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