Interactions Between Cells and their Environments (Sec 2 Week 5)

5 cell junction line

1. Tight junction (seals neighbouring cells together to prevent leakage and help polarize)

2. Adherent jucntion (Joins actin bundle to similar bundle

3. desmosome (joins the intermediate filaments inone cell to neighbour

4. Gap junction (Forms channels that allows small water-soluble molecules to pass

5. Hemidesmosome (anchors intermediate filaments)

First 3 are cell-cell anchoring, last 2 are cell to ECM anchoring

Tight Junctions

1. Creates tight seal between cells

2. Prevents mixing of membrane proteins

Tight junctions form…

Sealing strans

Tight junctions are composed of…

2 transmembrane proteins (Claudin and Occludin, two per junction - one on each cell)

Anchoring Junction

• Provide mechanical strength to epithelium

• Link cytoskeletons

Transmembrane proteins of anchoring junctions interact with…

other extracellular domain of other protein (side) or extracellular matrix (bottom)

Intracellular linker proteins

cytosolic protein that link transmembrane adhesion proteins to cytoskeletal filaments

Adheren Junctions

encircles the inside of the plasma membrane , transmembrane proteins are called cadhereins

Desmosomes and Hemidesmosomes

Link to intermediate filaments that provide the most structural strength

Desmosomes link to..

Keratin filaments and connect to neighbouring cell

Hemidesmosomes…

anchor keratin filaments to basal lamina

Desmosomes are made of…

Desmoglein, desmocollin - transmembrane adhesion proteins

Gap junctions

• couple cells electrically and metabolically

• Allows passage of ions and metabolites

• Are gated (Opened by extracellular or intracellular signals

Gap Junction structure

• Made of connexins

• 6 connexins form connexon

• 2 connexons form intercellular channel

Example use of gap junction gate

Gate will close if one cell is damaged causing drastic change in solute composition to preserve solute composition in other cell

Intercellular junction in plant cells

• lack cell junction

• has plasmodesmata that allow for communication between cells

Plasodesmata

• Continuous plasma membrane and ER across plasmodesmata

• similar to other junctions - allows movement of small soluble molecules

Callose

controls permeability of plasmodesmata through reversible deposition

Epithelial Tissue

• intestinal lining, skin epidermis

• Cells closely associated

• Limited ECM, cytoskeleton filament give mechanical strength

Extracellular matrix major macromolecules

• Glycosaminoglycans

• Fibrous proteins

• Glycoproteins

ECM is primary component of connective tissue

GAG (Glycosaminoglycans) structure

• repeating disaccharide chain - linear and long

• Very negative

where are GAG made

inside the cell, released via exocytosis

GAG function

Form hydrated gels that resist compression and fill space

Hyaluronan

Simple GAG that is spun on cell surface by plasma membrane enzyme

Proteoglycans

Subclass of glycoproteins with at least one sugar side chain that is a GAG

Percent of proteoglycan weight that is sugar

up to 95%

Collagen structure

Fibrous protein - three chains wound in triple helix that are assembled to form collagen fibril and than collagen fibers

Collagen attributes

Fibrous, provides tensile strength and resists stretching

Collagen secreted as…

Procollagen by fibroblasts (connective tissue) and osteoblasts (bone)

What helps connective tissue cells bind to collagen they secrete?

Integrin and fibronectin

Fibronectin binds to collagen, integrin binds to fibronectin and is bound to adaptor protein in the cell that is connected to actin filaments

Elastin qualities

Fibrous, gives tissue ela

Basal Lamina

Underlies all epithelia, thin, ECM is secreted by epithelial cells

Basal Lamina seperates…

epithelia from underlying tissue -

Basal lamina prevents… but allows…

prevents fibroblasts in connective tissue from interacting with epithelial cells

allows passage of macrophages and lymphocytes

epithelial cells are anchored to basal lamina by

hemidesmosomes (and their Transmembrane adhesion proteins - integrins)

Integrins bind to…

Laminin in the basal lamina

intracellular linker proteins then bind to

keratin filaments

Plant cell wall main components

cellulose (Strength) and pectin (Resistance to compression)

Plant cells synthesize…

Cellulose chains at plasma membrane - other cell wall components made at golgi and moved by exocytosis