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Questions and Answers
What is the characteristic of the genetic code that allows a single amino acid to be represented by multiple codons?
During translation initiation, which component binds first to the mRNA?
What role does GTP play during the initiation phase of translation?
What is the function of the A site in the ribosome during elongation?
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What is the role of peptidyl transferase during the elongation process?
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In what manner does the ribosome move during translocation?
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What is the result of reaching a stop codon during translation?
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Which of the following correctly describes the ambiguity of the genetic code?
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Study Notes
Genetic Code Characteristics
- Triplet of bases (codon) codes for an amino acid
- Shared by all living organisms
- Genetic code is universal
- More than one codon can code for the same amino acid (redundancy / degeneracy)
- A single codon codes for only one amino acid (non-ambiguous)
- Genetic code is non-overlapping
Translation: Formation of Amino Acids
1. Activation of tRNA
- tRNA: Has a specific anticodon that binds to aminoacyl-tRNA synthetase.
- Amino acid: Each amino acid links to its respective tRNA.
- Aminoacyl-tRNA synthetase: Activates tRNA by combining it with its corresponding amino acid.
- Active site: Each synthetase has a unique active site that fits only a specific tRNA and amino acid.
- ATP: Provides energy for the activation.
2. Translation Process
a) Initiation
- Small ribosomal subunit: Binds to mRNA.
- Initiator tRNA: Carries methionine and attaches to the mRNA start codon.
- Large ribosomal subunit: Attaches to form the translation initiation complex.
- Energy: Supplied by GTP hydrolysis.
- Ribosome structure:
- P site (Peptidyl-tRNA binding site): Holds the tRNA carrying the growing polypeptide chain.
- E site (Exit site): Where uncharged tRNAs exit the ribosome.
- A site (Aminoacyl-tRNA binding site): Where the incoming tRNA carrying the next amino acid binds.
- mRNA binding site: Where mRNA binds to the ribosome.
b) Elongation
i) Codon Recognition
- Aminoacyl-tRNA: Recognizes the codon in the A site and binds to the complementary anticodon on mRNA.
- GTP: Provides energy for the process.
ii) Peptide Bond Formation
- Peptide bond: Forms between the amino acid in the P site and the new amino acid in the A site.
- Peptidyl transferase / aminoacyl-tRNA transferase: Catalyzes peptide bond formation.
- Ribozyme: The large ribosomal subunit acts as an enzyme; it's a ribozyme.
iii) Translocation
- Ribosome movement: Ribosome moves one codon ahead (3 bases).
- P site -> E site: tRNA in the P site moves to the E site and then exits the ribosome.
- A site -> P site: tRNA moves from the A site to the P site.
- New tRNA entry: A new tRNA enters the A site.
c) Termination
- Elongation continues until a stop codon is reached.
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Description
This quiz covers key characteristics of the genetic code, including its universal nature and the redundancy of codons. It also explores the translation process in protein synthesis, focusing on the activation of tRNA and the initiation of translation.
