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Questions and Answers
What is the primary advantage of synthesizing RNA with a specific sequence in deciphering the genetic code?
What is the primary advantage of synthesizing RNA with a specific sequence in deciphering the genetic code?
- It allows for the creation of multiple reading frames
- It enables the control of nucleotide polymerization order
- It increases the chances of obtaining a start codon
- It facilitates the assignment of codons to amino acids (correct)
What is the outcome when a tube containing labelled phenylalanine has a high signal above background?
What is the outcome when a tube containing labelled phenylalanine has a high signal above background?
- Phenylalanine is the only amino acid radio-labelled (correct)
- All amino acids are radio-labelled equally
- Ribosomes are not stuck to the filter paper
- Only serine and leucine are radio-labelled
What is the purpose of the anticodon on the tRNA molecule?
What is the purpose of the anticodon on the tRNA molecule?
- To recognize the start codon during translation
- To release the amino acid from the ribosome
- To bind to the mRNA codon during translation (correct)
- To provide the sequence for protein synthesis
What is the consequence of the genetic code being read in triplets?
What is the consequence of the genetic code being read in triplets?
What is the purpose of the 'start codon' in the genetic code?
What is the purpose of the 'start codon' in the genetic code?
Why is it important to consider reading frames when deciphering the genetic code?
Why is it important to consider reading frames when deciphering the genetic code?
What is the significance of the 'stop codons' in the genetic code?
What is the significance of the 'stop codons' in the genetic code?
What was the main challenge faced by Nirenberg's lab initially?
What was the main challenge faced by Nirenberg's lab initially?
What is the consequence of the genetic code being degenerate?
What is the consequence of the genetic code being degenerate?
What is the purpose of wobble pairing in translation?
What is the purpose of wobble pairing in translation?
Which of the following amino acids is encoded by a single codon?
Which of the following amino acids is encoded by a single codon?
What is the significance of the first two letters in a codon?
What is the significance of the first two letters in a codon?
Which of the following is a consequence of wobble pairing?
Which of the following is a consequence of wobble pairing?
Which of the following anticodons could pair with the codon 5’ CUG 3’?
Which of the following anticodons could pair with the codon 5’ CUG 3’?
What is the significance of the third position in a codon?
What is the significance of the third position in a codon?
Which of the following codons could pair with a tRNA with anticodon 5’ GCA 3’?
Which of the following codons could pair with a tRNA with anticodon 5’ GCA 3’?
What is the consequence of having fewer than 61 tRNA molecules?
What is the consequence of having fewer than 61 tRNA molecules?
What is the function of the anticodon in the central loop of tRNA?
What is the function of the anticodon in the central loop of tRNA?
What is the purpose of wobble pairing in translation?
What is the purpose of wobble pairing in translation?
Which of the following is NOT a part of the initiation complex in prokaryotic translation?
Which of the following is NOT a part of the initiation complex in prokaryotic translation?
What is the purpose of the Shine-Dalgarno sequence in prokaryotic translation?
What is the purpose of the Shine-Dalgarno sequence in prokaryotic translation?
During elongation, what happens to EF-Tu after GTP hydrolysis?
During elongation, what happens to EF-Tu after GTP hydrolysis?
What is the net result of peptidyl transferase process during elongation?
What is the net result of peptidyl transferase process during elongation?
What is the function of aminoacyl-tRNA synthetases?
What is the function of aminoacyl-tRNA synthetases?
What is the analogous process in translation to building a wall by adding bricks?
What is the analogous process in translation to building a wall by adding bricks?
What is the result of combining 30S and 50S ribosomal subunits?
What is the result of combining 30S and 50S ribosomal subunits?
Where can polyribosomes be found in a cell?
Where can polyribosomes be found in a cell?
What is responsible for positioning the ribosome at the start codon?
What is responsible for positioning the ribosome at the start codon?
What is the initiator tRNA in eukaryotic cells?
What is the initiator tRNA in eukaryotic cells?
What is the role of initiation factors during translation initiation?
What is the role of initiation factors during translation initiation?
During which stage of translation is the nascent polypeptide synthesized?
During which stage of translation is the nascent polypeptide synthesized?
What is the function of a release factor during translation?
What is the function of a release factor during translation?
Which of the following is not a type of RNA?
Which of the following is not a type of RNA?
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Study Notes
Deciphering the Genetic Code
- The genetic code was deciphered using synthetic mRNA and evaluating which amino acids were incorporated
- Amino acids are encoded by triplets of nucleotide bases (codons)
- The code is degenerate – most amino acids are coded for by more than one codon
- One start codon (AUG) and three stop codons
- Where you begin to read the code will determine which triplets are produced
- Each possible grouping of triplets is called a ‘reading frame’
Translation: Requirements and Components
- RNA required for translation:
- mRNA (encodes proteins)
- tRNA (delivers amino acids to the ribosome)
- rRNA (structural and enzymatic component of the ribosome)
- Ribosomes are required for translation
Translation: tRNA Molecule
- tRNA is the adaptor molecule that links an mRNA codon with a specific amino acid
- tRNA molecule:
- 75-90 nucleotides
- Extensive internal base pairing
- Clover leaf structure
- Contains unusual bases
- CCA-OH sequence at 3’ end
- Anticodon on central loop
- Anticodon:
- A triplet of bases that are complementary to the codon
- These bases are unpaired and available for hydrogen bonding
Translation: Wobble Mechanism
- Wobble pairing allows a single tRNA anticodon to recognize more than one codon
- Often the first two letters in the codon are the same, and the third base can vary
- Third position less critical and can follow non-Watson-Crick base pairing between mRNA and tRNA
Translation: Initiation, Elongation, and Termination
- Initiation:
- Requires initiation factors (IFs)
- fMet-tRNAfMet in complex with IF2-GTP
- Hydrolysis of GTP accompanied by the binding of the large 50S subunit
- 16S rRNA binds the Shine-Dalgarno sequence in the mRNA to line up fMet-tRNAfMet with AUG start codon
- Elongation:
- Next aminoacyl tRNA binds to elongation factor EF-Tu GTP and enters A site in the ribosome
- If the anticodon of the incoming tRNA is complementary to the codon, then hydrolysis of GTP takes place, and EF-Tu GDP + Pi are released
- Peptidyl transferase process: the wall is built by lifting the incomplete wall, and placing the new brick underneath
- Termination:
- Requires a release factor that mimics the shape of a tRNA
Differences between Prokaryotic and Eukaryotic Translation
- Key differences between prokaryotic and eukaryotic translation
Learning Outcomes
- Recap of learning outcomes:
- Outline how the genetic code was deciphered
- Explain how amino acids are encoded by groups of three nucleotide bases
- Describe the components required for translation
- Outline the process of activation of an amino acid to form an amino acyl tRNA
- Describe the 3 stages of translation in prokaryotic cells
- Identify ways in which eukaryotic translation differs from prokaryotic translation
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