Updated: 5/14/2020

tRNA

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Topic
Overview
  •  Structure
    • cloverleaf structure
    • 3' aminoacyl end = CCA  
      • bound covalently to amino acid (AA)
  • Charging 
    • purpose
      • adds correct AA to correct tRNA
        • each AA has a specific tRNA
        • correct AA is only checked when attachment occurs by aminoacyl-tRNA synthetase to the tRNA
        • thus, if a AA is mischarged, it has no other correction mechanism and will insert for the AA specified by the tRNA anticodon
      • charged tRNA contains the needed energy for the formation of the peptide bond
    • process
      • tRNA + ATP + aa aa-tRNA + AMP + PPi
      • catalyzed by aminoacyl-tRNA synthetase
    • inhibited by tetracyclines
  • Wobble 
    • first 2 nucleotide positions provide specificity for an individual amino acid
      • e.g., mRNA triplets CUU, CUC, CUA, CUG all code for Leu
    • genetic code is degenerate
      • all amino acids except for one have more than one codon
    • explains silent mutations
      • mutation from CUU to CUC would not alter the protein 
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Questions (5)

(M1.BC.17.4708) A researcher is trying to decipher how mRNA codons contain information about proteins. He first constructs a sequence of all cytosine nucleotides and sees that a string of prolines is synthesized. He knows from previous research that information is encoded in groups of 3 so generates the following sequences: ACCACCACC, CACCACCAC, and CCACCACCA. Surprisingly, he sees that new amino acids are produced with the first two sequences but that the third sequence is still a string of prolines. Which of the following biochemical principles explains why this phenomenon was observed? Tested Concept

QID: 108474
1

Covalent alterations

4%

(4/103)

2

mRNA splicing

13%

(13/103)

3

Translational proofreading

5%

(5/103)

4

Trimming of proteins

2%

(2/103)

5

Wobble hypothesis

75%

(77/103)

M 1 C

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(M1.BC.15.74) A codon is an mRNA sequence consisting of 3 nucleotides that codes for an amino acid. Each position can be made up of any 4 nucleotides (A, U, G, C); therefore, there are a total of 64 (4 x 4 x 4) different codons that can be created but they only code for 20 amino acids. This is explained by the wobble phenomenon. One codon for leucine is CUU, which of the following can be another codon coding for leucine? Tested Concept

QID: 106620
1

AUG

3%

(6/223)

2

UAA

12%

(26/223)

3

CCC

1%

(3/223)

4

CCA

5%

(12/223)

5

CUA

78%

(173/223)

M 1 E

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(M1.BC.14.15) A 12-year-old boy presents to his primary care doctor with a new-onset rash (Figure A). He first noticed the rash about 3 days ago, after he returned home from summer camp. His primary doctor decides to prescribe a course of doxycycline, an antibiotic that inhibits binding of aminoacyl-tRNA to the 30S ribosome subunit. Which of the following tRNA sites is the binding site for amino acids? Tested Concept

QID: 100080
FIGURES:
1

5' tail

22%

(7/32)

2

Dihydrouracil arm

9%

(3/32)

3

Thymidine t-arm

16%

(5/32)

4

Anticodon

9%

(3/32)

5

CCA tail

38%

(12/32)

M 1 E

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Evidence (1)
Topic COMMENTS (11)
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