Videos made in Blender by Thomas Adams
Small molecules can pass through the cell membrane in a process called simple diffusion. Diffusion of molecules flows with the concentration gradient of molecules going from high to low concentration. Simple diffusion is a type of passive transport, meaning that it requires no energy and flows with the concentration gradient. In the example below, Carbon Dioxyde (CO2) diffuses through the plasma membrane. The arrow indicates the concentration gradient.
Facillitatied diffusion is for molecules that are either too large to pass through the membrane or if it has a polar charge. These molecules can pass through the membrane thanks to channel and carrier protiens. Facilitated diffusion is sitll a type passive diffusion, meaning that it takes no energy and flows with the concentration gradient. In the example, Water (H2O) passes through a auqaporin. Aquaporins are specialised channel protiens that speed up the passive transport of H2O molecules.
Video 3 and 4 are both types of active transport, requiring energy in the form of ATP and go against the concentration gradient. The example below is a sodium potassium pump both the sodium potassium pump and the proton pump are used to create an electrical gradient by pumping out positive ions, this is used often by nerve cells to send pulses. In the video an arrow shows the concentration gradient for sodium and potassium. Both the arrow for sodium and the sodium molecules are green. The arrow potassium and the potassium molecules are orange. First 3 sodium ions enter the pump, then an ATP (Adenosine Triphosphate) molecule approches the pump. The third phosphate in the chain breaks off into the pump, releasing the energy stored in the bond. The pump changes shape openin up on the extracellular space side, releasing the sodium ions. Next 2 potassium ions enter the pump, the singe phosphate breaks off from the pump. The pump changes back to its original state releasing the potassium ions, ready to do it all again.
The Proton pump is also used to maintain an electrical gradient like the sodium potassium pump. A proton pump can be used to maintain a 100 fold gradient between a lysosome and the cytoplasm of a cell. In the example below a proton pump is being used on the plasma membrane of a cell. The blue spheres are hydrogen ions and the arrow indicates the concentration gradient. First the hydrogen ion enters the pump, next an ATP molecule breaks its bond, releasing energy. The engery makes the protien squeeze the ion out of the cell.
Phagocytosis is the process in which a cell can engulf solids or even other cells and organisms. In the example below, a bacterium gets engulfed by a white blood cell. When a Pathogen-Associated Molecular Pattern (PAMP) attaches to one of the receptors on the cell membrane it recognizes that there is a bacterium in front of it, that is step 1. Step 2. The cell membrane will then engulf the bacterium and create a vesicule or sac that can the moved aroun the cell. Finaly in Step 3. a Lysosome comes and fuses with the vesicule to release its enzymes so it can kill and break down the bacterium.
Small molecules like can pass through the cell membrane individualy in a process called simple diffusion but pinocytosis however is much quicker due to the fact that the cell can take in a group of molecules. In this example a cell in a human intestinal wall absorbs nutrients from food. Step 1. receptors in the cell membrane detect the desired molecules in the Extracellular Matrix (ECM). Step 2. Psuedo pods extend out creating a pocket. Step 3. the pocket is closed traping liquid inside. Step 4. The closed or pocket or vesicule now is moved inside the cell where it can be moved to do many different things.
Exocytosis is the opposite of endocytosis (Phagocytosis and Pinocytosis). It takes waste and ejects it from the cell, it also however transports importants substances made in the cell so it can be taken to other cells. In the example below the digested waste from the bacterium digested in the Phagocytosis video is ejected from the cell. The vesicule simply fuses with the plasma membrane, releases the fluids and becomes part of the membrane again.