The document summarizes key aspects of cell membranes, including that membranes are composed of lipids, proteins, and carbohydrates. Transmembrane proteins can transport molecules like water and ions through the membrane and perform functions like transport, enzymatic activity, and signal transduction. Membranes are selectively permeable, allowing passive transport of solutes through diffusion, facilitated diffusion using transport proteins, and osmosis of water.

1. Biology and Human Concerns
Notes – 10/05/09
Cell Membrane
-A membrane is a fluid mosaic of lipids, proteins and carbohydrates.
Movement of phospholipids
-Saturated fatty acids have no double bonds, these phospholipids move
less because they are more tightly packed.
Transmembrane Proteins
-Provide a passageway through which molecules like water or ions can
travel through a membrane.
Functions of Transmembrane proteins
Transport Proteins
Enzymatic Activity
Signal Transduction - Receptor Proteins – Change is created within a
protein
Traffic Across Membranes
-A membrane’s molecular organization results in selective permeability
-Passive Transport
Diffusion => Movement of solutes from high concentration to low
concentration
Caused by molecular motion of original solution
Facilitated Diffusion => Specific proteins facilitate the passive
transport of selective solutes. Does not require energy.
Osmosis => The movement of water from a region of high water
concentration to a region of lower water concentration through a semi
permeable membrane. (Water concentration = room for water) Higher the
water concentration, the lower the solutes in water. Lower water
concentration, higher level of solutes

2. -Selectively Permeable => lipids and small molecules can travel through
cell membrane. Large molecules like glucose (C6H12O6 cannot travel through
without help.