Prokaryotes vs. Eukaryotes Overview
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Questions and Answers

What are the three parts of a bacterial flagellum?

  • Pili, fimbriae, capsule
  • Cell wall, cell membrane, cytoplasm
  • Nucleoid, ribosomes, cytoplasm
  • Filament, hook, basal body (correct)

    • How do bacteria achieve directional movement using flagella?

  • By using pili to attach to surfaces
  • By secreting enzymes that break down the surrounding environment
  • By changing the rotation of their flagella (correct)
  • By using a combination of flagella and axial filaments

    • What is the function of the bacterial glycocalyx?

  • It provides structural support for the cell
  • It is involved in the synthesis of proteins
  • It protects the cell from phagocytosis (correct)
  • It helps bacteria to move

    • What is the primary component of the bacterial cell wall?

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

    What is the main difference between gram-positive and gram-negative bacteria?

    <p>The thickness of their cell walls (A)</p> Signup and view all the answers

    Mycoplasmas lack a cell wall.

    <p>True (A)</p> Signup and view all the answers

    What are the small, bristle-like fibers that help bacteria attach to surfaces called?

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

    What type of bacterial arrangement is characterized by cells in a chain?

    <p>Streptococci (B)</p> Signup and view all the answers

    What is the function of endospores in bacteria?

    <p>To survive harsh environmental conditions (D)</p> Signup and view all the answers

    Flashcards

    Prokaryotes

    Cells without a nucleus and membrane-bound organelles.

    Eukaryotes

    Cells with a nucleus and membrane-bound organelles.

    Cell Wall in Bacteria

    Made of peptidoglycan, provides structural support.

    Gram-positive Bacteria

    Bacteria with a thick peptidoglycan layer, stain purple.

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    Gram-negative Bacteria

    Bacteria with a thin peptidoglycan layer and outer membrane, stain pink.

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    Flagella

    Long, whip-like structures for bacterial movement.

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    Pili

    Hair-like structures that enable attachment and DNA transfer.

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    Fimbriae

    Short threads that help bacteria stick to surfaces.

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    Glycocalyx

    A coating of polysaccharides that protects the cell.

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    Endospores

    Highly resistant dormant structures formed by some bacteria.

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    Chemotaxis

    Movement of bacteria toward or away from chemicals.

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    Bacterial Colonies

    Groups of bacteria that act together.

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    Plasmids

    Small, circular pieces of DNA that provide extra genetic info.

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    Ribosomes

    Sites of protein synthesis, made of rRNA and proteins.

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    Actin Cytoskeleton

    Structural components made of actin that help maintain cell shape.

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    Metabolism

    All chemical processes that occur within a cell.

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    Cytoplasm

    A gelatinous solution where cellular processes occur.

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    Capsules

    Thick glycocalyx layer that protects bacteria from the immune system.

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    Peptidoglycan

    Compound forming the bacterial cell wall, made of sugars and amino acids.

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    Osmotic Pressure

    The force exerted by water moving across a semi-permeable membrane.

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    Nucleoid

    Region in prokaryotic cells where DNA is concentrated.

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    Biofilms

    Communities of bacteria adhering to surfaces.

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    Capsule Stain

    A staining technique to visualize the presence of capsules.

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    Lipid A

    Component of lipopolysaccharide that acts as an endotoxin.

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    Biofilm Formation

    The process of bacteria sticking together in a protective layer.

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    Antibiotics Targeting Cell Wall

    Certain antibiotics inhibit peptidoglycan synthesis.

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    Osmoregulation

    The regulation of water and solute concentrations in the cell.

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    Nontypical Cell Walls

    Bacteria that do not fit the gram-positive or gram-negative classification.

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    Study Notes

    Prokaryotes vs. Eukaryotes

    • Prokaryotes lack a nucleus and their DNA is not wrapped around histones.
    • Prokaryotic cell walls can be peptidoglycan (bacteria) or made of other chemicals (archaea).
    • Prokaryotes lack complex, membrane-bound organelles.

    Bacterial Cell Structures

    • Common to all bacterial cells: cell membrane, cytoplasm, ribosomes, one (or a few) chromosomes.
    • Common to most bacterial cells: cell wall, glycocalyx (surface coating)
    • Common to some bacterial cells: flagella, pili, fimbriae, capsules, slime layers, inclusions, actin cytoskeleton, endospores.

    Bacterial Arrangements and Sizes

    • Bacterial cells carry out all necessary life activities (reproduction, metabolism, nutrient processing)
    • Bacteria can also act as a group, forming colonies and biofilms.
    • Cocci (spherical) exhibit diverse arrangements (single, pairs, tetrads, clusters).
    • Bacilli (rod-shaped) are less varied in arrangement (single, pairs, chains, palisades).
    • Spirilla (spiral-shaped) can be arranged singly or in short chains

    Bacterial Morphology (Shapes)

    • Coccus (round)
    • Bacillus (rod-shaped)
    • Spirillum (spiral-shaped)
    • Vibrio (curved rod)
    • Coccobacillus (short rod)

    External Structures (Appendages)

    • Appendages are cell extensions found in some but not all species.
    • They can provide motility (flagella, axial filaments) or attachment/mating (pili, fimbriae).
    • Flagella: filament, hook, basal body; vary in arrangement (polar, lophotrichous, peritrichous, amphitrichous).

    Flagellar Function

    • Chemotaxis (positive/negative) and phototaxis
    • Motility through runs and tumbles (counter-clockwise/clockwise rotation).
    • Axial filaments (periplasmic flagella) impart twisting/flexing motion to spirochetes.

    Capsules and Slime Layers

    • Glycocalyx is a sugar and/or protein coating.
    • Slime layer is loosely attached; protects against desiccation, helps in attachment
    • Capsules are firmly attached and more resistant; prevents recognition and destruction by hosts.

    Cell Wall

    • Rigid structure outside the cell membrane.
    • Provides structural support, maintains shape, and prevents bursting.
    • Gram-positive have a thick peptidoglycan layer.
    • Gram-negative have a thin peptidoglycan layer, an outer membrane.
    • The cell wall is the target of many antibiotics (penicillin, cephalosporins, lysozyme).

    Gram-Positive Cell Wall

    • Thick peptidoglycan layer with acidic polysaccharides.
    • Retains crystal violet dye (appears purple in Gram staining).
    • Contains teichoic and lipoteichoic acids (negatively charged).

    Gram-Negative Cell Wall

    • Thin peptidoglycan layer with an outer membrane.
    • Loses crystal violet dye easily (appears pink in Gram staining).
    • Lipopolysaccharide (LPS) in the outer membrane (endotoxin).
    • Periplasmic space between the outer membrane and the peptidoglycan layer.

    Bacterial Internal Structures

    • Cytoplasm: gelatinous, site for biochemical activities.
    • Chromosome: single circular DNA strand; aggregated in the nucleoid.
    • Plasmids: nonessential, double-stranded DNA circles; often confer drug resistance.
    • Ribosomes: RNA and protein complexes; 70S prokaryotic.
    • Inclusions: storage granules for nutrients and other substances (polyphosphate, sulfur, gas vesicles).
    • Actin cytoskeleton: long protein polymers; arranged in helical ribbons; contributes to cell shape.

    Endospores

    • Dormant cellular structures formed by some bacteria (Bacillus, Clostridium).
    • Extremely resistant to heat, drying, radiation, and chemicals.
    • Dehydrated state; very low metabolic activity, survival strategy.
    • Sporulation/ germination.
    • Medical Significance: several bacterial pathogens are endospore-forming.

    Mycoplasmas and other Cell Wall-Deficient Bacteria

    • Lack cell walls; cell membranes stabilized by sterols or hopanoids.
    • Resist lysis.
    • Very small; range in shape.
    • Can be grown on artificial media.

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    Description

    This quiz covers the fundamental differences between prokaryotes and eukaryotes, focusing on their cellular structures and arrangements. Explore key characteristics of bacterial cells, including their unique structures and functions in various group formations. Test your knowledge on the essential concepts of microbiology.

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