mRNA Processing Overview
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Questions and Answers

What is the role of the third position in mRNA codons according to the Wobble hypothesis?

  • It must be highly specific.
  • It allows flexibility in pairing. (correct)
  • It determines the amino acid type.
  • It is not involved in translation.

    • Which amino acid is the initial amino acid inserted in polypeptide chains in bacteria?

  • Leucine
  • Arginine
  • Methionine
  • N-formyl methionine (correct)

    • What type of DNA showed exceptions to the universal genetic code?

  • Transcribed mitochondrial DNA (correct)
  • Plasmid DNA
  • Chromosomal DNA
  • Nuclear DNA

    • Which codon is specifically known as the initiation codon?

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

    What implications does the universality of the genetic code have on genetic engineering?

    <p>Eukaryotic genes can be transcribed and translated in bacteria.</p> Signup and view all the answers

    What primarily directs the linear insertion of amino acids into a polypeptide chain?

    <p>Messenger RNA (mRNA)</p> Signup and view all the answers

    What do the four types of nucleotides in RNA correspond to in terms of amino acids?

    <p>They are triplet codons that specify each amino acid.</p> Signup and view all the answers

    Which statement correctly describes the genetic code?

    <p>It is triplet and nonoverlapping in nature.</p> Signup and view all the answers

    What are structural genes primarily responsible for?

    <p>Specifying the amino acid sequence of a polypeptide chain.</p> Signup and view all the answers

    What is the primary role of mRNA in the process of translation?

    <p>To transfer genetic information from DNA to ribosomes.</p> Signup and view all the answers

    How does a mutation in the nucleotide sequence of a gene potentially affect an organism?

    <p>It can disrupt the coded instructions for polypeptide formation.</p> Signup and view all the answers

    According to the Central Dogma of molecular genetics, what is the flow of genetic information?

    <p>DNA → RNA → Proteins</p> Signup and view all the answers

    Which type of RNA is not translated into a protein?

    <p>Both B and C</p> Signup and view all the answers

    What can potentially happen if there is a disruption in the sequence of nucleotides in a gene?

    <p>It can lead to the production of a nonfunctional or harmful polypeptide.</p> Signup and view all the answers

    What is the primary end product of genetic expression?

    <p>Polypeptide chains</p> Signup and view all the answers

    Which process describes the transfer of genetic information from DNA to RNA?

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

    Which of the following correctly describes RNA polymerase?

    <p>It directs the synthesis of all three types of RNA.</p> Signup and view all the answers

    What role does the sigma subunit play in the holoenzyme complex?

    <p>It helps recognize promoters for transcription initiation.</p> Signup and view all the answers

    What is the sequence of events in the process from DNA to protein synthesis?

    <p>Transcription, Genetic Expression, Translation</p> Signup and view all the answers

    In RNA synthesis, what type of nucleotides does RNA polymerase use?

    <p>Ribonucleotide triphosphates</p> Signup and view all the answers

    Which component is believed to have a regulatory function in the holoenzyme?

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

    What is a polypeptide chain composed of?

    <p>Amino acids linked by peptide bonds</p> Signup and view all the answers

    Which of the following properties of the genetic code indicates that a single amino acid can be encoded by multiple codons?

    <p>Degenerate nature</p> Signup and view all the answers

    What is the significance of the genetic code being described as 'comma-free'?

    <p>Codons are represented without any additional nucleotides separating them.</p> Signup and view all the answers

    Which amino acid is coded by the triplet codon 'AUG'?

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

    How many triplet codons serve as termination signals in the genetic code?

    <p>3</p> Signup and view all the answers

    Which of the following statements is true regarding the genetic code's universality?

    <p>The same genetic code applies to all forms of life including viruses and bacteria.</p> Signup and view all the answers

    Which amino acid is uniquely encoded by only one triplet in the genetic code?

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

    What does the property of 'wobble' in the genetic code suggest?

    <p>The third position of a codon can vary without changing the amino acid.</p> Signup and view all the answers

    Which of the following triplet codons codes for the amino acid Serine?

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

    In the genetic code dictionary, which codon variety is exclusively associated with Glutamic acid?

    <p>GAA and GAG</p> Signup and view all the answers

    Which property of the genetic code indicates that it does not have variations among different organisms?

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

    Study Notes

    mRNA Processing

    • Newly synthesized RNA undergoes post-transcriptional modifications (processing)
    • Initial mRNA (pre-mRNA or hnRNA) larger than the final mRNA in eukaryotes, unlike bacteria
    • Eukaryotic mRNA processing includes:

    Addition of Poly-A tail

    • A tail of adenine nucleotides (poly-A tail) added to the 3' end
    • Length typically up to 200 adenines
    • Essential for protecting mRNA from cytoplasmic enzymes

    Addition of a 5' cap

    • 7-methylguanosine (7mG) cap added to the 5' end
    • Linked in a 5'-to-5'方式 to the first nucleotide
    • Importance:
      • Protects mRNA from 5' end degradation
      • Aids transport of mature mRNA from nucleus to cytoplasm

    Excision of Intervening Sequences

    • Noncoding sequences (introns) within the gene are removed
    • Remaining coding sequences (exons) are spliced together
    • Example given in the text: beta-globin gene in rabbits with 126bp & 580bp introns
    • The final mRNA contains the exons, translated in cytoplasm

    mRNA Structure

    • mRNA (monocistronic) encodes a single polypeptide chain
    • In eukaryotes, all mRNAs are monocistronic
    • mRNA size varies from 150 to 12000 nucleotides depending on encoded polypeptide
    • Has a leader sequence (not translated)
    • Length 18-175 nucleotides typically
    • Leader sequence has specific sequence complementary to ribosomal RNA (16S RNA)
    • Leader sequence is important for ribosome binding

    Additional Notes

    • RNA polymerase holoenzyme binds DNA template
    • RNA polymerase proceeds in 5'-to-3' direction, antiparallel to DNA template
    • RNA synthesis stops when the enzyme encounters a termination signal
    • The genetic code is based on triplet codons
    • 64 possible codons with 20 amino acids, leading to degeneracy
    • Code is unambiguous—one codon codes for only one amino acid
    • Code is degenerate—multiple codons code for the same amino acid
    • Universally used by all organisms

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    Related Documents

    RNA and Genetic Code PDF

    Description

    This quiz covers the essential aspects of mRNA processing in eukaryotes, including the addition of poly-A tails and 5' caps. It also explores the excision of introns and the significance of these modifications for mRNA stability and transport. Test your knowledge on how pre-mRNA transitions to mature mRNA!

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