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BMS242 Cell and Molecular > L15 - Post Transcriptional Control > Flashcards

L15 - Post Transcriptional Control Flashcards

(70 cards)

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1
Q

At what levels can regulation of gene expression occur at

A

Almost every level: Transcription/translation etc.

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2
Q

% of genes in Drosophila and humans that have alternative splicing

A

40% of Drosophila

75% of Human genes

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3
Q

Describe alternative splicing: Optional exon

A

Middle exon is spliced out of the transcript

Acceptor site used of the first intron and the donor site of the last intron (so intron-exon-intron) spliced out

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4
Q

Describe alternative splicing: Optional intron

A

Where an intron is able to behave as an exon so is not spliced out

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5
Q

Describe alternative splicing: Mutually exclusive exons

A

Where exons are skipped but the two exons are mutually exclusive of each other (i.e. so if exon 1 is in one transcript an exon 2 is not) They are mutually exclusive of each other

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6
Q

Describe alternative splicing: Internal splice sites

A

Where there is a donor site within the intron so only a part of it is spliced out

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7
Q

Why do splice variants occur so frequently

A

Because donor and acceptor sites are only two bases hence they appear very frequently

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8
Q

What is the most spliced gene known

How many isoforms are there

A

Dscam - 38’000

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9
Q

What is an isoform

A

Functionally similar proteins but they do not have the same amino acid sequence - this could be as a result of alternative splicing

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10
Q

Describe the splicing of Dscam gene

A

38000 permutations of the gene

4 sets of mutually exclusive exons

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11
Q

What is special regarding the chromosomes in male and female drosophila

A

Male X
Female XX
There is no Y chromosome in drosophila

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12
Q

Sxl

A

Sex lethal

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13
Q

Tra

A

Transformer

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14
Q

Dsx

A

Double sex

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15
Q

What occurs to Sxl in males

A

Normal splicing occurs - non functional protein is produced

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16
Q

What occurs to Tra in males

A

Normal splicing occurs - non functional Tra protein is produced

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17
Q

What occurs to Dsx in males

A

Middle exon is spliced out

Forms a protein with 400AA at the N’ then a further 150 AA at the C’ this form of the protein is male specific

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18
Q

What occurs to Sxl in females, WHY?

A

Due to the DOUBLE X chr, some active Sxl is made

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19
Q

What is the function of active Sxl made in females (2)

A

Firstly feedbacks on splicing of Sxl (positive feedback) by causing the splicing out of a middle intron ==> leads to more of the active Sxl being made

Then binds to the intron;exon boundary of Tra to alter the splicing

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20
Q

What occurs to Tra in females

A

Different splicing due to the binding of sxl leads to production of functional Tra protein

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21
Q

What binds to the mRNA of Dsx in females to alter splicing

A

Functional Tra and Tra2

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22
Q

What occurs to DSx in females

A

Binding of Tra and Sxl to the mRNA of Dsx - changes the pattern of splicing and a protein with a 400AA at the N’ and then 30AA at the C’ is formed

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23
Q

Is N - 400 - 150 - C Dsx male or female specific

A

Male

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24
Q

Is N - 400 - 30 - C Dsx male of female specific

A

Female

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25
Active sxl represses splicing by blocking ...
U2AF
26
What type of feedback does Sxl use
Positive feedback - feedbacks on its own regualtion
27
What is special about an antibody gene
It has two possible positions for cleavage and poly adenylation
28
Describe what occurs when the cell produces the long transcript of an antibody gene
First stop codon is spliced out | Leads to the translation of a transmembrane domain
29
Describe what happens when the cell produces the short transcript of an antibody gene
Splice acceptor site is lost and so the first stop codon IS NOT spliced out Translation terminated at the first stop codon TM domain is not translated
30
What type of antibody is produced from the long transcript
Membrane bound (TM domain translated)
31
What type of antibody is produced when the cell produces the short transcript
Secreted
32
What does the optimal Kozk sequence describe
The sequence containing AUG which the ribosome is most likely to begin translation at
33
What is the Kozak sequence
ACCAUGG
34
What occurs if the sequence around the start AUG is less than perfect What is this known as
Ribosome can scan past the first AUG until it reaches the next or the next Leaky scanning
35
What cellular conditions would favour the ribosome to begin translation at the first AUG
High levels of eIF-4F inside of the cell
36
Describe the genome of HIV - What happens to it
Small genome which is integrated into the host genome
37
Describe the transcription of HIV Why does this present a problem
Transcribed in one piece - alternative splicing allows for many protein products to be made HOWEVER the full length RNA is required to make the new virions but it is unable to leave the nucelus as it is unspliced
38
How does HIV overcome the problem of not being able to get out of the nucelus without being spliced
By using Rev protein
39
What is the function of Rev protein
Binds to HIV introns and interacts with the nuclear pore to allow the exit of unspliced mRNA
40
What can levels of REV be used for
By clinicians to distinguish between the two phases of infection
41
Signals in the UTR of mRNA are able to ...
Direct it to a part of the cell
42
What can form in the 3' region of the UTR What is the singificance of this
Intermolecular forces allow the formation of stem-loop structures - these can be recongised by cellular proteins and then subsequently targetted to regions of the cell
43
What is the functional of ferritin
Stores Fe - leading to a decrease of Fe levels within the cell
44
What is the function of transferrin
Imports Fe - leading to an increase of Fe levels within the cell
45
What needs to happen (in terms on imported and stored) when Fe is lo
Fe needs to be imported and not stored
46
What needs to happen (in terms of imported and stored) when Fe is hi
Fe needs to be stored and not imported
47
Describe what happens to Ferritin mRNA when Fe is lo
Aconitase binds to the 5' UTR region - this physically blocks the ribosome and no ferrtin protein is made
48
Describe what happens to Transferrin receptor mRNA when Fe is lo
Aconitase binds to the 3' UTR region - this stabilises the mRNA and translation is able to proceed
49
Describe what happens to aconitase when Fe is hi
Fe binds to aconitase - this induces a conformational change so that aconistase is no longer able to bind to the UTRs of the two mRNAs
50
Describe what happens to ferritin mRNA when Fe is hi
Aconitase is unable to bind due to Fe binding to it. | Thus there is no block to translation and it is able to proceed
51
Describe what happens to transferrin receptor mRNA when Fe is hi
Aconistase is unable to bind due to Fe binding to it. Thus the mRNA is more unstable so it is degraded
52
Where does aconitase bind to transferrin R mRNA
3' UTR
53
Where does aconitase bind to ferritin mRNA
5' UTR
54
What initation factor must bind to the small ribosomal subunit in order for scannning to begin
EIF-2 with GTP bound
55
EIF-2B is a
GEF (guanine nucleotide exchange factor)
56
What is the effect of eIF-2B on eIF-2
GDP --> GTP | Activates
57
What is the effect of phosphorylation of eIF-2
Causes eIF-2B to bind very tightly - so eIF-2 remains associated with GDP and so is inactive
58
When does phosphorylation of eIF-2 occur (3 situations) What is the effect of this
Cells entering resting G0 (quiescent), cells that ae infected by a virus or cells which are lacking nutrition Turns down global translation
59
What does IRES stand for
Internal ribosome rentry sites
60
eIF-4g binds to
Tail
61
eIF-4e binds to
Cap
62
What are IRES, what are they able to do
Stem-loop strucutures which can initiate formation of the ribosome independent of the cap/polyA initiation complex being present
63
What is required for IRES bases initiation
eIF-4G
64
Where is IRES often found
In viral transcripts
65
What is the benifit of IRES being present in viral transcripts When else is this seen
It favours translation of their transcripts bu cleaving eIF-4G into a form which cant bind to eIF-4e but can still bind to IRES Also occurs during apoptosis - where certain genes which are involved in the process utilise IRES until they can be translated
66
What is the half life of mRNA
This is highly variable - from several minutes to hours
67
What length to poly A tails start at ... What can cleave them ... How short can they be cleaved ... What is the effect of cleavage this short ...
300 Exonucleases (cut the terminal A off) 30 Causes them to be degraded
68
What occurs in the cytoplasm to extend the life of an mRNA
Can be readenylated
69
What can bind to the mRNA to extend their half life
DAN able to compete with eIF-4E - if DAN binds translation is promoted and degradation of the mRNA is blocked
70
What should be wirtten in italics
Gene and species names

BMS242 Cell and Molecular (26 decks)

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