Lecture Notes on Bacteria and Archaea Structure

LO:

1. Understand that bacteria and archaea have complex membranes and surface layers
2. Understand that the bacterial cell is structured by proteins that are similar to the cytoskeleton of eukaryotes

Hard shiz:

• the names of the proteins FTSZ, M one and the C something one
• also the S shape and the other chapoe
• basically just do the FC on these to clear dis up

Overview

• Lecture focuses on the structure of bacteria and archaea, specifically the cell envelope.
• Lecture is divided into two shorter sessions, originally adapted for COVID times.
• Emphasizes the complexity of their membranes and surface layers compared to eukaryotes.
• Highlights that bacteria have a structured cytoskeleton with homologs to eukaryotic proteins.

Differences Between Bacteria, Archaea, and Eukaryotes

• Bacteria and Archaea (Prokaryotes):
  • Lack membrane-bound organelles (e.g., nucleus, mitochondria).
  • Have complex cell envelopes and structures like pili and flagella.
• Eukaryotes:
  • Have membrane-bound organelles.

Bacterial Cell Shapes

• Bacteria come in various shapes:
  • Bdellovibrio: similar to organism shown in diagram A.
  • Rods and Cocci: e.g., diagram D shows coccoid bacteria.
  • Helical Bacteria: e.g., Treponema pallidum (causes syphilis).
• Shapes determined by cytoskeletal proteins.

Bacterial Cytoskeleton

• Protein FTSZ: Controls cell diameter by forming a Z ring, homologous to tubulin.
• MRE Proteins: Involved in rod and spiral elongation, structurally similar to actin.
• Crescent-shaped cells: Controlled by protein CREs.

Bacterial Cell Envelopes

• Gram-Positive Bacteria:
  • Thick peptidoglycan layer outside the plasma membrane.
  • Capsule polysaccharides and secreted proteins may be present.
• Gram-Negative Bacteria:
  • Thin peptidoglycan layer between inner plasma membrane and outer membrane.
  • Outer membrane contains lipopolysaccharide (LPS), which provides a protective barrier.

Gram Staining

• Differentiates bacteria based on cell wall structure:
  • Gram-Positive: Stains black/purple due to thick peptidoglycan.
  • Gram-Negative: Stains red/pink due to thin peptidoglycan and outer membrane.

Archaeal Structures

• Diverse structures among archaea, some resembling gram-negative or gram-positive bacteria.
• Unique chemical make-up in their envelopes.

Capsules and S-Layers

• Capsules:
  • External to the cell wall, composed of polysaccharides or proteins.
  • Provide protection against phagocytosis, desiccation, and immune response.
• S-Layers:
  • Crystalline lattice of proteins found in some bacteria, providing additional protection.

Summary of Key Points

• Bacteria have complex envelopes with one or more membranes.
• Peptidoglycan provides a rigid structure but is porous, not a permeability barrier.
• External capsules and S-layers vary in chemistry, with diverse polysaccharide and peptide compositions.
• Cytoskeletal proteins help determine cell shape and are homologous to eukaryotic counterparts.