Cell Transport PDF

o It is the movement of substances across the cell membrane either into or out of the cell. Sometimes things just move through the phospholipid bilayer. Other times, substances need the assistance of a protein, like a channel protein or some other transmembrane protein, to cross the cell...

o It is the movement of substances across the cell membrane either into or out of the cell. Sometimes things just move through the phospholipid bilayer. Other times, substances need the assistance of a protein, like a channel protein or some other transmembrane protein, to cross the cell membrane. o Every cell is contained within a membrane punctuated with transport proteins that act as channels or pumps to let in or force out certain molecules. The purpose of the transport proteins is to protect the cell's internal environment and to keep its balance of salts, nutrients, and proteins within a range that keeps the cell and the organism alive.  There are two ways that substances can cross the plasma membrane: 1. Passive Transport o It occurs when substances cross plasma membrane without any input of energy from the cell. It includes simple diffusion, osmosis and facilitated diffusion. 2. Active Transport o It occurs when substance requires energy to cross plasma membrane of a cell. It includes pump transport and vesicle transport. o Diffusion is the process of a substance spreading out to evenly fill its container or environment. In a solution, a concentrated solute diffuses to spread evenly in its solvent. In air, gas molecules diffuse to mix thoroughly. Substances diffuse from areas of high concentration to low concentration. o Osmosis is defined as passage of solvent through a membrane from a dilute solution to a more concentrated one to equalize the osmolality of the fluids on both sides of the membrane. The membrane is impermeable to the solute but is permeable to the movement of solvent. There are three different types of osmosis solutions: o ISOTONIC SOLUTION o HYPERTONIC SOLUTION o HYPOTONIC SOLUTION o ISOTONIC SOLUTION one that has the same concentration of solutes both side and outside cell. o HYPERTONIC SOLUTION one that has higher solute concentration outside the cell than inside. Cell will shrink o HYPOTONIC SOLUTION one that has higher solute concentration inside the cell than outside. Cell will burst o Osmolarity refers to the number of solute per liter of the solution (solute plus solvent). o Dialysis. It is the process of separating substances in solution by selective diffusion through a semipermeable membrane. Excess fluids, electrolytes, waste products and toxic substances in blood can pass through an external semi- permeable membrane or the peritoneum for removal into the dialysate solution.  It is a type of diffusion that needs a help of transport proteins. There were two types of transport proteins, including channel proteins and carrier proteins. o CHANNEL PROTEINS form pores, or tiny holes, in the membrane. This allows water molecules and small ions to pass through the membrane without coming into contact with the hydrophobic tails of the lipid molecules in the interior of the membrane. o CARRIER PROTEINS binds with specific ions or molecules, and in doing so, they change shape. As carrier proteins change shape, they carry the ions or molecules across the membrane.  Primary active transport moves ions across a membrane and creates a difference in charge across that membrane, which is directly dependent on ATP. It is also called direct active transport or uniport. Sodium-potassium pump is an example of primary active transport. It helps to move potassium into the cell and carry sodium out.  Secondary active transport, also called coupled transport or cotransport, brings sodium ions, and possibly other compounds into the cell using energy in other forms than ATP. Cotransporting glucose and sodium using sodium-glucose transporter is an example. If a channel protein exists and is open, the sodium ions will be pulled through the membrane. This movement is used to transport other substances that can attach themselves to the transport protein through the membrane.