Cell Structure and Function Overview
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Questions and Answers

What effect do attractants have on the movement of bacteria during chemotaxis?

  • They cause the flagella to rotate counterclockwise, pushing the cell forward. (correct)
  • They cause the flagella to rotate clockwise, resulting in a tumble.
  • They prevent the cell from moving in any direction.
  • They cause the bacterium to stop moving completely.

    • How does a bacterium change direction when no attractants are present?

  • It stops moving altogether to reassess its environment.
  • It divides into two and explores different directions.
  • It rotates the flagella clockwise, causing a tumble. (correct)
  • It continues to run in the same direction until it encounters another attractant.

    • What is the role of chemoreceptors in chemotaxis?

  • They provide energy to the bacterium to facilitate movement.
  • They sense chemical gradients and help guide movement. (correct)
  • They assist in the replication of bacterial DNA.
  • They detect environmental light levels.

    • What structure in bacteria is primarily responsible for movement during chemotaxis?

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

    What happens to the behavior of a bacterium when the concentration of attractants increases?

    <p>The runs last longer, leading to net movement toward the attractants.</p> Signup and view all the answers

    What is a key characteristic that differentiates bacteria from eukaryotic cells?

    <p>Lack of a nucleus</p> Signup and view all the answers

    Which component comprises approximately 70% of the total weight of bacteria?

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

    Which type of bacteria is characterized by a thick cell wall outside the cell membrane?

    <p>Gram-Positive Bacteria</p> Signup and view all the answers

    What role does the bacterial cell membrane primarily serve?

    <p>Selectively permeable barrier</p> Signup and view all the answers

    Which of the following best describes the genetic material in bacterial cells?

    <p>Compact and minimal noncoding DNA</p> Signup and view all the answers

    What distinguishes Gram-Negative bacteria from other types?

    <p>Presence of an outer membrane with lipopolysaccharides</p> Signup and view all the answers

    Which specialized structure is involved in bacterial locomotion?

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

    What feature of Archaea allows them to survive in extreme environments?

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

    What is the composition of peptidoglycan in bacterial cell walls?

    <p>Polymers of disaccharides cross-linked with peptides.</p> Signup and view all the answers

    Which characteristic is specific to Gram-positive bacteria?

    <p>Presence of teichoic acids in thick cell wall.</p> Signup and view all the answers

    What is the role of porins in Gram-negative bacteria?

    <p>To allow nutrient passage through the outer membrane.</p> Signup and view all the answers

    Which protein is responsible for maintaining the diameter of bacterial cells?

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

    What regulates the constriction of the septum during bacterial cell division?

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

    What structure helps protect bacteria against phagocytosis?

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

    Which feature distinguishes Gram-negative bacteria from Gram-positive bacteria?

    <p>Thin peptidoglycan layer covered by an outer membrane.</p> Signup and view all the answers

    What is the main focus during the bacterial cell division process?

    <p>Synchronous growth and formation of all cell parts.</p> Signup and view all the answers

    What is the main structural difference between ether links and ester links in membrane lipids?

    <p>Ether links (C-O-C) are more stable than ester links, allowing growth at higher temperatures.</p> Signup and view all the answers

    Which fatty acid form is known for increasing membrane fluidity, particularly at low temperatures?

    <p>Cis form of Oleic Acid</p> Signup and view all the answers

    What is the function of cardiolipin in bacterial membranes?

    <p>Localizes to cell poles and increases under stress.</p> Signup and view all the answers

    What role do sterols, such as cholesterol, play in eukaryotic membranes?

    <p>Adding flexibility and stability to the membrane.</p> Signup and view all the answers

    What type of transport moves molecules against their concentration gradient using energy?

    <p>Active transport</p> Signup and view all the answers

    Which component primarily provides structural support to the cell envelope?

    <p>Cell wall</p> Signup and view all the answers

    Which type of molecules can permeate cell membranes easily?

    <p>Small uncharged molecules</p> Signup and view all the answers

    What unique feature do the membranes of Archaea possess compared to bacteria?

    <p>They have ether links instead of ester links.</p> Signup and view all the answers

    What is the primary role of the replisome in DNA replication?

    <p>Replicating DNA at each replication fork.</p> Signup and view all the answers

    How do prokaryotes achieve motility using their flagella?

    <p>By rotating the flagella using a motor powered by the proton motive force.</p> Signup and view all the answers

    Which of the following correctly describes the nucleoid region in prokaryotic cells?

    <p>DNA is coiled and bound to proteins, extending through the cytoplasm.</p> Signup and view all the answers

    What is the function of carboxysomes in prokaryotic cells?

    <p>Carbon dioxide fixation using Rubisco.</p> Signup and view all the answers

    What structural feature is distinct to monotrichous cells?

    <p>A single flagellum located at one end of the cell.</p> Signup and view all the answers

    Which of the following best describes thylakoids in photosynthetic bacteria?

    <p>Folded membranes packed with chlorophylls and electron carriers.</p> Signup and view all the answers

    What is a key outcome of the spatial orientation of septation in bacteria?

    <p>Determining the arrangement pattern of cocci.</p> Signup and view all the answers

    What are pili and fimbriae primarily used for in prokaryotic cells?

    <p>Attachment to surfaces and genetic exchange.</p> Signup and view all the answers

    Study Notes

    Cell Structure and Function Overview

    • Bacterial cells lack a nucleus.
    • Bacteria have a phospholipid bilayer membrane.
    • Archaea have unique membrane lipids supporting survival in extreme environments.
    • Eukaryotic cells possess a nucleus and extensive membranous organelles.

    Bacterial Cell Overview

    • Thick, complex outer envelope protects from environmental stress, mediating exchange with the environment.
    • Compact genome maximizes cell production from limited resources.
    • Tightly coordinated functions enable high reproduction rates.

    Biochemical Composition of Bacteria

    • Water (70% of total weight), essential ions, small organic molecules (lipids, sugars), and macromolecules (nucleic acids, proteins).
    • Variable composition depends on species, growth phase, and environmental conditions.

    Classification of Bacteria

    • Classified based on cell wall configuration:
      • Gram-positive bacteria have a thick cell wall outside the cell membrane.
      • Gram-negative bacteria have a thin cell wall with an outer membrane containing phospholipids and lipopolysaccharides.

    The Cell Membrane

    • Selectively permeable barrier separating internal components from the external environment.
    • Phospholipid bilayer with lipid-soluble proteins, consistent thickness (~8 nm).
    • Membrane lipids (glycerol with ester links to fatty acids).
    • Diversity varies with environmental conditions and phosphoryl head groups, and fatty acid side chains.
    • Cardiolipin increases under stress (e.g., starvation).
    • Fatty acids can be saturated, unsaturated, or polyunsaturated.
    • Cis form of oleic acid increases membrane fluidity.
    • Cyclopropane fatty acids decrease membrane fluidity especially during stress.
    • Eukaryotes have sterols (e.g., cholesterol).
    • Bacteria have hopanoids for structural support.
    • Archaea have ether links (C-O-C) instead of ester links between glycerol and fatty acids.
    • Archaea forms a monolayer membrane by fusing tails.
    • Membrane proteins support structural support (anchoring cell envelope layers) and detect environmental signals (e.g., temperature).

    Molecules Crossing the Cell Membrane

    • Mechanisms of molecule transport include semipermeable barriers, passive transport (high to low concentration using concentration gradient), and active transport (low to high concentration using energy).

    The Envelope and Cytoskeleton

    • Cell envelope includes structural support (typically the cell wall).
    • Additional layers (outer membrane or S-layer) may be present in some bacteria.
    • Mycoplasmas lack an outer layer.

    The Cell Wall

    • Confers shape and rigidity, withstanding turgor pressure.
    • Composed of peptidoglycan (murein) from repeating disaccharides (N-acetylglucosamine and N-acetylmuramic acid) cross-linked with peptides.
    • Peptidoglycan is a target for antibiotics like penicillin and vancomycin.
    • Gram-positive bacteria have a thick cell wall (3-20 layers) reinforced by teichoic acids; S-layer and Capsule layers are also present.
    • Gram-negative bacteria have a thin peptidoglycan layer (1-2 sheets), covered by an outer membrane.
    • Outer membrane components include lipopolysaccharide (LPS), lipid A, and O antigen.

    Bacterial Cytoskeleton

    • Proteins (FtsZ, MreB, CreS) shape and maintain cell structure (diameter, rod shape, crescent shape).

    Bacterial Cell Division

    • Highly coordinated growth, formation of cell parts, DNA replication, and cell wall expansion.
    • Septation forms the septum dividing the cell envelope.
    • FtsZ subunits assemble, treadmilling, and septal growth requires biosynthesis envelope components.
    • Divisome components include FtsZ for the Z-ring and FtsN regulating septum constriction.

    DNA Organization and Replication

    • Prokaryotic cells contain a nucleoid region in their cytoplasm.
    • DNA is attached to the envelope at the origin of replication with supercoiled loops bound to proteins.
    • Ribosomes bind mRNA and start translating proteins before transcription is complete.

    Specialized Structures

    • Thylakoids: Membrane-bound structures for photosynthetic reactions in bacteria.
    • Carboxysomes: Protein bodies for CO2 fixation.
    • Gas vesicles: Hollow structures for buoyancy.
    • Storage granules: glycogen, PHB, PHA and sulfur granules for energy storage.
    • Pili/Fimbriae: filaments for attachment, motility, and conjugation.
    • Stalks: Attachment organelles for holding fasts (enabling iron oxidation).
    • Rotary Flagella: Prokaryotic flagella for movement (peritrichous, lophotrichous, monotrichous).
    • Chemotaxis: Movement in response to chemical gradients (responding to attractants vs. repellents via CW vs CCW rotation).

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    Explore the essential features of bacterial and eukaryotic cells in this quiz. Understand the differences in cell composition, classification, and the unique adaptations that enable bacteria to thrive in various environments. Test your knowledge on cell structure and functions.

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