Prokaryotic Transcription and Translation - Dr. Michael Green
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Questions and Answers

What is the primary function of plasmids in prokaryotic cells?

  • Act as the sole genetic material in prokaryotes
  • Facilitate protein synthesis
  • Serve as carriers of extra genetic material (correct)
  • Coordinate gene expression

    • Which term refers to the organized units of gene expression in prokaryotes?

  • Centromeres
  • Ribosomes
  • Operons (correct)
  • Nucleosomes

    • What is the ultimate product of the process of translation in prokaryotic cells?

  • Operons
  • mRNA
  • Proteins (correct)
  • tRNA

    • During which stage of prokaryotic transcription does RNA polymerase bind to the promoter region?

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

    What is the significance of supercoiling in prokaryotic genomes?

    <p>Optimizes the packaging of genetic material</p> Signup and view all the answers

    How are the levels of gene expression regulated in prokaryotic cells?

    <p>Through operon control and other regulatory mechanisms</p> Signup and view all the answers

    What is the main translational unit responsible for synthesizing polypeptides?

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

    Which site on the ribosome accepts the incoming aminoacyl-tRNA during the translation process?

    <p>A SITE</p> Signup and view all the answers

    What is the function of the Shine-Delgarno (SD) sequence in prokaryotic mRNA?

    <p>Binds to the ribosome</p> Signup and view all the answers

    Which proteins assist in the process of elongation during translation?

    <p>EF-G and EF-Tu</p> Signup and view all the answers

    What is the role of tRNA in protein synthesis?

    <p>Transfers the amino acid to the growing peptide chain</p> Signup and view all the answers

    Which site on tRNA binds to the amino acid during protein synthesis?

    <p>Amino acid attachment site</p> Signup and view all the answers

    What is the primary function of the sigma factor in transcriptional initiation in prokaryotes?

    <p>To increase the binding affinity and specificity of RNA polymerase to the promoter</p> Signup and view all the answers

    What is the primary difference between constitutively expressed genes and non-constitutively expressed genes?

    <p>Constitutively expressed genes are always on, while non-constitutively expressed genes are switched on as needed</p> Signup and view all the answers

    What is the function of the 'core polymerase' in RNA synthesis?

    <p>To synthesize the RNA chain</p> Signup and view all the answers

    What is the purpose of the TTGACA sequence in prokaryotic promoters?

    <p>To serve as a consensus sequence for RNA polymerase binding</p> Signup and view all the answers

    What is the result of holoenzyme binding to the promoter region?

    <p>RNA polymerase is oriented correctly and transcription proceeds</p> Signup and view all the answers

    What is the role of the -10 region in prokaryotic promoters?

    <p>To serve as a consensus sequence for RNA polymerase binding</p> Signup and view all the answers

    What is the role of aminoacyl-tRNA synthetases?

    <p>Attach the correct amino acid to the correct tRNA</p> Signup and view all the answers

    What happens when the tRNA becomes charged?

    <p>It has an amino acid attached to it</p> Signup and view all the answers

    What is the energy requirement for the attachment of amino acids to tRNA?

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

    What is the function of release factors (RF1 and RF2) in translation termination?

    <p>Recognize the stop codon</p> Signup and view all the answers

    What is the outcome of the termination steps in translation?

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

    How do bacteria regulate gene expression in response to external stimuli?

    <p>By modulating the expression of genes</p> Signup and view all the answers

    What is the main function of Two-component Regulatory Systems (TCRS)?

    <p>Transducing signals from outside the cell to the nucleoid</p> Signup and view all the answers

    Which of the following is NOT a component of a Two-component Regulatory System (TCRS)?

    <p>Cytoplasmic transcription factor</p> Signup and view all the answers

    Why is it beneficial for E. coli to have lactose metabolizing genes induced only in the presence of lactose?

    <p>To ensure lactose metabolism occurs only when needed</p> Signup and view all the answers

    Which component of the lac operon is responsible for turning lactose into glucose and galactose?

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

    What is the function of LacY in the lac operon?

    <p>Moving lactose into the cell</p> Signup and view all the answers

    Why does it make sense for all lac metabolizing genes to be contained within one functional unit (operon)?

    <p>To ensure all lac genes respond to the same switch</p> Signup and view all the answers

    Study Notes

    Prokaryotic Genome Organisation

    • Prokaryotes lack a nucleus surrounded by a complex nuclear membrane.
    • They have a single large circular “chromosome” located in the ‘nucleoid’.
    • They have smaller circular extrachromosomal DNA called plasmids.
    • Prokaryotic genome is supercoiled.
    • Most prokaryotes are haploid.
    • They contain small amounts of non-coding DNA, with coding DNA organized into operons.

    Central Dogma of Molecular Biology

    • Protein synthesis occurs in two major steps: transcription and translation.
    • Protein synthesis requires three major types of RNAs: mRNA, tRNA, and rRNA.
    • The process is highly regulated, with not all genes expressed at the same time.
    • The ribosome is the main translational unit that synthesizes the polypeptide.

    Transcription

    • The goal of transcription is to synthesize a chain of RNAs (mRNA) via RNA synthesis.
    • Transcription occurs in three stages: initiation, elongation, and termination.
    • RNA polymerase is the main transcriptional unit.
    • Transcription begins when RNA polymerase binds to the promoter.
    • The association of sigma factor dramatically increases binding affinity and specificity.
    • Prokaryotic promoters have two characteristic features: TTGACA sequence and TATAAT sequence or Pribnow box.

    Initiation of Transcription

    • Holoenzyme first binds loosely to the -35 box in a closed complex.
    • It then binds tightly to the -10 and the DNA unwinds, forming the open complex.
    • RNA polymerase is then oriented correctly, sigma factor is released, and transcription proceeds at the next nucleotide.

    Translation

    • Translation occurs in three phases: initiation, elongation, and termination.
    • Translation requires mRNA, ribosomes, tRNA, and amino acids as well as other helper proteins.
    • The ribosome is a protein synthesizing machine composed of rRNA and ribosomal proteins.
    • The ribosome has 3 active sites: A SITE, P SITE, and E SITE.
    • EF-Tu and EF-G are other proteins that help the process along.

    Initiation of Translation

    • tRNA transfers the amino acid to the growing peptide chain.
    • Its key features are a 3 amino acid attachment site and an anticodon.
    • The correct amino acid must find the correct tRNA.
    • Initiation factor proteins deliver the small subunit to the mRNA.

    Elongation

    • The ribosome begins to read along the mRNA strand, building a protein one amino acid at a time.
    • EF-Tu and EF-G help this process along.

    Termination

    • Translation requires the recognition of the stop codon by release factors (RF1).
    • This forces the ribosome to release the finished polypeptide sequence from the P site.
    • Termination occurs in three steps: recognition of the stop codon, hydrolysis of the ester bond, and dissociation of RF1/RF2 with the help of RF3.

    Regulation of Gene Expression

    • Bacteria can regulate the expression of genes in response to external stimuli.
    • This is achieved through two-component regulator systems (TCRS) which transduce signals from outside the cell to the nucleoid.
    • TCRS’s consist of a membrane-bound sensor kinase and a DNA-binding response regulator.

    The lac Operon

    • The lac operon is a set of lactose metabolizing genes that are induced only in the presence of lactose.
    • The operon consists of three genes: lacA, lacZ, and lacY.
    • LacY is required for the movement of lactose into the cell via transmembrane protein transport.
    • LacZ turns lactose into glucose and galactose which can now be used by the cell.

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    Description

    Learn about prokaryotic genome organisation, the central dogma, protein synthesis, transcription (initiation, elongation, termination), translation (initiation, elongation, termination), regulation of gene expression, and the lac operon. Recap on prokaryotic genome organisation and its characteristics.

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