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USMLE Biochemistry > DNA Transcription > Flashcards

DNA Transcription Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the function of ribosomal RNA?

A

Forms ribosomes

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2
Q

What is the function of microRNA miRNA?

A
  • Regulates gene expression
  • Target mRNA molecules -> bind via base pairing
  • Block translation into protein
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3
Q

What is the function of small interfering RNA (siRNA)?

A
  • Regulates gene expression

- Cause degradation of mRNA

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4
Q

What is the function of small nuclear RNA (snRNA)?

A

Splices pre-mRNA

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5
Q

What does RNA polymerase not require?

A

A primer

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6
Q

What does RNA polymerase bind to and what does this require?

A

Binds promoter regions of DNA

- Requires transcription factors (proteins)

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7
Q

How many RNA polymerases do prokaryotes contain?

A

One RNA polymerase

- Multi subunit complex which makes all types of RNA

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8
Q

How many RNA polymerases do eukaryotes contain?

A

RNA polymerase I II and III

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9
Q

What does RNA polymerase I synthesise?

A

most rRNA (5.8S, 18S, 28S)

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10
Q

What does RNA polymerase II synthesise?

A

mRNA

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11
Q

What does RNA polymerase III synthesise

A

rRNA (5S), other RNA

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12
Q

What does Alpha amanitin (Amanita phalloides) (death cap mushroom) inhibit?

A

RNA polymerase II

- Causes liver failure

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13
Q

What antibiotic can inhibit bacterial RNA polymerase?

A

Rifampin

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14
Q

What chemotherapy drug can inhibit RNA polymerase?

A

Actinomycin D

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15
Q

What do prokaryotes have that act as transcription factors?

A

Protein factor (sigma factor)

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16
Q

What do transcription factors (TFIID, TFIIB, TFIIE) bind to to initiate transcription?

A

RNA polymerase II

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17
Q

What are promoters?

A

DNA regions that are not transcribed

  • They bind RNA polymerase and transcription factors
  • Bound RNA polymerase and open double helix
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18
Q

Name some promoter regions of DNA

A
  • TATA box
  • CAAT box
  • GC box
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19
Q

What do DNA enhancers do?

A

DNA sequences that increase the rate of transcription

  • May be upstream or downstream of the gene they regulate
  • Stabilise TF and RNA polymerase to enable more transcription
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20
Q

Transcription factors that bind to enhancers are known as what?

A

Activators

21
Q

How can an enhancer be many NTs away yet still enhance nearby DNA?

A

It is geometrically close due to DNA coiling

22
Q

DNA sequences that decrease the rate of transcription are known as what?

A

Silencers

23
Q

What do Silencers prevent?

A

RNA polymerase binding

24
Q

Silencers bind to TF known as what?

A

Repressors

- Prevent RNA polymerase binding preventing transcription

25
Q

What is the function of the 5’ untranslated region of mRNA??

A

Recognised by ribosomes to initiate translocation

26
Q

What is the function of the 3’ untranslated region of DNA?

A

Important for post-transcriptional gene expression

27
Q

Do introns or extrons leave the nucleus to become translated?

A

Extrons - exit nucleus

28
Q

What is the initial transcription of RNA called? (contains introns and extrons)

A

hnRNA

29
Q

What are the 3 key modifications that occur before RNA leaves the nucleus?

A
  • 5’ capping
  • Splicing out of introns
  • 3’ polyadenation
30
Q

What is 5’ capping?

A

Addition of 7-methylguanosine to 5’ end

  • Added soon after transcription begins
  • Distinguishes mRNA from other RNA
31
Q

What is the 5’ splice site of the intron coded with?

A

GU

32
Q

What is the 3’ splice site of the intron coded with?

A

AG

33
Q

What base is highly concentrated in snRNP

A

Uridine

  • 5 different U-RNPs identified
  • U1, U2, U4, U5 and U6
34
Q

RNA splicing occurs after the formation of what?

What does mRNA join with?

A

snRNPs combines with mRNA to form a splicesome

35
Q

What is the loop of mRNA called with the intron?

A

Lariat

- Released with the intron to form the exons

36
Q

What are anti-smith (Anti-Sm) antibodies antibodies against?

A

proteins in snRNPs

37
Q

What condition has anti-sm antibodies?

A

SLE

- antibodies against snRNPs

38
Q

What do anti-RNP antibodies attack?

A

U1 RNA (type of sn-RNP)

39
Q

What conditions are associated with anti-RNP (U1 RNA) antibodies?

A

Mixed Connective tissue disease (mainly)

Also:

  • SLE
  • Scleroderma
40
Q

What does alternative splicing allow for?

A

Many proteins from the same gene

41
Q

Splicing errors can lead to what diseases?

A
  • Beta thalassemia

- Oncogenesis - many splice site mutations/errors described

42
Q

What are the bases which code for 3’ Polyadenylation?

A

AAUAAA followed by 10-30 NTs then CA

43
Q

What are the 3 enzymes involved in 3’ Polyadenylation?

A
  • Cleavage and polyadenylation specificity factor (CSF) (AAUAA)
  • Cleavage stimulation factor (CstF) (CA)
  • Poly-A polymerase (PAP) (after transcription is terminated)
44
Q

What enzyme binds to AAUAA (3’ Polyadenylation)?

A

Cleavage and polyadenylation specificity factor (CSF)

45
Q

What enzyme binds to CA sequence (3’ Polyadenylation)?

A

Cleavage stimulation factor

46
Q

What does Poly-A polymerase (PAP) add to the 3’ end of mRNA?

A

~ 200 Adensoine nucleotides

47
Q

What can extensive binding of Micro RNA (miRNA) cause the removal of on mRNA?

A

poly-A tail

  • Exposes mRNA to degradation
  • Essentially modifies gene expression at mRNA level
48
Q

What are P-bodies? (processing bodies)

A

When miRNA binds to mRNA less extensively some mRNA can be moved to the P-bodies in the cytoplasm

  • can cause mRNA to be sequestered from ribsomes meaning no translation
  • When P-bodies hold the mRNA they can be degraded or held until a later point and then translated

USMLE Biochemistry (44 decks)

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