The Plasma Membrane

Plasma Membrane The outer layer of a cell is semi-permeable. Semi-permeable means that only certain molecules can pass through it.

Plasma Membrane Has two layers of lipid molecules -Phospholipid bilayer Polar heads point to the outside (Phosphate head) Non-polar (straight) tails form the inside of the membrane http://www.wisc-online.com/objects/index_tj.asp?objid=AP1101 1. The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism’s cells. As a basis for understanding this concept: a. Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings. The plasma membrane consists of two layers of lipid molecules organized with the polar (globular) heads of the molecules forming the outside of the membrane and the nonpolar (straight) tails forming the interior of the membrane. Protein molecules embedded within the membrane move about relative to one another in a fluid fashion. Because of its dynamic nature the membrane is sometimes referred to as the fluid mosaic model of membrane structure. Cell membranes have three major ways of taking in or of regulating the passage of materials into and out of the cell: simple diffusion, carrier-facilitated diffusion, and active transport. Osmosis of water is a form of diffusion. Simple diffusion and carrier-facilitated diffusion do not require the expenditure of chemical bond energy, and the net movement of materials reflects a concentration gradient or a volt-age gradient or both. Active transport requires free energy, in the form of either chemical bond energy or a coupled concentration gradient, and permits the net transport or “pumping” of materials against a concentration gradient.

Fluid Mosaic Membrane Its called a fluid mosaic membrane because it is a mosaic of different kinds of molecules. These include: lipids protein carbohydrate chains

The 3 Ways a Cell regulates what comes into a cell: Simple Diffusion – some materials move into and out of the cell without using energy. Carrier Facilitated Diffusion – movement into the cell through a protein in the plasma membrane Active Transport – use energy in the form of ATP to move other molecules into and out of the cell Cell membranes have three major ways of taking in or of regulating the passage of materials into and out of the cell: simple diffusion, carrier-facilitated diffusion, and active transport. Osmosis of water is a form of diffusion. Simple diffusion and carrier-facilitated diffusion do not require the expenditure of chemical bond energy, and the net movement of materials reflects a concentration gradient or a volt-age gradient or both. Active transport requires free energy, in the form of either chemical bond energy or a coupled concentration gradient, and permits the net transport or “pumping” of materials against a concentration gradient.

Comparison of Active Transport and Passive Transport (continued) Most solutes can cross the membrane only if there is a carrier protein or a channel protein to transfer them. Passive transport, in the same direction as a concentration gradient, occurs spontaneously, whereas transport against a concentration gradient (active transport) requires an input of energy. Only carrier proteins can carry out active transport, but both carrier proteins and channel proteins can carry out passive transport

Diffusion In a solution, molecules move constantly. They collide with each other and tend to spread out randomly. The molecules tend to move from an area where they are more concentrated to an area where they are less concentrated, a process known as diffusion. http://programs.northlandcollege.edu/biology/Biology1111/animations/dissolve.html

Diffusion Diffusion "goes from the higher concentration side to the lower concentration side". There is no energy input to cause diffusion; It simply occurs due to the random motion of the substance moving across the plasma membrane.

Diffusion Even after the solution has reached equilibrium, individual molecules continue to move rapidly across the membrane in both directions.

Osmosis Diffusion of water through a semi-permeable membrane. Not all substances can cross cell membranes. If something can cross the cell membrane then the membrane is permeable. The cell membrane is described as being selectively permeable. Cell membranes are selectively permeable, which means that some substances can pass across them and others cannot.

Osmosis Osmosis – the diffusion of water through a selectively permeable membrane.

Carrier Facilitated Diffusion Facilitated Diffusion – movement of specific molecules across cell membranes through protein channels

Active Transport Active Transport - when material moves from an area of lower concentration to an area of greater concentration Active transport requires the cell to spend energy, usually in the form of ATP.

Review Questions The ____ of a phospholipids is polar, and the long _______ are non-polar. What does the term “selectively permeable” mean in regards to a cell membrane. What are the three major ways of taking in or of regulating the passage of materials into and out of the cell? True or False, Osmosis of water is a form of diffusion. Standard 1a. Students know cells are enclosed within semi-permeable membranes that regulate their interaction with their surroundings. The plasma membrane consists of two layers of lipid molecules organized with the polar (globular) heads of the molecules forming the outside of the membrane and the nonpolar (straight) tails forming the interior of the membrane. Protein molecules embedded within the membrane move about relative to one another in a fluid fashion. Because of its dynamic nature the membrane is sometimes referred to as the fluid mosaic model of membrane structure. Cell membranes have three major ways of taking in or of regulating the passage of materials into and out of the cell: simple diffusion, carrier-facilitated diffusion, and active transport. Osmosis of water is a form of diffusion. Simple diffusion and carrier-facilitated diffusion do not require the expenditure of chemical bond energy, and the net movement of materials reflects a concentration gradient or a volt- age gradient or both. Active transport requires free energy, in the form of either chemical bond energy or a coupled concentration gradient, and permits the net transport or pumping of materials against a concentration gradient. http://science.nhmccd.edu/biol/bio1int.htm

Warm-Up – Label the diagram with as much detail as possible. Phospholipid Phosphate Head Hydrophilic Fatty Acid Tails Hydrophobic