Chapter 4: Cells and Their Environment October 29th 2007 Ms. Resendes

Question of the Day: Do you remember the definition of homeostasis? We are going to be keeping in mind this term as we learn this chapter. Write down some ways you think that cells could maintain their homeostasis?

Question of the Day Response: Cell membrane is composed of… Phospholipid bi-layer Proteins distributed Selectively permeable… Specific items are allowed to enter and exit the cell These two items are very important for a cell to maintain its homeostasis Why???

Section 4-1: Passive Transport (Random motion and concentration) Controlling the movement of substances into and out of the cell Passive Transport (break it down) Movement of particles across cell membrane that does not require energy to do so Items do not randomly enter or exit the cell membrane– homeostasis would never be maintained in this case

Random motion and concentration continued Concentration gradient (necessary) A difference in concentration of a substance High to low Example: Room filled with balls Energy? Equilibrium Concentration of substance is equal throughout a space

Movement of substances Diffusion Random motion of particles of a substance from high to low concentration Example: Room full of balloons Ions and molecules are small particles that break up and dissolve in cytoplasm and fluid outside of the cells Can a molecule or ion pass across the cell membrane? If yes, then what must be necessary for this to occur?

Brief Polarity Review Polar vs. Non-Polar molecules Polar = dissolves Non-polar = does not dissolve What about ions such as Cl- and Na+? What about lipids such as waxes and fats? Phospholipid bi-layer has a non polar interior Repels ions and most polar molecules Very small molecules and non polar molecules diffuse

Water Diffusion The diffusion of water is different than that of molecules and ions Keep in mind when a substance such as salt dissolves in water the water molecules “cling or grab onto” the ions (such as salt’s Na and Cl) and are not free to grab onto anything else Osmosis Diffusion of water through a selectively permeable membrane If no gradient, which way will it move….

If the fluid outside the cell has… Osmosis Chart If the fluid outside the cell has… Then outside fluid is… Water diffuses… Effect on cell …lower free water molecule concentration than cytoplasm …hypertonic solution …out of cell Cell shrinks …higher free water molecule concentration than cytoplasm …hypotonic solution …into cell Cell swells …same free water molecule concentration as cytoplasm …isotonic solution Equal rates in and out of cell Cell stays same size

Helpers in the Cell Membrane Ions and polar molecules are necessary for life. Therefore we need them to be able to get into our cells. How are they going to get inside our cells if they can not diffuse through the cell membrane due to non-polar lipids repelling them? Remember the moving purple protein???

Facilitated Diffusion Similar to simple diffusion, but aided by integral proteins and electrochemical gradients Ion Channel Doughnut-shaped transport protein with a polar pore through which ions can pass Neurons and Muscle cells **Electrical gradient** Carrier proteins Bind to the ion or molecule that’s normally to large to diffuse through the membrane, then is transported through the membrane and released

Visuals http://bcs.whfreeman.com/thelifewire/content/chp05/0502001.html http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html

Question of the Day (10/30/07) Explain the differences and similarities between the three types of passive transport we went over in yesterday’s class

Active transport (Section 4-2) The transport of a substance across the cell membrane against its concentration gradient which requires __________ Some molecules our cells need might lack a _______ concentration outside of the cell and force the cells out even though they are necessary Energy currency used in cells _________

Sodium Potassium Pump Transports ____ sodium ions (Na+) out of a cell and ____ potassium ions (K+) into the cell Normal concentrations of each: Na+ = outside cell = needs to move out of the cell K+ = Inside cell = needs to move in the cell Against concentration gradient therefore it requires ___________ in the form of ATP

4 Step Process: Step 1 Step 2 Three sodium ions inside the cell bind to the sodium potassium pump. ______________ group is removed from ATP and also binds to the pump Step 2 Pump changes shape, transporting the three sodium ions across the cell membrane and __________ outside of the cell

4 Steps continued Step 3 Step 4 The __________ is now exposed on the surface of the cell. Two potassium ions outside the cell bind to the pump. The ___________ group is released changing the _________ of the pump. Step 4 The pump is exposed to the inside of the cell. Two ____________ ions are transported across the cell membrane and are released ____________ the cell. The pump is ready to bind more sodium ions

Vesicle movement Substances exist that are larger than will fit through even our _______ proteins In this case the __________ will deposit theses polysaccharides or proteins using the following two processes. Endocytosis Movement of substance _____ a cell by a vesicle Exocytosis The movement of a substance by a vesicle ______ of a cell Nerve cells, proteins, glandular cells

Receptor Proteins A protein that binds to a specific ________ molecule, enabling the cell to respond to the __________ molecule Communication 3 functions _______________  permeability (open/close) Second Messengers Act as signal molecule in the cytoplasm Amplification Trigger Enzyme action

Edocytosis Exocytosis Receptor proteins Second messenger