Membranes and Membrane transport

• Membranes and Membrane Transport are a part of the theme Form and Function.
• Cells are the level of organisation for Lipid Bilayer, Phospholipids, Polar, Nonpolar, Hydrophobic, Hydrophilic, Amphipathic, Kinetic Theory, Simple Diffusion, Facilitated Diffusion, Concentration Gradient, Osmosis, Passive Transport, Integral Proteins, Transmembrane proteins, Peripheral Proteins.
• Phospholipids are composed of two fatty acid chains and a phosphate bonded to a glycerol molecule, with the fatty acid tails being nonpolar and hydrophobic, and the phosphate head being hydrophilic.
• Phospholipids are amphipathic, having hydrophobic and hydrophilic regions.
• Sodium-dependent glucose cotransporters are an example of indirect active transport.
• Cell-adhesion molecules (CAMs) are used for different types of cell–cell junctions.
• Endocytosis and exocytosis are examples of membrane fusion and formation processes.
• Nicotinic acetylcholine receptors are an example of a neurotransmitter-gated ion channel.
• Sodium and potassium channels are examples of voltage-gated channels.
• Cholesterol molecules are positioned in membranes and act as a modulator of membrane fluidity, stabilizing membranes at higher temperatures and preventing stiffening at lower temperatures.
• Sodium–potassium pumps are an example of exchange transporters.
• The tails of phospholipids can be saturated or unsaturated fatty acids.
• Phospholipids naturally form bi-layers when added to water, with the hydrophilic phosphate heads facing water, and the hydrophobic fatty acid tails in the middle of the bilayer.
• All membranes in cells are composed of a phospholipid bilayer.
• The phospholipid bilayer of plasma membranes separates the cytoplasm and cell contents from the environment, acts as a barrier for materials entering and exiting the cell, and allows only hydrophobic (uncharged) particles to pass through the hydrophobic fatty acid tails at the centre of the bilayer.
• Kinetic theory states that particles are in constant motion, with particles in gases, liquids and solutes in aqueous solutions moving in random directions.
• The random movement of particles allows diffusion and osmosis to occur, which are passive processes in cells as the cell does not provide any energy to move particles.
• Simple diffusion is the passive transport of particles from a region of high concentration to a region of low concentration, using no energy from the cell.
• Small uncharged particles (such as O2 and CO2) and fat soluble molecules (such as hydrophobic steroids) can diffuse across plasma membranes.
• Oxygen diffuses directly from the alveoli into the blood, and carbon dioxide diffuses directly from the blood into the alveoli of the lungs.
• Hydrophilic, charged particles cannot pass directly through cell membranes.
• Integral proteins are permanently attached to the plasma membrane, and penetrate into the centre of the phospholipid bilayer.
• Integral proteins contain a hydrophobic section (within the fatty acid tails) and two hydrophilic sections (one at each surface of the bilayer).
• Saturated Fatty Acids, Unsaturated Fatty Acids, Cholesterol, Steroid, Vesicles, Bulk Transport, Exocytosis, Endocytosis, Gated Ion Channels, Voltage Gated Ion Channels, Ligand Gated Ion Channels, Ligand, Acetylcholine, Potential Difference (Voltage), Sodium Potassium Pump, Exchange Transporter, Resting Potential, Axon, Cotransporters, Epithelial Cells, Cell Adhesion Molecules, Tissues, Cell Junctions, Tight Junctions, Gap Junctions, Adherens Junctions, Desmosomes.
• During the indirect active transport of glucose from the small intestine into epithelial cells, sodium ions (Na+) are actively pumped out of epithelial cells by the sodium potassium pump, resulting in a low concentration of Na+ in epithelial cells.
• Tissues are groups of cells that work together to carry out a function, and if a tissue is to carry out its function, the cells in the tissue must be able to adhere to each other.
• The extracellular matrix is composed of chemicals released by the cell, which form a gel-like material that supports cells.
• Sodium ions and glucose bind to the sodium-dependent glucose cotransporter protein, causing the protein to change shape, moving both glucose and sodium into an epithelial cell.
• Cell junctions are protein complexes that provide adhesion between animal cells.
• Cell adhesion is the process by which a cell uses a combination of an extracellular matrix and cell-adhesion molecules (CAMs) to adhere to other cells, and is required for development and maintenance of tissues, cell to cell communication, and cell regulation.
• The transport of glucose depends on the active transport of sodium out of the epithelial cells.
• There are a range of cell adhesion molecules (CAMs) which are used for different types of cell junctions: Tight junctions form a seal between cells, preventing substances leaking between the cells, Gap junctions are channels between cells that allow molecules to pass between cells, allowing cell communication, Adherens junctions use protein complexes to connect cells together, Desmosomes use protein complexes to form strong connections between cells, providing tissues with structural integrity.
• Cell adhesion molecules (CAMs) are a range of proteins which are used in different cell junctions.
• Lipid bilayers form continuous sheet-like structures in water due to the hydrophobic hydrocarbon chains that form their core.
• Facilitated diffusion and active transport allow selective permeability in membranes.
• Integral proteins are embedded in one or both of the lipid layers of a membrane.
• Movement of water molecules across membranes by osmosis involves aquaporins.
• Peripheral proteins are attached to one or other surface of the bilayer.
• Saturated fatty acids have higher melting points and make membranes stronger at higher temperatures.
• Lipid bilayers function as effective barriers between aqueous solutions due to the hydrophobic hydrocarbon chains that form their core.