Cell Membranes. PLO’s B9 - analyse the structure and function of the cell membrane Identify...

Cell Membranes

PLO’s

B9 - analyse the structure and function of the cell membrane Identify molecules in the membrane and how they

contribute the characteristics of the membrane Describe hydrophobic and hydrophilic regions

CELL MEMBRANE STRUCTURE

Fluid Mosaic Model:• Plasma membrane consists of a phospholipid

bilayer with protein molecules embedded in it• Phospholipids give a “fluid” consistency• Proteins form the “mosaic”

http://en.wikipedia.org/wiki/Image:Cell_membrane_detailed_diagram_edit2.svg:

http://www.bioteach.ubc.ca/Bio-industry/Inex/

Phospholipids

Phosphate end is polar and hydrophilic (attracted to water)

Fatty acid chains are non polar and hydrophobic

http://bioinfo.bact.wisc.edu/themicrobialworld/Structure.html

Since the membrane is surrounded by water inside and out, the phospholipids arrange themselves like this:

Membrane Proteins

Peripheral proteins - on the inner or outer surface

Integral proteins - extend right throughMany of the proteins are free to move around

laterally within the membrane

Membrane Protein Functions

Channels to allow materials in and out of the cell

Transport proteins that carry specific molecules in and out of the cell

Receptors for hormones, growth factors and other chemicals that bind to the outside of the cell

Enzymes to catalyze reactions in the cell

Connecting cells to other cells at junctions

Ex. Gap junctions (allow passage of materials from cell to cell), tight junctions (connect cells together)

Carbohydrates

Carbohydrate chains are attached to some lipid and protein molecules

(glycolipids & glycoproteins)Usually attached to the outer surfaceThese are different in each individualCell recognition - “ID cards”, enable the body

to recognize its own cells

Cholesterol

Embedded in the membraneHelps to maintain the

fluidity and flexibility of the membrane

Helps to hold the proteins in place

Reduces permeability of the membrane

Membrane Permeability

Cell membranes are differentially (selectively) permeable

Certain substances can move through freely (water, gases, small molecules, uncharged (non-polar) molecules

Others cannot, and require special processes to get through (larger molecules, ions)