Plasma Membrane and Plant Cell Wall

Cross-linking glycans

(Plant cell wall) cross-link cellulose fibrils into robust network, hold everything together

Phospholipids are composed of two classes

Phosphoglycerides (more common) Sphingolipid

Black membranes

planar lipid bilayers that are formed across a hole in partition between 2 aqueous compartments

Self-Assembly of Phospholipid membranes

Due to their amphiphilic nature, phospholipids can self-assemble into lipid bilayer membranes -Polar head groups associate with water on the outside of the membrane -Hydrocarbon tails associate with each other on the inside of the membrane -Arrangement minimizes free energy (energetically favorable) -Sphere formation

Plasma membrane is composed of:

Lipids (phospholipids and sterols) Proteins (integral and peripheral) Carbohydrates (glycoproteins and glycolipids)

Fluid Mosaic Model

bilayer is a planar fluid- molecules can diffuse laterally within each leaflet -diffusion between leaflets is rare Despite its fluidity, the plasma membrane contains micro domains with different compositions, and diffusion between domains can be limited Gives membrane mosaic pattern, built up from small domains within the larger fluid

Plant Cell wall- Cellulose

cellulose is interwoven with pectin that provides resistance to compression -Other components include additional cross-linking polysaccharides and lignin (waterproofing) -Fibrils confer tensile strength on all walls

Sterols

form of lipid, contain rigid ring structure that stiffen portions of the phospolipid, animals = cholesterol

Pectin

forms negatively charged, hydrophilic network that gives compressive strength to primary walls; cell-cell adhesion

amphiphilic

hydrophilic head (polar) hydrophobic tail (non-polar)

Proteins and glycoproteins

responsible for wall turnover and remodeling; help defend against pathogens

Membrane assymetry

some phospholipids are enriched in the inner membrane and some are enriched in the outer *This has important implications in signal transduction* several important phospholipids are found mainly on the cytosolic face This generates a charge difference across the membrane (Phosphatidylserine is usually found only in the inner leaflet- gives it a negative charge relative to the outer leaflet)

Liposomes

spherical vesicles that assemble spontaneously from phospholipids in water (can vary in size depending on conditions used)

Turgor pressure

structural rigidity of the plant cell wall allows the generation of large internal pressure -When intracellular environment has an excess of solutes, water will flow into the cell via osmosis -Without this, the cell would swell and burst