Protein Synthesis

Question 1

What THREE components are required for Translation?

Answer 1

• Ribosomes
• tRNA
• mRNA

Question 2

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

Answer 2

Amino Acid arm

Question 3

Which arms of tRNA contains dihyrouridine ribothymidine?

Answer 3

D & TyC arms

Question 4

Which arm of tRNA interacts with the codon in mRNA?

Answer 4

Anticodon arm

Question 5

How does tRNA interact with mRNA?

Answer 5

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

Question 6

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

Answer 6

5’ to 3’

Question 7

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

Answer 7

3’ to 5’

Question 8

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

Answer 8

5’ to 3’

Question 9

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

Answer 9

Non-Overlapping

Question 10

Which amino acid is coded for by CCC?

Answer 10

Proline

Question 11

Which amino acid is coded for by AAA?

Answer 11

Lysine

Question 12

Which amino acid is coded for by UUU?

Answer 12

Phenylalanine

Question 13

How many reading frames does mRNA contain?

Answer 13

3

Question 14

How many codons are there?

Answer 14

61 for amino acids and 3 stop codons

Question 15

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

Answer 15

• AUG
• Methionine

Question 16

What are the Stop Codons?

Answer 16

• UAA
• UAG
• UGA

Question 17

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

Answer 17

50 or more

Question 18

Are amino acids specified by more than one codon?

Answer 18

Yes.
Due to genetic code being Degenerate

Question 19

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

Answer 19

Wobble allows flexibility/speed

Question 20

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

Answer 20

In the first two bases

Question 21

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

Answer 21

Inosine

Question 22

Which bases can Inosine pair with?

Answer 22

U, C, or A

Question 23

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

Answer 23

First two bases

Question 24

Which bases determine the number of codons recognised by tRNA?

Answer 24

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

Question 25

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

Answer 25

One

Question 26

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

Answer 26

Two ## Footnote Less specific

Question 27

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

Answer 27

Three

Question 28

When are different tRNAs required?

Answer 28

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

Question 29

How many tRNAs are required to translate all 61 codons?

Answer 29

32

Question 30

What type of mutations is the Genetic Code resistant to?

Answer 30

Missense mutations (1bp change)

Question 31

What is the site of Protein Synthesis in the cell?

Answer 31

Ribosomes ## Footnote tRNA brings amino acids to mRNA at ribosomes

Question 32

What size ribosomes are present in Bacteria?

Answer 32

70s (50s & 30s subunits)

Question 33

What size ribosomes are present in Eukaryotes?

Answer 33

80s (60s & 40s subunits)

Question 34

What are the FIVE stages of Protein Synthesis?

Answer 34

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

Question 35

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

Answer 35

* Aminoacyl tRNA Synthetase * Proper placement of amino acid in polypeptide chain on tRNA

Question 36

Why are amino acids activated?

Answer 36

For peptide bond formation

Question 37

What terminus does Initiation begin at?

Answer 37

Amino (N) terminus

Question 38

What terminus are amino acids added to during Initiation?

Answer 38

C terminus

Question 39

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

Answer 39

Methionine with Special tRNA

Question 40

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

Answer 40

fMet-tRNA (N-formylmethionine)

Question 41

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

Answer 41

Near a Shine Delgarno sequence

Question 42

What is the purpose of the Shine Delgarno sequence?

Answer 42

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

Question 43

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

Answer 43

No. Only bacterial mRNA

Question 44

What are the THREE steps in Initiation?

Answer 44

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

Question 45

What are the THREE sites on the Ribosome?

Answer 45

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

Question 46

Which site does IF-1 bind on the Ribosome?

Answer 46

A site

Question 47

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

Answer 47

P site

Question 48

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

Answer 48

P site

Question 49

What are the steps for the FIRST part of Elongation?

Answer 49

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

Question 50

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

Answer 50

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)

Question 51

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

Answer 51

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

Question 52

What are the steps for Termination?

Answer 52

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

Question 53

What are Polysomes in bacteria?

Answer 53

Clusters of 10-100 ribosomes

Question 54

What is the function of Polysomes?

Answer 54

Translate mRNA simultaneously

Question 55

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

Answer 55

No nucleus in bacteria ## Footnote Protein synthesis occurs in the nucleus of eukaryotes

Question 56

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

Answer 56

Initiation

Question 57

What happens during Initiation in Eukaryotes?

Answer 57

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

Question 58

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

Answer 58

12

Question 59

Where does eIF4F bind to in Eukaryotic Initiation and why?

Answer 59

* Binds to 5' CAP and Poly A binding protein * To circularise mRNA with 40s subunit

Question 60

Which antibiotic inhibits peptide bond formation in protein synthesis?

Answer 60

Puromycin

Question 61

Which antibiotic inhibits the ribosomal A site in bacteria?

Answer 61

Tetracyclines

Question 62

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

Answer 62

Streptomycin

Question 63

What is the effect of Ricin on ribosomes?

Answer 63

De-purinates 28s adenine in 60s subunit