tRNA

Question 1

what it the role of tRNA?

Answer 1

tRNA carries amino acids to the ribosomes during translation of mRNA

Question 2

why does the tRNA molecule fold upon itself even though it is single stranded?

Answer 2

tRNA molecule folds upon itself due to hydrogen bonds formed between complementary regions at different parts of the molecule

Question 3

how does being single stranded allow tRNA to carry out its role?

Answer 3

• being single-stranded (structural feature)
• allows for the formation of hydrogen bonds between complementary base pairs at different regions, causing the tRNA molecule to fold back on itself (1st point about significance to its role)
• the folding of the tRNA upon itself forms a 3D L-shaped structure of the tRNA to fit into the respective exit site, peptidyl-tRNA site, and aminoacyl-tRNA site on the large ribosomal subunit (2nd point about significance to its role)

Question 4

how does having an amino acid attachment site at the 3’ end of the tRNA molecule allow tRNA to carry out its role?

Answer 4

• the amino acid attachment site at the 3’ end of the tRNA molecule (structural feature)
• allows for the attachment of specific activated amino acids to form an aminoacyl-tRNA complex, enabling the tRNA molecule to carry a specific amino acid to the ribosome during translation (significance to its role)

Question 5

how does having an anticodon enable tRNA to carry out its role?

Answer 5

• the anticodon (structural feature)
• forms complementary base pairs with the codon of the mRNA, ensuring that the correct amino acyl-tRNA complex occupies the ‘P’ site & ‘A’ site of the ribosome during translation (1st point about significance to its role),
• so that the amino acid sequence on the polypeptide chain that is coded for by the gene is correct (2nd point about significance to its role)

Question 6

what is amino acid activation?

Answer 6

it is the attachment of a specific amino acid to its tRNA

Question 7

what is amino acid activation?

Answer 7

it is the attachment of a specific amino acid to its tRNA

Question 8

where is the specific amino acid attached?

Answer 8

to the 3’ end of the tRNA molecule

Question 9

what is aminoacyl-tRNA synthetase, and what is its function?

Answer 9

aminoacyl-tRNA synthetase is an enzyme, and it catalyzes the attachment of a specific amino acid to its tRNA

Question 10

why is there a specific tRNA for each amino acid?

Answer 10

it is due to the specificity of the active site of aminoacyl-tRNA synthetase

Question 11

explain how aminoacyl-tRNA synthetase is specific [2]

Answer 11

• it has an active site consisting of 2 binding sites [0.5]
• with the binding sites being complementary in shape to the shape of the specific amino acid [0.5]
• and the shape of the anticodon of a specific tRNA molecule [0.5]
• the enzyme ensures that the specific amino acid is joined to the specific tRNA during amino acid activation [0.5]

Question 12

why are there at least 20 aminoacyl-tRNA synthetases?

Answer 12

• it is because there are at least 20 different tRNA molecules in a cell, with at least 1 for each of the 20 amino acids required for protein synthesis
• also, as each aminoacyl-tRNA synthetase is highly specific & attaches a specific amino acid correctly to a tRNA, hence, there are at least 20 aminoacyl-tRNA synthetases