 In this video I will cover the following objective, define the following terms, and be able to use and recognize examples of each. Active transport, solute pumping including primary transport and secondary transport. Exocytosis and endocytosis including phagocytosis, penocytosis, and receptor-mediated endocytosis. Active transport is the movement of solutes across the plasma membrane, which requires the input of energy usually in the form of ATP. In active transport, solutes move against their concentration, gradients leading to an accumulation of a solute on one side of the plasma membrane. Solute pumping is when a protein uses ATP to transport solutes against the concentration gradient, and so solute pumping is a major form of active transport. A primary active transport mechanism is where one protein uses ATP in order to pump a solute across the plasma membrane. The example that we see here is the sodium-potassium pump. The sodium-potassium pump will force sodium out of the cytosol and force potassium into the cytosol. Each time the sodium-potassium pump breaks down one ATP molecule, the energy released drives three sodium ions out of the cell and two potassium ions into the cell. Therefore, the sodium-potassium pump creates a concentration gradient where there is a high concentration of sodium outside the cell and a high concentration of potassium inside the cell. These concentration gradients will then enable facilitated diffusion if an ion channel was to open, enabling sodium to enter the cell by facilitated diffusion or potassium to exit the cell by facilitated diffusion. This primary active transport mechanism is a very important way in order to create those concentration gradients that will fuel other transport mechanisms and also be important for transmitting information rapidly through excitable cells like neurons and muscles. In contrast to primary active transport, secondary active transport is where the primary transport of one molecule will create a concentration gradient that can then be used as the energy source to drive another molecule against its concentration gradient. The example we see here is the secondary active transport of glucose driven by sodium. There is a higher concentration of sodium outside the cell than inside the cell, and sodium can move into the cell by facilitated diffusion. The sodium-linked glucose transporter is a protein that will allow glucose to move into the cell as sodium moves into the cell. Although there is already a high concentration of glucose inside of the cell, therefore glucose cannot enter the cell by facilitated diffusion. Glucose is also a polar molecule that's too large to cross the plasma membrane by simple diffusion. However, glucose can enter the cell by active transport. However, there are not any primary active transport proteins that can force glucose against its concentration gradient into the cell. It's only the secondary active transport mechanism that will force glucose into the cell, where the energy source that provides the driving action to pump glucose into the cell is the movement of sodium down its concentration gradient. Therefore, the primary active transport of sodium by the sodium-potassium pump creates a concentration gradient that can then be used to drive active transport of another solute, in this case glucose. Exocytosis is an active transport mechanism where a vesicle will fuse with the plasma membrane, and as that vesicle fuses with the plasma membrane, the contents of the vesicle spill out of the cell into the extracellular space. An example of exocytosis is the release of digestive enzymes from the exocrine organ, the pancreas, to help with digestion. The pancreas produces lots of digestive enzymes, and these digestive enzymes are produced inside of the pancreatic ACE in our cells. These digestive enzymes are proteins that are too large to exit the cell by simple diffusion, and they cannot exit the cell through facilitated diffusion either. These larger molecules, proteins, get packaged into secretory vesicles and then released from the cell by exocytosis. In contrast to exocytosis, endocytosis is an active transport mechanism that moves material from the extracellular space into the cytoplasm. There are three major forms of endocytosis. Phagocytosis literally translates to cell eating. In phagocytosis, a large particle is engulfed and brought into the cell to be contained within a vacuole. Then that vacuole can merge with a lysosome in order to digest the large particle, breaking it down into the building block molecules that can then be used by the cell to produce other molecules. Penocytosis literally translates to cell drinking. In penocytosis, the plasma membrane buds inward to take a sample of the extracellular fluid with any solutes that are dissolved in it to bring that into the cell to form the interior contents of a vesicle within the cell. Receptor mediated endocytosis is a specific interaction where a chemical substance in the extracellular environment known as the ligand binds to a protein embedded in the plasma membrane known as the receptor. The ligand receptor binding is very specific so that a receptor recognizes one specific ligand, for example a protein, and not a different protein or other solute in the extracellular environment. This ligand receptor interaction being very specific will allow the cell to regulate what moves in from the extracellular environment, only allowing this ligand to come into the cell when needed. After the ligand binds to the receptor, the endocytosis process will be initiated to form an inward bud from the plasma membrane. Eventually that inward bud will pinch off and create a vesicle. Inside of the vesicle is the ligand that has been brought in from the extracellular environment. This vesicle is known as a coated vesicle because it's coated with a protein, the clathrin protein that helps to regulate the receptor mediated endocytosis mechanism.