Cell membranes

Fluid mosaic model

A phospholipid bilayer (the membrane). This bilayer surrounds all cells and organelles (except for ribosomes).

Non-polar molecules can pass through, like oxygen and carbon dioxide.

Phospholipid heads and tails

Heads are hydrophilic, tails are hydrophobic.

Integral proteins

Found on bilayer. Integrated completely into the membrane.

Peripheral proteins

Found on exterior and interior surfaces of membrane. Attached to integral proteins or phospholipids.

Glycoproteins

Carbohydrates that are attached to protein on exterior surfaces of cell membrane.

Glycolipids

Carbohydrates that are attached to lipids on exterior surfaces of membrane.

Glycocalyx

Hydrophilic, allows cells to recognize one another, can determine if it is a self/nonself, aids in embryonic development, used in cell-to-cell attachments to form tissue.

Selective permeability of membrane

Some molecules can cross the membrane and others cannot.

Passive transport

Doesn’t require energy. Ex. Include diffusion, facilitated diffusion, and osmosis.

Active transport

Requires energy. Ex. Includes exocytosis and endocytosis.

Diffusion

Molecules move from an area with high concentration to low concentration.

Osmosis

Movement of water through a semiperm membrane according to the concentration gradient of a water. Only water moves during osmosis.

Hypotonic

Moving into cell

Hypertonic

Moving out of cell

Isotonic

Moving in and out of cell equally.

Osmoregulation

Controlling results of osmosis.

Facilitated diffusion

Material diffuse across membrane. Membrane proteins help during this process.

Active transport

Moves substances across cell membranes against concentration gradients. Requires ATP.

Endocytosis

Something coming into the cell - being pulled in.

Exocytosis

Something coming out of the cell - being pushed out.