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METABOLISM METABOLISM What is metabolism? Total of all chemical reactions occurring within the body Categories of metabolic reactions Catabolic reactions Degradation pathways Anabolic reactions Synthesis pathways 2 METABOLISM 3 ENERGY What is energy? No mass; does not take up space Has the capacity to do work (potential energy) or to put matter into motion (kinetic energy) Can be converted into different forms but is not created or destroyed 4 ENERGY What types of energy are there? Chemical Electrical Involves movement of charged particles Mechanical Energy stored in chemical bonds Involves movement of matter Electromagnetic (radiant) Energy traveling in waves 5 Quick Quiz: Potential energy can be “stored” in all of the following forms except… A) Electromagnetic energy B) Electrical energy C) Mechanical energy D) Chemical energy 6 ENERGY Where does our energy for metabolism come from? Chemical energy Nutrients (food) Electromagnetic energy Heat (thermal) Sun or geothermal sources Visible light 7 ENERGY Energy for cellular metabolism must be “refined”, or converted to useful types of energy Photosynthesis Electromagnetic energy (sunlight) chemical energy Aerobic respiration Chemical energy (chemical bonds of certain molecules) chemical energy (more usable form for cells) 8 ATP (adenosine triphosphate) 9 10 Quick Quiz: ATP is an example of which of the following energy forms? A) Electromagnetic energy B) Thermal energy C) Mechanical energy D) Chemical energy 11 Energy Flow & Nutrient Cycling in Biological Systems Energy 1-way flow Ultimately lost as heat Nutrients Cycled 12 Nutrients What are nutrients? Chemical substances needed for normal metabolism & growth O C Ca H N P K S Na Cl Mg I Fe Organic vs. inorganic nutrients Macronutrients Proteins Carbohydrates Lipids Nucleic acids 13 Quick Quiz: Which of the following is NOT recycled in an ecosystem? A) Carbon B) Electromagnetic energy C) Water D) Nitrogen 14 ENZYMES Chemical reactions Reactants are converted into products Atoms become combined in new forms O2 + 2 H2 2 H2O 15 ENZYMES Reaction rates Typically too slow to sustain life Need help to speed up Enzymes are biological catalysts Catalysts speed up reactions They do not make a reaction happen that wouldn’t have happened otherwise Enzymes are usually made out of protein 16 ENZYMES Reaction rates Typically too slow to sustain life Need help to speed up Enzymes are biological catalysts Catalysts speed up reactions They do not make a reaction happen that wouldn’t have happened otherwise Enzymes are usually made out of protein 17 ENZYMES In order to react, molecules go through awkward transitions Unstable, high-energy states: Transition states Enzymes help to speed up reactions by stabilizing transition states 18 ENZYMES Reactants: 2H2 O2 Free energy Activation energy Difference between free energy of reactants and products Time Products: 2H2O Quick Quiz: True or false: An enzyme makes a reaction that wouldn’t have happened A) True B) False 20 Quick Quiz: The difference between the amount of energy in reactants and the maximal amount of energy in the transition state is called… A) Activation energy B) Free energy C) Catalyst D) Potential energy 21 Photosynthesis C6H12O6 22 Photosynthesis Occurs in chloroplasts Outer membranes (2) Thylakoid membrane system Stroma 23 Photosynthesis Two distinct events 24 Light-dependent reactions (light reactions) Occurs in thylakoids of chloroplasts Energy from sunlight used to generate ATP & NADPH Splits H2O, releasing O2 as a byproduct Light-independent reactions (dark reactions) Occurs in stroma of chloroplasts Uses CO2, ATP & NADPH to synthesize glucose Photosynthesis Process summary 25 Photosynthesis How is light energy actually captured and converted into chemical energy? Photopigments capture photons of light Chlorophylls (a, b) Accessory pigments (carotenoids, phycobilins) Electron carriers transfer energy to form ATP & NADPH Calvin-Benson cycle uses the ATP & NADPH to “fix” CO2 into sugars (glucose) 26 Quick Quiz: Which stage of photosynthesis requires carbon dioxide? A) Light-dependent reactions B) Light-independent reactions 27 Quick Quiz: True or false: the goal of photosynthesis is to produce oxygen. A) True B) False 28 Light-Dependent Reactions Photopigments & the Electromagnetic Spectrum 29 Photopigments & the Electromagnetic Spectrum 30 Englemann’s Experiment 31 Light Capture & Energy Transport Two photosystems for capturing light energy 32 Quick Quiz: In a plant cell, which of the following is NOT where you would find chlorophyll? A) Photosystem I B) Photosystem II C) ATP synthase D) Thylakoid membrane 33 Quick Quiz: What is the final product of the “light reactions”? A) glucose B) starch C) ATP D) NADPH E) C and D only F) All of the above 34 Light-Independent Reactions Calvin-Benson cycle Occurs in stroma of chloroplast Use ATP & NADPH generated during light-dependent reactions Carbon fixation 6 CO2 + 6 RuBP 1 glucose Rubisco (enzyme) RuBP = ribulose bisphosphate 35 36 Photosynthesis Process summary C6H12O6 ATP + NADPH 37 Quick Quiz: How many carbon atoms does RuBP have? (Just press the number on your keypad that corresponds with your answer.) 38 Quick Quiz: Which of these is a product of the Calvin-Benson cycle (aka the “dark-reactions” or “lightindependent reactions”) A) ATP B) glucose C) NADPH D) CO2 39 Variations to Photosynthetic Systems in Plants Differences in environments (light intensity, temperature, rainfall, soil conditions, etc) can affect how photosynthesis proceeds in plants How to deal with hot, dry conditions 40 Stomata Allow gas exchange through leaves (O2, CO2, H2O) Close in hot dry weather to prevent excess water loss Causes increase in O2 levels; decrease in CO2 levels Triggers photorespiration (bad news!) 41 C3 Plants 42 E.g., evergreen trees (temperate zones) With stomata closed… Rubisco fixes O2 when CO2 levels drop Efficiency reduced by 1/2 C4 Plants E.g., grasses, corn, tropical plants Two carbon fixation steps Each fixed in different types of cells Maintain higher internal CO2 levels in the cells that make sugar than C3’s 43 Lose less water, make more glucose than C3 plants during hot/dry conditions CAM Plants 44 E.g., cactus, desert plants Stomata close during the day and open at night Carbon fixation occurs at night Most efficient under hot/dry conditions Quick Quiz: Which of the following plants uses a 4-carbon molecule in the Calvin cycle? A) Corn B) Douglas fir C) Saguaro cactus D) A and B E) A and C 45 “The Circle of Life” 46 “The Circle of Life” 36 ATP 47 Aerobic Respiration C6H12O6 + 6 O2 6 CO2 + 6 H2O + 36 ATP glucose oxygen carbon dioxide water 48 Aerobic Respiration Involves 3 linked processes Glycolysis Citric acid cycle TCA (tricarboxylic acid cycle) / Krebs cycle Oxidative phosphorylation Respiratory transport chain / electron transport chain ATP synthase 49 Aerobic Respiration 50 Glycolysis “Sugar splitting” Occurs in cytoplasm Net reaction: 1 glucose 2 pyruvate + 2 ATP + 2 NADH C6H12O6 C3H3O3 51 Glycolysis (part 1) 52 Glycolysis (part 2) 53 Glycolysis Bottom line… 1 glucose 2 pyruvate + 2 ATP + 2 NADH Glucose (6 C) split into 2 molecules of pyruvate (3C) To TCA cycle 54 Glycolysis Bottom line… 1 glucose 2 pyruvate + 2 ATP + 2 NADH Glucose (6 C) split into 2 molecules of pyruvate (3C) Uses 2 ATP, produces 4 ATP net yield of 2 ATP Available for immediate energy needs 55 Glycolysis Bottom line… 1 glucose 2 pyruvate + 2 ATP + 2 NADH Glucose (6 C) split into 2 molecules of pyruvate (3C) Uses 2 ATP, produces 4 ATP net 2 ATP Produce reducing potential (NADH) To electron transport (oxidative phosphorylation) 56 Quick Quiz: The end result of glycolysis is 2 molecules of ________. A) Carbon dioxide B) Oxygen C) Glucose D) Pyruvate 57 Quick Quiz: True or false: Plant cells have mitochondria. A) True B) False 58 TCA Cycle Occurs in mitochondria Matrix (inner compartment) Net reaction: 2 pyruvate 6 CO2 + 2 “ATP” + 8 NADH + 2 FADH2 59 TCA Cycle 60 TCA Cycle Bottom line… 2 pyruvate 6 CO2 + 2 “ATP” + 8 NADH + 2 FADH2 Glucose now completely oxidized to CO2 Diffuses from cell Generates lots of reducing potential (NADH, FADH2) To electron transport chain (ETC) 61 Quick Quiz: Which of the following is NOT a product (or byproduct) of the TCA cycle? A) NADH B) FADH2 C) ATP D) Pyruvate E) CO2 62 Oxidative Phosphorylation Occurs in mitochondria (inner membrane) Most efficient system for ATP generation Net reaction: 10 NADH + 2 FADH2 + 6 O2 32 ATP + 6 H2O 63 Oxidative Phosphorylation 64 Oxidative Phosphorylation ATP INNER COMPARTMENT ADP + Pi 65 Oxidative Phosphorylation 66 Oxidative Phosphorylation Bottom line… 10 NADH & 2 FADH2 + 6 O2 32 ATP + 6 H2O Use “energy carriers” (NADH, FADH2) from glycolysis and TCA cycle to generate ATP O2 is the terminal acceptor for the transferred electrons Involves ATP synthase Uses H+ concentration gradient 67 Aerobic Respiration 68 Quick Quiz: Where is the electron transport chain located? A) Cytoplasm B) Mitochondrial matrix C) Outer mitochondrial membrane D) Inner mitochondrial membrane E) Intermembrane space (outer compartment) 69 Quick Quiz: What would happen to oxidative phosphorylation if oxygen were not available? A) Oxidative phosphorylation would cease B) Oxidative phosphorylation would increase C) Oxidative phosphorylation would occur at the same rate 70 Anaerobic Respiration ATP generation in the absence of O2 Involve terminal electron acceptors other than oxygen E.g., O-containing salts (nitrates, nitrites, sulfates, sulfites) Anaerobic bacteria 71 Anaerobic Respiration ATP generation in the absence of O2 ATP produced through glycolysis with lactic acid and/or ethanol and CO2 as end products Fermentation Lactic fermentation Alcoholic fermentation Decreased efficiency; have to deal with by-products 72 Lactic Fermentation 73 Alcoholic Fermentation 74 Alternate Energy Sources & Biosynthesis 75 Quick Quiz: True or False – The TCA cycle can only be used to oxidize (process) pyruvate. A) True B) False 76