Ms. Hughes

 All living things respond to their environments.  Homeostasis is the maintenance of stable internal conditions in a changing environment.  One way that a cell maintains homeostasis is by controlling the movement of substances across the cell membrane.

 Every cell is surrounded by a cell membrane.  The cell membrane protects the cell and helps move substances and messages in and out of the cell.  By regulating transport the cell membrane helps the cell maintain homeostasis.

 Cells are suspended in a fluid environment.  Even cell membranes are fluid.  They are a sea of lipids in which proteins float.  They also provide structural support for the cytoplasm, recognizes foreign material and communicates with other cells.

 The cell membrane is made up of a phospholipid bilayer, which consists of a phosphate (hydrophilic/polar) head and a two fatty acid (hydrophobic/nonpolar) tails.  These phospholipids form a double membrane in which both heads are facing out of the cell.  The phospholipids forma barrier through which only small nonpolar substances can pass.

 Some proteins found within the membrane face out, some face in the membrane, and some stretch across the entire membrane.  Proteins are made of amino acids (some a.a. are polar and others are nonpolar).  Polar proteins are attracted to the outside water of the membrane while nonpolar proteins are forced inside the membrane.

 Cell surface markers  Receptor proteins  Enzymes  Transport proteins

 Similar to a name tag  A chain of sugar identifies each type of cell  These sugars are attached to the cell surface by proteins called glycoproteins.  Glycoproteins help cells work together.

 Enable a cell to sense its surroundings  They bind to certain substances outside the cell.  Once they are bound to the substances outside the cell changes within the cell take place.

 Proteins with in the cell membrane that help with important biochemical reactions inside the cell.  These can be to increase the speed of a reaction or decrease the speed of a reaction.

 Many substances the cell needs cannot pass through the lipid bilayer in between the two phosphate heads.  Transport proteins aid the movement of substances that cannot typically pass into and out of the cell through the cell membrane.

 Draw label and throughly explain the phospholipid bilayer.

 The cell must move substances of varying size, electrical charge, and composition into and out of the cell.  In active transport across the membrane the cell uses energy.  In passive transport across the membrane the cell does not use energy.

 Equilibrium: when a space is filled evenly.  Concentration: the amount of a particular substance in a given volume.  Concentration gradient: when one area has a higher concentration than another.  Substances move from an area of high concentration to an area of low concentration.  Some substance enter and exit the cell by diffusing across the cell membrane.

 Diffusion: movement from high concentration to low concentration (movement down the concentration gradient).  In passive transport substances enter the cell by diffusing across the cell membrane. ( This does not require energy)  Direction of diffusion depends on direction of the concentration gradient.  Diffusion can be through transport proteins and some is across the lipid bilayer.

 Food coloring example of simple diffusion.

 Small nonpolar molecules can pass directly through the lipid bilayer. (Simple diffusion)  Molecules must move down the concentration gradient.  Molecules which diffuse simply are nonpolar and fat soluble.  Diffusion can take place in both directions but with different molecules. ◦ Ex: oxygen diffuses in as carbon dioxide diffuses out of the cell.

 During facilitated diffusion transport proteins help substances diffuse through the cell membrane.  Two types of facilitated transport proteins: ◦ Channel proteins ◦ Carrier proteins

 Ions, sugars, and amino acids can diffuse through the cell membrane through channel proteins.  These proteins aka pores serve as tunnels through the lipid bilayer.  Each tunnel allows for a specific substance to diffuse through it. This substance has a specific size and charge.

 Transport substances that fit within their binding site.  A carrier protein binds to a specific substance on a specific side of the cell membrane.  This binding causes the substance to change shape.  As the shape changes the protein is moved across the membrane and release on the other side.

 Diffusion across a selectively permeable membrane.  Osmosis allows cells to maintain water balance as their environment changes.  Osmosis allows for water molecules to move down the concentration gradient to create an equilibrium between the cell and the external environment.

 Polar water molecules do not diffuse directly across the bilayer.  The cell membrane contains channel proteins that only water can pass through.  Osmosis in cells is a type of facilitated diffusion.

 Hypotonic – the fluid outside the cell is less concentrated. Water moves into the cell the cell swells.  Hypertonic – the fluid outside the cell is more concentrated. Water moves out of the cell, the cell shrinks.  Isotonic- water moves into and out of the cell at the same rate. The cell stays the same size.

 If left unchecked a hypotonic solution could cause a cell to burst.  Cell walls cause the cell from over swelling in plants and fungi.  Many plants are healthiest in hypotonic environments.

 Transportation against a concentration gradient.  Active transport requires energy to move substances against their concentration gradients.  Most often this energy is supplied directly or indirectly by ATP.

 Many active transport processes use carrier proteins to move substances.  In active transport the carrier proteins require energy to “pump” proteins against their concentration gradient.

 Sodium ions inside the cell bind to the carrier protein.  ATP is transfers energy to the protein.  The protein changes shape and releases the sodium ions outside the cell membrane.  Outside the cell potassium ions bind to the pump.  The pump returns to its original shape and releases the potassium ions inside the cell membrane.

 This pump prevents sodium ions from building up in the cell.  Osmosis results when sodium levels are high  The concentration gradients of sodium and potassium ions also help transport other substances, such as glucose across the cell membrane.

 McGraw – Hill video of sodium potassium pump

 Many proteins and polysaccharides are too large to enter the cell using carrier proteins, so they use vesicles.  Vesicles are membrane bound sacs.  The vesicle membrane is a lipid bilayer, so vesicles can bud off from the membrane, fuse with it or fuse with other vesicles.

 Endocytosis: movement of a large substance into the cell by means of a vesicle.  During endocytosis the membrane forms a pouch around the substance, pinches off and forms a vesicle inside the cell.

 Exocytosis: movement of material out of a cell by means of a vesicle.  During exocytosis a vesicles inside the cell fuse with the cell membrane. The contents of the vesicle are then release outside of the cell through the cell membrane.  Exocytosis is used to transport proteins modified by the Golgi apparatus.

 McGraw Hill video of endo and exo cytosis.

 We will now go outside and form the phospholipid bilayer and allow molecules to either diffuse through us or we will actively pump large molecules through.

 Create a story book of a molecules who are being transported. These molecules must experience active and passive transport.

 Cells communicate and coordinate activity by sending chemical signals that carry information to other cells.  Signaling cell – produces signal.  Target cell – receives signal intended for it.  Signal – molecule detected by target cell.  Typically target cells have specific proteins that recognize and respond to the signal.

 Cells can communicate through direct contact between their membranes.  Short-distance signals may act locally.  Long-distance signals are carried by hormones and nerve cells.  Hormones are made in one part of the body and distributed by the bloodstream but effect only specific cells.

 Most signal molecules originate within the body, some signals come from outside.  Ex: light has a great effect on the action of hormones in plants. Length of day determines when some plants flower.

 A target cell is bombarded by hundreds of signals.  It recognizes and responds to only a few specific signals  Signal: anything that serves to direct, guide, or warn.  Receptor protein: a protein that binds specific signal molecules, which causes the cell to respond.

 A receptor protein binds only to signals that match the specific shape of its binding site.  Only signals that have the specific shape can bind to the specific receptor, others have no effect.  Once bound the signal molecule the receptor protein changes its shape in the membrane. This change relays information to the cytoplasm of the target cell. (communication)

 Draw, label and explain a phospholipid bilayer.  Create a comic strip for cell signaling  List and explain the types of passive transport  Draw and explain hyper, hypo and isotonic  Be familiar with ALL vocabulary terms

 Permeability change: transport proteins may open or close due to a signal.  Enzyme activation: Enzymes may be activated by a signal or some proteins may be enzymes themselves.  Second messenger: a second message may be formed and sent. Ex: to the nucleus of the target cell.

 Create flow chart of steps for cell communication.

 Using index cards or paper: ◦ Write down the steps for cell communication and practice placing them in order.