أسئلة الخامسة جينتكس (بعد التعديل)
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Questions and Answers

What is the primary function of transcription in genetics?

  • Synthesis of protein from RNA
  • Synthesis of RNA from a DNA template (correct)
  • Synthesis of DNA from RNA
  • Synthesis of amino acids from RNA

    • Which of the following accurately describes an intron?

  • A non-coding sequence that remains in mature RNA
  • A sequence that is spliced out during RNA processing (correct)
  • A sequence that directly codes for a protein
  • A protein-coding sequence

    • What type of RNA does RNA polymerase II primarily transcribe?

  • Ribosomal RNA (rRNA)
  • Small nuclear RNA (snRNA)
  • Transfer RNA (tRNA)
  • Messenger RNA (mRNA) (correct)

    • Which nitrogenous base is found in RNA but not in DNA?

    <p>Uracil (U)</p> Signup and view all the answers

    Which strand of DNA serves as the template during transcription?

    <p>Template strand</p> Signup and view all the answers

    What starts the transcription process for RNA polymerase II?

    <p>Promoter region of DNA</p> Signup and view all the answers

    What is the direction of RNA synthesis during transcription?

    <p>5' to 3'</p> Signup and view all the answers

    Which RNA polymerase is responsible for transcribing tRNA?

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

    What is the primary role of the CAAT box in relation to RNA polymerase II?

    <p>Regulates the frequency of transcription events</p> Signup and view all the answers

    Which of the following correctly describes the difference between DNA replication and transcription?

    <p>Transcription involves a single strand of the genome</p> Signup and view all the answers

    What role does RNA polymerase play in the elongation phase of transcription?

    <p>It incorporates nucleoside monophosphates into the growing RNA chain</p> Signup and view all the answers

    Which transcription inhibitor is known for binding to RNA polymerase II specifically?

    <p>α-amanitin</p> Signup and view all the answers

    Which component is released by RNA polymerase during the elongation phase of transcription?

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

    What is the primary function of the TATA box in transcription?

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

    Which base pairing is unique to transcription when compared to replication?

    <p>A-U pairing</p> Signup and view all the answers

    What triggers the termination of transcription?

    <p>RNA polymerase reaching a terminator signal</p> Signup and view all the answers

    Which of the following statements about RNA polymerase is correct?

    <p>RNA polymerase II requires a promotor to initiate transcription.</p> Signup and view all the answers

    Which event occurs during the synthesis of a primary RNA transcript?

    <p>RNA is synthesized complementary to the template DNA strand.</p> Signup and view all the answers

    How are the nitrogenous bases in RNA different from those in DNA?

    <p>RNA contains uracil in place of thymine.</p> Signup and view all the answers

    What role does the template strand of DNA play during transcription?

    <p>It serves as the basis for creating the complementary RNA sequence.</p> Signup and view all the answers

    Which of the following is required for the initiation of transcription by RNA polymerase II?

    <p>Promoter region</p> Signup and view all the answers

    Which type of RNA is primarily produced by RNA polymerase I?

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

    What is the composition of the primary RNA transcript immediately after transcription?

    <p>It includes both exons and introns.</p> Signup and view all the answers

    Which of the following statements accurately describes the differences between DNA replication and transcription?

    <p>Replication requires a primer, transcription does not.</p> Signup and view all the answers

    What is the correct pairing of ribonucleotide bases during transcription?

    <p>A-U and G-C.</p> Signup and view all the answers

    How is the elongation phase of transcription initiated?

    <p>As ribonucleotide triphosphates are added to the growing RNA chain.</p> Signup and view all the answers

    Which element significantly impacts the frequency of transcription events?

    <p>TATA box and GC box.</p> Signup and view all the answers

    Which of the following statements about the RNA polymerase II enzyme is false?

    <p>It binds to the DNA template during replication.</p> Signup and view all the answers

    What is primarily released by RNA polymerase during the transcription process?

    <p>Pyrophosphate.</p> Signup and view all the answers

    Study Notes

    Transcription

    • Transcription is the process of converting DNA into RNA
    • Transcription is the first step of gene expression
    • Translation is the process of converting RNA into protein
    • Translation is the second step of gene expression

    DNA Structure

    • DNA is a double helix
    • DNA is made up of nucleotides
    • Nucleotides are made up of a sugar, a phosphate, and a nitrogenous base
    • There are four nitrogenous bases in DNA: adenine (A), guanine (G), cytosine (C), and thymine (T)
    • A pairs with T
    • G pairs with C

    RNA Structure

    • RNA is single stranded
    • RNA is made up of nucleotides
    • Nucleotides are made up of a sugar, a phosphate, and a nitrogenous base
    • There are four nitrogenous bases in RNA: adenine (A), guanine (G), cytosine (C), and uracil (U)
    • A pairs with U
    • G pairs with C

    Transcription Materials

    • Template DNA
    • Four ribonucleotide triphosphates (ATP, GTP, UTP, and CTP)
    • RNA polymerase enzymes
    • Transcription factors

    RNA Polymerase

    • RNA polymerase is an enzyme that catalyzes the synthesis of RNA from a DNA template
    • There are three types of RNA polymerases:
      • RNA polymerase I transcribes rRNA
      • RNA polymerase II transcribes mRNA
      • RNA polymerase III transcribes tRNA

    Transcription Initiation

    • RNA polymerase II binds to the promoter on DNA
    • The promoter is a sequence of DNA that signals the start of a gene
    • The promoter contains several sequences:
      • TATA box (TATAAA box)
      • CAAT box (CCAATC)
      • GC box (GGGCGG):
    • TATA box
      • Located 25 to 35 base pairs upstream of the start point
      • Binds several proteins "TFIID"
      • The first step in transcription
    • CAAT box
      • Located 70 to 80 base pairs upstream of the start point
    • GC box
      • Determines the frequency of transcription events

    Transcription Elongation

    • RNA polymerase adds ribonucleotides to the growing RNA chain
    • Ribonucleotides are added in a 5' to 3' direction
    • The order of ribonucleotides is determined by base pairing with the template DNA strand

    Transcription Termination

    • Transcription ends when RNA polymerase reaches a terminator sequence
    • The terminator sequence is a signal that tells RNA polymerase to stop transcription

    Inhibitors of Transcription

    • Actinomycin D inhibits:
      • The initiation of replication by binding to the DNA template interfering with the action of DNA polymerases
      • The initiation of transcription by binding to the DNA template interfering with the action of transcription enzymes and proteins
    • α- amanitin inhibits eukaryotic RNA Polymerase II

    Comparing DNA Replication and Transcription

    Feature DNA Replication Transcription
    Template Both strands Single strand
    Template Size Whole genome Small portion of genome
    Primer Yes No
    Enzyme DNA polymerase RNA polymerase
    Product dsDNA ssRNA
    Base Pairs Adenine - Thymine, Guanine - Cytosine Adenine - Uracil, Guanine - Cytosine, Thymine - Adenine

    Transcription

    • Transcription is the process of synthesizing RNA from a DNA template.
    • RNA polymerase catalyzes the synthesis of RNA from a DNA template.
    • The primary RNA transcript is synthesized from 5' to 3' and is complementary to the 3'-5' strand of DNA.
    • The RNA polymerase II promoter has common sequences such as the CAAT box and the TATA box.
    • The TATA box is located 25-35 base pairs upstream of the start point.
    • The GC box is located 70-80 base pairs upstream of the start point.
    • Alpha-amanitin is a eukaryotic RNA polymerase II inhibitor.
    • The template for replication is both strands of DNA, while the template for transcription is only a single strand.
    • The primer for replication is DNA, while there is no primer required for transcription.
    • The process of replication uses DNA polymerase, while transcription uses RNA polymerase.
    • The product of replication is double-stranded DNA, while the product of transcription is single-stranded RNA.
    • The base pairing for DNA is A-T, G-C, while the base pairing for RNA is A-U, G-C.

    RNA Structure (Ribonucleic Acid)

    • RNA is generally single-stranded.
    • It contains the base uracil (U) in place of thymine (T).
    • RNA contains the pentose sugar ribose.

    RNA Polymerases

    • RNA polymerase I transcribes rRNA.
    • RNA polymerase II transcribes mRNA.
    • RNA polymerase III transcribes tRNA.

    Transcription Steps

    • Initiation: RNA polymerase II binds to the promoter on DNA.
    • Elongation: Ribonucleotide triphosphates are added to the growing RNA chain according to complementary base pairing with the template DNA strand.
    • Termination: RNA polymerase reaches a terminator sequence and transcription stops.

    Inhibitors of Eukaryotic Transcription

    • Actinomycin D inhibits the initiation of replication and transcription by interfering with the action of DNA polymerases and transcription enzymes and proteins.

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