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Questions and Answers
What is the total S value for eukaryotic ribosomes?
What is the total S value for eukaryotic ribosomes?
Which of the following statements is true regarding the rRNA component of ribosomes?
Which of the following statements is true regarding the rRNA component of ribosomes?
Which type of mutation results in the introduction of a premature stop codon?
Which type of mutation results in the introduction of a premature stop codon?
What allows for the encoding of more than one amino acid by multiple codons?
What allows for the encoding of more than one amino acid by multiple codons?
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During translation, which sequence determines the reading frame of mRNA?
During translation, which sequence determines the reading frame of mRNA?
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What is the primary function of ribosomes in protein synthesis?
What is the primary function of ribosomes in protein synthesis?
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Which component of tRNA is responsible for matching with codons on mRNA?
Which component of tRNA is responsible for matching with codons on mRNA?
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During translation, where are new amino acids attached in the growing polypeptide chain?
During translation, where are new amino acids attached in the growing polypeptide chain?
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What is the role of the initiator tRNA during protein synthesis?
What is the role of the initiator tRNA during protein synthesis?
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What structural feature characterizes tRNA molecules?
What structural feature characterizes tRNA molecules?
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What is the role of amino acyl tRNA synthetase in protein synthesis?
What is the role of amino acyl tRNA synthetase in protein synthesis?
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What initiates the translation process in eukaryotic cells?
What initiates the translation process in eukaryotic cells?
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What can occur when multiple ribosomes translate the same mRNA simultaneously?
What can occur when multiple ribosomes translate the same mRNA simultaneously?
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In eukaryotes, why can transcription and translation not occur simultaneously?
In eukaryotes, why can transcription and translation not occur simultaneously?
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Study Notes
Bacterial Ribosomes
- Composed of two subunits: large and small
- Measured in Svedberg units (S)
- Large subunit is 50S, small subunit is 30S, together forming 70S
- S units are not linear but related to mass under centrifugal force
- Eukaryotic ribosomes are 60S + 40S = 80S
Ribosome Composition
- Composed of rRNA and proteins
- Proteins are structural; rRNA catalyzes reactions
- Prokaryotic ribosomes contain 23S rRNA
- Eukaryotic ribosomes contain 28S, 5.8S, 5S rRNAs
Ribosomal Function
- Ribosomes are protein synthesis factories
- mRNA carries genetic information in codons
- tRNA acts as an adaptor between codons and amino acids
- rRNA associates with proteins to form the ribosome
- Peptide bonds form between amino acids on the ribosome
Ribosome and mRNA Reading Frames
- mRNA is read in triplets (codons)
- Reading frame determines which amino acids are incorporated
- Frameshift mutations occur when the reading frame is altered
- This changes the amino acid sequence and protein function
Types of Point Mutations
- Missense mutation: One nucleotide substitution leads to a different amino acid
- Nonsense mutation: One nucleotide substitution creates a stop codon, prematurely terminating protein synthesis
- Frameshift mutation: Insertion or deletion of nucleotides shifts the reading frame, drastically altering the amino acid sequence
The Genetic Code
- 64 possible codons in the genetic code
- 61 of these specify amino acids, the other 3 are stop codons
- Some amino acids are specified by multiple codons (degeneracy)
- The genetic code is universal, but codon usage can vary
Amino Acids
- There are 20 proteinogenic amino acids
- Each amino acid has a specific three-letter and one-letter abbreviation
Ribosomal Activity During Translation
- First amino acid undergoes a nucleophilic attack from the next
- Peptide bond forms between amino acids
- Ribosome moves along the mRNA
- New amino acids are attached to the growing polypeptide chain (C-terminus)
- The ribosome exists as separate large and small subunits during the translation processes
Multiple Ribosomes
- Multiple ribosomes can translate the same mRNA molecule
- These are called polyribosomes or polysomes
- This process is possible in both prokaryotes and eukaryotes, but cotranscriptional translation does not occur in eukaryotes (as transcription occurs in the nucleus)
tRNA
- Single-stranded RNA molecule
- Adapters between codons and amino acids
- tRNA is encoded by clusters of genes
- Undergoes processing, which can include unusual base formation
- Has a cloverleaf structure
- Contains an anticodon that is complementary to a codon in mRNA
- Amino acid attached at the 3' end
Wobble Phenomenon
- Third position of codon in mRNA and first position in tRNA are relaxed in base pairing
- This allows one tRNA to recognize more than one codon
- Uses inosine as a base in the wobble position
Shine-Dalgarno Sequence
- Consensus sequence (5'-UAAGGAGGU-3')
- Used in prokaryotes to initiate translation by ribosomes recognising start codon in mRNA
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Description
Explore the structure and function of bacterial ribosomes in this quiz. Learn about their composition, measurement in Svedberg units, and the critical roles they play in protein synthesis. Discover the differences between prokaryotic and eukaryotic ribosomes.
