Prokaryotes

Shapes of Prokaryotes

Prokaryotes exhibit a variety of shapes, which are important for identification and classification.

• Coccus: Spherical shape (e.g., Streptococcus).

• Bacillus: Rod-shaped (e.g., Escherichia coli).

• Spirillum: Spiral-shaped (e.g., Spirillum volutans).

• Vibrio: Comma-shaped.

• Filamentous: Thread-like.

Cell Wall Composition: Bacteria vs. Archaea

The cell wall provides structural support and protection. Its composition differs between bacteria and archaea.

• Bacteria: Cell wall contains peptidoglycan, a polymer of sugars and amino acids.

• Archaea: Cell wall lacks peptidoglycan; may contain pseudopeptidoglycan or other unique polymers.

Gram Stain Technique

The Gram stain is a differential staining method used to classify bacteria based on cell wall structure.

1. Apply crystal violet dye.

2. Add iodine (mordant).

3. Wash with alcohol (decolorizer).

4. Counterstain with safranin.

• Gram-positive bacteria: Retain crystal violet, appear purple.

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

Cell Wall Differences: Gram Positive vs. Gram Negative

• Gram-positive: Thick peptidoglycan layer, no outer membrane.

• Gram-negative: Thin peptidoglycan layer, outer membrane containing lipopolysaccharides.

Cell Surface Structures

• Capsule: Sticky layer outside cell wall; protects against desiccation and immune response.

• Endospores: Dormant, resistant structures formed under stress.

• Fimbriae: Short, hair-like appendages for attachment.

• Pili: Longer appendages; involved in DNA transfer (conjugation).

Specialized Membranes

Some prokaryotes have infolded membranes for metabolic functions (e.g., photosynthesis, respiration).

Chromosome Arrangement

• Single, circular chromosome located in the nucleoid region.

• Plasmids: Small, circular DNA molecules separate from chromosome; carry accessory genes.

Binary Fission

Prokaryotes reproduce asexually by binary fission.

1. DNA replication.

2. Cell elongation.

3. Septum formation.

4. Division into two identical cells.

Genetic Diversity in Prokaryotes

• Transformation: Uptake of naked DNA from environment.

• Transduction: DNA transfer via bacteriophages (viruses).

• Conjugation: Direct transfer of DNA between cells via pilus.

Types of Metabolism Relative to Oxygen

• Obligate aerobes: Require oxygen.

• Obligate anaerobes: Cannot tolerate oxygen.

• Facultative anaerobes: Can use oxygen or not.

Heterocysts

Specialized cells in some cyanobacteria (e.g., Anabaena) for nitrogen fixation.

• Provide anaerobic environment for conversion of atmospheric nitrogen () to ammonia ().

Groups of Bacteria

Bacteria are classified into several groups based on characteristics.

Groups of Archaea

• Halophiles: Thrive in high salt environments.

• Thermophiles: Thrive in high temperature environments.

• Methanogens: Produce methane; anaerobic.

Symbiotic Relationships

• Mutualism: Both partners benefit.

• Commensalism: One benefits, other unaffected.

• Parasitism: One benefits, other harmed.

Endotoxins vs. Exotoxins

• Endotoxins: Components of outer membrane (e.g., lipopolysaccharides); released when cell dies.

• Exotoxins: Secreted proteins; cause disease symptoms.

Protists and Endosymbiosis

Basic Idea of Endosymbiosis

The endosymbiotic theory explains the origin of mitochondria and chloroplasts in eukaryotic cells.

• These organelles originated from prokaryotes engulfed by ancestral eukaryotes.

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

Major Groups of Protists

Additional info: The chart referenced likely compares these groups by features such as locomotion, nutrition, and representative species.

Fungi

Basic Structure of Fungi

Fungi are eukaryotic organisms with unique structural features.

• Hyphae: Filamentous structures; form the body of fungi.

• Mycelium: Network of hyphae; increases surface area for absorption.

Types of Hyphae

• Septate hyphae: Divided by cross-walls (septa).

• Coenocytic hyphae: No septa; multinucleate.

Types of Mycorrhizal Fungi

• Ectomycorrhizal fungi: Form sheaths around roots; do not penetrate cells.

• Arbuscular mycorrhizal fungi: Penetrate root cell walls; form arbuscules.

Fungal Life Cycle

Fungi reproduce sexually and asexually. Key stages include:

• Plasmogamy: Fusion of cytoplasm from two parent cells; creates heterokaryotic or dikaryotic stage (cells with two or more nuclei).

• Karyogamy: Fusion of nuclei; forms diploid zygote.

• Meiosis produces haploid spores.

Fungal Groups and Life Cycles

Fungi and Protists Relationship

The protist group most closely related to fungi is Unikonta (specifically, nucleariids).

Key Roles of Fungi

• Decomposers: Break down organic matter.

• Mutualists: Form symbiotic relationships (e.g., mycorrhizae, lichens).

• Pathogens: Cause diseases in plants and animals.

Lichens

Lichens are symbiotic associations between fungi and photosynthetic partners (algae or cyanobacteria).

• Make-up: Fungal hyphae provide structure; photosynthetic partner provides food.

• Reproduction: Can reproduce sexually (fungal spores) or asexually (fragmentation, soredia).

Additional info: Figure 31.5 likely illustrates the general fungal life cycle, including plasmogamy, karyogamy, and spore formation.