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CMB2001 > CMB2001/L08 Post-transcriptional Control II > Flashcards

CMB2001/L08 Post-transcriptional Control II Flashcards

1
Q

Describe polyadenylation. (2)

A

Endonuclease cleavage in nascent RNA
Addition of As by polyA polymerase

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2
Q

What is ‘USE’?

A

U-rich upstream element (5’ end)

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3
Q

Where is the G/U rich tract located?

A

Just downstream from the polyA site

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4
Q

Where is the conserved AAUAA sequence located?

A

10-35 nucleotides upstream of the polyA site

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5
Q

Which sequences are bound by proteins required for polyadenylation? (3)

A

Cleavage and polyadenylation specificity factor (CPSF) binds AAUAA
Cleavage stimulatory factor (CstF) binds G/U
PolyA polymerase

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6
Q

Give 3 functions of the polyA tail.

A

Enhances export of RNA
Stabilises 3’ end of mRNA
Enhances translation of mRNA

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7
Q

Which mRNAs have a 3’ polyA tail?

A

All except histones

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8
Q

How long is the polyA tail?

A

Approx 250 nts

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9
Q

Define RNA editing.

A

Nucleotide alterations which rsult in different or additional nucleotides in mature RNA

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10
Q

In which 3 major classes of RNA does RNA editing occur?

A

mRNA
tRNA
Ribosomal RNA (rRNA0

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11
Q

Give the 2 classes of editing.

A

Insertion/deletion
Modification (A to I, C to U, U to C)

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12
Q

Why is RNA editing in medicine and development significant?

A

Disease - atherosclerosis
Brain function - human higher brain function and depression
Development - Drosophila
Parasites Trypanosoma Leishmania and Trypanosoma
Mitochondria - potential target for drugs

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13
Q

Name 2 kinds of base modification.

A

Marked nucleotide (reversible)
Altered identity

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14
Q

Give 2 effects of mRNA editing on start codons.

A

Creation of start codons by U insertion
Creation of start codons by C to U changes

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15
Q

Give 2 effects of mRNA editing on stop codons.

A

Creation of stop codons by U insertion
Removal of stop codons by base conversions
Creation of stop codons by C to U changes

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16
Q

Give 2 other effects of mRNA editing on nucleotide sequence.

A

Creation of new ORFs by nucleotide insertion
Changes in encoded amino acids and splice site choice by base conversion

17
Q

Describe RNA editing by deamination.

A

Adenosine converted to inosine by adenosine deaminases
C to U by cytidine deaminases

18
Q

How is inosine read during translation?

A

As guanosine

19
Q

What enzyme carries out cytidine deamination?

A

APOBEC-1

20
Q

What is the enzyme APOBEC-1 linked to?

A

Cholesterol control
Cancer development
Inhibition of viral replication

21
Q

What level of editing occurs in the intestine and in the liver?

A

Intestine - editing to produce ApoB-48
Liver - no editing produces ApoB-100

22
Q

Which long form major component of low density lipoproteins is linked to artherosclerosis?

A

ApoB-100 including LDL-binding receptor

23
Q

Which enzyme carries out A to I editing in the Q/r site of glutamate receptors?

A

ADAR2

24
Q

How does A to I editing in the Q/R site of glutamate receptors affect Ca2+ permeability?

A

Decrease in Ca2+ permeability of channels containing ‘R’ version

25
Q

What is the result of mutations in the mouse ADAR2 gene result in?

A

Seizures
Post-natal death
Neurodegeneration in hippocampus

26
Q

Give 3 reasons for mRNA localisation.

A

Localised protein synthesis
Generate cell polarity
Prevents expression in the wrong place
Promotes efficiency of subsequent protein targeting
Local control of translation

27
Q

Describe diffusion based localisation.

A

mRNAs freely diffuse in cytoplasm and are locally entrapped by anchor proteins

28
Q

Describe active transport based localisation. (2)

A

mRNA recognised by specific trans-acting factors in the nucleus
Cytoplasmic factors ensure transport along a polarised cytoskeleton

29
Q

How is mRNA localised asymmetrically in the cytoplasm?

A

Localised to dendrites or axons enabling synaptic protein synthesis
In embryonic development, specific mRNAs localised to ant/posterior poles of cell to establish polarity and facilitate axis formation

30
Q

Which mechanisms are used to localise mRNAs?

A

Active or passive transport

CMB2001 (11 decks)

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