Transcription & RNA processing Flashcards

1
Q

Where is DNA converted to RNA

A

In the nucleus DNA is converted to RNA

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2
Q

Why must genetic code be copied and transferred out of nucleus

A

Because the DNA found in nucleus is too big to move out (carried from DNA in nucleus to ribosomes in cytoplasm)

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3
Q

Define proteome

A

All protein in a cell

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4
Q

Enzymes that synthesise RNA from DNA are called _____

A

RNA polymerases (Pol II)

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5
Q

RNA is synthesised from which strand of DNA and in what direction

A

RNA is synthesised from the TEMPLATE (antisense) DNA strand which runs 3’—5’

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6
Q

In which direction does RNA polymerase synthesise complementary RNA

A

RNA is synthesised 5’—3’ as we synthesise RNA from the template strand so complementary base pairing means it’s the right way round 5’—3’ when it’s made (in RNA U instead of T)

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7
Q

What are the 5 steps of mRNA synthesis

A

INITIATION: polymerase binds to gene

ELONGATION: polymerase transcribes gene

TERMINATION: polymerase stops transcribin gene

PROCESSING: pre mRNA—> mature mRNA is formed

EXPORT: mRNA leaves nucleus through nuclear pore to be translated

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8
Q

What region initiates transcription that the RNA polymerase binds to at beginning

A

RNA polymerase binds close to PROMOTER REGION to initiate transcription

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9
Q

The promoter acts as a template for assembly of ______. This brings Pol II to gene. Once bound, polymerase can transcribe

A

The promoter acts as a template for assembly of PREINITIATION COMPLEX. This brings Pol II to gene. Once bound, polymerase can transcribe

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10
Q

What are the polymerase positioning elements

A

• TATA box= initiator

• upstream + downstream elements that bind +ve & -vely acting transcription factors (enhancers + silencers)

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11
Q

What happens in elongation stage of transcription

A

RNA polymerase synthesises complementary RNA in 5’—3’ direction using NTPs ( ribonucleoside triphosphates)

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12
Q

List difference between RNA & DNA

A
  • different pentose sugar: deoxyribose in DNA, ribose in RNA

*DNA is double stranded; RNA is single stranded

*DNA has Thymine (T), RNA has Uracil (U)

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13
Q

How many bonds between
Thymine and Adenine
Uracil and Adenine

A

2 bonds between T & A
2 bonds between U & A

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14
Q

How many bonds between Guanine and Cytosine

A

3 bonds between G & C

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15
Q

What type of linkages form backbone of both DNA & RNA

A

PHOSPHODIESTER linkages form backbone of both DNA & RNA

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16
Q

Primary mRNA transcript needs to be modified before it’s exported into cytoplasm, explain the 2 caps and their role

A

5’ cap helps with efficient translation, prevents degradation of unstable mRNA molecule. Also directs pre mRNA splicing

3’ cap helps prevent degradation, assists splicing + nuclear export of mRNA

17
Q

What is the role of poly A and where is it

A

Poly A is AAAA at 3’ end of RNA it provides the mRNA with stability and prevents degradation.

18
Q

Describe RNA splicing (going from pre mRNA to final mature mRNA)

A

Cuts out INTRONS (non-coding RNA regions) are spliced out of pre-mRNA leaving the EXONS in the final mature mRNA

19
Q

Define intron

A

Non coding region

20
Q

Define exon

A

Coding region

21
Q

Alternative splicing of mRNA forms what?

A

Alternative splicing forms different ISOFORMS of a protein

I.e. pre-mRNA—> alt splicing—> isoform 1 + isoform 2

These isoforms are fundamentally the same proteins but with slightly different features

22
Q

Describe process of mRNA termination

A

RNA polymerase reaches TERMINATOR SEQUENCE —> transcription stops, mRNA is released

23
Q

Describe process of mRNA processing

A

Polyadenylated region (at PolyA tail on 3’ region) is CLEAVED, the rest of mRNA degrades.
Mature mRNA is ready to be released into cytoplasm

24
Q

What is the function of non-coding regions on DNA

A

Non-coding DNA corresponds to the portions of an organism’s genome that do not code for amino acids (build proteins).

Some non-coding DNA sequences are known to serve functional roles: e.g. regulation of gene expression, while other areas of non-coding DNA have no known function

25
Q

When we want to infer mRNA sequence, we know complementary base pairs line up to form non-template sense (?’) strand (but with U instead of T) from the template antisense (?’) strand

A

When we want to infer mRNA sequence, we know complementary base pairs line up to form non-template sense (5’) strand (but with U instead of T) from the template antisense (3’) strand

26
Q

Give some examples of Mis-regulated gene expression + disease

A

• general transcription factors can be mutated = e.g. cMyc-one is commonly amplified oncogene (large number of transcription factors important for development)

• mutated splice sites = e.g. cancer BRCA1 + 2, spinal muscular atrophy (SMN2), atypical cystic fibrosis (CFTR)

• mutated splicing machinery= retinitis pigmentosa, spinal muscular atrophy

27
Q

Where is information that codes for proteome stored

A

Information to code for proteome is stored in DNA

28
Q

Primary transcripts must be processed by 3 things:

A

Capping
Splicing
Polyadenylating
— this all forms mature mRNA that can be exported to ribosomes in cytoplasm

29
Q

_____ in transcription factors (activating + inactivating) + splice sites affect gene expression + cause disease

A

MUTATIONS in transcription factors (activating + inactivating) + splice sites affect gene expression + cause disease

30
Q

What’s the function of preinitiation complex

A

Regulates transcription + allows polymerase to attach to right part of the gene in order for transcription to be initiated

31
Q

What is the UTR + why is it important

A

Untranslated region (UTR) they are all the regions before + after stop and start codon
They’re important as it’s where RNA polymerase will bind, it’s where termination factors will bind, where preinitiation complexes bind. I.e. controls all proteins that control transcription but don’t contain any sequence that is translated

32
Q

We read DNA 5’ to 3’. We read RNA 5’ to 3’, why do we need to used 3’ to 5’ to synthesise RNA strand in 5’ to 3’

A

Because we use the template antisense strand (3’ to 5’) as RNA polymerase can complementary base pair to this strand and therefore form RNA 5’ to 3’ ( so RNA will be a copy of the 5’ to 3’ strand just with U instead of T)

33
Q

What determines alternative splicing and what exons are kept

A

Different proteins in different cells will determine where the splicing will occur. It requires proteins to bind to splice sites depending on cell. So always different

34
Q

In regards to exon splicing, how many can you splice out but still maintain function of protein

A

Depends on protein! Depends where functional domains are within the protein.

35
Q

If you get mutations in transcription factors that will affect _____

A

If you get mutations in transcription factors that will affect TRANSCRIPTION OF THE GENE I.e. transcription factor isn’t moving away after initiated transcription so the patient will be transcribing gene continuously. If this gene regulates growth or cell division= unregulated growth/ cell division = cause cancer

36
Q

Define oncogene

A

A gene in viruses (v-onc) + mammalian cells (c-onc) that can cause cancer. It results from a mutation of a normal gene