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Transcript
3.3 Cell Membrane KEY CONCEPT The cell membrane is a barrier that separates a cell from the external environment. 3.3 Cell Membrane Cell membranes are composed of two phospholipid layers. The fluid mosaic model is used to describe the structure of the cell membrane. Video: 3.3 Cell Membrane The cell membrane has two major functions. 1. forms a boundary between inside and outside of the cell 2. controls passage of materials into and out of the cell cell membrane inside cell outside cell 3.3 Cell Membrane The cell membrane is made of a phospholipid bilayer. • The phosphate “head” is polar. Water is polar. Therefore, they form hydrogen bonds with each other. • The fatty acid “tails” are non-polar and therefore repelled by water (hydrophobic). 3.3 Cell Membrane The cell membrane is made of a phospholipid bilayer. • There are other molecules embedded in the membrane. – Protein, cholesterol, carbohydrates cell membrane carbohydrate chain cholesterol protein protein channel protein 3.3 Cell Membrane Cholesterol’s role in the cell membrane Cholesterol is found in every cell of your body. It helps maintain the integrity of these membranes, and plays a role in facilitating cell signaling-- meaning the ability of your cells to communicate with each other. Cholesterol helps prevent extremes-- whether too fluid, or too firm-in the consistency of the cell membrane. Infer: Note that cholesterol is located between the fatty acid chains. Do you think cholesterol is polar or nonpolar? Explain your answer. 3.3 Cell Membrane The cell membrane is selectively permeable. - Some molecules can cross the membrane while others cannot. Connect: Describe a semipermeable membrane with which you are already familiar. 3.3 Cell Membrane Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. – Receptor is a protein that detects a signal molecule and performs and action in response. A ligand is the molecule the receptor binds to. Specific receptors bind to specific ligands. • There are two types of receptors. 1. intracellular receptor – “within, or inside, a cell” – are generally nonpolar – small in size -- Example: hormones can interact with the nucleus to turn on genes to make needed proteins. 3.3 Cell Membrane Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • There are two types of receptors. 2. membrane receptor •Cannot cross the membrane •The receptor sends the message to the cells interior by changing its shape •Example: receptors in red blood cells trigger processes to CO2 from the body tissues to the lungs Contrast: How do intracellular receptors differ from membrane receptors?