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Questions and Answers
How many total codons are there in the genetic code?
What is the primary function of nonsense codons?
Which feature of the genetic code indicates that one amino acid can be coded by multiple codons?
In what direction are codons read during translation?
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What does the term 'non ambiguous' refer to in the context of the genetic code?
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Which combination of nucleotides would correctly form a single codon?
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How many amino acids do the 61 codons represent?
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Which of the following best describes codons in the genetic code?
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What is the role of the wobble position in tRNA anticodon pairing?
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Which of the following codons does NOT code for any amino acid?
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In mitochondrial codons, what does the codon AUA code for?
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What does the initiator codon AUG code for?
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What evidence supports the universality of the genetic code?
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How does inosinate (I) contribute to tRNA function?
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Which statement is true regarding the codon GAG?
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What differentiates the mitochondrial genetic code from the cytoplasmic code?
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Which amino acid is specified by the homopolymer UUU?
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What type of nucleotides were used to synthesize the homopolymer in the experiments?
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Which amino acid is coded by the homopolymer AAA?
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What was the primary objective of the experiments conducted by Nirenberg and Matthaei?
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What is the significance of using a cell-free translation system in the experiments?
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During the experiment with poly(U) mRNA, how was radioactivity used?
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What was the result of using various RNA sequences in the experiments?
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What role does tRNA play during the translation process?
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What is the significance of the codon GUU in the experiment?
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How do unbound tRNAs behave in the experiment?
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What type of method was developed by Nirenberg and Leder?
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What happens when the ribosome translocates to a stop codon?
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Which of the following is true about the filter solution used in the experiment?
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Which tRNA is not mentioned as being unbound in the experiment?
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What type of molecule were the very short mRNAs synthesized in the experiment designed to represent?
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What does the ribosome do during the translation process when it is associated with mRNA?
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What is the function of the initiation codon AUG in protein synthesis?
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Which of the following amino acids is coded for by the codon UUU?
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What type of molecule serves as the genetic code for proteins?
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In the genetic code, how many bases make up a codon?
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Which of the following statements is true regarding the codon UGA?
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Which amino acid is coded for by the codon CAA?
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What is the role of codons in the process of translation?
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What amino acid does the codon GAA code for?
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Which amino acid is associated with the codon UAG?
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Which of the following codons would code for the same amino acid as UUA?
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Out of these amino acids, which one is not coded by codons starting with 'C'?
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How many different amino acids can be coded by the genetic code?
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Which of the following best describes the nature of the genetic code?
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Which bond forms between the amino acids during the synthesis of proteins?
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Study Notes
Genetic Code
- The genetic code is a set of rules that translates the sequence of nucleotides in DNA or RNA into the sequence of amino acids in a protein.
- Codons, sequences of three nucleotides, represent the code word for each amino acid.
- There are 64 possible codons, but only 61 code for amino acids.
- Three codons, UAA, UAG, and UGA - are stop codons, signaling the end of protein synthesis.
- The genetic code is universal across all living organisms, meaning that the same codons specify the same amino acids in bacteria, plants, animals, etc.
Salient Features of the Genetic Code
- Universal: The same codons code for the same amino acids in almost all organisms, signifying a common evolutionary origin.
- Non-ambiguous: Each codon corresponds to one specific amino acid, ensuring precise protein synthesis.
- Comma-less: Codons are read consecutively without any punctuation, ensuring uninterrupted translation.
- Degenerate: Multiple codons can code for the same amino acid, providing redundancy and flexibility.
- Non-overlapping: Three consecutive nucleotides code for only one amino acid, preventing reading errors or misinterpretations.
- Nonsense codon: UAA, UAG, and UGA act as stop codons, signifying the end of protein synthesis.
- Linear: The amino acid sequence in a protein directly corresponds to the nucleotide sequence in DNA or RNA, with codons encoding each amino acid.
- Triplet: Sixty-four codons are possible (4 x 4 x 4), with 61 coding for amino acids and 3 functioning as stop codons.
- Initiation codon: AUG typically starts protein synthesis, specifying methionine.
Wobble Hypothesis
- In many codons specifying the same amino acid, the third nucleotide position is variable.
- This "wobble" at the third position allows tRNA anticodons to recognize multiple codons, reducing the number of tRNA molecules needed for protein synthesis.
- The wobble position is the fifth position in the tRNA anticodon loop.
- Inosine (I), a modified base, contributes to wobble pairing due to its ability to form non-Watson-Crick base pairs.
Nirenberg and Mathaei experiment
- This landmark experiment used a cell-free translation system (all components except instructions) and various RNA sequences to decipher the genetic code.
- They used homopolymers - RNA chains with only one type of nucleotide (e.g., UUUUUUUUU).
- They identified the amino acid specified by each homopolymer by radiolabeling amino acids and measuring the radioactivity incorporated into the synthesized protein.
- They discovered that UUU codes for phenylalanine, AAA for lysine, and CCC for proline.
Nirenberg and Leder Experiment
- This experiment used short synthetic mRNA sequences and ribosomes to identify the amino acid specified by each codon.
- tRNAs carrying different amino acids were added to the mixture.
- Only the tRNA matching the codon in the mRNA bound to the ribosome.
- This allowed identification of the amino acid corresponding to each codon.
Termination of Translation
- When the ribosome reaches a stop codon (UAA, UAG, or UGA), no tRNA with an anticodon can bind to the A site.
- Release factors (RF-1 and RF-3) bind to the A site, releasing the polypeptide chain from the ribosome, thus terminating protein synthesis.
Conclusion
The genetic code is a complex and elegant system that allows cells to translate the information encoded in DNA into functional proteins, underpinning all life on Earth. Understanding the genetic code is crucial for understanding how genes are expressed and how proteins are made, which is fundamental to all biological processes.
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Description
Explore the fundamental aspects of the genetic code, which provides the rules for translating nucleotide sequences into proteins. Learn about codons, stop signals, and the code's universality across all organisms. This quiz highlights the key features such as its non-ambiguous and degenerate nature.
