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My Packs: UWO (BIOCHEM 2280) > (Dr. Heinemann) (Unit C) Topic 20 > Flashcards

(Dr. Heinemann) (Unit C) Topic 20 Flashcards

1
Q

How must primary RNA transcript be processed in eukaryotes?

A
  1. Capping of the 5’ end
  2. Polyadenylation
  3. Splicing
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2
Q

What is the 5’ end capped with?

A

7-methylguanosine

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3
Q

What is added in polyadenylation?

A

A long A-tract to the 3’ end

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4
Q

What is the process for polyadenylation?

A
  1. RNA is cleaved ~30 bases following an AAUAAA sequence
  2. A string of A residues is then added (around 300 bases long)
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5
Q

Why is polyadenylation important?

A
  1. Reduces the effects of 3’ exonucleases (stability)
  2. Role in nuclear export
  3. Role in translation
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6
Q

What are noncoding sequences in eukaryotes known as?

A

Introns

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7
Q

What are coding sequences in eukaryotes known as?

A

Exons

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8
Q

Differential splicing

A

mRNA can be put together in different ways genearting functionally related but distinct gene products

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9
Q

What sites are important in splicing (loss of these sites will result in defects in splicing)?

A
  1. 5’ junction
  2. Branch point
  3. 3’ junction
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10
Q

Spliceosome (snRNPs)

A

Remove introns as the result of catalytic activity

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11
Q

What are snRNPs?

A

Small nuclear ribonucleoprotein particles
* Complexes of RNA (snRNA) and protein

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12
Q

Function of RNA component in snRNPs

A

Recognition function
* Acting through base pairing with sequences on the precursor mRNA

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13
Q

True or False:

snRNPs are critical in arranging the ends into position

A

True

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14
Q

What is a spliceosome?

A

The assembly of snRNPs that catalyze splicing

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15
Q

How does splicing occur?

A

2 transesterification reactions

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16
Q

Explain the mechanism of the first transesterification reaction

A
  1. 2’ OH group of branch point adenosine residue (intron) attacks phosphate at 5’ end of intron
  2. Frees the 3’ end of the exon
  3. Forms a lariat-shaped intemediate (loop)
17
Q

Explain the mechanism of the second transesterification reaction

A
  1. Free 3’ OH on the first exon attacks the 5’ phosphate at the second exon
  2. Forms a phosphodiester bond
  3. The exon is kicked out in this reaction and degraded
18
Q

What is beta-thalassemia and how does it occur?

A

Disease characterized by anemia
* Beta subunit of hemoglobin not properly produced, results in excess alpha subunit
* Caused by splicing mutations

19
Q

When does RNA processing occur?

A

While transcription is ongoing

20
Q

Does exporting happens at the same time as processing?

A

No, export happens AFTER processing

21
Q

What is required for mRNA export from the nucleus?

A
  1. 5’ cap
  2. Poly-A binding protein
  3. Specific protein carriers (transport receptor)
22
Q

How is mRNA transport out of the nucleus?

A

Through nuclear pores
* Nuclear pore components recognize proteins associated with the mRNA

23
Q

What happens to mRNAs when they are exported?

A

Circularization
* Indicates a mRNA is processed properly

24
Q

How does mRNA undergo circularization?

A
  • elF4F “cap recognition” protein
  • poly(A) binding protein (PABP)

Interacts with the 5’ cap and poly(A) tail. Result reduces mRNA degradation

25
Q

List in order the steps of mRNA decay

A
  1. Deadenylase: Takes off 3’ PolyA tail
  2. Decapping enzyme: Removes 5’ cap
  3. 5’ and 3’ exonuclease: Degrade mRNA from both ends
26
Q

What is special about tRNA transcripts?

A

Covalently modified
* Highly modified, and often do not function UNLESS modified

27
Q

Are rRNA modified?

A

Yes they are also covalently modified

28
Q

What are some forms of covalent modifications?

A
  • Methylation
  • Hydroxylation
  • Deamination
29
Q

What is sequence specific RNA degradation known as?

A

RNA interference

30
Q

What does RNA interference require?

A
  1. Binding of second complementary RNA strand
  2. With help of several proteins, the mRNA is cleaved and degraded
31
Q

What is the second complementary RNA strand in RNA interference known as?

A

Small interfering RNA or microRNA

My Packs: UWO (BIOCHEM 2280) (25 decks)

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