Podcast
Questions and Answers
What do the letters U, C, A, and G represent in Model 1?
What do the letters U, C, A, and G represent in Model 1?
mRNA nucleotides
What do abbreviations such as Phe, Ile, Ala, and Gly represent in Model 1?
What do abbreviations such as Phe, Ile, Ala, and Gly represent in Model 1?
Amino acids
What is the significance of the reference to the language of mRNA as a 'triplet code'?
What is the significance of the reference to the language of mRNA as a 'triplet code'?
Three nucleotides are needed to code for one amino acid.
If an mRNA molecule had 300 nucleotides in the coding region, how many amino acids would be in the polypeptide synthesized?
If an mRNA molecule had 300 nucleotides in the coding region, how many amino acids would be in the polypeptide synthesized?
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How many different codons (triplets) code for the amino acid Proline (Pro)?
How many different codons (triplets) code for the amino acid Proline (Pro)?
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What are the similarities and differences among all codons for Proline?
What are the similarities and differences among all codons for Proline?
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What advantage is there for an organism to have multiple mRNA sequences code for the same amino acid?
What advantage is there for an organism to have multiple mRNA sequences code for the same amino acid?
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Complete the following based on the mRNA codon chart in Model 1: DNA-> TAC CTT CGG ATG CTG ACT; mRNA-> ___; polypeptide seq.-> ____ .
Complete the following based on the mRNA codon chart in Model 1: DNA-> TAC CTT CGG ATG CTG ACT; mRNA-> ___; polypeptide seq.-> ____ .
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What amino acid is at the beginning of every polypeptide according to the table in Model 1?
What amino acid is at the beginning of every polypeptide according to the table in Model 1?
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What might scientists conclude from the fact that codons shown in Model 1 are used in all species on Earth with very little variation?
What might scientists conclude from the fact that codons shown in Model 1 are used in all species on Earth with very little variation?
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What are the three stages of translation?
What are the three stages of translation?
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Define each of the terms used in your answer to part A as they are used in everyday language.
Define each of the terms used in your answer to part A as they are used in everyday language.
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According to Model 2, when the mRNA leaves the nucleus, to which cellular organelle does it attach?
According to Model 2, when the mRNA leaves the nucleus, to which cellular organelle does it attach?
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What is the significance of the sequence AUG, to which the mRNA attaches at the organelle?
What is the significance of the sequence AUG, to which the mRNA attaches at the organelle?
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Describe the movement of the ribosome as translation occurs.
Describe the movement of the ribosome as translation occurs.
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What sequence of nucleotides makes the anticodon on the tRNA molecule carrying Histidine (His)?
What sequence of nucleotides makes the anticodon on the tRNA molecule carrying Histidine (His)?
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What codon on mRNA would match the anticodon GUA?
What codon on mRNA would match the anticodon GUA?
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What anticodon would be found on a tRNA molecule carrying Glycine (Gly)?
What anticodon would be found on a tRNA molecule carrying Glycine (Gly)?
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Explain why tRNA is called transfer RNA.
Explain why tRNA is called transfer RNA.
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How many tRNA molecules are held in the ribosome during elongation?
How many tRNA molecules are held in the ribosome during elongation?
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What happens to the unattached tRNA once it has delivered the amino acid?
What happens to the unattached tRNA once it has delivered the amino acid?
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Describe two things that occur during termination as illustrated in Model 2.
Describe two things that occur during termination as illustrated in Model 2.
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How does the term 'translation' apply to the synthesis of proteins from the DNA instructions?
How does the term 'translation' apply to the synthesis of proteins from the DNA instructions?
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Show mathematically that there are 64 permutations possible when three bases are used.
Show mathematically that there are 64 permutations possible when three bases are used.
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Show mathematically that two bases as a codon would not be sufficient to code all 20 known amino acids.
Show mathematically that two bases as a codon would not be sufficient to code all 20 known amino acids.
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Write a code for an original DNA strand and mutate it so the final protein is unaffected.
Write a code for an original DNA strand and mutate it so the final protein is unaffected.
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Give two reasons why translation in prokaryotic cells can begin before transcription is finished, unlike in eukaryotic cells.
Give two reasons why translation in prokaryotic cells can begin before transcription is finished, unlike in eukaryotic cells.
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Study Notes
Gene Expression - Translation Overview
- The letters U, C, A, and G represent mRNA nucleotides.
- Abbreviations like Phe, Ile, Ala, and Gly signify different amino acids.
- The "triplet code" nature of mRNA indicates three nucleotides code for one amino acid.
Polypeptide Coding
- A mRNA molecule with 300 nucleotides can code for 100 amino acids (300 divided by 3).
- Four different codons code for the amino acid Proline (Pro).
- All Proline codons start with CC, differing only in the third base.
Genetic Redundancy and Errors
- Multiple mRNA sequences coding for the same amino acid provide a backup in case of transcription or replication errors.
mRNA and Protein Synthesis
- DNA sequence: TAC CTT CGG ATG CTG ACT translates to mRNA sequence: AUG GAA GCC UAC CAG UGA, leading to polypeptide sequence: Met (start), Glu, Ala, Tyr, Gln.
- AUG is the start codon, signaling the beginning of every polypeptide.
Evolutionary Implication
- Universal use of codons across all species supports the theory of common ancestry and evolution.
Stages of Translation
- Translation consists of three phases: initiation, elongation, and termination.
- Everyday meanings:
- Initiation: the beginning of a process
- Elongation: the process of lengthening or adding to something
- Termination: the conclusion or ending of a process
Ribosome Functionality
- mRNA attaches to the ribosome after leaving the nucleus.
- Ribosomes move along the mRNA chain from 5' to 3' direction.
tRNA's Role
- The tRNA carrying Histidine (His) has an anticodon sequence of GUA, which matches the mRNA codon CAU.
- Possible anticodons for Glycine (Gly) include CCA, CCU, CCG, and CCC.
- Transfer RNA (tRNA) transfers specific amino acids in the correct order to the ribosome for protein synthesis.
Elongation and Termination
- During elongation, a maximum of two tRNA molecules can be held in the ribosome concurrently.
- Unattached tRNA is released after delivering its amino acid, ready to pick up new amino acids.
- Termination occurs when a release factor binds to the last codon, halting further amino acid addition, and a water molecule is added to complete the amino acid chain.
Concept of Translation
- "Translation" refers to decoding DNA's nitrogen base sequence (in sets of three, called codons) into the protein language (amino acids).
Codon Combinations
- With three bases, there are 64 possible codon permutations (4x4x4).
- Only using two bases provides only 8 codon combinations (2x2x2), insufficient for coding all 20 known amino acids.
Silent Mutations and Genetic Structure
- An example of a silent mutation: Original DNA: TAC AAA CCC GGA mutated to TAC AAG CCC GGA still produces the same protein.
Differences Between Cell Types
- In prokaryotes, simultaneous transcription and translation are feasible due to the absence of a nucleus.
- Eukaryotes have distinct transcription (in the nucleus) and translation (in cytoplasm) processes, with introns needing removal from pre-mRNA before translation.
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Test your knowledge on gene expression and translation with these flashcards. Each card covers essential terms and concepts, such as mRNA nucleotides and amino acids. Ideal for students studying molecular biology.