Questions and Answers
What happens during the process of translation?
Where does translation take place?
Cytoplasm
When can translation begin in prokaryotes?
Once the mRNA transcript is made
What are the three main molecular components of translation?
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What is a codon?
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The genetic code is ______.
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The tRNA molecule brings together ______ and ______.
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Which enzyme charges the tRNA by attaching the appropriate amino acid?
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What part of the ribosome plays the catalytic role in translation?
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What percentage of RNA transcribed in cells is rRNA?
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The small ribosomal subunit binds first to the mRNA template during translation initiation.
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What is the role of the Kozak's rules in eukaryotic translation?
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The initiator tRNA carries the amino acid ______.
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What happens during translocation in translation?
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What molecule facilitates peptide bond formation?
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What class of proteins helps newly translated proteins to fold properly?
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What is a mutation?
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What is the difference between induced and spontaneous mutations?
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What is a point mutation?
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What happens if a nucleotide is deleted from an mRNA sequence?
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Which class of mutation results in a STOP codon?
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What does the term 'reading frame' mean?
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What is a signal sequence?
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Study Notes
Translation Overview
- Translation converts the linear sequence of mRNA nucleotides into a linear sequence of amino acids to form proteins.
- Occurs in the cytoplasm; can initiate immediately in prokaryotes after mRNA synthesis, while in eukaryotes it begins post-mRNA processing and transport from the nucleus.
Molecular Components of Translation
- mRNA is the template containing the genetic code.
- tRNA is responsible for reading the mRNA code and bringing the corresponding amino acids.
- Ribosomes (comprised of rRNA and proteins) catalyze peptide bond formation between amino acids.
Codons and Genetic Code
- A codon is a triplet of nucleotides that specifies a single amino acid.
- The genetic code is degenerate, meaning multiple codons can code for the same amino acid.
- It is virtually universal; all organisms share the same genetic code.
Role and Structure of tRNA
- tRNA reads the mRNA codons and links them to their respective amino acids.
- The 3' end of tRNA carries the amino acid, while the anticodon loop pairs with the codon in an anti-parallel manner.
- tRNA exhibits a distinct stem-loop structure.
Charging of tRNA
- Aminoacyl-tRNA synthetase enzymes charge tRNA by covalently linking the correct amino acid to the tRNA’s 3' end, utilizing energy from ATP hydrolysis.
Ribosome Composition and Function
- Ribosomes consist of a large and a small subunit, formed from numerous proteins and rRNA.
- rRNA provides the catalytic function during translation, specifically through peptidyl transferase action.
rRNA in Cells
- 80% of RNA in cells is rRNA, produced from clustered rRNA gene copies found primarily in the nucleolus.
Translation Initiation
- Initiation involves assembling a ribosome at the mRNA starting point (AUG).
- Small ribosomal subunit binds first, aided by initiation factors (IFs) and GTP.
- The large ribosomal subunit joins after the first tRNA has associated with the mRNA, ensuring proper orientation.
Eukaryotic vs Prokaryotic Initiation
- In prokaryotes, the Shine-Dalgarno sequence aligns the ribosome.
- In eukaryotes, the small subunit scans for the AUG after binding to the 5' cap, aided by Kozak's rules.
Reading Frame
- The reading frame is established at AUG; it dictates how the sequence is read in sets of three nucleotides.
- Misalignment of the reading frame can lead to severe translation consequences.
Elongation and Termination
- Elongation adds amino acids sequentially via tRNA that recognizes codons, peptide bonds are formed through peptidyl transferase, and translocation shifts the ribosome along the mRNA.
- Termination occurs when a stop codon is reached, triggering release factors that assist in releasing the polypeptide chain.
Types of Mutations
- Mutations are changes in the nucleotide sequence; they can be induced (from external factors) or spontaneous.
- Point mutations affect single nucleotides and can be classified as missense, nonsense, sense, silent, or frameshift mutations.
- Trinucleotide repeats can lead to genetic diseases and involve sequences repeated multiple times.
Genetic Code Structure
- The genetic code’s redundancy offers protection against harmful mutations; substitutions in the third nucleotide often lead to silent mutations or result in similar property amino acids.
Effects of Nucleotide Insertions/Deletions
- Inserting or deleting nucleotides can result in frameshift mutations, leading to dramatic changes in protein structure and function, as R-group interactions are crucial for proper folding.
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Description
This quiz focuses on the concepts of translation as discussed in Chapter 15 of the biology syllabus. It covers the definition of translation, its location in prokaryotes and eukaryotes, and the timing of its initiation. Test your understanding with these flashcards!
