biological membranes

• The fused site opens, releasing the substance.
• The role of the cell surface membrane is to regulate transport of substances into and out of the cell, separate cell’s internal components and external environment, and allow cell to change or maintain shape.
• The cell surface membrane contains antigens for self-recognition by immune cells and receptors for cell signalling and communication.
• The cell surface membrane may release chemicals or signalling and may contain enzymes for metabolic pathways.
• The role of organelle membranes is to divide cells into compartments to make organelles self-contained and more efficient, regulate transport of materials in and out of cell, and may be site of chemical reactions.
• The cell surface membrane has a fluid mosaic model structure, with phospholipids that can move somewhat and proteins embedded in the membrane of different shapes and sizes.
• Not all cells have the same composition of proteins and lipids.
• Factors affecting membrane structure and permeability include solvents, temperature, and number of unsaturated fatty acids.
• Phospholipids have a hydrophobic tail and a hydrophilic head, therefore they will never move the tail into an aqueous environment.
• Phospholipids allow small, non-polar substances to diffuse through and prevent large polar substances from diffusing through.
• Proteins help during active transport through channel and carrier proteins, help cells adhere to each other, provide structural support, and act as antigens, cell receptors, neurotransmitters for enzymes, and receptors for hormones.
• Glycolipids are lipids joined to a polysaccharide (carbohydrate) and serve as a cell surface receptor for cell recognition and attaching to other cells to form tissues.
• Glycoproteins are proteins attached to a polysaccharide (carbohydrate) and serve as a cell surface receptor for cell recognition, helping in active transport, and acting as antigens.
• Intrinsic proteins are proteins which span the entire width of the cell surface membrane.
• Carrier proteins are proteins which change shape as the molecule pushes through.
• Channel proteins form a channel through which large, polar substances can easily pass through.
• Extrinsic proteins are proteins which do not span the entire width of the cell surface membrane and can be joined to an intrinsic protein or be free on the surface.
• On the extracellular side, usually glycoproteins serve as cell recognition, act as cell receptors, receptors for hormones, and neurotransmitters for enzymes.
• Facilitated diffusion is the net movement of polar molecules from an area of high concentration to low concentration, with the aid of carrier and channel proteins.
• Water moves into the cell by osmosis.
• Osmosis is the net movement of water molecules from an area of high concentration to low concentration through a partially permeable membrane.
• Factors affecting simple diffusion include temperature, diffusion distance, surface area, size of diffusing molecule, concentration gradient, and the presence of carrier proteins.
• A membrane-bound vesicle, containing the substance, is moved towards the cell surface membrane.
• On the cytosolic side (facing inside the cell, to the cytoplasm), cell signalling is used in chemical reactions inside the cell.
• Active transport is the net movement of a substance from an area of low concentration to an area of high concentration, using ATP energy and carrier proteins.
• Carrier proteins have specific regions that combine reversibly with only certain solute molecules/ions, and also have a region that binds to and allows the hydrolysis a molecule of ATP to release energy.
• Fat-soluble molecules like steroid hormones can diffuse through as they dissolve in the bilayer.
• The concentration gradient is maintained as many molecules enter the cell, then pass into organelles where they are used for metabolic reactions.
• Molecules bind to the pump, ATP binds to the pump, and is hydrolysed, energy released enables protein to change its shape so that the molecules are transported.
• Types of transport through the cell surface membrane include simple diffusion, facilitated diffusion, osmosis, active transport, and bulk transport.
• A segment of the plasma membrane encloses the particle and brings into the cell enclosed in a vesicle.
• Aquaporins are specific water channel proteins needed to allow water molecules to move through.
• Water potential is a measure of the tendency of water molecules to diffuse from one region to another, with pure water potential being 0kPa, and water potential decreasing and becoming a negative number as the concentration of the solute increases.
• The cell surface membrane and the membrane of the vesicle fuse together.
• In animal cells, cell is cytolysed (bursts open) when water moves in.
• In plant cells, cell becomes turgid when water moves in.
• Simple diffusion is the net movement of a substance from an area of high concentration to low concentration, does not require energy, and the cell surface membrane is partially permeable, allowing only small, nonpolar molecules like oxygen and carbon dioxide to diffuse through.
• Endocytosis is the movement of molecules into the cell by active transport.
• Cells can control the types of molecules that pass through the membrane by having different proportions of channel and carrier proteins.
• Exocytosis is the movement of molecules out of the cell by active transport.