

29
Q

The movement that RNA polymerase takes determines what?

A

Which of the 2 DNA strands serves as a template for the synthesis of RNA

30
Q

How is the polymerase direction determined?

A

By the promoter sequence

31
Q

What is the promoter sequence?

A

The site at which RNA polymerase begins transcription

32
Q

What is supercoiling?

A

The creation of a super helix

33
Q

If DNA with a fixed end unwinds 10 DNA base pairs what happens?

A

The DNA helix must rotate one turn

34
Q

If DNA with fixed ends unwinds 10 DNA base pairs what happens?

A

DNA helix forms one supercoil

35
Q

What is the role of topoisomerases?

A

They release supercoils to allow progression of RNA synthesis

36
Q

Where does transcription for a gene start?

A

At its promoter

Sequences in the DNA tell RNA polymerases where to start transcription

37
Q

What are the promoter elements for RNA polymerase 2?

A

BRE - GCGCG (Lots of Gs and Cs)
TATA - TATA (Lots of Ts and As)
INR - CANT
DPE = AGAG

38
Q

What are the general transcription factors for each of the RNA polmerase II promoter elements

A 
BRE = TFIIB
TATA = TBP (TATA binding protein)
INR = TFIID
DPE = TFIID
39
Q

Where does the TATA binding protein bind to?

A

Directly to the DNA ie it binds on to the TATA box

40
Q

TBP is a subunit of what?

41
Q

How many nucleotides does the TATA box usualy lie upstream from the transcription start site?

42
Q

What are the two important roles of the TATA box?

A

It is the DNA sequence that signals the start if transcription
Binding of TFIID causes distortion of the DNA = physical landmark for the location of an active promoter

43
Q

What is formed once a transcription factor has bound to DNA?

A

A transciption initiation complex

44
Q

Which proteins does a transcription initation complex consist of?

A 
General Transcription factors
RNA polymerases
Mediators
Chromatin remodelling complexes
Histone acetlyases
45
Q

How many proteins are there in the complex?

46
Q

What are the 3 ways RNA is processed?

A

Splicing of introns
Capping of the 5’ end
Polyadenylation

47
Q

What is splicing?

A

Where non coding regions of mRNAs are eliminated ti generate mature mRNA for protein synthesis

48
Q

Why is 5’ end capping done?

A

Neccessary for stability, binding of mRNA to ribosomes and initiation of translation

49
Q

What is polyadenylation of the 3’ end?

A

Part of the termination process (addition of the Poly-A tail)
Determines mRNA stabilty, helps mRNA nuclear export and translation

50
Q

Splicing is specific to what type of cell?

A

Eukaryotes

51
Q

Where are introns and exons both present?

A

In DNA and pre-mRNA

52
Q

What is it called when mRNA is spliced in more than one way?

A

Alternative splicing

53
Q

What are the steps involved in splicing?

A

1) The 5’ OH of the branch site in the intron attacks a phosphodiester bond on donor site G
2) Cleavage at the donor site forms a lariat
3) 3’ OH of the donor site attacks a phosphodiester bond on acceptor site G freeing the lariat
4) The lariat is degraded

54
Q

What is a spliceosome?

A

Large and complex molecular machine
Assembled from snRNAs and SR protein.
Removes introns from a transcribed pre-mRNA

55
Q

What is the spliceosome structure?

A

Nuclear complex made of about 150 proteins plus 5 RNAs

56
Q

What are the three functions of the spliceosome?

A

1) Recognise the 5’ donor and branch sites
2) Bring these sites together
3) Catalyses RNA cleavage

57
Q

Which mRNAs have a 5’ cap?

A

All eukaryotic mRNAs

58
Q

When is the cap added?

A

When mRNA is 20-40 nucleotides long

59
Q

What is unusal about the 5’ cap?

A

It has a 5’ to 5’ linkage of guanosine

60
Q

What happens to the guanine in the 5’ cap?

A

It is methylated

61
Q

Where does mRNA cleavage occur after the polyA signal?

A

About 10 to 30 nucleotides downstream

62
Q

What is the polyA signal?

63
Q

Up to how many A can be added?

64
Q

Polyadenylation only occurs on products of which RNA polymerase?

A

RNA polymerase 2

65
Q

What is the role of CPSF?

A

It catalyses the cleavage of the mRNA 10 to 30 nucleotides downstream of the complexes binding site

Cell and Molecular Biology (17 decks)

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