Processes of Life

Overview

All living organisms share certain fundamental processes that define life. These include growth, reproduction, responsiveness, metabolism, and cellular structure. Viruses, while capable of some processes, do not fulfill all criteria for life.

• Growth: Increase in size; occurs in bacteria, archaea, eukaryotes, but not in viruses.

• Reproduction: Production of offspring; occurs in bacteria, archaea, eukaryotes, and some viruses (via host cell machinery).

• Responsiveness: Ability to react to environmental stimuli; present in bacteria, archaea, eukaryotes; viruses respond to host cells.

• Metabolism: Chemical reactions for energy and building blocks; occurs in bacteria, archaea, eukaryotes, but not in viruses.

• Cellular Structure: Organized, membrane-bound structures; present in all except viruses.

Prokaryotic & Eukaryotic Cells

Key Differences

• Prokaryotes: Lack nucleus, generally smaller, simpler structure, DNA in nucleoid region, no membrane-bound organelles.

• Eukaryotes: Have nucleus, larger, complex structure, DNA in nucleus, contain membrane-bound organelles.

Examples

• Prokaryotes: Bacteria and archaea

• Eukaryotes: Fungi, animals, plants, protozoa, algae

Bacterial Cell External Structures

Glycocalyces

Gelatinous, sticky substances surrounding the cell, composed of polysaccharides, polypeptides, or both.

• Capsule: Organized, firmly attached; protects from desiccation, phagocytosis, and helps bacteria adhere to surfaces.

• Slime Layer: Loosely attached, water-soluble; aids in adherence and prevents dehydration.

Flagella

Long, whip-like structures used for motility.

• Composed of filament, hook, and basal body.

• Rotation propels bacteria; direction and speed controlled by cell.

• Arrangements: monotrichous (single), lophotrichous (tuft), amphitrichous (both ends), peritrichous (all over).

Fimbriae and Pili

• Fimbriae: Short, bristle-like; used for attachment to surfaces and other cells.

• Pili: Longer than fimbriae, shorter than flagella; usually 1-2 per cell; involved in conjugation (DNA transfer).

Bacterial Cell Wall

Structure and Function

• Provides shape, protection, and prevents osmotic lysis.

• Composed mainly of peptidoglycan (sugar and peptide chains).

• Target for many antibiotics (e.g., penicillin).

Gram Stain Differences

Bacterial Cytoplasmic Membrane

Structure

• Phospholipid bilayer with embedded proteins (integral and peripheral).

• Functions as a selective barrier, site of energy generation, and transport.

Transport Mechanisms

• Passive Transport: Diffusion, facilitated diffusion, osmosis (no energy required).

• Active Transport: Requires energy (ATP); moves substances against concentration gradient.

Bacterial Cytoplasm

• Cytosol: Liquid portion, contains enzymes, nutrients, ions, and DNA (in nucleoid).

• Inclusions: Storage granules for nutrients, gases, or other substances.

• Endospores: Dormant, highly resistant structures for survival in harsh conditions.

Eukaryotic Cell Structure

External Structures

• Glycocalyces: Less organized than in prokaryotes; help in cell recognition and protection.

• Cell Walls: Present in fungi, algae, plants; composed of cellulose, chitin, or other polysaccharides.

• Flagella & Cilia: Used for movement; structurally more complex than in prokaryotes.

Cytoplasmic Membrane

• Phospholipid bilayer with sterols (e.g., cholesterol) for stability.

• Contains membrane proteins for transport, signaling, and cell recognition.

Membranous Organelles

• Nucleus: Contains DNA, nucleolus, surrounded by nuclear envelope.

• Endoplasmic Reticulum (ER): Network of membranes; rough ER (with ribosomes) synthesizes proteins, smooth ER synthesizes lipids.

• Golgi Body: Modifies, packages, and sorts proteins and lipids for transport.

• Lysosomes, Peroxisomes, Vacuoles, Vesicles: Involved in digestion, storage, and waste removal.

• Mitochondria: Site of cellular respiration and ATP production; contains its own DNA and 70S ribosomes.

• Chloroplasts: Site of photosynthesis in plants and algae; contains its own DNA and 70S ribosomes.

Nonmembranous Organelles

• Ribosomes: Protein synthesis; 80S in eukaryotes, 70S in prokaryotes and mitochondria/chloroplasts.

• Cytoskeleton: Network of fibers for shape, support, and movement.

• Centrioles: Involved in cell division in animal cells.

Archaeal Cell Structure & Cytoplasmic Membranes

• Similar to bacteria but with unique membrane lipids and cell wall components (no peptidoglycan).

• Some have unique external structures (e.g., hami for attachment).

Summary Table: Prokaryotes vs. Eukaryotes

Key Terms

• Peptidoglycan: Polymer of sugars and amino acids forming bacterial cell wall.

• Lipopolysaccharide (LPS): Component of Gram-negative outer membrane; can trigger immune response.

• Endospore: Highly resistant, dormant structure formed by some bacteria for survival.

• Conjugation: Transfer of genetic material between bacteria via pili.

1. Four Processes of Life 🧬

• Growth: Increase in size.

• Reproduction: Production of new cells or organisms.

• Responsiveness: Ability to respond to environment.

• Metabolism: Chemical reactions for energy and building blocks.

2. Prokaryotic vs. Eukaryotic Cells 🔬

• Prokaryotes: No nucleus, smaller, no membrane-bound organelles.

• Eukaryotes: Nucleus present, larger, have organelles (e.g., mitochondria).

3. Capsules vs. Slime Layers

• Capsules: Organized, firmly attached to cell wall, protect against phagocytosis.

• Slime Layers: Unorganized, loosely attached, help with adhesion.

4. Fimbriae, Pili, and Flagella

• Fimbriae: Short, numerous, for attachment.

• Pili: Longer, few, for DNA transfer (conjugation).

• Flagella: Long, for motility (movement).

5. Bacterial Shapes & Arrangements

• Cocci: Spherical

• Bacilli: Rod-shaped

• Spirilla: Spiral

• Arrangements: Chains (strepto-), clusters (staphylo-), pairs (diplo-)

6. Gram-Positive, Gram-Negative, Acid-Fast Cell Walls

• Gram-Positive: Thick peptidoglycan, teichoic acids.

• Gram-Negative: Thin peptidoglycan, outer membrane with lipopolysaccharides.

• Acid-Fast: Waxy mycolic acids, resist decolorization.

7. Gram Staining Reactions

• Gram-Positive: Retain crystal violet, appear purple.

• Gram-Negative: Lose crystal violet, take up safranin, appear pink/red.

8. Cytoplasmic Membrane Structure & Function

• Structure: Phospholipid bilayer with proteins.

• Function: Controls entry/exit, energy generation, communication.

9. Passive vs. Active Transport

• Passive: No energy, moves down concentration gradient (e.g., diffusion, osmosis).

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

10. Bacterial Endospores

• Formation: Produced in harsh conditions for survival.

• Function: Resistant to heat, chemicals, desiccation.

11. Major Eukaryotic Organelles

• Nucleus: DNA storage.

• Mitochondria: ATP production.

• Chloroplasts: Photosynthesis (plants/algae).

• ER & Golgi: Protein/lipid processing.

• Lysosomes: Digestion.

12. Archaeal vs. Bacterial Cells

• Archaea: Unique membrane lipids, no peptidoglycan, often extremophiles.

• Bacteria: Peptidoglycan cell wall, diverse environments.

13. Endosymbiotic Theory

• Mitochondria and chloroplasts originated from free-living bacteria engulfed by ancestral eukaryotes.

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