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Chapter 3 part 2: Cell dynamics Membrane transport: Diffusion, osmosis, active transport Cellular respiration Lecture outline • ATP and cell energy • Cell membrane dynamics – Diffusion – Osmosis – Active transport • Cell respiration ATP The Energy Currency of the Cell (Text review: Chapter 2, pg. 34) ATP is the energy currency of all living things Adenine Phosphate groups Ribose ATP: Adenosine Triphosphate ATP belongs in which category of molecule? 1. 2. 3. 4. 5. Carbohydrates Lipids Proteins Nucleic Acids None of these How ATP works • ATP ADP + P + energy • Energy from ATP can do work in the cell • When we eat food, we use its energy to reconvert: • ADP + P + energy ATP • Humans use food to make ATP by the process of Aerobic Respiration LE 8-9 P P P Adenosine triphosphate (ATP) H2O Pi Inorganic phosphate + P P Adenosine diphosphate (ADP) + Energy How ATP Performs Work • When ATP breaks, the P can be added to a protein • The recipient protein then changes shape, and behaves differently When proteins change shape, work can get done Energy from food Regenerates ATP ATP Energy for cellular work (endergonic, energyconsuming processes) Energy from catabolism (exergonic, energyyielding processes) ADP + P i Your body breaks down and re-builds your own weight in ATP each day Cell membranes Cell Membrane review • What is the cell membrane made out of? • What is the purpose of the cell membrane? One way in, one way out Everything which enters or exits a cell must pass through the cell membrane The cell membrane must therefore: -Keep things the cell needs -Get things it wants from its environment -Get rid of wastes without losing desirable substances -All parts of the cell membrane work to these tasks Parts of the cell membrane • • • • Phospholipid bilayer Cholesterol (animal cells only) Membrane proteins Some carbohydrates Cell membranes are made of a phosphlipid bilayer Phospholipids are amphipathic • Similar in structure to triglycerides • Phosphate is polar • Lipids are nonpolar • Degree of saturation influences shape and fluidity Fatty acid saturation influences fluidity of cell membranes Saturated fatty acids pack into membranes more easily, making membranes tighter (and less fluid) Cholesterol can stabilize the fluidity of animal cell membranes • Higher temperature also influences fluidity of membranes Proteins comprise ~50% of cell membranes The membrane is a fluid mosaic The membrane is Selectively permeable Proteins assist in allowing things to pass in and out Transmembrane proteins serve a variety of functions Some things can pass through easily, others require help • Substances which can pass without help: – Water – Small nonpolar molecules • Substances that require help: – Ions – Polar small molecules – Large molecules Membrane dynamics: Ways things can enter or leave the cell Diffusion, Osmosis, and Active Transport Things can enter the cell in three ways • Diffusion (Can be Passive or facilitated) • Osmosis • Active transport Diffusion: the movement of a substance from a high concentration to a low concentration • Simple diffusion • Facilitated diffusion Diffusion is the movement of a substance from a high concentration to a low concentration What happens next? Membranes can change the way diffusion works What determines the rate of diffusion here? On what properties of the dye and membrane does the diffusion depend? Figure 5.12 The cell membrane can’t control simple diffusion Small, nonpolar molecules can pass easily through the phospholipid bilayer: -Oxygen -Carbon dioxide -Alcohol -Steroids -gasoline (Water is polar but very small- it can pass the membrane at low rates ) Facilitated diffusion allows passage of desirable molecules Membrane proteins allow ions and small polar molecules to pass in and out -Potassium ions (K+), other things -Sugars and other nutrients Diffusion • Diffusion is the movement of substances from a high concentration to a low concentration • Liquids and gasses diffuse spontaneously Osmosis: the diffusion of water across a selectively permeable membrane Osmosis is the diffusion of water What can we infer about the permeability of this membrane? Osmosis • The diffusion of water • Requires no energy • Water moves from a high concentration to a low concentration • Water can pass through membranes Osmosis can do work When only water can pass, Osmosis can cause a cell to shrivel, or to swell The bag gains and loses the same amount of water and maintains its shape. The bag loses more water than it gains and shrivels. (a) Hypertonic Solution (90% water 10% sugar) 98% water 2% sugar (b) Isotonic solution (98% water 2% sugar) The bag gains more water than it loses and swells. (c) Hypotonic solution (100% water, distilled) Figure 5.14 Isotonic- equal concentrations of solutes inside and out • Water flows equally into and out of cells • Necessary for animal cells • A wilted state in plant cells Hypotonic- A low concentration of solutes outside the cell • Water flows in • This keeps plants in proper shape • This can lyse an animal cell Hypertonic- A greater concentration of solutes outside the cell • Water flows from a high concentration (inside the cell) to a low concentration (outside the cell) What kind of solution are these plants in? Active Transport • Substances are moved by the cell from low concentration to high • Spending cellular energy to move substances against a concentration gradient Membrane proteins can do Active Transport to bring needed items into the cell What kind of substances might a cell wish to bring into the cell in this way? Figure 3.10 ATP can be used to power Active Transport Active transport for very large things • When substances are too big to be brought in through a channel, the cell can do endocytosis • Substances can be shipped out of the cell by exocytosis • Both are forms of active transport Endocytosis and Exocytosis • When things are too big to fit through the membrane, they can be brought in by endocytosis • …or released by exocytosis Endocytosis • The vesicle then travels into the cell and through the cytoplasm • Two types – Phagocytosis (cell eating) – large particles or bacteria – Pinocytosis (cell drinking) – droplets of fluid Endocytosis Figure 3.11a Endocytosis Figure 3.11b Exocytosis- a vesicle fuses with the membrane, freeing the contents Figure 3.12 Figure 5.17 Figure 5.18 Membrane transport review The “powerhouse of the cell” is the_________. 1. 2. 3. 4. 5. Nucleus. Mitochondrion. Golgi complex. Ribosome. None of these Mitochondrial structure review Cellular respiration provides us with the energy we use Slow-twitch muscles have more mitochondria than fast-twitch Cellular Respiration All Living Things Require and Consume Energy • Ultimate source of energy for all life on earth is the sun • We get our energy from food Aerobic respiration of glucose is the most basic means for cells to acquire energy C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l) This is a combustion reaction Respiration at the cellular level necessitates our breathing The more our cells respire, the more oxygen (& food) we need The Stages of Cellular Respiration • Cellular respiration has three stages: – Glycolysis – The citric acid cycle (a.k.a. the Krebs cycle) – The electron transport chain LE 9-6_1 Glycolysis Pyruvate Glucose Cytosol Mitochondrion ATP Substrate-level phosphorylation LE 9-6_2 Glycolysis Citric acid cycle Pyruvate Glucose Cytosol Mitochondrion ATP Substrate-level phosphorylation ATP Substrate-level phosphorylation LE 9-6_3 Electrons carried via NADH and FADH2 Electrons carried via NADH Glycolysis Citric acid cycle Pyruvate Glucose Cytosol Oxidative phosphorylation: electron transport and chemiosmosis Mitochondrion ATP Substrate-level phosphorylation ATP Substrate-level phosphorylation ATP Oxidative phosphorylation Overview of respiration • Glycolysis: Glucose is split, 2 pyruvates are formed, a little ATP is gained ( 2 ATP/ glucose) • The Citric Acid Cycle: Pyruvates are brokent into CO2, Redox molecules NAD+ and FAD are charged up, a little ATP is gained (2 ATP/ glucose) • Electron transport: Lots of ATP is made by ATP synthase (~32 ATP/ glucose) Step 1: Glycolysis In: 1 glucose, 2 NAD+ Out: 2 ATP (net), 2NADH, pyruvate 2 Glycolysis converts glucose to pyruvate • Glycolysis (“breaking of sugar”) breaks down glucose into two molecules of pyruvate • Glycolysis occurs in the cytoplasm and has two major phases: – Energy investment phase – Energy payoff phase Overview of Glycolysis • • • • Actually a 10- step process Glucose (6C) 2 Pyruvate ( 3 C ea.) 2 ATPs net profit 2 NAD+’s are charged LE 9-9a_2 Glucose ATP Hexokinase ADP Glucose-6-phosphate Phosphoglucoisomerase Fructose-6-phosphate ATP Phosphofructokinase ADP Fructose1, 6-bisphosphate Aldolase Isomerase Dihydroxyacetone phosphate Glyceraldehyde3-phosphate Glycolysis Citric acid cycle ATP ATP Oxidation phosphorylation ATP LE 9-9b_2 2 NAD+ Triose phosphate dehydrogenase 2 NADH + 2 H+ 1, 3-Bisphosphoglycerate 2 ADP Phosphoglycerokinase 2 ATP 3-Phosphoglycerate Phosphoglyceromutase 2-Phosphoglycerate 2 H 2O Enolase Phosphoenolpyruvate 2 ADP Pyruvate kinase 2 ATP Pyruvate Step 2: The Krebs Cycle Bonds in pyruvate are stripped of their energy The Krebs cycle strips all the electrons off of glucose’s carbon atoms, forming CO2 The electrons are used to charge up electron carriers NAD+ ( NADH) and FAD ( FADH2) Step 3: Electron transport In which the electron transport chain generates a proton gradient, and ATP synthase makes tons of ATP The electron transport chain uses electrons to generate a proton gradient H+ H+ Protein complex H+ Intermembrane space H+ H+ H+ H+ Electron carrier 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 Some poisons can disrupt e- transport, creating a lethal e- traffic jam Oxygen is the final e- resting place in the chain • ATP synthase uses the potential energy in the proton gradient to generate ATP LE 9-14 INTERMEMBRANE SPACE H+ H+ H+ H+ H+ A rotor within the membrane spins as shown when H+ flows past it down the H+ gradient. H+ H+ A stator anchored in the membrane holds the knob stationary. A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob. H+ ADP + P ATP i MITOCHONDRAL MATRIX Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP. ATP Bookkeeping Electron shuttles span membrane CYTOSOL 2 NADH Glycolysis Glucose MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 Pyruvate 2 Acetyl CoA 6 NADH Citric acid cycle + 2 ATP + 2 ATP by substrate-level phosphorylation by substrate-level phosphorylation Maximum per glucose: About 36 or 38 ATP 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis + about 32 or 34 ATP by oxidation phosphorylation, depending on which shuttle transports electrons form NADH in cytosol Review of Cellular Respiration STEP Glycolysis Krebs e- transport Key Players Glucose, pyruvate NAD+/NADH, CO2 e- transport chain, ATP synthase ATP 2/glucose 2/glucose 32-34/glucose The portion of aerobic respiration which generates the most ATP is 1. 2. 3. 4. 5. Glycolysis The Citric Acid/Krebs cycle Electron transport All of these make the same amount of ATP None of these make ATP Review of Cellular Respiration Oxygen is the final acceptor in the electron transport chain Review of Cellular Respiration STEP Glycolysis Krebs e- transport Key Players Glucose, pyruvate NAD+/NADH, CO2 e- transport chain, ATP synthase ATP 2/glucose 2/glucose 32-34/glucose Human cells can do glycolysis faster than human lungs can take in oxygen Q: What happens if there is not enough oxygen? A: It depends on what kind of creature you are… Without O2, yeast make alcohol, and CO2 is a waste product This is alcohol fermentation Humans make lactic acid instead of ethanol This is lactic acid fermentation Lactic Acid in muscles creates a burning sensation • Overworked muscles can become anoxic • In low oxygen environments, pyruvate is converted to lactate to regenerate NAD+ • Lactic acid causes great suffering Where is aerobic respiration here? Metabolism can build up, or break down The Versatility of Catabolism • Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration • Glucose- 4 calories/gram • Proteins- 4 calories/gram • Fats- 9 calories/gram Anabolic process are fueled with ATP Which of the following produces the most ATP per glucose? A) aerobic respiration B) anaerobic respiration C) alcoholic fermentation D) lactic acid fermentation E) All produce approximately the same amount of ATP per molecule of glucose