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ML2001: Introductory Molecular Biology > Protein Synthesis > Flashcards

Protein Synthesis Flashcards

1
Q

What THREE components are required for Translation?

A
  • Ribosomes
  • tRNA
  • mRNA
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2
Q

Which arm of tRNA carries amino acids attached to 3’ Adenosine?

A

Amino Acid arm

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3
Q

Which arms of tRNA contains dihyrouridine ribothymidine?

A

D & TyC arms

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4
Q

Which arm of tRNA interacts with the codon in mRNA?

A

Anticodon arm

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5
Q

How does tRNA interact with mRNA?

A

Via triplet bases in the tRNA with the triplet code in mRNA

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6
Q

Which direction does base pairing occur on the Codon in mRNA?

A

5’ to 3’

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7
Q

Which direction does base pairing occur on the Anti-Codon in tRNA?

A

3’ to 5’

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8
Q

Which direction are Codon and Anti-Codon positions read when bound together?

A

5’ to 3’

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9
Q

Is the genetic code in mRNA an overlapping code or non-overlapping code?

A

Non-Overlapping

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10
Q

Which amino acid is coded for by CCC?

A

Proline

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11
Q

Which amino acid is coded for by AAA?

A

Lysine

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12
Q

Which amino acid is coded for by UUU?

A

Phenylalanine

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13
Q

How many reading frames does mRNA contain?

A

3

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14
Q

How many codons are there?

A

61 for amino acids and 3 stop codons

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15
Q

What is the Initiation Codon and which amino acid does it specify?

A
  • AUG
  • Methionine
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16
Q

What are the Stop Codons?

A
  • UAA
  • UAG
  • UGA
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17
Q

How many codons are represented by the Open Reading Frame (ORF)?

A

50 or more

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18
Q

Are amino acids specified by more than one codon?

A

Yes.
Due to genetic code being Degenerate

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19
Q

What allows tRNAs to recognise more than one codon in mRNA, and what does this allow?

A

Wobble allows flexibility/speed

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20
Q

Where do codons read 5’ to 3’ have most specificity?

A

In the first two bases

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21
Q

What nucleoside can tRNA anti-codons sometimes contain at their first codon?

A

Inosine

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22
Q

Which bases can Inosine pair with?

A

U, C, or A

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23
Q

Which bases give strong base pairing between the Codon and Anti-Codon?

A

First two bases

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24
Q

Which bases determine the number of codons recognised by tRNA?

A

The first base in the anti-codon and the third base in the codon

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25
Q

How many codons are recognised if the first base of the anti-codon is C or A?

A

One

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26
Q

How many codons are recognised if the first base of the anti-codon is U or G?

A

Two

Less specific

27
Q

How many codons are recognised if the first base of the anti-codon is I?

A

Three

28
Q

When are different tRNAs required?

A

If the amino acid is specified by several codons, the codons that differ in either of their first 2 bases

29
Q

How many tRNAs are required to translate all 61 codons?

A

32

30
Q

What type of mutations is the Genetic Code resistant to?

A

Missense mutations
(1bp change)

31
Q

What is the site of Protein Synthesis in the cell?

A

Ribosomes

tRNA brings amino acids to mRNA at ribosomes

32
Q

What size ribosomes are present in Bacteria?

A

70s
(50s & 30s subunits)

33
Q

What size ribosomes are present in Eukaryotes?

A

80s
(60s & 40s subunits)

34
Q

What are the FIVE stages of Protein Synthesis?

A
  1. Activation of amino acids
  2. Initiation
  3. Elongation
  4. Termination and Release (Ribosome recycled)
  5. Folding & Post-Translational Processing
35
Q

What enzyme is involved in amino acid activation & what does it do?

A
  • Aminoacyl tRNA Synthetase
  • Proper placement of amino acid in polypeptide chain on tRNA
36
Q

Why are amino acids activated?

A

For peptide bond formation

37
Q

What terminus does Initiation begin at?

A

Amino (N) terminus

38
Q

What terminus are amino acids added to during Initiation?

A

C terminus

39
Q

What is the first amino acid added to the N terminus in Eukaryotes during Initiation?

A

Methionine with Special tRNA

40
Q

What is the first amino acid added to the N terminus in Bacteria during Initiation?

A

fMet-tRNA
(N-formylmethionine)

41
Q

Where is the Initiating 5’ AUG codon in bacterial mRNA?

A

Near a Shine Delgarno sequence

42
Q

What is the purpose of the Shine Delgarno sequence?

A
  1. Guide ribosome small subunit to initiation site on mRNA
  2. Base pairs with complementary sequence in 16s rRNA in 30s subunit of ribosome
  3. Positions starting 5’ AUG at righ position in ribosome to bind to fMet tRNA
43
Q

Can Shine Delgarno sequences be found in both Eukaryotic & Bacterial mRNA?

A

No.
Only bacterial mRNA

44
Q

What are the THREE steps in Initiation?

A
  1. 30s subunit bonds two initiation factors; IF-3 & IF-1
  2. GTP IF-2 and fMet-tRNA come in
  3. 50s subunit associates
45
Q

What are the THREE sites on the Ribosome?

A
  1. Aminoacyl (A) site
  2. Peptidyl (P) site
  3. Exit (E) site
46
Q

Which site does IF-1 bind on the Ribosome?

A

A site

47
Q

Where does the start codon (AUG) locate to on the Ribosome?

A

P site

48
Q

Which site on the Ribosome can only fMet tRNA bind to?

A

P site

49
Q

What are the steps for the FIRST part of Elongation?

A
  1. Incoming aminoacyl tRNA binds to EF-Tu-GTP
  2. tRNA complex binds to A site on ribosome
50
Q

What are the steps for peptide bond formation in the SECOND part of Elongation?

A
  1. Amino group at A site acts as a nucleophile
  2. Displaces tRNA in P site
  3. 23s rRNA acts as a catalyst (peptidyl transferase activity)
51
Q

What are the steps for translocation in the THIRD part of Elongation?

A
  1. Anticodon in tRNA moves from A site to P site
  2. Deacylated (uncharged) tRNA moves from E site into cytosol
  3. Growing polypeptide chain remains attached to tRNA of most recently inserted amino acid at P site
52
Q

What are the steps for Termination?

A
  1. Stop codons and release factors RF1, RF2, &RF3 bind
  2. Hydrolysis of terminal peptidyl tRNA bond
  3. Release of free polypeptide
  4. Dissociation of 70s ribosome into 50s and 30s
53
Q

What are Polysomes in bacteria?

A

Clusters of 10-100 ribosomes

54
Q

What is the function of Polysomes?

A

Translate mRNA simultaneously

55
Q

What is Transcription & Translation tightly coupled in bacteria and not Eukaryotes?

A

No nucleus in bacteria

Protein synthesis occurs in the nucleus of eukaryotes

56
Q

Which part of protein synthesis is different in eukaryotes to that of bacteria?

A

Initiation

57
Q

What happens during Initiation in Eukaryotes?

A
  • Ribosome scans for first AUG
  • Pre-initiation complex forms at ribosome 40s subunit with the first Met-tRNA, and then with the mRNA
58
Q

How many initiation factors (eIFs) are involved in Eukaryotic Initiation?

A

12

59
Q

Where does eIF4F bind to in Eukaryotic Initiation and why?

A
  • Binds to 5’ CAP and Poly A binding protein
  • To circularise mRNA with 40s subunit
60
Q

Which antibiotic inhibits peptide bond formation in protein synthesis?

A

Puromycin

61
Q

Which antibiotic inhibits the ribosomal A site in bacteria?

A

Tetracyclines

62
Q

Which antibiotic affects the reading of genetic code and initiation in bacteria?

A

Streptomycin

63
Q

What is the effect of Ricin on ribosomes?

A

De-purinates 28s adenine in 60s subunit

ML2001: Introductory Molecular Biology (18 decks)

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