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Molecular Biology & Genetics > Translation > Flashcards

Translation Flashcards

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1
Q

Translation

What are the 3 different RNAs needed for translation?

A

mRNA (messenger RNA)
rRNA (ribosomal RNA)
tRNA (transfer RNA)

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2
Q

Translation

What is the role of mRNA in translation?

A

Delivers messages containing gene code

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3
Q

Translation

What is the role of rRNA in translation?

A

Major component of ribosomes
Site of translation
Enzymatic activity

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4
Q

Translation

What is the role of tRNA in translation?

A

Translates mRNA code to amino acid code

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5
Q

Translation

Where do you find ribosomes in the cytoplasm?

A

Associated to the ER

Or free moving

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6
Q

Translation

What do all ribosomes consist of?

A

A small and a large subunit

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7
Q

Translation

How are ribosome subunits and rRNA classified?

A

According to size

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8
Q

Translation

What units are used to measure ribosome size?

A

Svedberg units (S)

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9
Q

Translation

What forms the scaffold part of the ribosome?

A

Ribosomal proteins

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10
Q

Translation

What is the size of a bacterial ribosome?

A

70S

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11
Q

Translation

What is the size of a eukaryotic ribosome?

A

80S

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12
Q

Translation

What is the principle of the Svedberg unit?

A

S = the speed a particle will travel (um/s) under an acceleration of a million gravities
A larger particle will have a large S value

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13
Q

Translation

What is weird about the S value of the whole ribosome when compared to it’s subunits?

A

The subunits S value doesn’t add together to equal that of the whole

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14
Q

Translation

Are ribosomes conserved?

A

Very much so

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15
Q

Translation

What are the sizes of the subunits in prokaryotic ribosomes?

A

Large subunit = 50S

Small subunit = 30S

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16
Q

Translation

What makes up the small subunit in prokaryotic ribosomes?

A

16S rRNA

21 proteins

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17
Q

Translation

What makes up the large subunit in prokaryotic ribosomes?

A

23S rRNA
5S rRNA
34 proteins

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18
Q

Translation

What are the sizes of the subunits in eukaryotic ribosomes?

A

Large subunit = 60S

Small subunit = 40S

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19
Q

Translation

What makes up the small subunit in eukaryotic ribosomes?

A

18S rRNA

33 proteins

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20
Q

Translation

What makes up the large subunit in eukaryotic ribosomes?

A

28S rRNA
5S rRNA
5.8S rRNA
50 proteins

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21
Q

Translation

How are bacterial rRNA genes organised?

A

As a single operon

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22
Q

Translation

How many rRNA genes does the human genome contain?

A

> 200

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23
Q

Translation

How are the 28S, 5.8S and 18S rRNA units coded in the human genome?

A

In a single transcription unit (45S)
Two internally transcribed spaces separate them
5 clusters of them

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24
Q

Translation

What are the clusters of rRNA genes called?

A

Nuclear organiser regions (NORs)

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25
Q

Translation

How does the 5S subunit appear in the human genome?

A

In tandem arrays
On chromosome 1q41-42
Number of repeats is variable

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26
Q

Translation

What are the nuclear organiser regions that code for multiple rRNA subunits transcribed by?

A

RNA polymerase I

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27
Q

Translation

What are the tandem arrays of 5S rRNA subunit transcribed by?

A

RNA polymerase III

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28
Q

Translation

What is a pseudoknot?

A

The extensive tertiary structures formed rRNAs

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29
Q

Translation

What is responsible for catalytic reactions within the ribosome?

A

rRNA

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30
Q

Translation

What is the enzymatic function of 28S RNA?

A

Catalyses the synthesis of peptide bonds between amino acids

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31
Q

Translation

What are the rRNA subunits that perform enzymatic functions called?

A

Ribozymes

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32
Q

Translation

What is the enzymatic function of 18S rRNA?

A

Binds mRNA

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33
Q

Translation

What is the site of translation?

A

rRNA component of ribosome

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34
Q

Translation

How does the ribosome know which frame is the open reading frame?

A

It searches for the initiation codon and reads from there

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35
Q

Translation

What is the initiation codon in mRNA and what does it code for?

A

AUG - methionine

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36
Q

Translation

What happens when the ribosomes recognises the initiation codon?

A

The initiation codon is bound by initiator tRNA

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37
Q

Translation

Describe the structure of tRNA

A 
100bp long
Complex
4 double stranded stems/arms
3 loop regions
Clover leaf structure
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38
Q

Translation

What are the 4 double stranded arms in tRNA?

A

Acceptor arm
Anticodon arm
D arm
TΨC arm

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39
Q

Translation

Which arm of tRNA doesn’t have a loop and what does it have instead?

A

Acceptor arm

Made up of free 3’ end of tRNA

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40
Q

Translation

What is the triplet at the 3’ end of tRNA that carries amino acids?

A

CAA

41
Q

Translation

What is the role of the acceptor arm in tRNA?

A

To carry the amino acid

42
Q

Translation

What is the role of the anticodon loop in tRNA?

A

Recognises it’s complimentary mRNA triplet

43
Q

Translation

What are the roles of the D and T arms in tRNA?

A

They promote binding

44
Q

Translation

What is eukaryotic tRNA transcribed by?

A

RNA polymerase III

45
Q

Translation

What are the steps of tRNA transcription?

A

Endo- and exo-ribonucleases cleave the primary transcript
CAA added by tRNA nucletidyl transferase
Introns spliced out
Bases chemically modified

46
Q

Translation

What is the difference between eukaryotic and prokaryotic tRNA transcription?

A

Prokaryotic tRNA doesn’t need cleaving or splicing

47
Q

Translation

What enzyme adds the CAA codon to the 3’ end of tRNA?

A

tRNA nucletidyl transferase

48
Q

Translation

What do the modifications to the bases in tRNA affect?

A

Conformation and base pairing

49
Q

Translation

What process does the term “charging” describe when used on tRNA?

A

The binding of the specific amino acid to its matching tRNA by a equally specific enzyme

50
Q

Translation

What are the enzymes that matches the corresponding amino acid to it’s tRNA?

A

Aminoacyl tRNA synthetases

51
Q

Translation

What does the term tRNA wobble refer to?

A

When the 1st position of the anticodon (5’ end) of tRNA can form a non-standard base pair with sequence of mRNA

52
Q

Translation

What does the term codon bias refer to?

A

When some codons are used more often than others

53
Q

Translation

What can cause the translation rate to be slower?

A

Uncommon codons called choke points

54
Q

Translation

What can cause an increased translation rate?

A

Common codons called Slippery sequences

55
Q

Translation

What can lead to ribosome slip?

A

Slippery sequences (common codons)

56
Q

Translation

What can happen when a codon slips?

A

A frameshift in the protein

57
Q

Translation

What could be the effects of a frameshift mutation in translation?

A

Introduction of STOP codon that causes a truncated protein

Protein sequence altered downstream of the mutation

58
Q

Translation

What mutation doesn’t alter the amino acid sequence?

A

Silent mutations

59
Q

Translation

What mutations add a premature STOP codon?

A

Nonsense mutations

60
Q

Translation

What mutations alter the amino acid sequence?

A

Missense mutations

61
Q

Translation

What is the pre-initiation complex?

A

A free small ribosome subunit binds to the mRNA Accompanied by the initiation tRNA and initiation factors

62
Q

Translation

What makes up the pre-initiation complex?

A

The small subunit
Initiation tRNA
Initiation factors

63
Q

Translation

What does the initiation factor IF2 do?

A

Binds to tRNA

64
Q

Translation

What dos the initiation factor IF3 do?

A

Recognises AUG start codon

Prevents large subunit prematurely binding

65
Q

Translation

What are the steps of forming the initiation complex in prokaryotes?

A 
Initiation factors bind to 30S subunit
16S rRNA anneals to mRNA
tRNA binds to initiation codon
IF3 is released
Large subunit binds
IF1 and IF2 are released
66
Q

Translation

What is the role of elF2 in eukaryotic translation?

A

Chaperones tRNA onto the small subunit

67
Q

Translation

What is the role of elF4 in eukaryotic translation?

A

Loops mRNA

Bridges PABP & mRNA cap

68
Q

Translation

What is the role of elF3 in eukaryotic translation?

A

Guides looped mRNA into the correct position

69
Q

Translation

What are elF3 and elF4 known as together?

A

Cap-binding complex

70
Q

Translation

What is the S value of the pre-initiation complex in eukaryotic translation?

A

48S

71
Q

Translation

How is mRNA recognised in eukaryotic translation?

A

By its cap structure

72
Q

Translation

What are the steps for forming the initiation complex in eukaryotes?

A 
Pre-initiation complex scans downstream of the cap-binding complex
tRNA binds to the initiation sequence
elF4 released
mRNA loop released
elF5 mediates binding of large subunit
elF2 and elF3 released
73
Q

Translation

What is the role of elF5?

A

Mediates the binding of the large subunit

74
Q

Translation

What are the 3 binding sites on the large subunit?

A

Aminoacyl site
Peptidyl site
Exit site

75
Q

Translation

Which part of the ribosome has the 3 binding sites?

A

The large subunit

76
Q

Translation

What happens in the aminoacyl site in elongation?

A

Site where the charged tRNA binds to the mRNA

77
Q

Translation

What happens in the peptidyl site in elongation?

A

The growing peptide chain is carried here

78
Q

Translation

What is the purpose of the exit site in elongation?

A

Allows the empty tRNAs to exit the ribosome

79
Q

Translation

What elongation factor escorts the aminoacyl tRNA to the A site in prokaryotes?

A

EF-Tu

80
Q

Translation

What elongation factor escorts the aminoacyl tRNA to the A site in eukaryotes?

A

Ef-1

81
Q

Translation

What are the steps of enlogation?

A

Aminoacyl tRNA binds at A site
Peptide bond formed between the amino acids in the P site and the A site
tRNAs are displaced and mRNA moves one codon sideways compared to ribosome

82
Q

Translation

What mediates ribosome movement in eukaryotes?

A

EF-2

83
Q

Translation

What mediates ribosome movement in prokaryotes?

A

EF-G

84
Q

Translation

What are the steps of translation termination?

A

Ribosome encounters a STOP codon
Release factors bind to the A site
Peptide cleaved from final tRNA
Ribosome dissociates

85
Q

Translation

What release factors are involved in prokaryotic translation termination?

A

RF1
RF2
RF3

86
Q

Translation

What release factors are involved in eukaryotic translation termination?

A

eRF1

87
Q

Translation

What can allow termination suppression?

A

Wobble at stop codon allows the delivery of an amino acid even though it doesn’t fully match

88
Q

Translation

Polycistronic mRNA

A

One mRNA that encodes for several proteins

Each gene has its own Shine-Delgarno sequence, initiation codon and stop codon

89
Q

Translation

What is different about translation with a polycistronic mRNA?

A

Codes for more than one protein
Ribosomes stay attached to mRNA at termination
Recruits new tRNA and IFs

90
Q

Translation

Shine-Delgarno sequence

A

Sequence close to the start of the front of mRNA that is recognised by the ribosome
Only found in prokaryotic cells

91
Q

Translation

Kozak sequence

A

Marks the initiation site on the mRNA in eukaryotic translation

92
Q

Translation

What do proteins pass through if they are destined for the endomembrane or secretion?

A

Endoplasmic reticulum

93
Q

Translation

What aids with the transportation of newly translated proteins and how?

A

Signal recognition particles

Bind ribosomes to the ER

94
Q

Translation

How are proteins further modified as they pass through the ER and golgi body?

A

Folded
Cleaved
Sugar groups added

95
Q

Translation

When a peptide bond is formed between the amino acid in the A site and the P site, which groups are joined?

A

The carboxyl group of the amino acid in the P site

The amino group of the amino acid in the A site

96
Q

Translation

What RNA is produced by RNA polymerase I?

A

rRNA
28S RNA
5.8S RNA
18S RNA

97
Q

Translation

What RNA is produced by RNA polymerase II?

A

mRNA
snRNA
miRNA

98
Q

Translation

What RNA is produced by RNA polymerase III?

A

tRNA
5S rRNA
snRNA
snoRNA

Molecular Biology & Genetics (8 decks)

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