Plasma Membrane and Plant Cell Wall

Plasma Membrane

A regulated cell boundary composed mostly of phospholipids

Phospholipids

Amphipathic molecules with a polar head and two non polar fatty acid tails

Saturated Hydrocarbon Tail

Contains no double bonds

Unsaturated Hydrocarbon Tail

Contains one cis double bond which prevents lipids from packing tightly together

Phosphatidylserine

Negatively charged phospholipid that is found only on the inner leaflet of a healthy cell membrane

Sterols

A type of lipid that stiffens the plasma membrane when placed between phospholipids

Animal Cell Sterol

Cholesterol

Plant Cell Sterols

Phytosterols

Fungi Sterols

Ergosterol

Sterol Structure

Rigid steroid ring, polar head group, one non polar hydrocarbon tail

Lipid Micelles

Sphere of lipids with the polar head on the outside and only the hydrocarbon tails on the inside

Entropy of Lipid Membranes

Entropy is maximized when water molecules are free to rotate and interact in all directions with other polar groups

Fluid Mosaic Model

Molecules can move laterally through the membrane which is composed of microdomains

Microdomains

Unique portions of the plasma membrane that serve a specific purpose and allow for easy diffusion of specific molecules

Lipid Rafts

A less dense portion of the cell membrane with a high concentration of cholesterol

Membrane Asymmetry

Property of the plasma membrane where some lipids are only found on the inner leaflet while others are only found on the outer leaflet

Peripheral Proteins

Proteins bound to the surface of the membrane

Integral Proteins

Proteins that pass into the interior of the membrane

Liposomes

Spherical vesicles that assemble spontaneously from phospholipids in water and can be used to study the properties of membranes

Black Membrane

Artificial planar lipid bilayer membrane that can be used to study how molecules change or diffuse through a membrane

Plant Cell Wall

A carbohydrate matrix that surround all plant cells

Cellulose

A polymer of glucose and major component of the plant cell wall that provides tensile strength

Pectin

A complex mixture of polysaccharides that provides resistance to compression in the plant cell wall

Turgor Pressure

The force used to keep a plant upright and the driving force for cell expansion during cell growth