Microbiology Lecture: Cell Anatomy

Overview

• Study of prokaryotic and eukaryotic cells, focusing on microorganisms.
• Differences between prokaryotes and eukaryotes.

Prokaryotic vs. Eukaryotic Cells

Eukaryotic Cells

• Paired chromosomes in nucleus
• Divide by mitosis
• Contain organelles

Prokaryotic Cells

• Single circular chromosome
• No nucleus or organelles
• Cell walls made of peptidoglycan
• Divide by binary fission

Bacterial Cells

Size & Shape

• Average size: 0.2 to 2.0 micrometers
• Most are monomorphic (single shape)
• Vocabulary of shapes: bacillus (rod), coccus (spherical), vibrio (comma-shaped), spirochetes (spiral)

Arrangement

• Diplo (pairs), Staphylo (clusters), Strepto (chains), Tetra (groups of four)

Exterior Structures

• Glycocalyx: Capsule (organized) or Slime layer (loose)
• Flagella: Used for motility; different arrangements like peritrichous, amphitrichous
• Axial Filaments: Found in spirochetes, enable movement in viscous environments
• Fimbriae and Pili: Attachment and motility

Cell Wall

Composition

• Made of peptidoglycan (proteins + carbohydrates)
• NAG (N-acetylglucosamine) and NAM (N-acetylmuramic acid) joined by protein bridges

Types of Bacteria

• Gram-positive: Thick peptidoglycan layer
• Gram-negative: Thin peptidoglycan and outer membrane with lipopolysaccharides (LPS, toxic)

Atypical Cell Walls

• Acid-fast bacteria: Contain mycolic acid; e.g., Mycobacterium
• Mycoplasmas: Lack cell walls

Internal Structures

Plasma Membrane

• Phospholipid bilayer with embedded proteins
• Functions: selective permeability, fluid mosaic model
• Passive (no energy) vs. Active (requires energy) processes

Diffusion Processes

• Simple Diffusion: Movement from high to low concentration
• Facilitated Diffusion: Requires help from transporter proteins
• Osmosis: Movement of water through aquaporins

Solutions

• Isotonic: Equal solute concentration
• Hypotonic: Water enters the cell
• Hypertonic: Water leaves the cell

Cytoplasm

• Contains cytoskeleton for shape and movement
• Nucleoid: Contains circular DNA
• Ribosomes: Sites of protein synthesis (70S ribosome)

Endospores

• Produced by some bacteria (e.g., Bacillus, Clostridium) under nutrient-limited conditions
• Highly resistant cells

Eukaryotic Cells

Organelles

• Nucleus: Contains DNA, double membrane
• Endoplasmic Reticulum: Rough (with ribosomes) for protein synthesis; Smooth for lipid synthesis
• Golgi Complex: Modifies and packages proteins
• Lysosomes: Cleanup through digestive enzymes
• Mitochondria: ATP production, double membrane
• Chloroplasts: Photosynthesis, contain thylakoids and chlorophyll
• Peroxisomes: Detoxify hydrogen peroxide

Endosymbiotic Theory

• Describes evolution of eukaryotic cells from prokaryotic organisms
• Larger bacteria engulfed smaller ones which became organelles (e.g., mitochondria, chloroplasts)
• Symbiotic relationships led to development of eukaryotic cells