B2.1 Membranes and Membrane Transport

• Phospholipids are composed of two fatty acid chains and a phosphate bonded to a glycerol molecule.
• The fatty acid tails are nonpolar and are hydrophobic.
• The phosphate head is charged and is hydrophilic.
• Phospholipids are amphipathic, as they have hydrophobic and hydrophilic regions.
• All membranes in cells are composed of a phospholipid bilayer.
• The phospholipid bilayer acts as a barrier for materials entering and exiting the cell.
• kinetic theory states that particles are in constant motion.
• Diffusion and osmosis are passive processes in cells, as the cell does not provide any energy to move particles.
• Diffusion is the passive transport of particles from a region of high concentration to a region of low concentration.
• Integral proteins are permanently attached to the plasma membrane, they can be glycoproteins, channels, or protein pumps.
• Peripheral proteins are temporarily attached to one side of the membrane. They can be receptors and enzymes.
• Osmosis is the passive transport of water molecules from a region of low solute concentration to a region of high solute concentration through a semipermeable membrane.
• Aquaporins are integral channel proteins that selectively transport water rapidly through membranes. This speeds up the process of osmosis.
• Osmosis through aquaporins is an example of facilitated diffusion.
• Facilitated diffusion is the passive transport of molecules from a region of high concentration to a region of low concentration through channel proteins.
• ATP stands for adenosine triphosphate
• Active transport is the movement of particles from a region of low concentration to a region of high concentration using protein pumps and ATP energy.
• Facilitated diffusion is a selective process, as only specific particles can pass through the protein channels.
• Active transport is a selective process as protein pumps are specific to the particles that they can transport.
• Simple diffusion is not a selective process, as any small or hydrophobic particle is able to pass through the phospholipid bilayer.
• Glycoproteins are membrane proteins with a carbohydrate chain attached.
• Glycolipids are phospholipids with a a carbohydrate chain attached.
• glycoproteins and glycolipids act as receptors for hormones, they allow cell to cell communication through neurotransmitters, they provide the cell with immune response to distinguish between self and non-self, as well as cell to cell adhesion.
• Antigens are substances which stimulate an immune response and the production of antibodies.
• the fluid mosaic model is used to describe the structure of phospholipid bilayers.
• Saturated fatty acids have single bonds between the carbons on the hydrocarbon chain. They are linear with high melting points.
• Unsaturated fatty acids have at least one double bond between carbons on the hydrocarbon chain. They bend at the position of the double bond and have low melting points.
• cholesterol is a modulator
• Cholesterol helps regulate the fluidity of the membrane.
• At higher temperatures, cholesterol reduces fluidity and melting point of phospholipids, resulting in stable membranes.
• At lower temperatures, the presence of cholesterol between phospholipids maintains fluidity of the membrane and prevents crystallization of the phospholipids.
• Antigens are substances which stimulate an immune response and the production of antibodies.
• Glycoproteins and glycolipids act as antigens if the carbohydrate chain is not recognized as self by the immune system.
• bulk transport is considered endocytosis and exocytosis
• vesicles transport materials within cells
• exocytosis is the release of large particles from a cell. It involves the fusion of a vesicle with the plasma membrane, releasing the content outside of the cell.
• Endocytosis is the process of which large particles enter the cell. The large particles are surrounded by the plasma membrane, which buds off inside the cell to form a vesicle. (formation)
• bulk transport (endocytosis and exocytosis) are active processes requiring ATP energy.
• Tissues are groups of cells that work together to carry out a function.