Chapter 4Membrane Structure and Function

http://www.youtube.com/watch?v=ULR79TiUj80&feature=player_embedded

Phospholipid - amphipathic molecule

Membrane Lipids - phospholipid & cholesterol

Membrane Proteins - integral & peripheral

FLUID• due to lipid content

• unsaturated fats = more fluidity• hydrocarbon tails wiggle; move laterally

Why don't phospholipid molecules flip laterally??

• cholesterol• keeps membrane from freezing at decreased temperatures• stiffens the membrane at increased temperatures

MOSAIC• due to protein content

• number and types of proteins vary

• proteins in no set position

Carbohydrates• glycolipids & glycoproteins

• only occur on outside surface

glycocalyx• protection• facilitates adhesion between cells• reception of signaling molecules• cell-to-cell recognition

Aquaporins

DIFFUSION

physical process due to the random motion of particles

OSMOSISwater moves from an area of HIGH water concentration (low solute concentration) to an area of LOW water concentration (high solute concentration)

Tonicity - the ability of a solution to cause a cell to gain or lose water

Osmotic Pressure - measure of difference in solute concentrations; force needed to stop osmotic flow

Hydrostatic Pressure - pressure of the cytoplasm pushing against the plasma membrane

cytolysiscrenation

plasmolysisturgor pressure

Maintaining Osmotic Balance

http://www.youtube.com/watch?v=4z98WIeNtjM

Active Transport• needs ATP• moves UP the concentration

gradient• uses highly selective protein

carriers

http://www.youtube.com/watch?v=GTHWig1vOnY

Cotransport

Endocytosis and Exocytosis

Exocytosis• vesicle fuses with plasma membrane =

secretion• Plants - export materials to construct

cell wall• Animals - secrete hormone,

neurotransmitters and digestive enzymes

Endocytosis• take in substances by vesicle formation• viruses, food, another cell, liquid

A is a bacterium

B is a WBC

EXTRACELLULAR MATRIX

• meshwork of proteins and polysaccharides • collagen resists stretching• elastin gives resilience• fibronectin (adhesive) binds to

integrin• integrin makes contact with

cytoskeleton - plays role in cell signaling

• proteoglycans help resist compression; play role in cell signaling

CELL JUNCTIONS• allows coordination of cells

• adhesive junctions• attach adjacent cells

• tight junctions• plasma membrane proteins attach to

each other

• gap junction• allows cells to communicate

Plasmodesmata• pass through cell wall• allows water and small solutes to pass

freely