The Plasma Membrane

Regulates Passage of Molecules into and out of Cells

The Phospholipid Bilayer

The Phospholipid Bilayer is two layers of phospholipids arranged so that their hydrophiliac tails are facing inwards and their hydrophobic heads are facing outwards. The phospholipid bilayer is the primary structure of the membrane. In the Fluid Mosaic Model, there are proteins, phospholipids, glycoproteins, and glycolipids.


Proteins

There are several types of proteins present in the plasma membrane. They are:

Channel Proteins: Channel proteins have a channel that allows molecules to move across the membrane

Carrier Proteins: Carrier proteins combine with a substance and help it move across the membrane

Cell Recognition Proteins: Cell Recognition Proteins are glycoproteins that recognize foreign invaders

Receptor Proteins: Receptor proteins have a binding site for specific molecules. The binding of this molecule causes the protein to change shape and cause a cellular reaction.

Enzymatic Proteins: Enzymatic proteins carry out metabolic reactions directly

Junction Proteins: Junction Proteins link cells together

Cell Transport

Active Transport

Active Transport is cell transport that requires energy (ATP). A form of active transport is the sodium potassium pump. The sodium potassium pump combines with ATP and undergoes a change of shape that allows it to combine with sodium and potassium ions to move them across the membrane.



Another form of active transport is bulk transport. Bulk transport occurs when fluid or particles are brought into or out of a cell by vacuole formation. Bulk transport into a cell is called endocytosis. Bulk transport out of the cell is called exocytosis. Phagocytosis is bulk transport of solids into a cell, and pinocytosis is the transport of liquids into a cell.

Passive Transport

Passive Transport is cell transport that doesn't require energy. Simple diffusion is a type of passive transport. Simple diffusion is the movement of particles from a higher concentration to a lower concentration through the membrane. Facilitated diffusion is when molecules bind with a carrier protein and diffuse rapidly across the membrane.


Osmosis is the movement of water from a higher concentration to a lower concentration through a semi-permeable membrane. A hypotonic solution has a lower concentration of solutes outside the cell, and a higher concentration of solutes inside of the cell. Water floods into the cell and the cell bursts. A hypertonic solution has a higher concentration of solutes outside the cell, and a lower concentration of solutes inside of the cell. Water floods from the cell, and the cell shrivels up. In an isotonic solution, the concentration of solutes inside and outside of the cell are the same. The cell stays the same.