2.5 Bio membranes

• The hydrophilic heads of the phospholipids orient towards the surface of the bilayer and interact with surrounding water molecules.
• Membrane proteins are embedded within the lipid bilayer, with some extending through it to both sides.
• The fluid mosaic model describes the structure of cellular membranes.
• Biological membranes act as a barrier, regulating the movement of substances in and out of cells.
• Cholesterol is embedded within the lipid bilayer, stabilizing it by preventing excessive fluidity or rigidity.
• Glycolipids are carbohydrate-containing lipids found on the outer surfaces of cells, particularly those of nerve cells and red blood cells.
• Glycolipids and glycoproteins have carbohydrate chains attached to either lipids or proteins on the outer surfaces of cells.
• Cell signaling involves communication between cells using chemical signals called ligands.
• Membrane proteins are responsible for transporting materials across the membrane.
• Integral proteins can be transmembrane (spanning through the whole membrane) or glycoproteins (attached to carbohydrates).
• Cell recognition involves identifying other cells based on differences in carbohydrate composition.
• Carbohydrates can be used for identification purposes due to their specificity.
• Exocytosis releases materials into the extracellular environment via fusion with the plasma membrane.
• Channel proteins allow specific molecules to pass through them directly without being bound first.
• Carrier proteins bind with specific molecules and undergo conformational changes to facilitate their passage across the membrane.
• The plasma membrane has two layers of phospholipids with hydrophilic heads facing outward and hydrophobic tails facing inward.
• Endocytosis is the process by which substances enter the cell from outside, involving vesicles that pinch off from the plasma membrane.
• Phagocytosis is the engulfment of large particles such as bacteria or dead cells.
• Pinocytosis is the uptake of small molecules and fluids.
• Active transport requires energy input, such as ATP hydrolysis, to move substances against their concentration gradient.
• Passive transport does not require energy input and occurs down the concentration gradient.
• Ion channel proteins selectively allow certain types of ions to move through the cell membrane.
• Osmosis is the movement of water from an area of high water potential to low water potential.
• specific substances such as large non-polar molecules (lipid soluble), small polar molecules, and molecules without charge (ions) can pass through the phospholipid bilayer without the use of proteins.
• A hypertonic solution is when the water potential is higher on the inside of the cell body than on the outside, causing the cell to shrink as the water moves out of the cell by osmosis.
• A hypotonic solution is when the water potential is higher outside of the cell, causing water to move into the cell by osmosis.
• An isotonic solution has equal water potential in the cell body and in the extracellular environment meaning there is no net movement of water across the membrane.
• when an animal cell is placed into the hypertonic solution it will become crenated.
• when an animal cell is placed into a hypotonic solution it will undergo cytolysis.
• when a plant cell is placed in a hypertonic solution is will be plasmolysed and become flaccid.
• When a plant cell is placed in a hypotonic solution it becomes turgid.
• when a plant or animal cell is placed in an isotonic solution, nothing will happen as there is no net movement.