Molecular Biology: Gene Expression
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Questions and Answers

What is the name of the process by which the information in DNA is used to synthesize a chain of amino acids?

  • Transcription
  • Central dogma of molecular biology
  • Translation (correct)
  • Gene expression

    • What is the name of the RNA molecule that carries genetic information from DNA to the site of protein synthesis?

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

    • What is the process by which an RNA copy of a gene is synthesized from a DNA template?

  • Transcription (correct)
  • Gene expression
  • Central dogma of molecular biology
  • Translation

    • What is the term used to describe the process of converting the information in RNA into a sequence of amino acids?

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

    What is the name of the enzyme responsible for synthesizing RNA from a DNA template?

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

    What is the name of the strand of DNA that is used as a template for RNA synthesis?

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

    What is the term used to describe the process of converting the genotype into the phenotype?

    <p>Gene expression</p> Signup and view all the answers

    What is the name of the process by which the sequence of nucleotides in RNA is used to build a chain of amino acids?

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

    What is the primary function of the σ subunit in the holoenzyme?

    <p>To recognize specific signals in DNA and locate the beginning of genes</p> Signup and view all the answers

    What is the name of the site where transcription starts?

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

    What is the function of the β and β' subunits in the core polymerase?

    <p>To form the active site of the enzyme that binds to the DNA template</p> Signup and view all the answers

    What is the term for a chain of nucleotides in a strand of DNA that begins at a start code and continues to the end code?

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

    What is the function of the core polymerase?

    <p>To synthesize RNA using a DNA template, but cannot initiate synthesis accurately</p> Signup and view all the answers

    What is the term for the site that forms a recognition and binding site for the RNA polymerase?

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

    What is the numbering system used to denote the bases upstream and downstream of the start site?

    <p>The first base transcribed is called +1, and this numbering continues downstream until the last base is transcribed</p> Signup and view all the answers

    What is the term for the site that signals the end of transcription?

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

    What is the name of the region containing the RNA polymerase, DNA template, and the growing RNA transcript?

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

    What is the approximate rate of transcription in bacterial DNA?

    <p>50 nt/sec</p> Signup and view all the answers

    What happens to the DNA after the transcription bubble passes?

    <p>It rewinds</p> Signup and view all the answers

    What signals the RNA polymerase to stop at the end of a transcription unit?

    <p>A terminator sequence</p> Signup and view all the answers

    What forms in the GC region of the RNA transcript, causing the RNA polymerase to pause?

    <p>A hairpin structure</p> Signup and view all the answers

    What is the weakest of the four hybrid basepairs in the transcription bubble?

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

    What happens to the RNA strand when the polymerase pauses over the run of uracils?

    <p>It dissociates from the DNA</p> Signup and view all the answers

    What type of factors also act at terminators to aid in terminating transcription?

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

    What is a key feature that distinguishes prokaryotic transcription from eukaryotic transcription?

    <p>The coupling of transcription and translation</p> Signup and view all the answers

    What is the primary function of RNA polymerase I in eukaryotes?

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

    What is the term for a group of functionally related genes in prokaryotes?

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

    Why is it not possible for prokaryotic-style coupling of transcription and translation to occur in eukaryotes?

    <p>Because transcription occurs in the nucleus and translation occurs in the cytoplasm</p> Signup and view all the answers

    What is the primary difference between prokaryotic and eukaryotic RNA polymerases?

    <p>The structure and function of RNA polymerases</p> Signup and view all the answers

    What is the role of promoters in eukaryotic transcription?

    <p>To provide a binding site for RNA polymerase</p> Signup and view all the answers

    What is a characteristic of prokaryotic mRNA?

    <p>It is always polycistronic</p> Signup and view all the answers

    What is the function of RNA polymerase III in eukaryotes?

    <p>Transcribing tRNA and some small RNAs</p> Signup and view all the answers

    What is the primary function of transcription factors in eukaryotic transcription initiation?

    <p>To recruit RNA polymerase II to the promoter</p> Signup and view all the answers

    What is the function of the 5' cap in eukaryotic transcripts?

    <p>To increase RNA stability and facilitate translation</p> Signup and view all the answers

    What is the role of the carboxy terminal domain (CTD) of RNA polymerase II?

    <p>To recruit other factors to form the transcription elongation complex</p> Signup and view all the answers

    What is the function of poly-A polymerase in eukaryotic transcription?

    <p>To add a 3' poly-A tail to the transcript</p> Signup and view all the answers

    What is the purpose of the poly-A tail in eukaryotic transcripts?

    <p>To increase RNA stability and facilitate translation</p> Signup and view all the answers

    What is the mechanism of transcription termination in eukaryotes?

    <p>The polymerase pauses around the poly site and the remaining transcript is progressively removed by an exonuclease</p> Signup and view all the answers

    What is the purpose of the exonuclease in eukaryotic transcription?

    <p>To remove the remaining transcript after polyadenylation</p> Signup and view all the answers

    What is the significance of the AAUAAA sequence in eukaryotic transcription?

    <p>It is the site of transcript cleavage prior to polyadenylation</p> Signup and view all the answers

    Study Notes

    Gene Expression

    • Gene expression is the conversion of genotype into phenotype, requiring the information stored in DNA to be converted to protein.
    • The central dogma of molecular biology describes the flow of information in cells from DNA to RNA to protein.

    Transcription

    • Transcription is the process of producing an RNA copy of the information in DNA, directed by the enzyme RNA polymerase.
    • Only one of the two DNA strands needs to be copied, with the copied strand called the template strand and the other strand called the coding strand.
    • The RNA transcript's sequence is complementary to the template strand.
    • The RNA transcript used to direct the synthesis of polypeptides is termed messenger RNA (mRNA).

    Prokaryotic Transcription

    • Prokaryotes have a single RNA polymerase.
    • The RNA polymerase of prokaryotes exists in two forms: the core polymerase and the holoenzyme.
    • The core polymerase can synthesize RNA using a DNA template, but it cannot initiate synthesis accurately.
    • The holoenzyme can accurately initiate synthesis and is formed by the addition of a σ (sigma) subunit to the core polymerase.
    • Initiation occurs at promoters, requiring two sites in DNA: a promoter that forms a recognition and binding site for the RNA polymerase, and a start site where transcription starts.
    • The σ subunit of the holoenzyme recognizes promoter elements at –35 and –10 and binds to the DNA.
    • The transcription bubble is created by RNA polymerase, which moves down the bacterial DNA at a constant rate, with the growing RNA strand protruding from the bubble.
    • Termination occurs at specific sites, marked by terminator sequences that signal "stop" to the polymerase.

    Prokaryotic Transcription Termination

    • The simplest terminators consist of a series of G–C base-pairs followed by a series of A–T base-pairs.
    • The RNA transcript of this stop region can form a double-stranded structure in the GC region called a hairpin, which is followed by four or more uracil (U) ribonucleotides.
    • Formation of the hairpin causes the RNA polymerase to pause, placing it directly over the run of four uracils.
    • The pairing of U with the DNA's A is the weakest of the four hybrid basepairs, and it is not strong enough to hold the hybrid strands when the polymerase pauses.

    Prokaryotic Gene Expression

    • In prokaryotes, the mRNA produced by transcription begins to be translated before transcription is finished, making them coupled.
    • The mRNA produced in prokaryotes may contain multiple genes, often clustered together and referred to as an operon.

    Eukaryotic Transcription

    • The basic mechanism of transcription by RNA polymerase is the same in eukaryotes as in prokaryotes, but with differences in details.
    • Eukaryotes have three RNA polymerases (I, II, and III), each distinguished by structure and function, and each responsible for transcribing different types of RNA.
    • Each polymerase recognizes a different promoter structure.
    • Initiation and termination differ from those in prokaryotes, with eukaryotic initiation being more complex and involving a host of transcription factors.
    • The 5′ cap is added to the transcript, important for translation, RNA stability, and further processing.
    • Polyadenylation is involved in terminating mRNA transcripts, with the eukaryotic transcript being cleaved downstream of a specific site and a series of adenine residues being added to form the 3′ poly-A tail.

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    Description

    This quiz covers the process of gene expression, where genetic information is converted from DNA to protein, and the central dogma of molecular biology. Learn about the flow of information from genes to RNA and proteins.

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