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Cell Membranes, Transport & Communication 1 Cell Membrane Most often seen in books Real cell membrane (electron microscope) Cell Membrane Structure Basic Structure Phospholipid Cell Membrane Structure But wait, there’s more... Cell Membrane Structure Carbohydrates FUNCTION: cell-cell recognition Within membrane Attached to proteins (glycoproteins) Attached to lipids (glycolipids) Cell Membrane Structure Cholesterol FUNCTION: Membrane fluidity High temp (37°C): makes membrane less fluid Lowers temp required for membrane to solidify by disrupting packing of phospholipid tails Cholesterol and membrane fluidity Remember lipid structure Saturated fats = no double bonds, straight tails, pack tightly Unsaturated fats = double bonds, kinked tails, pack loosely Cholesterol and membrane fluidity Remember lipid structure Saturated fats = no double bonds, straight tails, pack tightly Unsaturated fats = double bonds, kinked tails, pack loosely Membrane Fluidity Membranes must be fluid to function Different organisms have different compositions in their membranes Types of proteins Types of phospholipids Amount of cholesterol Fluid Mosaic Model human cell mouse cell + Membrane components move laterally around in the membrane Phospholipids can travel the length of a bacteria cell in 1 second! Animation: Starr Ch 6 – Fluid Mosaic Cell Membrane Structure Proteins Each type of protein in a membrane has a specific function Adhesion proteins Recognition proteins Receptor proteins Enzymes Transport proteins (active and passive) Cell Membrane Structure Adhesion Protein Enzyme Receptor Protein Recognition Protein Passive Transporter Active Transporter Cell Membrane Structure Froze membrane, then split apart Some proteins go all the way through (INTEGRAL PROTEINS) Some proteins are on one side or the other (PERIPHERAL PROTEINS) Complete Membrane Structure 14 How does it all get into the membrane? Proteins synthesized in? Secreted proteins Transmembrane proteins Lipids synthesized in? Carbohydrate modifications (glycolipid or glycoprotein) added in? Shipped via vesicles to membrane Fate of proteins Cell Membrane: Gate and Gatekeeper Structure allows cell to control what can pass through the membrane Selectively permeable barrier Allows some things through but not others 16 What needs to go across the membrane? INTO the cell: Sugars Amino Acids O2 Other nutrients OUT OF the cell: Metabolic waste CO2 Regulation of concentrations of ions : Na+, K+, Ca2+, Cl- Muscle Cells Selectively Permeable What goes through the membrane? Small, uncharged molecules (oxygen, carbon dioxide) What doesn’t go through the membrane? Charged molecules Larger polar or nonpolar molecules (sugars, amino acids) Textbook Figure Aquaporins – “water channels” Allows 3 x 109 water molecules to pass through membrane per second Concentration Gradients Concentration The amount of something in a certain space Concentration Gradient Movement of substances into and out of cells GENERAL RULE #1: Movement from HIGH concentration to LOW concentration does not require energy 22 Passive Transport Passive Transport What can be Passively Transported? Membrane is selectively permeable to small molecules (oxygen, carbon dioxide) Larger molecules and ions enter through protein carriers Small Molecules Ion channels Carrier proteins 25 What can be Passively Transported? Membrane is selectively permeable to small molecules (oxygen, carbon dioxide) – movement from high concentration to low concentration (passive) DIFFUSION © 2006 W.W. 26 What can be Passively Transported? Larger molecules and ions (water, salt, sugars, amino acids) enter through protein carriers Osmosis Water moving passively across the membrane 2% sucrose 2% sucrose 10% sucrose water 28 Osmosis Red blood cells in various salt concentrations 29 Tonicity Ability of a solution to cause a change in water content via osmosis TONIC refers to the SOLUTE Same concentration of solute inside and outside the cell Salt concentration outside HIGHER than inside the cell Salt concentration outside LOWER than inside the cell Example of Passive Transport: Osmosis Water moving passively across the membrane Isotonic Plant Cells Solution Hypertonic Hypotonic compared to cell: “the solution is hypertonic to the cell” Animal Cells 31 Osmosis – Turgor pressure Factors that affect passive transport Size Temperature Steepness of the concentration gradient Charge Pressure Movement of substances into and out of cells GENERAL RULE #2: Movement from LOW concentration to HIGH concentration requires added energy 34 Active Transport What must be Actively Transported? Anything moving against the concentration gradient (low to high) Active carriers use energy from ATP Energy changes the shape of the carrier Energy 36 Example of Active Transport: Endocytosis and Exocytosis 37 EXOCYTOSIS: Outward budding of the membrane Forms a vesicle Remove waste, release molecules the cell has made Exocytosis Animation Example of Active Transport: Endocytosis and Exocytosis 38 ENDOCYTOSIS: Inward budding of the membrane Forms a vesicle Take in food, remove cholesterol from blood, immune cells “eat” invaders ANIMATION: Endocytosis Cain Ch6 2b Endocytosis Exocytosis coated pit lysosome Golgi Transport into and out of cells Example in Real Life Paramecium are a single-celled organism that is found in freshwater ponds. Which direction would osmosis (passive transport) cause water to move with respect to the Paramecium? Example in Real Life What would happen to the Paramecium if this continued? Example in Real Life The contractile vacuole of a Paramecium constantly pumps water out of the cell. Is this active or passive transport? Example in Real Life You have probably heard that eating a lot of salt will make your body retain water so you gain weight. When you eat a lot of salt, it is transported inside your cells. Why would eating a lot of salt make your body retain water? Example in Real Life A shipwrecked sailor is stranded on a small desert island with no fresh water to drink. She knows she could last without food for up to a month, but if she didn't have water to drink she would be dead within a week. Hoping to postpone the inevitable, her thirst drove her to drink the salty seawater. She was dead in two days. Why did drinking seawater kill the sailor faster than not drinking any water at all? Example in Real Life Describe why oxygen would diffuse into cells inside your lungs. Example in Real Life Why does putting salt on a slug kill it? Scientific Method Practice OBSERVATION: Cells gain or lose water via osmosis when placed in different concentrations of salt. Design an experiment to determine the concentration of salt inside a human red blood cell. Hypothesis, Prediction, Independent variable, dependent variable, control, constants Scientific Method Practice Hypothesis: RBCs contain 5% salt. Prediction: HYP TRUE - RBCs in <5% salt will swell, RBCs in >5% salt will shrink. HYP FALSE – other observation about cell size Independent variable: % salt in water Dependent variable: size of cell (shrink, grow) Control: RBC in blood serum (shouldn’t change) Constants: source of RBCs, amount of liquid added, time after addition, # of RBCs observed Real-life Results Hypotonic Isotonic Hypertonic 100 mOs 500 mOs 300 mOs Cell Communication in Multicellular Organisms Cells are specialized for different jobs, but cooperate so organism functions Cells need to coordinate their activities Neighboring cells communicate via direct connections Distant cells communicate via chemicals: hormones 51 Direct Communication Indirect Communication Cells release small proteins or molecules Hormones, Pheromones, Steroids, Neurotransmitters Other cells have protein receptors Signaling molecules produce changes in the receiving cell ANIMATION: Campbell Ch 11 – Signaling Overview 53 Lab 6 Debriefing 0.9% NaCl Isotonic Plant Cells 0% 4% NaCl NaCl Hypertonic Hypotonic Solution compared to cell: “the solution is hypertonic to the cell” Animal Cells 54 Osmosis – Turgor pressure 0.9% NaCl 4% NaCl Dialysis Tube Experiment Iodine Iodine Glucose Diffusion 56 Photosynthesis (briefly) and Cellular Respiration 57 Capturing Energy Sun is primary source of energy Energy flows through life systems Producers Sugars out O2 out Photosynthesis Primary consumers Secondary consumers Respiration CO2 and H2O out 58 What this means… All energy needs are met by the plant kingdom All this energy originally comes from the sun Photosynthesis converts the energy in sunlight into chemical energy that can be stored in the plant 59 Energy in the Cell CELLULAR RESPIRATION PHOTOSYNTHESIS Photosynthesis and Cellular Respiration An exchange of molecules and energy © 2006 W.W. 61 Sunlight energy ECOSYSTEM Photosynthesis transforms kinetic energy (light) into potential energy (chemical bonds in glucose) Cellular respiration moves energy stored in glucose into ATP, which can be used for cellular work Photosynthesis in chloroplasts CO2 Glucose H2O O2 Cellular respiration in mitochondria ATP (for cellular work) Heat energy ANIMATION: Starr Ch 6 – Energy Changes 62 H2O Cellular Respiration O2 CO2 Think of what happens when you breathe – closely related to CR 63 Cellular Respiration and Gasses Breathing brings O2 into the body from the environment O2 is distributed to cells in the bloodstream In cellular respiration, mitochondria use O2 to harvest energy and generate ATP Breathing disposes of the CO2 produced as a waste product of cellular respiration 64 Summary Equation Remember laws of thermodynamics! First law? Second law? HEAT Glucose Oxygen gas Carbon dioxide Water Energy 65 ATP – An Energy Carrier Molecules Temporarily stores and transfers energy ATP stores energy in phosphate bonds Transfers this energy with phosphate Phosphorylation 66 Other Energy Carriers NADP+ and NAD+ Pick up electrons NADPH and NADH Donate these electrons and energy 67 Energy in Bonds Energy is contained in the arrangement of electrons in a molecule An electron on Carbon has more energy than an electron on Oxygen 68 Burning sugar Electrons “fall” from carbon in glucose to oxygen in water Energy released rapidly as light and heat 69 Cellular Respiration Electron “fall” is carefully controlled Energy released in small amounts and stored in ATP What does the cell use to carefully control the energy release? 70 Where are these electrons that are moving? What is moving from a carbon to an oxygen? 71 Oxidation – Reduction Reactions Oxidation: loss of electrons from an atom (loss of a H atom) Reduction: addition of electrons to an atom (gain of a H atom) Think: reduction in CHARGE due to more e- Always paired (one loses an e-, one gains) 72 What molecule gets OXIDIZED (loses e-)? What molecule gets REDUCED (gains e)? 73 More Redox Reactions What molecule gets OXIDIZED (loses e-)? What molecule gets REDUCED (gains e-)? 74 Redox Reactions in Cellular Respiration Glucose loses electrons (in H atoms) and becomes oxidized 75 Redox Reactions in Cellular Respiration Glucose loses electrons (in H atoms) and becomes oxidized O2 gains electrons (in H atoms) and becomes reduced Along the way, the electrons lose potential energy, and energy is released 76 Redox Reactions in Cellular Respiration Glucose loses electrons (in H atoms) and becomes oxidized O2 gains electrons (in H atoms) and becomes reduced Electrons lose potential energy, and energy is released 77 Important Players Dehydrogenase removes electrons from glucose What type of molecule is dehydrogenase? How are the electrons removed? 78 Important Players Electrons are transferred to the coenzyme NAD+, which is converted to NADH Is this oxidation or reduction? NAD+ shuttles electrons in CR redox reactions 79 These reactions NAD+ Function Animation (Online) Oxidation Dehydrogenase Reduction NAD NADH 2H 2H 2 e H (carries 2 electrons) 80 Bigger picture Electron transfer to NAD+ is the first step in an ELECTRON TRANSPORT CHAIN NADH NAD H ATP 2e Controlled release of energy for synthesis Series of redox reactions Pass from different carrier molecules eventually to O2 of ATP 2 H 2e 1 2 O2 H2O 81 Cellular Respiration STEP 0: Eat to get glucose Glucose is absorbed by cells in small intestine Glucose enters the bloodstream and is transported to all the cells in your body How is this different in a plant? 82 Inside a cell STEP 1: Glycolysis STEP 2: Citric Acid Cycle STEP 3: Oxidative Phosphorylation 83 Cellular Respiration GLUCOSE 84 STEP 1: Glycolysis Occurs in CYTOPLASM Glucose is split into 2 molecules of pyruvate 2 ATP and 2 NADH are made for each pyruvate 85 STEP 1: Glycolysis Animation: Campbell Ch 6 – Glycolysis GLYCOLYSIS ANIMATION (online) 86 STEP 1: Glycolysis Summary Preparatory phase: Glucose is energized using 2 ATPs Splits into 2 three-carbon intermediates 87 STEP 1: Glycolysis Summary Energy Payoff phase: Redox reaction generates NADH 2 ATP and pyruvate produced per intermediate 88 STEP 1: Glycolysis Summary 2 ATP 2 NAD 2 NADH 2 H Glucose 2 Pyruvate 4ADP 4 P 4 ATP 1. One glucose (6C) converted into 2 pyruvates (3C) 2. 2 ATP in 4 ATP out 3. Two NAD+ are converted into 2 NADH & 2H+ (These go to Electron Transport.) 89 Cellular Respiration Organizer glucose 2 ATP ATP 6 carbon sugar Glycolysis 2 NADH 2 pyruvate 4 ATP (2 net) ATP CYTOPLASM 3 carbon sugar 90 So far… 91 Glycolysis Citric Acid (Krebs) Cycle 92 Mitochondria Structure Two membranes Mitochondrion Outer membrane Intermembrane space Inner membrane Folded into cristae Contains fluid mitochondrial matrix Outer membrane Intermembrane space Inner membrane Cristae Matrix TEM 44,880 93 STEP 2: The Citric Acid Cycle Occurs inside matrix of MITOCHONDRIA Completes breakdown of glucose to CO2 Makes 1 ATP per pyruvate Passes electrons to ETC 94 STEP 2: Citric Acid Cycle Animation: Campbell Ch 6 – TCA Also called TCA (The Citric Acid cycle) Also called the Krebs Cycle ONLINE: TCA ANIMATION REMEMBER: There’s TWO pyruvates!! 95 STEP 2: TCA Summary Pyruvate (x2) is groomed for TCA cycle: Carbon atom released as CO2 2C compound oxidized; NAD+ reduced to NADH Coenzyme A joins 2C 96 STEP 2: TCA Summary Completes oxidation of glucose: Releases 2 CO2 molecules Net energy yield per pyruvate (there’s 2!) = 1 ATP, 4 NADH (1 from prep, 3 from TCA), 1 FADH2 97 Cellular Respiration Organizer glucose 2 ATP ATP Glycolysis 4 ATP (2 net) ATP 2 NADH 2 pyruvate 2 Coenzyme A Krebs Cycle MITOCHONDRIAL MATRIX 6 CO2 2 ATP ATP 8 NADH, 2 FADH2 98 So far… 99 TCA Electron Transport Chain and Chemiosmosis 100 Step 3: Electron Transport Chain Occurs ON inner mitochondrial membrane 101 Step 3: Electron Transport Chain Electrons passed down from NADH to ETC H+ ions pumped inside inner mitochondrial membrane Electrons passed down ETC to O2 which accepts electrons and becomes 2 H2O 102 STEP 3: Electron Transport Chain Animation: Campbell Ch 6 – ETC 103 STEP 3: ETC Summary Electons passed from NADH and FADH to proteins in ETC to O2 H H H Protein complex Intermembrane space H H Electron carrier H H H H ATP synthase Inner mitochondrial membrane Electron flow Mitochondrial matrix FADH2 FAD NAD NADH H 1 2 O2 2 H H H H2O Electron Transport Chain OXIDATIVE PHOSPHORYLATION ADP P ATP H Chemiosmosis 104 STEP 3: ETC Summary Transports H+ into inner membrane space in mitochondria creating a gradient H H H Protein complex Intermembrane space H H Electron carrier H H H H ATP synthase Inner mitochondrial membrane Electron flow Mitochondrial matrix FADH2 FAD NAD NADH H 1 2 O2 2 H H H H2O Electron Transport Chain OXIDATIVE PHOSPHORYLATION ADP P ATP H Chemiosmosis 105 STEP 3: ETC Summary H+ gradient is POTENTIAL energy H H H Protein complex Intermembrane space H H Electron carrier H H H H ATP synthase Inner mitochondrial membrane Electron flow Mitochondrial matrix FADH2 FAD NAD NADH H 1 2 O2 2 H H H H2O Electron Transport Chain OXIDATIVE PHOSPHORYLATION ADP P ATP H Chemiosmosis 106 STEP 3: ETC Summary CHEMIOSMOSIS: H+ flowing (downhill) from high to low concentration releases KINETIC energy H H H Protein complex Intermembrane space H H Electron carrier H H H H ATP synthase Inner mitochondrial membrane Electron flow Mitochondrial matrix FADH2 FAD NAD NADH H 1 2 O2 2 H H H H2O Electron Transport Chain OXIDATIVE PHOSPHORYLATION ADP P ATP H Chemiosmosis 107 STEP 3: ETC Summary Energy from H+ flowing downhill is stored in bond of ATP H H H Protein complex Intermembrane space H H Electron carrier H H H H ATP synthase Inner mitochondrial membrane Electron flow Mitochondrial matrix FADH2 FAD NAD NADH H 1 2 O2 2 H H H H2O Electron Transport Chain OXIDATIVE PHOSPHORYLATION ADP P ATP H Chemiosmosis 108 STEP 3: CHEMIOSMOSIS Generates majority of ATP (34) 109 Cellular Respiration Organizer glucose 2 ATP ATP Glycolysis 4 ATP (2 net) ATP CYTOPLAS M 2 NADH 2 pyruvate Krebs Cycle MITOCHONDRIAL MATRIX 6 CO2 2 ATP ATP 8 NADH, 2 FADH2 ATP oxygen Electron Transfer Chain Chemiosmosis 32 ATP INNER MITOCHONDRIAL MEMBRANE 110 So far… 111 Cellular Respiration Overview Animation NML_Cain3_CD3/Student_Animations/Full /Macintosh/cain_ch08a02.app 112 Cellular Respiration Aerobic metabolism: three steps Glycolysis, Citric Acid Cycle, & Oxidative Phosphorylation Releases LOTS of energy – typically 36 ATP per molecule of glucose 113 “Aerobic” Respiration? Requires OXYGEN – WHY and WHERE? Last e- acceptor in ETC 114 Some poisons interrupt CR Rotenone H+ H+ H+ NA D H+ H+ H+ H+ H+ H+ ATP synthase FAD FADH2 NADH H+ 1 2 + O2 + 2 H+ H+ H+ Electron Transport Chain H2O ADP + P ATP Chemiosmosis Rotenone: binds with ETC proteins and prevents e- from passing on 115 Some poisons interrupt CR Rotenone Cyanide, carbon monoxide H+ H+ H+ NAD H+ H+ H+ H+ 1 2 + ATP synthase O2 + 2 H+ H+ H+ H+ FAD FADH2 NADH H+ H+ Electron Transport Chain H2O ATP ADP + P Chemiosmosis Cyanide, CO: block passage of electrons to O2 116 Some poisons interrupt CR Rotenone Cyanide, carbon monoxide H+ H+ H+ NAD H+ H+ H+ H+ H+ 1 2 + ATP synthase O2 + 2 H+ H+ H+ H+ FAD FADH2 NADH Oligomycin H+ Electron Transport Chain H2O ADP + P ATP Chemiosmosis Oligomycin: Blocks passage in ATP Synthase so H+ gradient can’t be used 117 Some poisons interrupt CR Rotenone Cyanide, carbon monoxide H+ H+ H+ Oligomycin H+ H+ H+ H+ H+ H+ ATP synthase DNP FAD FADH2 NAD NADH 1 2 + O2 + 2 H+ H+ H+ H+ Electron Transport Chain H2O ATP ADP + P Chemiosmosis DNP (uncouplers): make mitochondrial membrane “leaky” to H+ so gradient can’t be formed 118 Atkins Diet Use fats for glycolysis in the absence of sugars Fats are broken down and enter as ActylCoA Produce ketones when metabolized and change pH of blood 119 Respiration Practice Complete Respiration Practice Worksheet 120 Cellular Respiration Review Occurs in all eukaryotes Generates ATP Involves oxidation – reduction reactions Oxidation = loss of electron / H atom; gain of charge Reduction = gain of electron / H atom; loss of charge Glycolosis Takes place in cytoplasm Starts with glucose Uses 2 ATP to prepare glucose Generates 2 NADH Is this oxidation or reduction? Generates 4 ATP NET YIELD: 2 NADH (goes to ETC) and 2 ATP The Citric Acid (Krebs) Cycle Takes place in mitochondrial matrix Uses Coenzyme A to prepare pyruvate Completes breakdown of glucose to CO2 Each molecule of pyruvate processed generates 4 NADH 1 FADH2 1 ATP So far… 124 ETC and Chemiosmosis ETC: Takes place on inner mitochondrial membrane Electrons from NADH and FADH2 pass electrons down ETC O2 is the final oxygen acceptor Generates a H+ gradient Chemiosmosis Chemiosmosis: H+ gradient powers ATP Synthase enzyme to phosphorylate ADP to make ATP ADP + P ATP Yield = 32-34 ATP molecules So far… 127 What if there’s no Oxygen? O2 can’t act as final electron acceptor ETC can’t happen Can still get 2 ATP from glycolysis (doesn’t require O2) What if there’s no Oxygen? Can generate 2 ATP Makes 2 NADH What if there’s no Oxygen? PRESENCE OF O2 NADH goes to ETC ABSENCE OF O2 •ETC can’t function •NADH must be oxidized back to NAD+ Anaerobic Respiration Cellular respiration in the absence of oxygen Oxidizes NADH to replenish NAD+ Lactic Acid Fermentation Ethanol Fermentation Anaerobic Respiration LACTIC ACID FERMENTATION Occurs in muscle cells Oxidizes NADH to NAD+ by reducing pyruvate to lactate (lactic acid) Anaerobic Respiration AlCOHOL FERMENTATION Occurs in yeast Oxidizes NADH to NAD+ by reducing pyruvate to ethanol (ethyl alcohol) Why we like fermentation Often used by bacteria to make tasty foodies Used for thousands of years Method of preserving food Other Organic Molecules as Fuel Carbohydrates: Enter at beginning of glycolysis •Examples: Starch, Glycogen Other Organic Molecules as Fuel Fats: Hydrolyze fatty acids off of glycerol Glycerol glycolysis Fatty Acids broken into 2-C pieces and sent to TCA 1 g fat yields 2x ATP as 1g starch Other Organic Molecules as Fuel Proteins: Hydrolyze to amino acids, build more proteins Can be used in glycolysis or TCA Other Organic Molecules as Fuel From what organic molecule can we get the most ATP per gram? Why does fat contain so much energy? Energy is stored in the C – C bonds within a molecule