Presentation on theme: "Ch 5 Membrane Structure and Function Control the movement of materials into and out of the cell."— Presentation transcript:
Ch 5 Membrane Structure and Function Control the movement of materials into and out of the cell.
Membrane Structure Phospholipids: arranged in a bilayer due to polarity of molecule. Glycolipids: Similar to phospholipids mono or polysaccharides instead of phosphates. Cell to cell communication Cholesterol: lipid found in animal plasma membranes, reduces permeability and provides rigidity.
Membrane structure Fluid Mosaic Model: The composition of phospholipids will contribute to the degree of permeability, and the proteins are free to move laterally w/in the plasma membrane.
QOD 1. How would you expect the saturation levels of membrane fatty acids to differ in plants adapted to cold environments and plants adapted to hot environments?
Answers 1. Plants adapted to cold environments would be expected to have more unsaturated fatty acids in their membranes, since those remain fluid at lower temperatures. Plants adapted to hot environments would be expected to have more saturated fatty acids, which would allow the fatty acids to “stack” more closely, making the membranes less fluid and therefore helping them to stay intact at higher temperatures.
Selective Permeability Some substances can freely move across the membrane whereas others cannot. Hydrophobic (nonpolar) molecules, such as hydrocarbons, carbon dioxide, and oxygen, can cross with ease. Small Polar molecules (H 2 O) can pass between the phospholipids
Selective Permeability contd Macromolecules cannot pass through membrane Transported by vesicle formation Transported by vesicle formation Ions and charged molecules cannot Carrier and channel proteins transport these. Carrier and channel proteins transport these. Transport across the plasma membrane includes: Passive transport Facilitated transport Active transport Membrane assisted
Passive Transport Diffusion: The spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area. The diffusion of a substance across a biological membrane = passive transport The diffusion of a substance across a biological membrane = passive transport
Note that each substance diffuses down its own concentration gradient, unaffected by the concentration differences of other substances
Passive Transport contd Osmosis: The diffusion of water across the plasma membrane. Solutions: a liquid that is a homogeneous mixture of two or more substances. Has 2 parts 1. Solvent: The dissolving agent of a solution (liquid portion). Water is the most versatile solvent known. 2. Solute: A substance that is dissolved in a solution.
Passive Transport contd Tonicity: The ability of a solution to cause a cell within it to gain or lose water. 3 types Hypertonic: A solution with a higher concentration of solute than inside the cell. Water diffuses out. Water diffuses out. Hypotonic: A solution with a lower concentration of solute than inside the cell. Water diffuses into. Water diffuses into. Isotonic: A solution with equal concentrations of solute on both sides of the membrane. No net movement of water into or out of. No net movement of water into or out of.
Turgid: A walled cell becomes turgid if it has a greater solute concentration than its surroundings, resulting in entry of water. (turgor pressure) (Tonicity?) Plasmolysis: A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment. Crenate
Transport by Proteins Molecules that cannot diffuse across the plasma membrane, can be transported by integral membrane proteins. Channel & Carrier Proteins: Specific to the molecule they transport Required for facilitated and active transport. Required for facilitated and active transport.
Facilitated Transport An integral protein (channel or carrier) assists the movement of a molecule down its concentration gradient.
Facilitated Diffusion Increases the rate at which the solute crosses the plasma membrane Faster than diffusion Faster than diffusion
Active Transport The movement of molecules against their concentration gradient
Active Transport Movement from low concentration to high concentration. Requirements: Transport protein (specific) aka pumps Energy (ATP)
The sodium–potassium pump: a specific case of active transport. The sodium–potassium pump: a specific case of active transport. -pumps ions against steep concentration gradients -Sodium ion concentration (represented as [Na+]) is high outside the cell and low inside, while potassium ion concentration ([K+]) is low outside the cell and high inside. -The pump oscillates between two conformational states in a pumping cycle that moves three sodium ions out of the cell for every two potassium ions pumped into the cell. - ATP powers the changes in conformation by phosphorylating the transport protein (that is, by transferring a phosphate group to the protein). Fig 5.11
Proton pumps, the main electrogenic pumps of plants, fungi, and bacteria, are membrane proteins that store energy by generating voltage (charge separation) across membranes.
Membrane Assisted Transport The formation of vesicles by the plasma membrane to enable the transport of macromolecules (too big for transport proteins) - Bulk transport
Membrane Assisted Transport Exocytosis: “out of cell” Vesicles (formed by Golgi) fuse with plasma membrane to secrete specific molecules to external environment.
Membrane Assisted Transport Endocytosis: “into cell” invagination and pinching off of plasma membrane to form a vesicle to take in certain substances into cell. Types: Phagocytosis: “cell eating” solids such as food particles or other cells. Phagocytosis: “cell eating” solids such as food particles or other cells. Pinocytosis: “cell drinking” liquids. Pinocytosis: “cell drinking” liquids.