Cell Structure and Function

Characteristics of Living Organisms

• Cellular Organization: All living organisms are composed of one or more cells, which are the basic units of life.

• Metabolism: Living organisms carry out chemical reactions to obtain and use energy.

• Growth and Development: Organisms increase in size and complexity over time.

• Reproduction: Living things can produce new individuals, either sexually or asexually.

Prokaryotes vs. Eukaryotes

• Prokaryotes: Cells lack a true nucleus and membrane-bound organelles (e.g., Bacteria, Archaea).

• Eukaryotes: Cells possess a true nucleus and various membrane-bound organelles (e.g., Fungi, Protists, Plants, Animals).

• Key Differences: Size, complexity, presence of organelles, and modes of reproduction.

Glycocalyx: Composition and Function

• Composition: Polysaccharide and/or polypeptide layer outside the cell wall.

• Function: Protection from desiccation, adherence to surfaces, evasion of host immune response.

Human Health Relevance of Glycocalyx

• Helps pathogenic bacteria evade phagocytosis, contributing to virulence.

• Example: Streptococcus pneumoniae uses its capsule to avoid immune detection.

Capsules vs. Slime Layers

• Capsule: Organized, firmly attached to cell wall.

• Slime Layer: Loosely attached, unorganized.

Bacterial Flagella: Structure and Function

• Structure: Composed of flagellin protein, anchored in cell membrane and wall.

• Function: Motility; enables bacteria to move toward or away from stimuli (chemotaxis).

Bacterial Arrangements

• Cells may form chains (strepto-), clusters (staphylo-), pairs (diplo-), or remain single.

Types of Bacterial Flagella Arrangements

• Monotrichous: Single flagellum at one end.

• Lophotrichous: Tuft of flagella at one end.

• Amphitrichous: Flagella at both ends.

• Peritrichous: Flagella distributed over entire cell surface.

Fimbriae and Pili

• Fimbriae: Short, hair-like structures for attachment to surfaces.

• Pili: Longer, involved in conjugation (transfer of DNA between cells).

Bacterial Cell Walls: Gram-Positive vs. Gram-Negative

• Gram-Positive: Thick peptidoglycan layer, teichoic acids, stains purple.

• Gram-Negative: Thin peptidoglycan, outer membrane with lipopolysaccharide (LPS), stains pink.

Unusual Bacteria: Mycobacterium and Mycoplasma

• Mycobacterium: Waxy cell wall (mycolic acid), acid-fast staining.

• Mycoplasma: Lack cell walls, resistant to antibiotics targeting cell wall synthesis.

Bacterial vs. Archaeal Cell Walls

• Bacteria: Peptidoglycan present (except in Mycoplasma).

• Archaea: No peptidoglycan; may have pseudopeptidoglycan or protein layers.

Plasma Membrane: Structure and Function

• Structure: Phospholipid bilayer with embedded proteins.

• Function: Selective permeability, transport, energy generation, cell signaling.

• Fluid Mosaic Model: Describes dynamic nature of membrane components.

Passive and Active Transport

• Passive Transport: Movement down concentration gradient (diffusion, facilitated diffusion, osmosis).

• Active Transport: Requires energy (ATP); moves substances against gradient (e.g., pumps).

Osmosis and Tonicity

• Osmosis: Diffusion of water across a semipermeable membrane.

• Tonicity: Effect of surrounding solution on cell volume (isotonic, hypotonic, hypertonic).

Inclusions, Endospores, and Storage

• Inclusions: Reserve deposits of nutrients (e.g., glycogen, polyphosphate).

• Endospores: Dormant, resistant structures formed by some bacteria (e.g., Bacillus, Clostridium).

Ribosomes: Prokaryotic vs. Eukaryotic

• Prokaryotic Ribosomes: 70S (50S + 30S subunits).

• Eukaryotic Ribosomes: 80S (60S + 40S subunits).

Endosymbiotic Theory

• Explains origin of mitochondria and chloroplasts as formerly free-living prokaryotes engulfed by ancestral eukaryotic cells.

• Evidence: Double membranes, own DNA, ribosomes similar to bacteria.

Table: Comparison of Prokaryotic and Eukaryotic Cells

Example: Gram Staining

• Gram-Positive: Staphylococcus aureus (purple after staining)

• Gram-Negative: Escherichia coli (pink after staining)

Additional info: Academic context and examples have been added to expand on the study guide points and ensure completeness for exam preparation.