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Applied Science Cell Membrane

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Applied Science Cell Membrane Cell membranes Plasma Membrane Structure and Function The plasma membrane separates the internal environment of the cell from its surroundings. The plasma membrane is a phospholipid bilayer with embedded proteins. The plasma membrane has a fluid consistency and a mosaic pattern of embedded proteins. The cell-surface membrane controls the movement of substances into and out of the cell. Cell membranes are made up of…. Phospholipids Phospholipids allow…. • Lipid- soluble substances to enter and leave the cell • Prevent water-soluble substances entering and leaving the cell • Make the membrane flexible and self-sealing. Make a note of this information Proteins are also found in the bilayer…. http://www.youtube.com/watch?v=moPJkCbKjBs&feat ure=rhttp://www.youtube.com/watch?v=moPJkCbKj Bs&feature=relatedelated http://www.youtube.com/watch?v=moPJkCbKjBs&f eature=related The fluid-mosaic model of the cell-surface membrane http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter 2/animation__how_facilitated_diffusion_works.ht ml Movement across membranes Molecules can pass across membranes by: • Simple diffusion • Facilitated diffusion • Active transport The Permeability of the Plasma Membrane The plasma membrane is partially permeable. Macromolecules cannot pass through because of their size, and tiny charged molecules do not pass through the nonpolar interior of the membrane. Small, uncharged molecules such as oxygen and carbon dioxide pass through the membrane, down their concentration gradient. How molecules cross the plasma membrane Diffusion Diffusion is the passive movement of molecules from a higher to a lower concentration until equilibrium is reached. Gases move through plasma membranes by diffusion. Process of diffusion Gas exchange in the lungs occurs by diffusion Facilitated diffusion During facilitated diffusion, substances pass through a carrier protein following their concentration gradients. Facilitated diffusion does not require energy. For example, the carrier protein for glucose has two conformations and switches back and forth between the two, carrying glucose across the membrane. Facilitated diffusion of glucose Channel protein Movement of materials across a membrane may be passive or active. Passive transport does not use chemical energy; diffusion and facilitated diffusion are both passive. Active transport requires chemical energy and usually a carrier protein. Active transport During active transport, ions or molecules are moved across the membrane against the concentration gradient – from an area of lower to higher concentration. Energy in the form of ATP is required for the carrier protein to combine with the transported molecule and move it across the membrane. Active transport Transport by Carrier Proteins Some biologically useful molecules pass through the plasma membrane through channel proteins and carrier proteins that span the membrane. Carrier proteins are specific and combine with only a certain type of molecule. Facilitated diffusion and active transport both require carrier proteins. Carrier protein Carrier proteins involved in active transport are called pumps. The sodium-potassium pump is active in all animal cells, and moves sodium ions to the outside of the cell and potassium ions to the inside. The sodium-potassium pump carrier protein exists in two conformations; one that moves sodium to the inside, and the other that moves potassium out of the cell. The sodium-potassium pump FACILITATED DIFFUSION Movement from high to lower concentration Use of carrier/channel protein Proteins specific Changes shape of protein and passes through channel/membrane No energy/ATP needed ACTIVE TRANSPORT Movement against concentration gradient Use of carrier/intrinsic/pump proteins Protein specific (to ion) Energy/ATP required Energy used to change shape of proteins/attach ion to protein Ions moved through membrane as proteins change shape/position Active transport Diffusion May move substances Substances moved against concentration down concentration gradient; gradient; Requires ATP/energy; Does not require Requires membrane ATP/energy; proteins/carriers Does not (necessarily) require membrane proteins/carriers Homework – find out about the role of extrinsic proteins in a cell membrane. Be ready to explain this to a small group next lesson. Cell recognition protein In animal cells, the carbohydrate chains of cell recognition proteins are collectively called the glycocalyx. The glycocalyx can function in cell-to-cell recognition, adhesion between cells, and reception of signal molecules. The diversity of carbohydrate chains is enormous, providing each individual with a unique cellular “fingerprint”. Receptor protein Enzymatic protein Summary The structure of the plasma membrane allows it to be differentially permeable. The fluid phospholipid bilayer, its mosaic of proteins, and its glycocalyx make possible many unique functions of the plasma membrane. Passive and active methods of transport regulate materials entering and exiting cells..
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