Protein Synthesis: L18
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Questions and Answers

What must occur before translation in the protein synthesis process?

  • Ribozyme activation
  • Amino acid assembly
  • Transcription (correct)
  • Protein folding

    • Which component is crucial for ensuring high fidelity during protein synthesis?

  • The ribosome only
  • The energy supply
  • The sequence of the template (correct)
  • The type of amino acids used

    • What is required for protein synthesis to occur effectively?

  • Pre-synthesized enzymes
  • Only building blocks
  • A supply of proteins
  • Energy and a coding template (correct)

    • What process must follow protein synthesis for proteins to be functional?

    <p>Modification and targeting</p> Signup and view all the answers

    What is the typical accuracy rate of amino acid incorporation during protein synthesis?

    <p>1 error per 10,000 amino acids</p> Signup and view all the answers

    What mutation is associated with increased infectivity in SARS-CoV-2?

    <p>D614G</p> Signup and view all the answers

    Which of the following statements is true about tRNA structure?

    <p>The 3'-terminus of every tRNA ends in CCA.</p> Signup and view all the answers

    What is the main role of the D loop in tRNA?

    <p>It is involved in maintaining the overall L-shape of the tRNA.</p> Signup and view all the answers

    Which of the following is a feature of the tRNA anticodon?

    <p>It recognizes mRNA codons through antiparallel base pairing.</p> Signup and view all the answers

    What is a characteristic of the tRNA molecules?

    <p>They possess numerous unusual post-transcriptionally modified bases.</p> Signup and view all the answers

    What is the primary purpose of translation in protein synthesis?

    <p>To convert mRNA into a polypeptide chain</p> Signup and view all the answers

    Which molecular components are essential for the translation process?

    <p>Ribosomes, mRNA, tRNA, and aminoacyl-tRNA synthetases</p> Signup and view all the answers

    What are the three stages of translation?

    <p>Initiation, elongation, and termination</p> Signup and view all the answers

    How do codons on mRNA interact with tRNA?

    <p>Codons match with specific anticodons on tRNA</p> Signup and view all the answers

    What is a key difference between transcription and translation?

    <p>Transcription does not involve ribosomes</p> Signup and view all the answers

    What characteristic of the genetic code relates to its universal nature?

    <p>It is shared among almost all living organisms</p> Signup and view all the answers

    What denotes the start of protein synthesis during translation?

    <p>A start codon on the mRNA</p> Signup and view all the answers

    Why is the process of translation described as involving a large molecular complex?

    <p>Because ribosomes consist of both RNA and proteins</p> Signup and view all the answers

    What role does PKR play in virus-infected cells?

    <p>Reduces protein synthesis</p> Signup and view all the answers

    Which initiation factor prevents elongator tRNAs from entering the ribosome's A-site?

    <p>IF1</p> Signup and view all the answers

    What is the significance of the Shine-Dalgarno sequence in prokaryotic mRNA?

    <p>It ensures the start codon is correctly positioned.</p> Signup and view all the answers

    What is formed when mRNA binds with fMet-tRNAf and the 30S subunit?

    <p>Initiation complex</p> Signup and view all the answers

    Which factor primarily helps to ensure the fidelity of initiation codon selection?

    <p>IF3</p> Signup and view all the answers

    How does the activation of PKR affect the state of neighboring cells?

    <p>Induces an anti-viral state</p> Signup and view all the answers

    Which subunit dissociates during the formation of the initiation complex?

    <p>50S subunit</p> Signup and view all the answers

    What is the primary function of GTP in the formation of the initiation complex?

    <p>To facilitate fMet-tRNAf binding to IF2</p> Signup and view all the answers

    What initiates the translation process in eukaryotes?

    <p>Formation of the 48S pre-initiation complex</p> Signup and view all the answers

    Which site on the ribosome is responsible for the exit of tRNA during translation?

    <p>E site</p> Signup and view all the answers

    How many ATP molecules are consumed to add each amino acid during translation?

    <p>4 ATP</p> Signup and view all the answers

    What ensures the correct amino acid addition during the elongation phase of translation?

    <p>Elongation factors</p> Signup and view all the answers

    What is the purpose of the 5’ cap in eukaryotic mRNA?

    <p>To protect mRNA from degradation</p> Signup and view all the answers

    What is the role of initiation factors during translation initiation?

    <p>To align the small ribosomal subunit with mRNA</p> Signup and view all the answers

    Which component is essential for the initiation of translation in eukaryotes?

    <p>5’ cap</p> Signup and view all the answers

    What happens during the termination stage of translation?

    <p>The polypeptide is released</p> Signup and view all the answers

    How does mRNA circularization contribute to translation in eukaryotes?

    <p>It enhances the ribosome's ability to scan for AUG</p> Signup and view all the answers

    Which RNA plays a role in carrying amino acids to the ribosomes during translation?

    <p>tRNA</p> Signup and view all the answers

    Which molecules are involved in the recycling of ribosomal subunits after termination?

    <p>RRF in prokaryotes and ABCE1 in eukaryotes</p> Signup and view all the answers

    What specifies each amino acid in the genetic code?

    <p>Triplet code of three RNA bases</p> Signup and view all the answers

    Why is pseudouridine (ψ) considered beneficial for stability in tRNA?

    <p>It has a greater possibility for hydrogen bonding.</p> Signup and view all the answers

    What is the role of amino acyl-tRNA synthetases in protein synthesis?

    <p>They ensure the correct linkage of specific amino acids to their respective tRNA.</p> Signup and view all the answers

    What is an essential feature of the ester bond formed between an amino acid and tRNA?

    <p>It helps drive the synthesis of peptide bonds.</p> Signup and view all the answers

    What is the overall error rate for amino acid activation by amino acyl-tRNA synthetases?

    <p>1 in 10,000</p> Signup and view all the answers

    In the two-step process of amino acid activation, what molecule is released during the first reaction?

    <p>PPi</p> Signup and view all the answers

    What is the primary reason that amino acyl-tRNA synthetases have a low error rate?

    <p>They undergo a proofreading mechanism during tRNA binding.</p> Signup and view all the answers

    Which component is directly linked to the terminal adenosine during amino acid activation?

    <p>Carboxyl group of the amino acid</p> Signup and view all the answers

    How many ATP equivalents are used in the overall process of amino acid activation?

    <p>2 ATPs due to enzyme reactions</p> Signup and view all the answers

    Study Notes

    Translation - Lecture 1

    • Translation is the process of protein synthesis, decoding RNA to create a polypeptide chain.
    • The central dogma of molecular biology describes the flow of genetic information: DNA makes RNA makes protein.
    • mRNA carries genetic information from DNA to ribosomes in the cytoplasm for protein synthesis.
    • tRNA carries amino acids to the ribosome.
    • Ribosomes are the protein synthesis machinery composed of ribosomal RNA (rRNA) and proteins.
    • Translation occurs in three stages: initiation, elongation, and termination.
    • Initiation involves bringing together components like mRNA, initiator tRNA, and ribosomal subunits.
    • Elongation adds amino acids to the polypeptide chain one at a time.
    • Termination ends the process when a stop codon is reached.
    • Translation requires numerous proteins, including initiation factors (IFs), elongation factors (EFs), and release factors.

    Learning Outcomes

    • Understand translation's role in protein synthesis within the central dogma.
    • Identify the different stages of translation.
    • Understand the functions of ribosomes, mRNA, tRNA, and aminoacyl-tRNA synthetases.
    • Understand the function of codons and how they're recognized by anticodons on tRNA.
    • Define the characteristics of the genetic code, including redundancy, universality, start codons and stop codons.

    Lecture Structure

    • Translation lectures take place over several dates throughout December, 2024, plus one further lecture in January 2025.
    • Topics covered include: introduction, tRNA and charging, ribosomes, and translational control.
    • Review of translation is included alongside an overview of the exam.

    Key Concepts

    • Translation requires the cooperation of ribosomal RNAs, transfer RNAs, messenger RNAs, and numerous proteins.
    • Translation is performed by the ribosome.
    • The steps of translation are grouped into three distinct stages (initiation, elongation and termination), different from the transcription stages.
    • Proteins are made by joining amino acids.

    Protein Synthesis Components

    • Components needed for protein synthesis include a template, building blocks (amino acids), something to assemble the blocks (ribosomes), ways to decode correctly (rules), and energy.

    Protein synthesis stages

    • Initiation - requires base-pairing between mRNA and tRNA, brings together all elements necessary for translation, ribosomal and initiation sites.
    • Elongation - amino acid addition to the polypeptide chain, one by one.
    • Termination - stops the process when a stop codon is reached, the release or mRNA and associated elements.

    Ribosomes

    • Ribosomes are complex molecular machines made of rRNA and proteins.
    • Ribosomes have three sites for tRNA to bind: A-site, P-site and E-site.
    • mRNA slides through a channel on the small ribosomal subunit.

    mRNA

    • mRNA (messenger RNA) is a template for translation, carries the genetic code from DNA to ribosomes.
    • Consists of ribonucleotides (A, C, G, and U)
    • Contains non-coding regions (UTRs).

    tRNA

    • tRNA (transfer RNA) carries amino acids to the ribosome.
    • tRNA molecules have an anticodon that recognizes a specific codon on mRNA.
    • tRNAs are highly conserved, L-shaped structures.
    • The 3' end of the tRNA has the amino acid attached.

    Initiation in Eukaryotes

    • Eukaryotic initiation differs significantly from bacterial initiation.
    • Initiation requires elF2, the small 40S ribosome, methionyl-tRNA, GTP, and other initiation factors.
    • The mRNA is scanned by the 40S subunit for the AUG initiation codon.

    Initiation in Bacteria

    • Bacterial initiation uses more factors than eukaryotes.
    • A Shine-Dalgarno sequence helps position the initiation codon on the ribosome.
    • Uses initiation factors IF1, IF2 and IF3 to assemble an initiation complex.

    Differences between Eukaryotic and Bacterial mRNA

    • Eukaryotic mRNA contains a 5' cap and a poly(A) tail, while bacterial mRNA does not.
    • Eukaryotic mRNAs lack a Shine-Dalgarno sequence while bacterial mRNA does have a Shine-Dalgarno sequence.

    tRNA Modifications

    • Specific bases in tRNA are post-transcriptionally modified.
    • These modifications contribute to tRNA stability.
    • Inosine is a modified base that allows tRNA to recognize multiple codons.

    Amino Acid Activation and tRNA Charging

    • Amino acids are activated before attachment via ester bonds to tRNAs by aminoacyl-tRNA synthetases.
    • This activation is an energy-requiring two-step process, using ATP.
    • High accuracy is required when attaching the amino acids to their tRNA, ensuring fidelity.
    • Proofreading mechanisms within the enzyme are critical for high accuracy.

    Wobble Hypothesis

    • The anticodon's first base can pair with multiple codons.
    • This allows a single tRNA to read multiple codons.

    Control of Translation

    • Cellular processes regulate the availability and activity of factors involved in translation.
    • Factors like eIF2 and eIF4E can be regulated to control the speed and accuracy of protein synthesis.
    • Ribosomes recognize the tRNA first, not the amino acid carried by the tRNA itself.

    Ribosomal Structure

    • Ribosomal structure determines the arrangement of tRNA binding sites.
    • tRNA binding sites are located in the ribosome.

    Summary of Key Roles of tRNA

    • To activate the amino acid as a tRNA ester
    • To work with the correct synthetase, to ensure the correct amino acid attaches to the correct tRNA.
    • To base pair its anticodon triplet with the correct codon (this allows wobble).
    • To bring the correct amino acid to the ribosome
    • To facilitate peptide bond formation.

    Additional Resources

    • Videos are available to provide additional context and information.

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    Related Documents

    BIOL2010 Translation Lecture 1 2024 PDF

    Description

    Test your knowledge of the protein synthesis process, focusing on the roles of translation and tRNA. This quiz covers essential components, stages, and functions related to protein synthesis and the accuracy of amino acid incorporation. Assess your understanding of mutations and their implications in viruses like SARS-CoV-2.

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