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Molecules to Cells - Genetics and Virology > Lecture 28. Protein translation and alternative splicing > Flashcards

Lecture 28. Protein translation and alternative splicing Flashcards

1
Q

What does RNA splicing regulate in eukaryotes ?

A

The complexity of gene expression products

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2
Q

What are gene coding sequences called in eukaryotes ?

A

Exons

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3
Q

What are exons ?

A

Expressed regions

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4
Q

What are introns ?

A

Intervening regions

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5
Q

What are gene coding sequences interrupted by ?

A

non-coding sequences called introns

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6
Q

What is pre mRNA splicing carried out by ?

A

A large molecular complex called the splicesome

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7
Q

What is the function of a spliceosome ?

A

Recognizes the junctions between introns and exons and can exise the introns to produce a fully splice mRNA molecule

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8
Q

What studies show that genes were comprised of uninterrupted stretches of coding sequences ?

A

Studies in bacteria

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9
Q

Do introns evolve rapidly ?

A

Yes

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10
Q

What is the donor site ?

A

5’ splice site

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11
Q

What is the acceptor site ?

A

3’ splice site

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12
Q

What is a major source of protein diversity in higher eukaryotes ?

A

Alternative splicing

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13
Q

When does alternative splicing occur?

A

When the pre mRNA is processed in different ways to produce mature transcripts lacking one or more exons

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14
Q

What is the product of alternative splicing ?

A

Splice variants

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15
Q

Do splice variants have the same or different function to the full length splice form ?

A

Different function

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16
Q

What is alternative splicing regulated by ?

A

Molecules that sit on the pre-mRNA

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17
Q

What do molecules that sit on the pre-mRNA prevent ?

A

Access of the splicing machinery to different splice sites

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18
Q

What is the calcitonin/neuropeptide gene ?

A

Two completely different proteins made in thyroid cells verses neurons

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19
Q

What is the DSCAM gene in drosphilia for ?

A

Involved in specifying neural circuitry

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20
Q

How many different possible protein isoforms are there in the DSCAM gene in drosphilia ?

A

38000

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21
Q

Where are mRNAs translated into proteins ?

A

Ribosomes

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22
Q

Where does the process of translation begin ?

A

cytoplasm

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23
Q

What happens in the process of translation in the cytoplasm ?

A

mRNA binds with ribosomes

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24
Q

What are ribosomes ?

A

Protein synthesis machines

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25
How many binding sites do ribosomes have ?
3
26
What are the roles of the binding sites in ribosomes ?
1. Binding of mRNA | 2. Attach tRNA molecules that carry amino acids to the mRNA template and are labelled
27
What are the three labels on one of the domains used to attach tRNA molecules ?
1. Aminoacyl site 2. Peptidyl site 3. Exit site
28
How do tRNAs bring amino acids to the ribosomes ?
in a manner dictated by the coding sequence of the mRNA
29
What is tRNA function defined by ?
Structure of the molecule
30
What is the structure of tRNAs ?
Cloverleaf shaped polynucleotide sequences
31
What does the tRNA tail end have ?
An acceptor stem
32
What is the function of the acceptor stem ?
Binds a specific amino acid
33
What does the head of tRNA have ?
Three nucleotides that form the anticodon
34
What is the function of an anticodon ?
Recognises the corresponding codon sequence of the mRNA molecule
35
What do tRNA anticodons bind complementary to ?
Triplet codons of the mRNA
36
What are the three stages of translation ?
1. Initiation 2. Elongation 3. Termination
37
Initiation: When does translation begin?
When the mRNA molecule binds to the small subunit of the ribosome
38
Initiation: Where does mRNA molecule bind to the ribosome in prokaryotes and eukaryotes ?
30S in prokaryotes and 40S in eukaryotes
39
Initiation: What makes the mRNA bind to the ribosome in both eukaryotes and prokaryotes ?
1. The recognition of the 5' cap of eukaryotic mRNAs | 2. A sequence upstream of the AUG codon in prokaryotic mRNAs
40
Initiation: What is the shine Dalgarno sequence ?
AGGAGG - A sequence upstream of the initiator AUG codon in prokaryotic mRNA
41
Initiation: What is protein synthesis initiated by ?
An AUG codon on the mRNA
42
Initiation: What does the AUG codon signal ?
Both the interaction of the ribosome with mRNA and also the tRNA with the anticodon (UAC)
43
Initiation: What happens once the AUG codon is recognised ?
The large ribosomal subunit associates with the mRNA and the small ribosomal subunit and protein synthesis begins
44
Initiation: What does the start codon always code for ?
The amino acid methionine (AUG)
45
Initiation: Where does the start codon enter ?
The P site on the ribosome
46
Initiation: Where does the second codon enter ?
The A site
47
Initiation: Where does the anticodon of the tRNA carrying methionine base pair with ?
Temporarily with the start codon
48
Initiation: Where does the second anticodon complementary to the mRNA codon to the A site form a temporary base pair ?
The codon of the mRNA in the A site
49
Initiation: What does the amino acid attached to the tRNA in the A site and the methionine in the P site form ?
A polypeptide bond
50
Initiation: What is the polypeptide bond catalysed by ?
Peptidyl transferase
51
Elongation: What does the A (aminoacyl) site do ?
Binds incoming charged aminoacyl tRNAs
52
Elongation: What does the P (peptidyl) site do ?
Binds charged tRNAs carrying amino acids that have formed polypeptide bonds with the growing polypeptide chain but have not yet dissociated from their corresponding tRNA
53
Elongation: What does the E (exit) site do ?
Releases dissociated tRNAs so that they can be recharged with free amino acids
54
Elongation: Why does the ribosome move along the mRNA sequence and the tRNA that resided in the A site moves over to the P site ?
Due to ratchet like conformational change
55
Elongation: Where does the ratchet like conformational change take place ?
Between the two subunits of the ribosome
56
Elongation: Where is the energy for each peptide bond formation from ?
GTP hydrolysis
57
Elongation: Where does the tRNA that was previously in the P site move to ?
The exit site and then leaves the ribosome
58
Elongation: Where is the growing peptide chain attached to the tRNA left ?
The P site
59
Elongation: What enters the A site ?
A new mRNA codon
60
Elongation: What does the tRNA carrying a complementary amino acid connect with ?
The bases of the new codon in the A site
61
Elongation: What forms a new peptide ?
Two adjacent amino acids
62
Elongation: What is GTP hydrolysis catalysed by ?
A separate elongation factor
63
Elongation: Where does the tRNA molecule from the P site move to ?
The E site and is released into the cytoplasm where it binds to an amino acid of the same type
64
Elongation: What does a tRNA complementary to the new codon in the A site do ?
Creates a new peptide bond between the amino acid and the currently formed peptide chain
65
Termination: When does the process of translation stop ?
Until one of the stop codons enters the A site of the ribosome
66
Termination: What are the three stop codons ?
1. TUU 2. TUG 3. TGU
67
Termination: When does the protein chain move to the cytoplasm ?
Once the final peptide bond is created
68
Termination: Where is the protein chain connected ?
Connected only to the tRNA located in the P site
69
What is the ribosome composed of ?
Two sub-units which are comprise of ribosomal RNAs and specific ribosomal proteins
70
How is the ribosome formed ?
The two sub units fit to each other and form a spherical structure
71
What do prokaryotic ribosomes have ?
70S ribosomes
72
Prokaryotic ribosomes: What is their structure ?
One large (50S) and one small (30S) subunit
73
Prokaryotic ribosomes: What is the small subunit built from ?
A 16S RNA subunit
74
Prokaryotic ribosomes: How long is the small subunit ?
1540 nucleotides
75
Prokaryotic ribosomes: How many ribosomal proteins does the small RNA subunit bind to ?
21
76
Prokaryotic ribosomes: What does the large subunit contain ?
A 5S RNA and a 23S RNA
77
Prokaryotic ribosomes: How long is each of the RNAs in the large subunit ?
120 and 2900 nucleotides
78
Prokaryotic ribosomes: How many proteins does the ribosomal RNA molecules bind to ?
31
79
Eukaryotic ribosomes: What does the eukaryotic have ?
One large (60S) and one small (40S) subunit
80
Eukaryotic ribosomes: What does the ne large (60S) and one small (40S) subunit form ?
A 80S ribosome
81
Eukaryotic ribosomes: How many proteins does the small subunit contain ?
33
82
Eukaryotic ribosomes: Where does the small subunit bind to and how long is it ?
1. 18S RNA | 2. 1900 nucleotides long
83
Eukaryotic ribosomes: How many RNAs do eukaryotes have in their large subunit ?
3
84
Eukaryotic ribosomes: What are the 3 RNAs in the large subunit and how long are each of them ?
1. 28S - 4700 nucleotides 2. 5.8S - 160 nucleotides 3. 5S - 120 nucleotides
85
Eukaryotic ribosomes: How many proteins does 3 ribosomal RNAs bind to ?
46

Molecules to Cells - Genetics and Virology (16 decks)

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