Protein Synthesis Overview
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Questions and Answers

What occurs during the initiation of translation?

  • The aminoacyl-tRNA binds to the ribosome. (correct)
  • Ribosomes disassemble into subunits.
  • Amino acids are linked by peptide bonds.
  • mRNA is synthesized from a DNA template.

    • Which statement is true regarding the formation of peptide bonds?

  • Peptide bonds are formed during transcription.
  • Peptide bonds are broken by aminoacyl-tRNA synthetases.
  • Peptide bonds require ATP as the energy source.
  • Peptide bonds connect amino acids during translation. (correct)

    • How does transcription differ from translation?

  • Transcription synthesizes RNA while translation synthesizes protein. (correct)
  • Transcription occurs in the ribosome while translation occurs in the nucleus.
  • Transcription uses tRNA whereas translation uses mRNA.
  • Transcription translates genetic code directly into amino acids.

    • Which of the following antibiotics would hinder protein synthesis in prokaryotic cells?

    <p>Tetracycline, which blocks aminoacyl-tRNA binding.</p> Signup and view all the answers

    What is the role of the large ribosomal subunit during translation?

    <p>It catalyzes the formation of peptide bonds between amino acids.</p> Signup and view all the answers

    What is the primary function of the aminoacyl-tRNA synthetase?

    <p>To attach the correct amino acid to its corresponding tRNA.</p> Signup and view all the answers

    What distinguishes prokaryotic ribosomes from eukaryotic ribosomes?

    <p>Eukaryotic ribosomes contain more proteins than prokaryotic ribosomes.</p> Signup and view all the answers

    Which statement about Svedberg (S) values is correct?

    <p>Svedberg values indicate the rate of sedimentation in a centrifuge.</p> Signup and view all the answers

    What is the Svedberg value of eukaryotic ribosomes?

    <p>80S</p> Signup and view all the answers

    Which subunits make up the prokaryotic ribosomes?

    <p>30S and 50S</p> Signup and view all the answers

    Which site is responsible for the charged tRNA binding to the mRNA codon during translation?

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

    What is the role of the P site in the ribosome?

    <p>Holding the growing polypeptide chain</p> Signup and view all the answers

    Which RNA component is part of the 30S subunit in prokaryotic ribosomes?

    <p>16S RNA</p> Signup and view all the answers

    Why are Svedberg units not additive in ribosomal structure?

    <p>Because they consider size and shape</p> Signup and view all the answers

    Which binding site is utilized by tRNA before it is released and recycled?

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

    Which of the following statements regarding ribosomes is correct?

    <p>Eukaryotic ribosomes are larger than prokaryotic ribosomes</p> Signup and view all the answers

    What components are essential for forming the initiation complex in procaryotes?

    <p>mRNA, 30s ribosomal subunit, fmet tRNA, GTP, initiation factors</p> Signup and view all the answers

    How does the 40s ribosomal subunit form a complex in eucaryotes?

    <p>By linking with 4 initiation factors and Met tRNA</p> Signup and view all the answers

    Which role does peptidyl transferase play in peptide bond formation?

    <p>It catalyzes the peptide bond formation between amino acids.</p> Signup and view all the answers

    What occurs when the A site of the ribosome encounters a stop codon?

    <p>Translation is terminated.</p> Signup and view all the answers

    What is the role of elongation factor eEF-2 during translation?

    <p>It moves the ribosome along the mRNA by one codon.</p> Signup and view all the answers

    Which of the following factors do NOT participate in the initiation complex formation in Eucaryotes?

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

    During which stage of protein synthesis is the peptide bound to the A site transiently?

    <p>Peptide bond formation</p> Signup and view all the answers

    Which of the following describes the relationship between transcription and translation?

    <p>Transcription synthesizes mRNA, which is then translated into proteins.</p> Signup and view all the answers

    Study Notes

    Protein Synthesis Overview

    • Protein synthesis is a crucial biological process converting genetic information into functional proteins.
    • The process involves two major steps: transcription and translation.

    Eukaryotic mRNA Structure

    • Eukaryotic mRNA molecules are composed of a 5' cap, untranslated region, coding sequence, and a 3' untranslated region and a poly(A) tail.
    • The AUG codon signals the start of translation, and a stop codon indicates the end.

    tRNA Structure

    • Transfer RNA (tRNA) molecules have a specific three-nucleotide anticodon loop that base pairs with a complementary codon on mRNA.
    • The amino acid is attached to the acceptor stem by an aminoacyl tRNA synthetase.

    Translation: Codon-Anticodon Interactions

    • During translation, anticodons of tRNA molecules pair with codons on mRNA.
    • Codons and anticodons are composed of three nucleotides.
    • The genetic code is based on triplets.
    • mRNA is decoded in a 5' to 3' direction.
    • Protein synthesis occurs from amino terminus (NH2) to carboxyl terminus (COO-).

    The Genetic Code

    • The genetic code describes the relationship between codons and the amino acids they specify.
    • Many amino acids have more than one codon. This is known as redundancy.
    • Each codon codes for only one amino acid (or stop codon). This is unambiguous.
    • The start codon is AUG.
    • Several codons signal the end of translation.

    Aminoacyl-tRNA Synthesis

    • Aminoacyl-tRNA synthetases are responsible for attaching the correct amino acid to its corresponding tRNA molecule.
    • Two steps are used.
      • Activation of amino acids.
      • Linking of amino acids to tRNA.
    • Each amino acid has a specific tRNA and synthetase for ensuring fidelity.

    Translation Phases

    • Translation occurs in three phases:
      • Initiation: The ribosome assembles on the mRNA molecule.
      • Elongation: Amino acids are brought in, and peptide bonds are formed.
      • Termination: The ribosome disassembles, and the polypeptide chain is released.

    Components of Translation

    • Amino acids are the building blocks of proteins.
    • Transfer RNA (tRNA) molecules carry amino acids to the ribosome.
    • Aminoacyl-tRNA synthetases attach amino acids to tRNA.
    • Ribosomes are the sites of protein synthesis.
    • mRNA carries the genetic code.

    Ribosomes

    • Ribosomes are composed of proteins and ribosomal RNA (rRNA).
    • Prokaryotic ribosomes have 70S subunits (30S and 50S).
    • Eukaryotic ribosomes have 80S subunits (40S and 60S).
    • Svedberg units describe sedimentation rate, not an additive property.
    • Ribosomes have three tRNA-binding sites: A, P, and E.

    Initiation of Translation (Prokaryotes)

    • Initiation complex requires mRNA, 30S ribosomal subunit, initiator tRNA, GTP, and initiation factors. • 16S rRNA binds Shine-Dalgarno sequence on mRNA. • AUG codon codes for methionine (N-formylmethionine in prokaryotes). • Initiation factors are released after GTP hydrolysis

    Initiation of Translation (Eukaryotes)

    • 40S ribosomal subunit forms a complex with initiation factors and methionine tRNA. • Initiation factors bind to the mRNA 5' cap. • The complex scans the mRNA until the AUG start codon is found. • The 60S subunit binds, GTP is hydrolyzed, and initiation factors are released.

    Translocation and Peptide Bond Formation

    • Peptidyl transferase, a ribozyme, catalyses peptide bond formation between amino acids.
    • Elongation factors move the ribosome along the mRNA.
    • 'Empty' tRNA moves to the E site and is released.
    • tRNA with the growing peptide moves to the P site.
    • A site is ready for the next aminoacyl-tRNA.

    Termination

    • Translation ends when a stop codon (UAA, UAG, or UGA) is reached.
    • Release factors bind to the stop codon, causing polypeptide chain release and ribosome disassembly.
    • The finished protein is cleaved off.

    Antibiotics Targeting Protein Synthesis

    • Antibiotics can target different stages of protein synthesis in bacteria and eukaryotes.
    • Examples are Tetracycline, Streptomycin, Erythromycin, Chloramphenicol, Puromycin, and Cycloheximide (toxic to humans).

    Reading Frames

    • The genetic code can be read in three different reading frames.
    • The starting point of translation determines the reading frame.

    Types of Mutations

    • Mutations can alter the protein-coding sequence.
    • Missense mutations change an amino acid.
    • Nonsense mutations introduce a stop codon.
    • Silent mutations do not change the amino acid.
    • Frameshift mutations shift the reading frame.

    Effects of Mutations

    • Mutations can have various effects on protein synthesis. • Missense, nonsense, or silent mutations can alter the amino acid sequence or length of the protein, potentially affecting function.

    Protein Targeting

    • Proteins destined for specific locations within the cell have signal peptides.
    • Signal peptides are recognized by signal recognition particles (SRPs).
    • Protein targeting ensures proteins are delivered to their proper location in the cell by targeting their appropriate mRNA sequence (Shine Dalgarno Sequence in prokaryotic mRNA and 5' cap in eukaryotic mRNA).

    Post-translational Modifications

    • Proteins undergo modifications after synthesis, such as glycosylation, disulfide bond formation, and folding.
    • These ensure structural integrity and proper functionality of the protein.
    • Proteolytic cleavage is also important.

    Free and Bound Ribosomes

    • Free ribosomes synthesise proteins that function in the cytosol, nucleus, and mitochondria.
    • Bound ribosomes synthesise proteins destined for the endoplasmic reticulum, Golgi apparatus, plasma membrane, and secretion.

    Protein Folding

    • Proteins must fold into their correct 3D shape to function.
    • Molecular chaperones assist in protein folding.

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    Related Documents

    Protein Synthesis AY24-25 PDF

    Description

    Dive into the fundamental process of protein synthesis, focusing on the steps of transcription and translation. Learn about the structure of eukaryotic mRNA and tRNA, including how codon-anticodon interactions drive the synthesis of proteins. This quiz will enhance your understanding of the genetic code and its translation into functional proteins.

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