Cell Theory and Prokaryotic Cell Structure (2B) - Bio & Biochem

1. Identify the correct classification: a cell has a nucleoid, plasmids, and $70S$ ribosomes.

   Prokaryotic cell. These features indicate a prokaryote, lacking eukaryotic nuclear membranes and larger ribosomes.

2. Which cell structures are present in both prokaryotes and eukaryotes?

   Plasma membrane, cytosol, DNA, and ribosomes. These universal components enable basic cellular functions like enclosure, metabolism, heredity, and protein synthesis across all cell types.

3. What is the nucleoid in a prokaryotic cell?

   Non-membrane-bound region containing the bacterial chromosome. The nucleoid organizes the prokaryotic genome without a nuclear envelope, allowing direct cytoplasmic access.

4. What modification to cell theory accounts for heredity in modern cell theory?

   Cells contain hereditary information (DNA) passed to daughter cells. This addition incorporates the role of DNA in inheritance, reflecting advances in genetics since the original cell theory.

5. What are fimbriae, and what is their primary role in bacteria?

   Short surface appendages used mainly for attachment. Fimbriae promote adherence to host tissues or surfaces, crucial for colonization and biofilm formation.

6. What is the bacterial cell wall primarily made of in most bacteria?

   Peptidoglycan (murein). Peptidoglycan provides rigidity and shape, unique to bacterial cell walls and absent in eukaryotes.

7. What is a sex pilus, and what process does it enable?

   Conjugation pilus; transfers DNA between bacteria. The sex pilus forms a bridge for horizontal gene transfer during conjugation, enabling genetic diversity.

8. Which step of cell theory is violated by the claim that cells arise from nonliving matter?

   The tenet that cells arise only from preexisting cells. This claim supports spontaneous generation, contradicting the biogenesis principle of cell theory.

9. What modification to cell theory accounts for shared chemistry in modern cell theory?

   All cells have fundamentally similar chemical composition. This reflects the universal biochemical similarities among cells, supporting evolutionary relatedness.

10. What are the subunits of a prokaryotic $70S$ ribosome?

    $50S$ large subunit and $30S$ small subunit. The $70S$ ribosome assembles from these subunits to facilitate protein synthesis in prokaryotes.

11. What is binary fission in prokaryotes?

    Asexual division producing two genetically identical daughter cells. Binary fission ensures rapid reproduction without genetic variation, typical of prokaryotic growth.

12. What is the primary function of bacterial flagella?

    Motility via rotation driven by a proton motive force. Flagella enable chemotaxis and movement, powered by ion gradients across the membrane.

13. Which statement best describes spontaneous generation relative to cell theory?

    It is rejected; new cells arise only from preexisting cells. Cell theory's third tenet directly opposes spontaneous generation by asserting biogenesis.

14. What is the size of prokaryotic ribosomes, and what is the eukaryotic cytosolic size?

    Prokaryotic $70S$; eukaryotic cytosolic $80S$. Ribosome sizes differ due to subunit compositions, with prokaryotic ones being smaller and targeted by certain antibiotics.

15. Identify the Gram stain result: a bacterium has an outer membrane and LPS; what color stains?

    Pink (Gram-negative). Gram-negative bacteria have these structures, leading to decolorization and pink staining with safranin.

16. What modification to cell theory accounts for metabolism in modern cell theory?

    Energy flow (metabolism) occurs within cells. This emphasizes that cells are sites of biochemical activity, aligning with modern understanding of cellular energetics.

17. What is the periplasmic space in Gram-negative bacteria?

    Space between inner and outer membranes containing thin peptidoglycan. The periplasm houses enzymes and the cell wall, providing a compartment for processes like nutrient breakdown.

18. Which bacterial group has a thin peptidoglycan layer plus an outer membrane and stains pink?

    Gram-negative bacteria. The outer membrane prevents crystal violet retention, allowing counterstain with safranin for pink appearance.

19. Which bacterial group has a thick peptidoglycan layer and stains purple on Gram stain?

    Gram-positive bacteria. The thick layer retains crystal violet dye during Gram staining, indicating structural differences from Gram-negative bacteria.

20. What is a plasmid in bacteria?

    Small circular extrachromosomal DNA that replicates independently. Plasmids provide bacteria with accessory genes, often for advantages like antibiotic resistance, separate from the main chromosome.

21. What are the three classical tenets of cell theory?

    All organisms are cellular; cells are basic unit; cells arise from cells. These tenets, established by Schleiden, Schwann, and Virchow, form the foundation of understanding cellular organization and reproduction in biology.

22. What is the defining structural feature of a prokaryotic cell compared with a eukaryotic cell?

    No membrane-bound nucleus or membrane-bound organelles. Prokaryotes lack compartmentalization provided by membranes, distinguishing them from eukaryotes with true nuclei and organelles.

23. Which structure is directly targeted by lysozyme: peptidoglycan, LPS, or cholesterol?

    Peptidoglycan. Lysozyme hydrolyzes $\beta$-1,4 linkages in peptidoglycan, weakening bacterial cell walls.

24. What is the capsule (glycocalyx) in some bacteria, and what is its main function?

    External polysaccharide layer; protects and aids adhesion/biofilms. The capsule enhances virulence by evading host immunity and facilitating surface attachment.

25. What molecule in Gram-negative bacteria is a major endotoxin and strong immune activator?

    Lipopolysaccharide (LPS), especially lipid A. LPS in the outer membrane triggers intense immune responses, contributing to pathogenicity in Gram-negative infections.

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