HO - 05.1 Eukaryotes

BIOL 107 Topic 5: Eukaryotes Cell Exteriors

  • Instructor: Dr. Damián Cirelli, University of Alberta

Extracellular Matrix (ECM)

  • Components:

    • Collagen

    • Elastin

    • Chondroitin

    • Hyaluronan

    • Hydroxyapatite

Collagen

  • Function: Strengthens the ECM

  • Characteristics:

    • Most abundant protein in mammals

    • Lack of collagen leads to scurvy

    • Composed of peptide chains cross-linked by hydroxyproline

    • Hydroxylation of proline requires Vitamin C

Procollagen Structure

  • A triple helix structure

  • Each strand synthesized in the endoplasmic reticulum (ER) lumen

  • Ends of procollagen are trimmed by procollagen peptidase post-secretion

  • Network of Transmembrane Proteins:

    • Form independent strands between cells

    • Only found in vertebrates

    • Invertebrate equivalent: septate junctions

Desmosomes

  • Function: Provide strong mechanical adhesion

  • Role: Channel-like interconnection for direct cytoplasmic communication without cytoplasmic migration (e.g. electrical signals)

Microvilli

  • Structure: Covered by plasma membrane

  • Types of Cilia:

    • Non-Motile (Primary): Singular, sensory function

    • Motile (Secondary): ATP-powered, used for movement

  • Animal Cells: Have cilia but they are non-external

Diatoms

  • Classification: Unicellular microalgae (Stramenopiles or Heterokonts)

  • Structure: Enclosed in a frustule formed by two thecae made of silicon biopolymer

  • Building Block: Use silicic acid as a monomer to construct their frustule

    • Parts: Epitheca and Hypotheca

Fungi Cell Walls

  • Composition: Contain chitin, similar to the exoskeleton of arthropods

  • Components:

    • Example: Saccharomyces cerevisiae

    • β-glucans and Mannoproteins

Complexity of Fungal Cell Walls

  • Example: Candida albicans

  • Layers of Cell Wall:

    • Outer Wall: Hydrophobicity and adhesiveness

    • Inner Wall: Flexible, viscoelastic frame providing strength and shape

Plant Cell Walls

  • Functions:

    • Protection: Physical and chemical

    • Structural Support: Creates high internal pressure

    • Cell Adhesion: Uses the cell wall as "brick" and middle lamella as "mortar"

  • Components:

    • Primary Wall

    • Middle Lamella

    • Secondary Wall: Composed of cellulose fibers in a lignin matrix

  • Materials:

    • Cellulose (most abundant polymer on Earth)

    • Hemicellulose and Pectin (some cells, e.g., wood)

    • Lignin: Varies in orientation and component ratios

Plasmodesmata

  • Structure: Tube-like channels interconnecting plant cells

  • Explanation: Framework is complex and not fully understood

Exam Content Overview

  • Extracellular Structures Functionality:

    • Protect the cell

    • Resist forces pulling apart cells

    • Seal spaces between cells

    • Enable exchange of small molecules between neighboring cells

    • Support whole organism

  • Vitamins: Required in diet; Vitamin C is essential for collagen production

  • Questions to Consider:

    • What is the extracellular matrix in animals?

    • Compare fungi cell walls to plant and bacterial cell walls

    • Differentiate animal cilia from bacterial cilia.