Plasma Membrane Permeability

The plasma membrane of a cell is extremely important to the transportation of substances into and out of the cell. The outer membrane of a cell is made up of lipids and proteins. Most of the lipids in plasma membranes are phospholipids. The phospholipids have a hydrophilic head and two hydrophobic tails. When engulfed in water, they arrange themselves such that all the hydrophobic tails clump together, surrounded by the hydrophilic heads, protecting the tails from the exposure to the water. In cells, which are usually both surrounded by and filled with water, they form a phospholipid bilayer. The phospholipid bilayer surrounds the cell with the heads exposed to the water inwards and outwards, while the tails are enclosed between the heads. However, this membrane is not locked together or rigid; it is selectively permeable. Selective permeability allows some substances to pass through it. The membrane is fluid, allowing certain molecules to pass through by diffusion. This type of passage through a cell is called passive transport, when no energy is required for a molecule to pass through a selectively permeable membrane. The proteins that make up parts of the cell membrane also play a key role in the transport of materials in and out of a
ATP, or adenine triphosphate, acts as an immediate source of energy in an organism. It powers chemical, transport, and mechanical cellular work. ATP contains three phosphate groups, a sugar ribose, and a nitrogenous base adenine. The phosphate chain is bonded to the ribose, which is bonded to the adenine. The bond between the phosphate and the ribose can be broken through hydrolysis. When the phosphate breaks off, the ATP becomes adenine diphosphate, or ADP. This chemical reaction released 7.3 kcal of energy per mole of ATP hydrolyzed. An example of ATP supplying transport work in the cell is when ATP phosphorylates transport proteins on cellular membranes. ATP powers the active transport pump in and out of the