Microorganism Week 1 Reading
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Questions and Answers

What is the main difference between scanning electron microscopy (SEM) and transmission electron microscopy (TEM)?

  • In TEM, the electron beam travels through the object, while in SEM, it is scattered from the surface. (correct)
  • In SEM, detection is the main focus, while in TEM, resolution is the primary goal.
  • In SEM, the electron beam is absorbed by an electron-dense metal stain, while in TEM, it generates a 3D appearance.
  • In SEM, the object's 3D depth is generated, while in TEM, the smallest distance between two objects is determined.

    • What does 'resolution' refer to in microscopy?

  • The smallest distance by which two objects can be separated and still be distinguished as separate. (correct)
  • The generation of a 3D appearance of an object.
  • The ability to determine the presence of an object.
  • The increase in the apparent size of an image.

    • Can all Eukaryotic microbes be resolved under a light microscope?

  • Yes, but only if stained with an electron-dense metal stain.
  • Yes, because they are generally large enough to be resolved.
  • No, because they are generally too small to be resolved.
  • No, but some can be resolved while others cannot. (correct)

    • What do Bacteria and Archaea have in common regarding their visibility under a light microscope?

    <p>They are generally too small for subcellular resolution by a light microscope.</p> Signup and view all the answers

    What does chemical imaging microscopy reveal about cells?

    <p>The chemical composition of a cell.</p> Signup and view all the answers

    What is a difference between Bacterial and Eukaryotic cells?

    <p>Bacterial cells have a compact genome, while Eukaryotic cells have extensive membranous organelles</p> Signup and view all the answers

    What is the function of the chemoreceptor 'nose' in a Bacterial cell?

    <p>To find food</p> Signup and view all the answers

    What trait is shared by Archaea and Bacteria?

    <p>Compact genome</p> Signup and view all the answers

    What enables Archaea to survive in extreme environments?

    <p>Unique membrane and envelope structures</p> Signup and view all the answers

    Why do Prokaryotic genomes tend to be compact?

    <p>To maximize the production of cells from limited resources</p> Signup and view all the answers

    What powers the rotation of the bacterial flagellum?

    <p>Proton current across the inner membrane</p> Signup and view all the answers

    Where are the chemoreceptors usually situated in motile bacteria?

    <p>At the forward-facing pole opposite the flagella</p> Signup and view all the answers

    How is the bacterial nucleoid different from the nucleus of Eukaryotic cells?

    <p>It is not enclosed by a membrane</p> Signup and view all the answers

    What is the function of agarose-gel electrophoresis in isolating DNA and RNA molecules in bacteria?

    <p>To separate the negatively charged molecules in an electrical field</p> Signup and view all the answers

    How are cell parts isolated for structural and biochemical analysis in cell fractionation?

    <p>Using cell lysis and ultracentrifugation</p> Signup and view all the answers

    What is the main function of membrane proteins in the cell membrane?

    <p>To mediate transport of molecules across the membrane</p> Signup and view all the answers

    Which type of molecules can easily permeate the cell membrane by passive diffusion?

    <p>Small uncharged molecules like oxygen and carbon dioxide</p> Signup and view all the answers

    What is the role of ion gradients across the cell membrane?

    <p>To store energy for cell functions</p> Signup and view all the answers

    Why do individual membrane lipids differ in structure?

    <p>To provide stability at high temperatures and extreme acidity</p> Signup and view all the answers

    What is a unique feature of Archaeal membrane lipids compared to Bacterial and Eukaryotic membranes?

    <p>All Archaeal phospholipids replace the ester link with an ether link</p> Signup and view all the answers

    What is one of the most common agents of resistance to antibiotics in Bacteria?

    <p>Beta-lactamase</p> Signup and view all the answers

    What is the function of the cell wall cross-bridge enzyme called sortase in Gram-positive Bacteria?

    <p>Forms a peptide bond from a cell wall cross-bridge to a protein extending from the cell</p> Signup and view all the answers

    What is the main function of the S-layer in Bacteria and Archaea?

    <p>Prevents phagocytosis and protects cells in extreme environments</p> Signup and view all the answers

    What are the components of the capsule, another common extracellular structure in Bacteria?

    <p>Loosely bound polysaccharides</p> Signup and view all the answers

    In Gram-negative Bacteria, which class of transporters found in the outer membrane permits the entry of nutrients and various molecules, including antibiotics?

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

    What is the most common structural support in the cell envelope of Bacteria and Archaea?

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

    Which type of amino acid form is incorporated by ribosomes into protein in Bacteria and Archaea?

    <p>L-form</p> Signup and view all the answers

    What is unique to Bacteria in terms of cell wall structure?

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

    What makes the enzymes of peptidoglycan biosynthesis excellent targets for new antibiotics?

    <p>They bind the antibiotic penicillin</p> Signup and view all the answers

    What is the role of ion gradients across the cell membrane in Bacteria and Archaea?

    <p>Generating energy for cellular processes</p> Signup and view all the answers

    What is the major function of proton transport?

    <p>To form the proton motive force that powers ATP synthesis</p> Signup and view all the answers

    What do ABC transporters use to move solutes against their concentration gradients?

    <p>Energy from ATP hydrolysis</p> Signup and view all the answers

    What is the primary role of symport and antiport transporter proteins?

    <p>To drive the transport of a second molecule up, or against, its concentration gradient</p> Signup and view all the answers

    What is the function of coupled transport systems such as antiport and symport?

    <p>To drive the transport of molecules against their concentration gradient</p> Signup and view all the answers

    How do transport proteins utilize the energy released when an ion moves down its concentration gradient?

    <p>By harnessing it to drive the transport of a second molecule against its concentration gradient</p> Signup and view all the answers

    How do bacteria divide at the end of DNA synthesis?

    <p>By forming a Z-ring using a protein complex called the divisome</p> Signup and view all the answers

    What manages the overall process of septation in bacteria?

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

    What is the role of FtsN in bacteria?

    <p>To regulate the timing of constriction of the septum</p> Signup and view all the answers

    What determines the shape and arrangement of cocci in bacterial cells?

    <p>Septation in random orientations</p> Signup and view all the answers

    In most bacterial species, how is the DNA organized?

    <p>Attached to the cell membrane at the origin of replication</p> Signup and view all the answers

    What may occur if bacterial cells always septate in parallel planes?

    <p>Formation of chains of cells</p> Signup and view all the answers

    What triggers Z-ring formation in bacterial cell division?

    <p>Completion of DNA replication</p> Signup and view all the answers

    What determines cell size in a given bacterial species?

    <p>Genetic regulators and environmental constraints</p> Signup and view all the answers

    What distinguishes the genome of Bacteria and Archaea from the Eukaryotic cell's genome?

    <p>Bacteria and Archaea have a single circular chromosome, while Eukaryotic cells have multiple linear chromosomes</p> Signup and view all the answers

    How is DNA organized in Bacteria?

    <p>In loops called domains extending throughout the cytoplasm</p> Signup and view all the answers

    What initiates DNA replication in Bacteria?

    <p>Binding proteins that melt open the DNA double helix at the origin of replication</p> Signup and view all the answers

    What is the role of DNA-binding proteins in Bacteria?

    <p>They compact the DNA within the domains</p> Signup and view all the answers

    How does bidirectional replication occur in Bacterial cells?

    <p>Two replisomes form, each replicating in one direction around the genome</p> Signup and view all the answers

    Where are two replisomes located in a rapidly growing Bacterial cell?

    <p>Near the middle of the growing cell</p> Signup and view all the answers

    What happens as the termination site replicates in a Bacterial cell?

    <p>The two replisomes separate from the DNA</p> Signup and view all the answers

    What is the function of a replisome in DNA replication?

    <p>It synthesizes new DNA strands in both directions at a replication fork</p> Signup and view all the answers

    What is the role of transcription and translation in gene expression?

    <p>Transcription converts DNA to RNA, and translation synthesizes proteins from mRNA</p> Signup and view all the answers

    What is unique about coordination of replication, transcription, and translation in rapidly growing Bacteria?

    <p>Translation is tightly coupled to transcription, allowing rapid cell division</p> Signup and view all the answers

    What drives bidirectional replication in Bacterial cells?

    <p>Two replisomes working together to replicate both strands at once</p> Signup and view all the answers

    What causes supercoiling of DNA in Bacterial cells?

    <p>Inherent twists in the structure of the DNA double helix</p> Signup and view all the answers

    What is the main function of thylakoids in cyanobacteria?

    <p>Maximizing the collecting area of photosynthetic membranes</p> Signup and view all the answers

    In the absence of light, how do cyanobacteria obtain energy?

    <p>By digesting thylakoids</p> Signup and view all the answers

    What is the purpose of gas vesicles in some Bacteria and Archaea?

    <p>Increasing buoyancy and keeping the cell afloat</p> Signup and view all the answers

    What is the role of the pilus in Bacteria?

    <p>It provides a form of motility called 'twitching.'</p> Signup and view all the answers

    How do rotary flagella benefit Bacterial cells?

    <p>They enable the cell to move and relocate rapidly.</p> Signup and view all the answers

    What triggers a change in the direction of rotation of the flagella in Bacterial cells?

    <p>Chemotaxis toward attractants or away from repellents</p> Signup and view all the answers

    What is the primary function of flagella in bacterial cells?

    <p>Rotary motion to enable motility</p> Signup and view all the answers

    What structure do Cyanobacteria possess for carbon dioxide fixation?

    <p>Thylakoid membrane organelles</p> Signup and view all the answers

    What is the main role of adherence structures in Prokaryotes?

    <p>Remain in an environment with favorable environmental factors</p> Signup and view all the answers

    What is the mechanism by which cells migrate up a gradient of an attractant substance?

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

    What type of growth curve is generated by binary fission of cells?

    <p>Exponential curve</p> Signup and view all the answers

    At which stage of growth do cells grow and divide at the maximum rate possible in the medium and growth conditions provided?

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

    What is the rate at which cells die in the death phase proportional to?

    <p>Number of cells that existed at the beginning of the time period</p> Signup and view all the answers

    In continuous culture, what type of growth pattern is achieved?

    <p>Exponential growth</p> Signup and view all the answers

    What is the process by which a typical bacterium grows and divides?

    <p>Binary fission</p> Signup and view all the answers

    What is the ultimate factor that determines the survival of any species?

    <p>Ability to generate offspring</p> Signup and view all the answers

    How does a eukaryotic microbe divide?

    <p>By mitosis</p> Signup and view all the answers

    What is the process called when a parental cell splits into two equal daughter cells in bacteria?

    <p>Binary fission</p> Signup and view all the answers

    What distinguishes bacterial and archaeal chromosomes from eukaryotic chromosomes?

    <p>Bacterial and archaeal chromosomes are circular, while eukaryotic chromosomes are linear</p> Signup and view all the answers

    Which type of DNA is found in larger amounts in eukaryotes compared to bacterial and archaeal genomes?

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

    What distinguishes the size range of bacterial and archaeal chromosomes from that of eukaryotic chromosomes?

    <p>Bacterial and archaeal chromosomes range from approximately 106 to 16,000 kilobase pairs, while eukaryotic chromosomes range from 2,900 kb to over 100,000,000 kb</p> Signup and view all the answers

    In what process can some plasmids be transferred only if a self-transferable plasmid resides in the same cell?

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

    How do plasmids replicate?

    <p>By rolling circle replication or bidirectional replication</p> Signup and view all the answers

    What is the significance of plasmid-encoded gene in the context of antibiotic resistance?

    <p>It provides the genetic basis for antibiotic resistance</p> Signup and view all the answers

    Which process is required for cell-to-cell contact to move a plasmid from a donor cell to a recipient?

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

    Study Notes

    Resolution and Microscopy

    • Resolution is the smallest distance between two objects that allows us to see them as separate objects.
    • In the human eye, the finest resolution of two separate points is perceived by the fovea, the portion of the retina with the highest density of photoreceptors.
    • The distance between two foveal "pixels" (groups of cones with neurons) limits our resolution to 100-200 micrometeres (um).

    Microorganisms

    • Many Prokaryotes (Bacteria and Archaea) are smaller than 10um.
    • Bacteria and Archaea form similarly shaped rods/bacilli and cocci, which evolved independently within different taxa.

    Light Microscopy

    • Resolves images of individual bacteria by their absorption of light.
    • The specimen is commonly viewed as a dark object against a light-filled field or background, called bright-field microscopy.

    Electron Microscopy

    • Uses beams of electrons to resolve details several orders of magnitude smaller than those seen under light microscopy.

    Cellular Structure

    • Cytoplasm consists of a gel-like network composed of proteins and other macromolecules.
    • The cytoplasm is contained by a cell membrane or plasma membrane.

    Cell Membrane

    • Composed of phospholipids, transporter proteins, and other molecules.
    • Prevents cytoplasmic proteins from leaking out and maintains gradients of ions and nutrients.

    Cell Wall

    • A fortress-like structure composed of sugar chains linked covalently by peptides (peptidoglycan).
    • Forms a single molecule that surrounds the cell.
    • In gram-negative bacteria, the cell wall lies within the periplasm, a water-filled space containing nutrient-binding proteins and secretion machines.

    Outer Membrane

    • Composed of phospholipids and lipopolysaccharide (LPS), a class of lipids attached to long polysaccharides (sugar chains).
    • Lies outside the cell wall in gram-negative bacteria.

    Cell Envelope

    • Consists of the inner membrane, cell wall, and outer membrane in gram-negative bacteria.

    Membrane Lipids

    • Most membrane lipids are phospholipids.
    • A phospholipid possesses a charged phosphoryl "head" that contacts the water interface and a hydrophobic "tail" of fatty acids packed within the bilayer.

    Membrane Proteins

    • Serve functions such as transport, environmental communication, and structural support.
    • Examples include transport proteins, ion channels, and structural support proteins.

    Selective Permeability

    • Achieved in three ways: substrate-specific carrier proteins, nutrient-binding proteins, and membrane-spanning protein channels, or pores.
    • Allows cells to gain sustenance from the environment while maintaining internal homeostasis.

    Nutrient Transport

    • Facilitated diffusion transports nutrients across a membrane only from a higher concentration compartment to a lower concentration compartment.
    • Active transport moves molecules against a concentration gradient, requiring energy input.

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    Test your knowledge about the resolution of human vision, particularly related to the fovea and cone cells responsible for perceiving fine details and color. Understand the concept of the smallest distance between two objects that allows them to be seen as separate.

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