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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

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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
Q

How many binding sites do ribosomes have ?

A

3

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26
Q

What are the roles of the binding sites in ribosomes ?

A
  1. Binding of mRNA

2. Attach tRNA molecules that carry amino acids to the mRNA template and are labelled

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27
Q

What are the three labels on one of the domains used to attach tRNA molecules ?

A
  1. Aminoacyl site
  2. Peptidyl site
  3. Exit site
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28
Q

How do tRNAs bring amino acids to the ribosomes ?

A

in a manner dictated by the coding sequence of the mRNA

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29
Q

What is tRNA function defined by ?

A

Structure of the molecule

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30
Q

What is the structure of tRNAs ?

A

Cloverleaf shaped polynucleotide sequences

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31
Q

What does the tRNA tail end have ?

A

An acceptor stem

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32
Q

What is the function of the acceptor stem ?

A

Binds a specific amino acid

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33
Q

What does the head of tRNA have ?

A

Three nucleotides that form the anticodon

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34
Q

What is the function of an anticodon ?

A

Recognises the corresponding codon sequence of the mRNA molecule

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35
Q

What do tRNA anticodons bind complementary to ?

A

Triplet codons of the mRNA

36
Q

What are the three stages of translation ?

A
  1. Initiation
  2. Elongation
  3. Termination
37
Q

Initiation: When does translation begin?

A

When the mRNA molecule binds to the small subunit of the ribosome

38
Q

Initiation: Where does mRNA molecule bind to the ribosome in prokaryotes and eukaryotes ?

A

30S in prokaryotes and 40S in eukaryotes

39
Q

Initiation: What makes the mRNA bind to the ribosome in both eukaryotes and prokaryotes ?

A
  1. The recognition of the 5’ cap of eukaryotic mRNAs

2. A sequence upstream of the AUG codon in prokaryotic mRNAs

40
Q

Initiation: What is the shine Dalgarno sequence ?

A

AGGAGG - A sequence upstream of the initiator AUG codon in prokaryotic mRNA

41
Q

Initiation: What is protein synthesis initiated by ?

A

An AUG codon on the mRNA

42
Q

Initiation: What does the AUG codon signal ?

A

Both the interaction of the ribosome with mRNA and also the tRNA with the anticodon (UAC)

43
Q

Initiation: What happens once the AUG codon is recognised ?

A

The large ribosomal subunit associates with the mRNA and the small ribosomal subunit and protein synthesis begins

44
Q

Initiation: What does the start codon always code for ?

A

The amino acid methionine (AUG)

45
Q

Initiation: Where does the start codon enter ?

A

The P site on the ribosome

46
Q

Initiation: Where does the second codon enter ?

A

The A site

47
Q

Initiation: Where does the anticodon of the tRNA carrying methionine base pair with ?

A

Temporarily with the start codon

48
Q

Initiation: Where does the second anticodon complementary to the mRNA codon to the A site form a temporary base pair ?

A

The codon of the mRNA in the A site

49
Q

Initiation: What does the amino acid attached to the tRNA in the A site and the methionine in the P site form ?

A

A polypeptide bond

50
Q

Initiation: What is the polypeptide bond catalysed by ?

A

Peptidyl transferase

51
Q

Elongation: What does the A (aminoacyl) site do ?

A

Binds incoming charged aminoacyl tRNAs

52
Q

Elongation: What does the P (peptidyl) site do ?

A

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
Q

Elongation: What does the E (exit) site do ?

A

Releases dissociated tRNAs so that they can be recharged with free amino acids

54
Q

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 ?

A

Due to ratchet like conformational change

55
Q

Elongation: Where does the ratchet like conformational change take place ?

A

Between the two subunits of the ribosome

56
Q

Elongation: Where is the energy for each peptide bond formation from ?

A

GTP hydrolysis

57
Q

Elongation: Where does the tRNA that was previously in the P site move to ?

A

The exit site and then leaves the ribosome

58
Q

Elongation: Where is the growing peptide chain attached to the tRNA left ?

A

The P site

59
Q

Elongation: What enters the A site ?

A

A new mRNA codon

60
Q

Elongation: What does the tRNA carrying a complementary amino acid connect with ?

A

The bases of the new codon in the A site

61
Q

Elongation: What forms a new peptide ?

A

Two adjacent amino acids

62
Q

Elongation: What is GTP hydrolysis catalysed by ?

A

A separate elongation factor

63
Q

Elongation: Where does the tRNA molecule from the P site move to ?

A

The E site and is released into the cytoplasm where it binds to an amino acid of the same type

64
Q

Elongation: What does a tRNA complementary to the new codon in the A site do ?

A

Creates a new peptide bond between the amino acid and the currently formed peptide chain

65
Q

Termination: When does the process of translation stop ?

A

Until one of the stop codons enters the A site of the ribosome

66
Q

Termination: What are the three stop codons ?

A
  1. TUU
  2. TUG
  3. TGU
67
Q

Termination: When does the protein chain move to the cytoplasm ?

A

Once the final peptide bond is created

68
Q

Termination: Where is the protein chain connected ?

A

Connected only to the tRNA located in the P site

69
Q

What is the ribosome composed of ?

A

Two sub-units which are comprise of ribosomal RNAs and specific ribosomal proteins

70
Q

How is the ribosome formed ?

A

The two sub units fit to each other and form a spherical structure

71
Q

What do prokaryotic ribosomes have ?

A

70S ribosomes

72
Q

Prokaryotic ribosomes: What is their structure ?

A

One large (50S) and one small (30S) subunit

73
Q

Prokaryotic ribosomes: What is the small subunit built from ?

A

A 16S RNA subunit

74
Q

Prokaryotic ribosomes: How long is the small subunit ?

A

1540 nucleotides

75
Q

Prokaryotic ribosomes: How many ribosomal proteins does the small RNA subunit bind to ?

A

21

76
Q

Prokaryotic ribosomes: What does the large subunit contain ?

A

A 5S RNA and a 23S RNA

77
Q

Prokaryotic ribosomes: How long is each of the RNAs in the large subunit ?

A

120 and 2900 nucleotides

78
Q

Prokaryotic ribosomes: How many proteins does the ribosomal RNA molecules bind to ?

A

31

79
Q

Eukaryotic ribosomes: What does the eukaryotic have ?

A

One large (60S) and one small (40S) subunit

80
Q

Eukaryotic ribosomes: What does the ne large (60S) and one small (40S) subunit form ?

A

A 80S ribosome

81
Q

Eukaryotic ribosomes: How many proteins does the small subunit contain ?

A

33

82
Q

Eukaryotic ribosomes: Where does the small subunit bind to and how long is it ?

A
  1. 18S RNA

2. 1900 nucleotides long

83
Q

Eukaryotic ribosomes: How many RNAs do eukaryotes have in their large subunit ?

A

3

84
Q

Eukaryotic ribosomes: What are the 3 RNAs in the large subunit and how long are each of them ?

A
  1. 28S - 4700 nucleotides
  2. 5.8S - 160 nucleotides
  3. 5S - 120 nucleotides
85
Q

Eukaryotic ribosomes: How many proteins does 3 ribosomal RNAs bind to ?

A

46

Molecules to Cells - Genetics and Virology (16 decks)

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