Elongation and Termination in Protein Synthesis
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Questions and Answers

During translocation, what is the energy source that allows tRNA to shift from the A site to the P site?

  • ATP
  • AMP
  • ADP
  • GTP (correct)

    • What is the role of a release factor during translation?

  • Reading the genetic code on the mRNA
  • Adding an amino acid to the growing polypeptide chain
  • Initiating the translation process
  • Terminating the translation process (correct)

    • What type of proteins do free ribosomes primarily synthesize?

  • Proteins that are embedded in the cell membrane
  • Proteins that are secreted from the cell
  • Proteins of the endomembrane system
  • Proteins that function in the cytosol (correct)

    • What is the result of the polypeptide chain shifting from the P site to the A site during translation?

    <p>The tRNA in the P site is released</p> Signup and view all the answers

    Bound ribosomes synthesize proteins that are primarily:

    <p>Part of the endomembrane system</p> Signup and view all the answers

    What is the purpose of translocation during translation?

    <p>To shift the mRNA by one codon along the ribosome</p> Signup and view all the answers

    What is the result of the release factor binding to the A site during translation?

    <p>The release of the polypeptide chain from the ribosome</p> Signup and view all the answers

    What is the role of GTP during translocation?

    <p>To provide energy for the translocation process</p> Signup and view all the answers

    What is the purpose of the E site during translation?

    <p>To exit the tRNA from the ribosome</p> Signup and view all the answers

    What occurs when a stop codon reaches the A site during translation?

    <p>The translation process is terminated</p> Signup and view all the answers

    What is the function of RNA polymerase in transcription?

    <p>To catalyze the synthesis of RNA</p> Signup and view all the answers

    What is the role of the 5' cap in RNA modification?

    <p>All of the above</p> Signup and view all the answers

    What is the function of RNA splicing?

    <p>To remove introns and join exons</p> Signup and view all the answers

    What is the structure of tRNA?

    <p>An L-shaped molecule with a 5' and 3' end</p> Signup and view all the answers

    What is the function of ribosomes in translation?

    <p>To translate mRNA into protein</p> Signup and view all the answers

    What is the genetic code?

    <p>A triplet code that translates into amino acids</p> Signup and view all the answers

    What is the result of alternative splicing?

    <p>Different proteins are formed from the same gene</p> Signup and view all the answers

    What is the function of ribozymes?

    <p>To catalyze the splicing of RNA</p> Signup and view all the answers

    What is the role of the TATA box in transcription?

    <p>To bind RNA polymerase</p> Signup and view all the answers

    What is the function of RNA polymerase III?

    <p>To synthesize snRNA and miRNA</p> Signup and view all the answers

    What is the result of the addition of a water molecule during translation?

    <p>Release of the polypeptide</p> Signup and view all the answers

    During translation, what is the purpose of the energy from GTP?

    <p>To translocate the mRNA along the ribosome</p> Signup and view all the answers

    What is the primary function of free ribosomes?

    <p>To synthesize proteins that function in the cytosol</p> Signup and view all the answers

    What occurs during elongation, when a tRNA is in the A site and the polypeptide chain shifts from the P site?

    <p>The tRNA in the A site shifts to the P site</p> Signup and view all the answers

    What is the role of the A site during termination?

    <p>It binds to the release factor</p> Signup and view all the answers

    What is the purpose of translocation during translation?

    <p>To shift the mRNA along the ribosome</p> Signup and view all the answers

    What is the primary function of elongation factors during translation?

    <p>To facilitate the formation of peptide bonds</p> Signup and view all the answers

    What is the result of peptide bond formation during translation?

    <p>A new amino acid is added to the C-terminus of the growing chain</p> Signup and view all the answers

    What is the role of initiation factors during translation?

    <p>To bring the small subunit to the mRNA and initiate translation</p> Signup and view all the answers

    What is the purpose of translocation during translation?

    <p>To shift the tRNA from the A site to the P site</p> Signup and view all the answers

    What occurs during the codon recognition step of elongation?

    <p>The tRNA is positioned on the A site of the ribosome</p> Signup and view all the answers

    What is the result of the polypeptide chain being shifted from the A site to the P site during translation?

    <p>The next amino acid is added to the growing chain</p> Signup and view all the answers

    What is the role of poly-A tail in RNA modification?

    <p>To increase the stability of the mRNA</p> Signup and view all the answers

    What is the function of the 5' cap in RNA modification?

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

    What is the result of RNA modification during transcription?

    <p>The mRNA is protected from hydrolytic enzymes and facilitated for export</p> Signup and view all the answers

    What is the function of RNA splicing during post-transcriptional modification?

    <p>To remove introns and join exons</p> Signup and view all the answers

    During what stage of translation does the polypeptide chain undergo post-translational modifications?

    <p>After translation is complete</p> Signup and view all the answers

    Which of the following factors is NOT involved in the formation of peptide bonds during translation?

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

    What is the primary function of elongation factors during translation?

    <p>To facilitate the translocation of tRNA during elongation</p> Signup and view all the answers

    During translocation, which site does the tRNA in the A site move to?

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

    What is the energy source that allows the tRNA to shift from the A site to the P site during translocation?

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

    What is the role of initiation factors during translation?

    <p>To facilitate the binding of mRNA to the ribosome</p> Signup and view all the answers

    What is the primary function of poly-A tail in RNA modification?

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

    During peptide bond formation, which of the following occurs?

    <p>The amino acid is attached to the 3' end of the tRNA</p> Signup and view all the answers

    What is the role of initiation factors during translation?

    <p>To bring the small subunit to the ribosome</p> Signup and view all the answers

    What is the primary function of elongation factors during translation?

    <p>To facilitate the addition of amino acids to the growing polypeptide chain</p> Signup and view all the answers

    During translocation, what occurs?

    <p>The tRNA moves from the A site to the P site</p> Signup and view all the answers

    What is the energy source that allows the tRNA to shift from the A site to the P site during translocation?

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

    Which of the following is NOT a function of initiation factors during translation?

    <p>Releasing the completed polypeptide chain</p> Signup and view all the answers

    What is the result of the polypeptide chain being shifted from the A site to the P site during translation?

    <p>The polypeptide chain is lengthened by one amino acid</p> Signup and view all the answers

    Which of the following occurs during the elongation stage of translation?

    <p>The polypeptide chain is lengthened by one amino acid</p> Signup and view all the answers

    What is the result of the addition of a water molecule during translation?

    <p>The amino acid is hydrolyzed from the tRNA</p> Signup and view all the answers

    Study Notes

    Translation

    • Polypeptide chain shifts from P site to A site, requiring energy from GTP.
    • Translocation: mRNA shifts one codon along the ribosome, allowing tRNA to shift from A site to P site and exit through E site.
    • Elongation continues until a stop codon reaches the A site.
    • Release factor binds to A site, causing hydrolysis and releasing the polypeptide chain.
    • Ribosomal subunits dissociate after termination.

    Free and Bound Ribosomes

    • Free ribosomes synthesize proteins that function in the cytosol.
    • Bound ribosomes (attached to ER) synthesize proteins of the endomembrane system and secreted proteins.

    Transcription

    • RNA synthesis is catalyzed by RNA polymerase.
    • RNA polymerase does not require a primer.
    • Base-pairing rules are the same as DNA, except uracil substitutes for thymine.
    • Transcription unit: a segment of DNA that is transcribed into a single RNA molecule.
    • Promoter: a sequence that RNA polymerase binds to.
    • Terminator: a sequence that signals the end of transcription.

    Initiation Stage of Transcription

    • RNA polymerase binds to the promoter, opening up the DNA strand.
    • TATA Box is a sequence that RNA polymerase binds to.
    • RNA transcript is complementary to DNA, formed from 5' to 3'.

    Elongation Stage of Transcription

    • RNA polymerase untwists the double helix.
    • Transcription occurs at a rate of 40 nucleotides per second in eukaryotes.
    • DNA is read 3' to 5', RNA transcript is formed 5' to 3'.

    Termination Stage of Transcription

    • In bacteria, RNA polymerase stops transcription at the terminator.
    • In eukaryotes, RNA modification occurs, including 5' cap and 3' poly A tail.
    • Polyadenylation: poly A tail of RNA transcript that only has adenine bases on the 3' end.
    • 5' cap: a modified nucleotide at the 5' end of mRNA.

    Importance of RNA Modification

    • Protects mRNA from hydrolytic enzymes.
    • Helps ribosome attach to the 5' end.
    • Facilitates export.
    • If cap and tail are not present, RNA is hydrolyzed and loses function.

    RNA Polymerase I

    • Synthesizes ribosomal RNA (rRNA).
    • In eukaryotes, rRNA has 4 components: 28S, 5.8S, 5S, and 18S.
    • Large subunit: 28S, 5.8S, and 5S.
    • Small subunit: 18S.

    RNA Polymerase II

    • Synthesizes messenger RNA (mRNA).
    • Synthesizes small nucleolar RNA (snRNA) and micro RNA (miRNA).
    • miRNA is involved in RNA silencing and post-transcriptional regulation of genes.

    RNA Polymerase III

    • Synthesizes transfer RNA (tRNA).
    • Synthesizes 5S rRNA.

    RNA Splicing

    • Introns: non-coding regions.
    • Exons: coding regions.
    • RNA splicing removes introns by splicing at splice sites and joining exons by DNA ligase.
    • Bacterial cells have no introns, so no splicing is required.

    Ribozymes

    • Ribozymes are enzymes that can splice RNA.
    • They can cleave and ligate RNA molecules.

    Translation

    • Polypeptide chain shifts from P site to A site, requiring energy from GTP.
    • Translocation: mRNA shifts one codon along the ribosome, allowing tRNA to shift from A site to P site and exit through E site.
    • Elongation continues until a stop codon reaches the A site.
    • Release factor binds to A site, causing hydrolysis and releasing the polypeptide chain.
    • Ribosomal subunits dissociate after termination.

    Free and Bound Ribosomes

    • Free ribosomes synthesize proteins that function in the cytosol.
    • Bound ribosomes (attached to ER) synthesize proteins of the endomembrane system and secreted proteins.

    Transcription

    • RNA synthesis is catalyzed by RNA polymerase.
    • RNA polymerase does not require a primer.
    • Base-pairing rules are the same as DNA, except uracil substitutes for thymine.
    • Transcription unit: a segment of DNA that is transcribed into a single RNA molecule.
    • Promoter: a sequence that RNA polymerase binds to.
    • Terminator: a sequence that signals the end of transcription.

    Initiation Stage of Transcription

    • RNA polymerase binds to the promoter, opening up the DNA strand.
    • TATA Box is a sequence that RNA polymerase binds to.
    • RNA transcript is complementary to DNA, formed from 5' to 3'.

    Elongation Stage of Transcription

    • RNA polymerase untwists the double helix.
    • Transcription occurs at a rate of 40 nucleotides per second in eukaryotes.
    • DNA is read 3' to 5', RNA transcript is formed 5' to 3'.

    Termination Stage of Transcription

    • In bacteria, RNA polymerase stops transcription at the terminator.
    • In eukaryotes, RNA modification occurs, including 5' cap and 3' poly A tail.
    • Polyadenylation: poly A tail of RNA transcript that only has adenine bases on the 3' end.
    • 5' cap: a modified nucleotide at the 5' end of mRNA.

    Importance of RNA Modification

    • Protects mRNA from hydrolytic enzymes.
    • Helps ribosome attach to the 5' end.
    • Facilitates export.
    • If cap and tail are not present, RNA is hydrolyzed and loses function.

    RNA Polymerase I

    • Synthesizes ribosomal RNA (rRNA).
    • In eukaryotes, rRNA has 4 components: 28S, 5.8S, 5S, and 18S.
    • Large subunit: 28S, 5.8S, and 5S.
    • Small subunit: 18S.

    RNA Polymerase II

    • Synthesizes messenger RNA (mRNA).
    • Synthesizes small nucleolar RNA (snRNA) and micro RNA (miRNA).
    • miRNA is involved in RNA silencing and post-transcriptional regulation of genes.

    RNA Polymerase III

    • Synthesizes transfer RNA (tRNA).
    • Synthesizes 5S rRNA.

    RNA Splicing

    • Introns: non-coding regions.
    • Exons: coding regions.
    • RNA splicing removes introns by splicing at splice sites and joining exons by DNA ligase.
    • Bacterial cells have no introns, so no splicing is required.

    Ribozymes

    • Ribozymes are enzymes that can splice RNA.
    • They can cleave and ligate RNA molecules.

    Translation

    • Polypeptide chain shifts from P site to A site, requiring energy from GTP.
    • Translocation: mRNA shifts one codon along the ribosome, allowing tRNA to shift from A site to P site and exit through E site.
    • Elongation continues until a stop codon reaches the A site.
    • Release factor binds to A site, causing hydrolysis and releasing the polypeptide chain.
    • Ribosomal subunits dissociate after termination.

    Free and Bound Ribosomes

    • Free ribosomes synthesize proteins that function in the cytosol.
    • Bound ribosomes (attached to ER) synthesize proteins of the endomembrane system and secreted proteins.

    Transcription

    • RNA synthesis is catalyzed by RNA polymerase.
    • RNA polymerase does not require a primer.
    • Base-pairing rules are the same as DNA, except uracil substitutes for thymine.
    • Transcription unit: a segment of DNA that is transcribed into a single RNA molecule.
    • Promoter: a sequence that RNA polymerase binds to.
    • Terminator: a sequence that signals the end of transcription.

    Initiation Stage of Transcription

    • RNA polymerase binds to the promoter, opening up the DNA strand.
    • TATA Box is a sequence that RNA polymerase binds to.
    • RNA transcript is complementary to DNA, formed from 5' to 3'.

    Elongation Stage of Transcription

    • RNA polymerase untwists the double helix.
    • Transcription occurs at a rate of 40 nucleotides per second in eukaryotes.
    • DNA is read 3' to 5', RNA transcript is formed 5' to 3'.

    Termination Stage of Transcription

    • In bacteria, RNA polymerase stops transcription at the terminator.
    • In eukaryotes, RNA modification occurs, including 5' cap and 3' poly A tail.
    • Polyadenylation: poly A tail of RNA transcript that only has adenine bases on the 3' end.
    • 5' cap: a modified nucleotide at the 5' end of mRNA.

    Importance of RNA Modification

    • Protects mRNA from hydrolytic enzymes.
    • Helps ribosome attach to the 5' end.
    • Facilitates export.
    • If cap and tail are not present, RNA is hydrolyzed and loses function.

    RNA Polymerase I

    • Synthesizes ribosomal RNA (rRNA).
    • In eukaryotes, rRNA has 4 components: 28S, 5.8S, 5S, and 18S.
    • Large subunit: 28S, 5.8S, and 5S.
    • Small subunit: 18S.

    RNA Polymerase II

    • Synthesizes messenger RNA (mRNA).
    • Synthesizes small nucleolar RNA (snRNA) and micro RNA (miRNA).
    • miRNA is involved in RNA silencing and post-transcriptional regulation of genes.

    RNA Polymerase III

    • Synthesizes transfer RNA (tRNA).
    • Synthesizes 5S rRNA.

    RNA Splicing

    • Introns: non-coding regions.
    • Exons: coding regions.
    • RNA splicing removes introns by splicing at splice sites and joining exons by DNA ligase.
    • Bacterial cells have no introns, so no splicing is required.

    Ribozymes

    • Ribozymes are enzymes that can splice RNA.
    • They can cleave and ligate RNA molecules.

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