CELL BOUNDARIES CHAPTER 7

CELL MEMBRANE CELL MEMBRANE (PLASMA MEMBRANE): REGULATES WHAT ENTERS AND LEAVES THE CELL AND ALSO PROVIDES PROTECTION AND SUPPORT. It is a thin, flexible barrier CELL MEMBRANE STRUCTURE: Double layer known as a lipid bilayer Gives cells its flexible nature while still controlling a barrier between the cell and its surroundings

CELL MEMBRANE

CELL MEMBRANE PARTS THE CELL MEMBRANE IS COMPOSED OF: A PHOSPHOLIPID BILAYER EMBEDDED PROTEINS CAN FORM CHANNELS AND PUMPS FOR MOLECULAR TRANSPORT INTO AND OUT OF THE CELL CARBOHYDRATE CHAINS ATTACH TO THE PROTEINS AND ACT LIKE CHEMICAL IDENTIFICATION CARDS CHOLESTEROL THE CELL MEMBRANE IS KNOW AS “MOSAIC” A MOSAIC IS A WORK OF ART MADE OF INDIVIDUAL TILES OR OTHER PIECES ASSEMBLED TO FORM A PICTURE OR DESIGN

PHOSPHOLIPID BILAYER THE IMAGE IS SHOWING THE PARTS OF A PHOSPHOLIPID. NOTICE THE FLUID (WATER) NEVER TOUCHES THE TAILS OF THE PHOSPHOLIPID.

SINGLE PHOSPHOLIPID NUMBER 1 IS THE HEAD: THE HEAD OF THE PHOSPHOLIPID IS HYDROPHILIC. HYDROPHILIC MEANS IT LIKES WATER. NUMBER 2 ARE THE TAILS: THE TAILS ARE HYDROPHOBIC. HYDROPHOBIC MEANS THEY DO NOT LIKE WATER; THEREFOR, WATER WILL BE FOUND IN THIS SECTION OF THE CELL MEMBRANE.

CELL WALL FOUND IN MANY ORGANISMS (PLANTS, ALGAE, FUNGI, AND MANY PROKARYOTES) CELL WALLS LIE OUTSIDE CELL MEMBRANES, AND CONTAIN PORES TO ALLOW COMMUNICATION BETWEEN CELLS AND MOLECULES TO PASS THROUGH FROM CELL TO CELL. MAIN FUNCTION: IS TO PROVIDE SUPPORT AND PROTECTION FOR THE CELL

WHAT MAKES UP A CELL WALL? MOST OF THE FIBERS IN A CELL WALL CONSIST OF CARBOHYDRATE AND PROTEIN FILAMENTS THE FILAMENTS ARE PRODUCES INSIDE THE CELL AND THEN RELEASED THROUGH THE CELL MEMBRANE AND REBUILT OUTSIDE THE CELL MEMBRANE PLANT CELL WALLS: CONTAIN MOSTLY CELLULOSE (A TOUGH CARBOHYDRATE)

MEMBRANE’S MOST IMPORTANT FUNCTION ONE OF THE MOST IMPORTANT FUNCTIONS OF A CELL MEMBRANE IS TO REGULATE THE MOVEMENT OF DISSOLVED MOLECULES FROM THE LIQUID ON ONE SIDE OF THE MEMBRANE TO THE LIQUID ON THE OTHER SIDE OF THE MEMBRANE

PASSIVE TRANSPORT cell uses no energy molecules move randomly Molecules spread out from an area of high concentration to an area of low concentration. (HighLow) Three types: Diffusion Facilitative Diffusion – diffusion with the help of transport proteins Osmosis – diffusion of water

DIFFUSION MEASURING CONCENTRATION: CONCENTRATION OF A SOLUTION IS THE MASS OF SOLUTE IN A GIVEN VOLUME OF SOLUTION (M/V) EX: IF YOU DISSOLVED 12 G OF SALT IN 3 L OF WATER WHAT WOULD THE CONCENTRATION BE? 12G /3L = 4G/L EX: IF YOU DISSOLVED 12 G OF SALT IN 6 L OF WATER WHAT WOULD THE CONCENTRATION BE? 12G/6L=2G/L THEREFORE THE CONCENTRATION OF THE FIRST SOLUTION IS TWICE AS CONCENTRATED AS THE SECOND SOLUTION

DIFFUSION IN A SOLUTION PARTICLES ARE CONSTANTLY MOVING DIFFUSION: WHEN PARTICLES MOVE FROM AN AREA OF HIGH CONCENTRATION (4G/L) TO AN AREA OF LOW CONCENTRATION (2G/L) MOLECULES TEND TO DO THIS NATURALLY, WITHOUT THE USE OF ENERGY, UNTIL THE CELL REACHES EQUILIBRIUM (SAME CONCENTRATION IN THE CELL EVEN WHEN EQUILIBRIUM IS REACHED PARTICLES WILL CONTINUE TO MOVE ACROSS THE MEMBRANE IN BOTH DIRECTIONS

DIFFUSION

PERMEABILITY OF A MEMBRANE PERMEABLE: A CELL MEMBRANE IS PERMEABLE IF A SUBSTANCE IS ABLE TO DIFFUSE ACROSS THE MEMBRANE IF A MOLECULE CANNOT GO THROUGH THE CELL MEMBRANE THEN IT IS SAID TO BE IMPERMEABLE MOST MEMBRANES ARE SELECTIVELY PERMEABLE MEANING THAT SOME THINGS MAY GO ACROSS THE MEMBRANE AND OTHER MAY NOT

OSMOSIS OSMOSIS: DIFFUSION OF WATER THROUGH A SELECTIVELY PERMEABLE MEMBRANE, MOVING WATER FROM AN AREA OF HIGH CONCENTRATION TO AN AREA OF LOW CONCENTRATION HOW IT WORKS: WATER MOVES THROUGH A MEMBRANE THAT MOLECULES CANNOT GET THROUGH. IF YOUHAVE A GLASS OF SUGAR WATER AND YOUR SUGER HAS A HIGHER CONCENTRATION ON ONE SIDE AND A LOWER CONCENTRATION OF THE OTHER SIDE THE WATER IS GOING TO MOVE FROM THE SIDE OF LOWER CONCENTRATION OF SUGAR TO THE SIDE OF HIGH CONCENTRATION OF SUGAR

OSMOSIS

RESULTS OF MEMBRANE TRANSPORT ISOTONIC: “SAME STRENGTH” (DYNAMIC EQUILIBRIUM) THE CONCENTRATION OF THE SOLUTES IS THE SAME INSIDE AND OUTSIDE THE CELL HYPERTONIC: “ABOVE STRENGTH” SOLUTION HAS A HIGHER SOLUTE CONCENTRATION THAN THE CELL, CAUSING WATER TO LEAVE THE CELL AND IT TO SHRIVLE (PLASMOLYSIS) HYPOTONIC: “BELOW STRENGTH” SOLUTION HAS A LOWER SOLUTE CONCENTRATION THAN THE CELL, CAUSING WATER TO ENTER THE CELL AND IT TO SWELL (CYTOLYSIS)

OSMOTIC PRESSURE CAN BE DANGEROUS FOR CELLS THAT DO NOT COME INTO NORMAL CONTACT WITH FRESH WATER OSMOSIS CAN CAUSE A CELL TO BECOME SWOLLEN WITH WATER AND EVENTUALLY BURST LUCKILY ANIMAL CELLS DO NOT COME INTO CONTACT WITH FRESH WATER, MOST OF OUR CELLS ARE IN A LIQUID SUITABLE FOR THE CELL TO SURVIVE ANIMAL CELLS ARE CONTAINED IN LIQUID SUCH AS BLOOD PLANT CELLS ARE ALWAYS IN CONTACT WITH FRESH WATER, WHICH IS ANOTHER IMPORTANT REASON THEY CONTAIN A CELL WALL THE CELL WALL KEEPS THE CELL FROM SWELLING AND EXPLODING

DEALING WITH OSMOSIC PRESSURE 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. A protist 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.

FACILITATED DIFFUSION Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane Transport Proteins are specific – they “select” only certain molecules to cross the membrane Transports larger or charged molecules

FACILITATEDDIFFUSION High Concentration Low Concentration Cell Membrane Glucose molecules Protein channel Transport Protein Through a  High Low

ACTIVE TRANSPORT cell uses energy actively moves molecules to where they are needed Movement from an area of low concentration to an area of high concentration (Low  High) Three Types: PROTEIN PUMPS ENDOCYTOSIS EXOCYTOSIS

ACTIVE TRANSPORT Protein Pumps -transport proteins that require energy to do work Energy is required due to the proteins changing shape. Example: Sodium / Potassium Pumps are important in nerve responses.

ACTIVE TRANSPORT Endocytosis: taking bulky material 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 PHAGOCYTOSIS “CELL EATING” EXTENSIONS OF THE CYTOPLASM SURROUND A PARTICLE AND PACKAGE IT WITHIN A FOOD VACUOLE

PINOCYTOSIS “CELL DRINKING” TAKING UP OF LIQUID IN THE SURROUNDING ENVIRONMENT BY TINY POCKETS FORMING ALONG THE MEMBRANE CREATING VACUOLES

ACTIVE TRANSPORT . Exocytosis: Forces material out of cell in bulk membrane surrounding the material fuses with cell membrane Cell changes shape – requires energy EX: Hormones or wastes released from cell