Cell Membranes

Cell Membrane More than a protection...

Cell Membrane Protects the cell. Allows certain molecules to enter the cell and not others. Contains the cytoplasm and organelles. Is constituted by a bilayer of phospholipids, with proteins trapped in the membrane.

Membranes are formed of phospholipids. Phospholipids are amphipathic molecules: they have in the same molecule hydrophilic and hydrophobic regions Phospholipids are the most abundant lipid in membranes.

Phospholipids

Simple model of membrane

The membrane is fluid “horizontally”

“Fluid Mosaic” Model of cell membrane with proteins

In this model, you see how the cytoskeleton attaches to proteins of the membrane

There are also proteins attached to the membrane There are also proteins attached to the membrane. They have various functions.

Passive diffusion: from a high concentration to a low concentration.

Passive transport: Use a protein as a carrier, or channel, from high concentration to low concentration.

Osmosis: Diffusion of water only.

Comparing two different concentrations of solutes. Hypertonic: the solution with the higher concentration Hypotonic: the solution with the lower concentration. Isotonic: same concentration of solute.

Osmosis: Hypertonic, Hypotonic

Facilitated diffusion by transport

Ligand Gated channels

Active transport Against the concentration gradient, from low to high concentration. Requires energy. Uses a transmembrane protein for transport

Types of active transports

Transport by vesicle Endocytosis: Phagocytosis Pinocytosis

Receptor mediated endocytosis (coated pits)

Exocytosis