(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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the 5’ end capped with?

A

7-methylguanosine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is added in polyadenylation?

A

A long A-tract to the 3’ end

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why is polyadenylation important?

A
  1. Reduces the effects of 3’ exonucleases (stability)
  2. Role in nuclear export
  3. Role in translation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are noncoding sequences in eukaryotes known as?

A

Introns

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are coding sequences in eukaryotes known as?

A

Exons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Differential splicing

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Spliceosome (snRNPs)

A

Remove introns as the result of catalytic activity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are snRNPs?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Function of RNA component in snRNPs

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

True or False:

snRNPs are critical in arranging the ends into position

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is a spliceosome?

A

The assembly of snRNPs that catalyze splicing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How does splicing occur?

A

2 transesterification reactions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
List in order the steps of mRNA decay
1. **Deadenylase**: Takes off 3' PolyA tail 2. **Decapping enzyme**: Removes 5' cap 3. **5'** and **3' exonuclease**: Degrade mRNA from both ends
26
What is special about tRNA transcripts?
Covalently modified * Highly modified, and often do not function UNLESS modified
27
Are rRNA modified?
Yes they are also covalently modified
28
What are some forms of covalent modifications?
* Methylation * Hydroxylation * Deamination
29
What is sequence specific RNA degradation known as?
RNA interference
30
What does RNA interference require?
1. Binding of second complementary RNA strand 2. With help of several proteins, the mRNA is cleaved and degraded
31
What is the second complementary RNA strand in RNA interference known as?
Small interfering RNA or microRNA