CELLS MOVEMENT ACROSS THE MEMBRANE

Plasma Membrane STRUCTURE This is the boundary between the cell cytoplasm & the environment Is selectively permeable Here we see a cross section of the cell membrane you should notice two different structures: The phospholipids are the round yellow structures with the blue tails The proteins are the lumpy structures that are scattered around among the phospholipids.

Plasma Membrane STRUCTURE This is a simple representation of a phospholipid. The yellow structure represents the hydrophilic or water loving section. The blue tails that come off of the sphere represent the hydrophobic or water fearing end.

Plasma Membrane FUNCTION Controls movementControls movement of substances in & out of the cell recognitionForms a recognition site so that the body’s immune system can recognize its own cells receptor siteActs as a receptor site for the attachment of specific hormones and neurotransmitters.

Plasma Membrane FUNCTION Not fixed – Proteins float Three categories –Marker –Receptor –Transport

Membrane Proteins MARKER PROTEINS IdentifyIdentify the cell The immune system uses these proteins to tell friendly cells from foreign invaders. They are as unique as fingerprints. They play an important role in organ transplants. If the marker proteins on a transplanted organ are different from those of the original organ the body will reject it as a foreign invader

Membrane Proteins RECEPTOR PROTEINS intercellular communication.These proteins are used in intercellular communication. In this animation you can see the a hormone binding to the receptor. This causes the formation of a second messenger second messenger signal moleculeThe second messenger acts as a signal molecule releasing a signal to perform some action.

Membrane Proteins TRANSPORT PROTEINS Two Forms Carrier proteins are do not extend all the way through the membrane. They move specific molecules through the membrane one at a time. Channel proteins extend through the bi-lipid layer. They form a pore through the membrane that can move molecules in several ways.

How do molecules cross the plasma membrane? Passive transportPassive transport – movement that requires no energy from the cell Active transportActive transport – movement that requires energy from the cell Endocytosis and exocytosisEndocytosis and exocytosis – a special type of active transport

CELLS PASSIVE TRANSPORT cell uses no energy molecules move randomly concentration is from high to low three types SIMPLE DIFFUSION FACILITATED DIFFUSION OSMOSIS high low Weeee!! !

Molecules are always moving Molecules move randomly and bump into each other and other barriers

Diffusion occurs because the particles in gases and liquids are moving.

Particles in a liquid or gas spread out… … from regions of high concentration… … to regions of low concentration… …until the particles are evenly spread out. Dissolving KMnO 4 crystal DIFFUSION

High concentration gradient Fast rate of diffusion Low concentration gradient Slow rate of diffusion The difference between the regions of high concentration and low concentration is called the concentration gradient

Concentration gradient Concentration Gradient - change in the concentration of a substance from one area to another.

Diffusion will continue until equilibrium is reached. This means there will be an equal distribution of molecules throughout the space. This is why food coloring moves throughout a beaker of water; why odors smell strong at first and then disappear over time. Equilibrium, a result of diffusion, shows the uniform distribution of molecules of different substances over time as indicated in the above diagram.

WHAT AFFECTS DIFFUSION? Movement of molecules from an area of high concentration to an area of lower concentration. Factors that affect the rate of diffusion: size of molecules, size of pores in membrane, temperature, pressure, and concentration.

transport proteinsDiffusion using transport proteins found in the membrane CHANNEL PROTEINS In some cases they act in passive transport. Molecules diffuse randomly through the opening, requiring no energy, moving from an area of high concentration to an area of low concentration. ion channelExample: ion channel Passive Transport: Facilitated Diffusion

A semi-permeable membrane will allow certain molecules to pass through it, but not others. Generally, small particles can pass through… Partially permeable membrane …but large particles cannot SEMI-PERMEABLE MEMBRANES

Partially-permeable membrane More free water molecules on this side of membrane Water-solute particle is too large to pass through membrane Free water molecules diffuse in this direction

Diffusion of waterDiffusion of water through a selectively permeable membrane Water moves from high to low concentrations Water is so small and there is so much of it the cell can’t control its movement through the cell membrane. Water moves freely through pores. Solute (green) too large to move across. OSMOSIS

Hypotonic Solution The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water) Result: Water moves from the solution to inside the cell. The cell swells and bursts open (cytolysis)! Osmosis Animations for isotonic, hypertonic, and hypotonic solutionsOsmosis

Hypertonic Solution The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water) Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)! Osmosis Animations for isotonic, hypertonic, and hypotonic solutionsOsmosis shrink s

Isotonic Solution The concentration of solutes in the solution is equal to the concentration of solutes inside the cell. Result: Water moves equally in both directions and the cell remains same size! (Equilibrium) Osmosis Animations for isotonic, hypertonic, and hypotonic solutionsOsmosis

What type of solution are these cells in ? A CB HypertonicIsotonicHypotonic

How Organisms Deal with Osmotic Pressure Paramecium (protist) removing excess water videoParamecium (protist) removing excess water video Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called tugor pressure. Protists like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding. Salt water fish pump salt out of their specialized gills so they do not dehydrate. Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.

CELLS ACTIVE TRANSPORT high low This is gonna be hard work!! Cell uses energy Actively move molecules to where they are needed Concentration is from low to high Three types PROTEIN PUMPSPROTEIN PUMPS EXOCYTOSISEXOCYTOSIS ENDOCYTOSISENDOCYTOSIS

Active Transport 1. Protein Pumps transport proteinsSome transport proteins actively use energy from ATP in the cell to drag molecules from area of low concentration to areas of high concentration (working directly against diffusion) sodium/potassium pump.An example of this is the sodium/potassium pump. Here the energy of a phosphate (shown in red) is used to exchange sodium atoms for potassium atoms. Sodium Potassium Pumps Sodium Potassium Pumps (Active Transport using proteins) Protein changes shape to move molecules: this requires energy!

Active Transport 2. Endocytosis Taking large molecules into a cell Uses energy Cell membrane in-folds around food particle “cell eating” Forms food vacuole & digests food This is how white blood cells eat bacteria!

Active Transport 3. Exocytosis Forces large molecules out of cell Membrane surrounding the material fuses with cell membrane Cell changes shape – requires energy Hormones or wastes released from cell Endocytosis & Exocytosis Endocytosis & Exocytosis animations