4. & 5 Cellular Biology

Chapter 5: Eukaryotic Cells

Evolution of Eukaryotic Cells

• Eukaryotic Cells: Cells that have a nucleus and membrane-bound organelles.

• Archaea: A domain of single-celled organisms, distinct from bacteria.

• Endosymbiotic Theory: Proposes that eukaryotic cells evolved through the engulfment of ancient bacteria by ancestral eukaryotic cells.

• Example: Engulfment of proteobacteria led to the formation of mitochondria.

• This theory is supported by evidence:

  • Presence of double membranes in mitochondria and chloroplasts.

  • Circular DNA reminiscent of bacterial genomes.

  • Similarity in 70S ribosomes between mitochondria, chloroplasts, and bacteria.

Neutrophils vs. Bacteria

• Neutrophils: Type of white blood cell that hunts and absorbs bacteria.

  • Uses vesicle called an endosome to transport bacteria to lysosomes for destruction.

  • Endosomes contain hydrolytic enzymes that break down pathogens.

Eukaryotic Cell Biology

Cell Structure

• Nucleus: Contains Nuclear Pore Complex (NPC).

• Ribosomes: Composed of protein and RNA, featuring a large and small subunit.

• Types of Proteins:

  • Cytosolic Protein

  • Membrane Protein

  • Secretory Protein

• Endoplasmic Reticulum (ER): Two types:

  • Rough ER: Studded with ribosomes, responsible for protein synthesis.

  • Smooth ER: Lacks ribosomes, involved in lipid synthesis and detoxification.

Golgi Apparatus

• Functions as a protein post office, modifying, sorting, and packaging proteins for transport.

• Also synthesizes complex carbohydrates.

Cytoskeleton

• Provides structure and shape to cells.

  • Composed of:

  • Actin Filaments: Involved in cell movement.

  • Intermediate Filaments: Provide tensile strength.

  • Microtubules (tubulin): Maintain cell shape and assist in intracellular transport.

Bacterial Cell Overview

Cell Types

• Spherical Bacteria (Coccus): Arrangement based on plane of division:

  • Diplococci: Two cells in pairs.

  • Streptococci: Chains of bacteria.

  • Tetrads: Groups of four.

  • Sarcinae: Groups of eight to sixty-four.

  • Staphylococci: Clusters resembling grapes.

Morphology Reference

• Coccus shapes include Staphylococcus aureus (clusters) and Streptococcus pneumoniae (chains).

• Bacillus: Rod-shaped bacteria with potential arrangements of diplo- and streptobacilli.

• Spiral shapes include Vibrio, Spirillum, and Spirochete.

Components of a Bacterial Cell

Structure

• Cell Envelope:

  • Chromosomal DNA is compacted, not freely floating.

  • Plasmid DNA, separate from chromosomal DNA, plays a role in gene transfer.

  • Structural Maintenance of Chromosomes (SMC): Protein responsible for DNA organization.

Bacterial Membrane and Ribosomes

• Bacterial Ribosomes: Have a molecular weight of 2.4 million, composed of ribosomal RNA and proteins.

• Target for Antibiotics:

  • Chloramphenicol & Erythromycin inhibit 50S subunit.

  • Streptomycin & Tetracycline inhibit 30S subunit.

Cell Wall Structures

• Gram-Positive Bacteria: Feature thick peptidoglycan layer including teichoic acids.

• Gram-Negative Bacteria: Possess a thin peptidoglycan layer with an outer membrane of lipopolysaccharides (LPS).

  • LPS acts as an endotoxin, causing immune reactions in humans.

• Cell wall composed of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).

Cell Wall Synthesis

• Involves polymerization of NAG-NAM and crosslinking by Penicillin Binding Proteins (PBPs).

  • Penicillin inhibits PBPs, preventing cell wall synthesis.

Bacterial Cell Structure

Endospores

• Endospore: Resistant structure formed by bacteria under adverse conditions, allowing survival.

Capsule and Cytoskeleton

• Capsule: External layer composed of carbohydrates, protects against immune responses by preventing phagocytosis.

• Cytoskeleton: Bacterial shape is maintained by filament proteins such as MreB.

Bacterial Accessory Appendages

• Structures include pili, flagella, and stalks.

• Flagella: Help with movement; homologous to components of Type III secretion systems (T3SS).

  • Flagella structure includes a basal body, hook, and filament (made of flagellin).

• Pilus: Involved in attachment and genetic material transfer during conjugation.