Eukaryotic Transcription and Translation Quiz
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Questions and Answers

What structure forms during transcription termination in bacteria?

  • TATA box
  • Sigma factor
  • Poly(A) signal
  • Hairpin structure (correct)

    • Which of the following accurately describes a characteristic of eukaryotic transcription?

  • Uses a single RNA polymerase
  • Involves general transcription factors (correct)
  • Produces fully functional mRNA
  • Transcription takes place in the cytoplasm

    • What happens to the initial primary transcript in eukaryotes after transcription?

  • It is translated immediately
  • It remains unchanged
  • It undergoes RNA processing (correct)
  • It is degraded

    • What is the role of introns in eukaryotic genes?

    <p>They are removed during RNA processing</p> Signup and view all the answers

    Which component is responsible for recognizing promoters in eukaryotic transcription?

    <p>General transcription factors</p> Signup and view all the answers

    What must occur for mature mRNA to be produced from a primary transcript in eukaryotes?

    <p>Introns must be removed and exons joined</p> Signup and view all the answers

    Which of the following statements about RNA polymerase in eukaryotes is true?

    <p>It utilizes three different types of RNA polymerases</p> Signup and view all the answers

    What is the role of ribosomes in translation?

    <p>They synthesize proteins from amino acids.</p> Signup and view all the answers

    Which statement accurately describes the pulse-chase experiment performed by Britten and colleagues?

    <p>It involved the incorporation of radioactive sulfur into amino acids.</p> Signup and view all the answers

    How does the translation process differ between bacteria and eukaryotes?

    <p>Translation begins before transcription is complete in bacteria.</p> Signup and view all the answers

    What happens to mRNA in eukaryotes after transcription?

    <p>It undergoes processing before being transported to the cytoplasm.</p> Signup and view all the answers

    What are polyribosomes?

    <p>Multiple ribosomes attached to a single mRNA molecule.</p> Signup and view all the answers

    What is one hypothesis regarding how mRNA specifies amino acids?

    <p>Codons on mRNA interact directly with amino acids.</p> Signup and view all the answers

    Which of the following components is not involved in the translation process?

    <p>DNA polymerase</p> Signup and view all the answers

    What occurs after proteins are synthesized at ribosomes?

    <p>They are released into the cytoplasm.</p> Signup and view all the answers

    In bacteria, what is the primary advantage of coupling transcription and translation?

    <p>It allows for faster protein synthesis.</p> Signup and view all the answers

    What is the primary function of transfer RNA (tRNA)?

    <p>To hold the amino acid in place while interacting with a codon.</p> Signup and view all the answers

    What structure is formed by tRNA due to its folding?

    <p>Stem-and-loop</p> Signup and view all the answers

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

    <p>To attach amino acids to their corresponding tRNAs.</p> Signup and view all the answers

    How many aminoacyl-tRNA synthetases are there in relation to amino acids?

    <p>20, one for each amino acid.</p> Signup and view all the answers

    What concept did Crick propose to explain how one tRNA can read multiple codons?

    <p>Wobble pairing</p> Signup and view all the answers

    Which part of the ribosome is primarily responsible for peptide bond formation?

    <p>Large subunit</p> Signup and view all the answers

    How many different tRNAs are typically present in most cells?

    <p>40</p> Signup and view all the answers

    What is the significance of the CCA sequence at the 3′ end of tRNA?

    <p>It is the amino acid binding site.</p> Signup and view all the answers

    What does the anticodon in tRNA do?

    <p>It binds to the mRNA codon.</p> Signup and view all the answers

    What nucleotide sequence would be found at the 3′ end of a typical tRNA molecule?

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

    What initiates the process of translation in protein synthesis?

    <p>The binding of the initiator tRNA to the start codon</p> Signup and view all the answers

    Which function does the active site of the ribosome serve?

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

    What happens to the tRNA in the P site during translocation?

    <p>It is released from the ribosome</p> Signup and view all the answers

    Which sequence of events occurs during elongation?

    <p>Aminoacyl tRNA arrives, peptide bond forms, uncharged tRNA is ejected</p> Signup and view all the answers

    How does translocation affect the ribosome's sites?

    <p>It allows for the ejection of tRNA from the E site</p> Signup and view all the answers

    What is the function of the A site in the ribosome?

    <p>It binds tRNA carrying an amino acid.</p> Signup and view all the answers

    Which of the following statements correctly describes translation elongation?

    <p>A peptide bond forms between the amino acids at the A and P sites.</p> Signup and view all the answers

    What occurs after a peptide bond is formed during translation?

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

    Where does the initiator tRNA bind during the initiation phase of translation in bacteria?

    <p>To the Shine-Dalgarno sequence.</p> Signup and view all the answers

    What is the correct order of the translation process phases?

    <p>Initiation, Elongation, Termination</p> Signup and view all the answers

    During which phase of translation is the ribosomal subunit bound to the Shine-Dalgarno sequence?

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

    What modification does the initiator tRNA carry in bacterial translation?

    <p>Formylated methionine (f-Met)</p> Signup and view all the answers

    In which site does the tRNA exit the ribosome after fulfilling its role?

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

    Which of the following explains the addition of amino acids during translation?

    <p>Amino acids are added to the carboxyl end (C-terminus) of the polypeptide.</p> Signup and view all the answers

    What happens to tRNA in the E site during the process of translation?

    <p>It exits the ribosome after delivering its amino acid.</p> Signup and view all the answers

    Study Notes

    Chapter 17: Transcription, RNA Processing, and Translation

    • This chapter covers the processes of transcription, RNA processing, and translation.
    • These processes are crucial for cells to synthesize proteins, which perform various roles within the cell.
    • The building blocks for cell proteins come from instructions encoded within the genome.
    • Cells use these instructions to create proteins: first transcribing DNA to RNA, then translating mRNA into a protein.

    RNA Polymerases and Transcription

    • RNA polymerases synthesize an RNA version of DNA's instruction set.
    • They use ribonucleoside triphosphates (NTPs).
    • They match complementary bases with one DNA strand forming the template strand.
    • Only one DNA strand is the template, the non-template strand matches the mRNA sequence (with Uracil instead of Thymine).
    • Transcription happens in the 5' to 3' direction.
    • Bacteria have a single RNA polymerase, eukaryotes have multiple types (I, II, and III).
    • RNA polymerases do not require a primer to start transcription.

    Bacterial Transcription Initiation

    • Bacterial RNA polymerase's initiation capability is dependent on a sigma protein.
    • This joins to the RNA polymerase to create a holoenzyme.
    • Holoenzymes find promoter sites, regions containing sequences (-35 box and -10 box) where transcription begins.
    • Sigma recognizes and binds to the promoter region.
    • This process opens the DNA helix.
    • Once initiation is complete, the sigma protein detaches and the core enzyme continues transcribing..
    • Promoters are relatively short sequences of DNA (40-50 base pairs). The -10 box is about 10 bases upstream of the transcription start site and a -35 box is located about 35 bases from the transcription start site.
      • Downstream refers to the same direction as RNA polymerase movement, upstream the opposite direction.

    Events Inside the Holoenzyme (Detailed)

    • Transcription begins when sigma binds to -35 and -10 boxes.
    • Sigma's binding orientation determines which DNA strand is the template.
    • Once the DNA helix is open, the template strand is threaded through the RNA polymerase's active site.
    • Incoming NTPs enter the channel in the active site, pairing with complementary DNA bases and polymerization begins.

    Elongation and Termination in Bacteria

    • During elongation, RNA polymerase reads the DNA template, adding nucleotides to the 3' end of the RNA.
    • Termination occurs when RNA polymerase transcribes a transcription-termination signal that causes a hairpin loop to form on the RNA.
    • The hairpin structure causes the RNA to separate from RNA polymerase, halting transcription.

    Transcription in Eukaryotes

    • Eukaryotic transcription has three RNA polymerases.
    • Eukaryotic promoters are more diverse than in bacteria, often including a TATA box.
    • General transcription factors (instead of sigma proteins) recognize promoters.
    • Instead of hairpins, termination often involves a poly(A) signal.
    • The RNA downstream of the poly(A) signal is cut creating a mature mRNA molecule.
    • Transcription happens in the cell's nucleus, whereas translation happens in the cytoplasm.

    RNA Processing

    • Primary RNA transcripts (pre-mRNAs) in eukaryotes are not immediately functional.
    • They undergo processing before becoming a functional mRNA.
    • Introns (non-coding regions) are removed through a process called splicing.
    • The spliceosome (a complex of small nuclear ribonucleoproteins, snRNPs) catalyzes the removal process.
    • A 5' cap and a 3' poly(A) tail are added to the mature mRNA, protecting it and providing binding sites necessary for the ribosome to accurately recognize it and initiate translation.
    • Pre-mRNA is made in the cell's nucleus; after processing, mature mRNA travels to the cytoplasm for translation.

    Translation: Overview

    • The process of translation converts the sequence of mRNA bases into an amino acid sequence.
    • Ribosomes are the crucial sites for protein synthesis, where the mRNA codons are translated.
    • Ribosomes and tRNAs (with their amino acids) cooperate to accomplish this process.
    • Ribosomes are made of proteins and rRNA (ribosomal RNA).
    • Each ribosome is made from two subunits.

    Ribosome Structure and Function

    • tRNAs fit into three sites in the ribosome to align with mRNA codons: the A (acceptor, aminoacyl), P (peptidyl), and E (exit) sites.
    • The A site receives the aminoacyl tRNA carrying an amino acid.
    • The P site holds the tRNA with the growing polypeptide chain.
    • The E site holds the tRNA that will exit.
    • The ribosome synthesizes proteins in a three-step sequence.

    Translation Initiation

    • Initiation in bacteria involves the binding of the small ribosomal subunit to the mRNA's ribosome binding site.
    • The initial tRNA (initiator tRNA) carries a modified methionine (Methionine but often called f-Met).
      • It binds to a start codon (AUG)
    • The large ribosomal subunit binds completing the ribosome.
    • Translation initiation is a three-step process.

    Translation Elongation

    • Elongation begins when a charged aminoacyl tRNA binds to the codon in the A site.
    • Peptide bond formation joins the amino acid on the P-site tRNA to the growing polypeptide chain on the A-site tRNA.
    • Translocation (movement of the ribosome) moves the tRNA-polypeptide complex to the P site. The uncharged tRNA is moved to the E site and exits. The A-site is ready to receive the next aminoacyl-tRNA matching the next codon).

    Translation Termination

    • Termination occurs when the ribosome reaches a stop codon.
    • A release factor (a protein) enters the A site.
    • This release factor hydrolyzes the bond linking the final tRNA and the polypeptide chain.
    • The polypeptide is released, and the ribosomal subunits separate.

    Table 17.1 (Summary of Differences in Bacterial and Eukaryotic Transcription and Translation)

    • This table summarizes the differences in the processes of transcription and translation between bacteria and eukaryotes in terms of RNA polymerase types, promoter structures, protein organization and RNA processing steps.

    Post-Translational Modifications

    • Most proteins go through post-translational modifications to become functional.
    • These modifications occur after the initial translation.
    • These processes can involve protein folding, addition of sugar or lipid groups, or adding phosphate groups.
    • These modifications may happen at various locations within the cell.

    Web Activities

    • These are activities related to concepts in the chapters. They do not provide information that needs summarization for study notes.

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    Biological Science Chapter 17: Transcription, RNA Processing, and Translation - PDF

    Description

    Test your knowledge on the processes of transcription and translation in eukaryotic cells. This quiz covers key concepts such as the roles of RNA polymerase, introns, polyribosomes, and the distinctions between bacterial and eukaryotic translation. Ideal for students studying molecular biology and genetics.

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