Cell Transport - Biology PDF

CELL TRANSPORT  Active / passive transport Co-transport Main points Facilitated transport Vesicular transport Transport across the cell membrane Lipid bilayer of cell membranes restricts the passage of most polar molecules Specialized me...

CELL TRANSPORT  Active / passive transport Co-transport Main points Facilitated transport Vesicular transport Transport across the cell membrane Lipid bilayer of cell membranes restricts the passage of most polar molecules Specialized membrane transport proteins Two main classes of membrane transport proteins: Transporters and channels Transporters and channel proteins A transporter alternates between two conformations, so that the solute-binding site is sequentially accessible on one side of the bilayer and then on the other. A channel protein forms a pore across the bilayer through which specific solutes can passively diffuse. Cell transport  The movement of materials in and out of cells (cell transport) can be passive or active  Passive Transport: Does NOT require energy  Active Transport: Requires energy  Different forms of membrane transport and the influence of the membrane. Passive transport down a concentration gradient (or an electrochemical gradient— see B below) occurs spontaneously By diffusion: through the lipid bilayer directly or through channels or passive transporters. Active transport requires an input of metabolic energy Mediated by transporters that pump the solute against its concentration or electrochemical gradient. TRANSPORTERS AND ACTIVE MEMBRANE TRANSPORT  Transporters functioning as uniporters, symporters and antiporters Please watch this video for animated explanation of these transporters and which need ATP: https://app.jove.com/embed/player?id=11874&access=a43f7b574e&t=1&s=1&fpv=1  Transporters functioning as uniporters, symporters and antiporters Uniporters transport molecules down the concentration gradient (from high to low concentration), and so do not need energy to work. Symporters and antiporters do use energy (from ATP), and transport two molecules – either both in the same direction (symporters) or in opposite directions (antiporters)  CO-TRANSPORT: MECHANISM OF GLUCOSE TRANSPORT FUELED BY A NA+ GRADIENT Sodium Glucose Co-transporter: binds extracellular sodium ions (moving down the concentration gradient) which increases affinity to glucose. Once glucose binds the protein changes conformation and releases the sodium in the cytoplasm (again, following the concentration gradient). This lowers the affinity to glucose, releasing it into the cytoplasm. Note that glucose moves against the concentration, going from low concentration to high concentration. CO-TRANSPORT: MECHANISM OF GLUCOSE TRANSPORT FUELED BY A NA+ GRADIENT Please watch this video, as it is important to show the nature of co transport and the energy here is electrochemical as opposed to ATP: https://app.jove.com/embed/player?id=10707&access=b84359ef06&t=1&s=1&fpv=1  THREE TYPES OF ATP-DRIVEN PUMPS Please watch this for the different ATP driven pumps: https://app.jove.com/embed/player?id=11877&access=610c5daef0&t=1&s=1&fpv=1 for P-type pump: https://app.jove.com/embed/player?id=12217&access=8d46bc64e0&t=1&s=1&fpv=1 For ABC transporter: https://app.jove.com/embed/player?id=11878&access=21f40ea264&t=1&s=1&fpv=1  THREE TYPES OF ATP-DRIVEN PUMPS ATP-driven pumps are divided into four groups. P-type pumps are widely used for ion transport across bacteria, plants and animals, and ABC transporters perform the same function for small molecules such as amino acids and sugars. V-type and F-type transporters are more specialist, and transport protons (hydrogen ions) for acidification of plant vacuoles (V-type) and formation of ATP in mitochondria (F-type) – note the F-type takes in ADP and releases ATP, not the other way around!  E Exocytosis and Endocytosis Exocytosis - a transport vesicle fuses with the plasma membrane. Its content is released into the extracellular space, while the vesicle membrane (red) becomes continuous with the plasma membrane. Endocytosis - a plasma membrane patch (red) is internalized, forming a transport vesicle. Its content derives from the extracellular space.