THE ENERGY OF LIFE LESSON 5 Note: Recycle Aerobic (oxygen-requiring) CELLULAR RESPIRATION oxidizes fuel molecules and generates ATP for cellular work. (Aerobic Harvesting of Energy) Sugar is broken down to carbon dioxide (CO2) and water (H2O). The cell captures some of the released energy to make ATP. Chapter 6 Chapter 6 BREATHING vs. RESPIRATION Breathing supplies O2 for use in cellular respiration and removes CO2. Note: تنفس In breathing, CO2 and O2 are exchanged between your lungs and the air. In cellular respiration, cells use the O2 obtained through breathing to break down fuel, releasing CO2 as a waste product. Chapter 6 CELLULAR RESPIRATION BANKS ENERGY IN ATP MOLECULES Cellular respiration is an exergonic process that transfers energy from glucose to form ATP. can produce up to 32 ATP molecules for each glucose molecule. uses about 34% of the energy stored in glucose with the rest of the energy lost as heat. Cellular respiration provides energy for body maintenance and voluntary activities. Note: How do cells extract energy from fuel molecules? CELLS CAPTURE ENERGY FROM ELECTRONS “FALLING” FROM ORGANIC FUELS TO OXYGEN During cellular respiration, electrons are transferred from glucose (or other organic fuels) to oxygen, releasing energy. Redox (reduction-oxidation) reaction The hydrogen movements represent electron transfers because each hydrogen atom consists of an electron and a proton. Chapter 6 Chapter 6 Electrons removed from fuel molecules (oxidation) are transferred to NAD+ (reduction). The hydrogen atoms are not transferred directly to oxygen, but instead are usually passed first to an electron carrier, a coenzyme, NAD+ (nicotinamide adenine dinucleotide). Note: Stepping down an energy staircase NADH passes electrons to an electron transport chain. Energy is released as electrons “fall” from carrier to carrier and finally to O2. • Hydrogens, electrons, and oxygen combine to form water Chapter 6 STAGES OF CELLULAR RESPIRATION Chapter 6 Note: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate. Anaerobic production of ATP GLYCOLYSIS “SUGAR SPLITTING” Glucose (6C sugar) is split into two Pyruvates (3C sugars) which are oxidized and rearranged in the cytosol. The net energy produced by glycolysis is 2ATP and 2NADH. ATP is formed by substrate-level phosphorylation, in which a phosphate group is transferred from an organic molecule to ADP. Chapter 6 GLYCOLYSIS Chapter 6 Chapter 6 PYRUVATE OXIDATION Note: Chapter 6 TCA (e.g. citric acid) In eukaryotic cells, the citric acid cycle occurs in the matrix of the mitochondrion. PYRUVATE OXIDATION When O2 is present, the pyruvate enters a mitochondrion via active transport, and converts to Acetyl CoA and yields CO2 and NADH. CITRIC ACID CYCLE = Krebs Cycle = tricarboxylic acid (TCA) cycle completes the oxidation of organic molecules, generating many NADH and FADH2 (flavin adenine dinucleotide). • Acetyl CoA is broken down to 2CO2 molecules. • The cycle generates 1ATP per turn, but most chemical energy is transferred to NAD+ and FAD producing 3NADH and FADH2. CITRIC ACID CYCLE Chapter 6 The reduced coenzymes, NADH and FADH2, shuttle their cargo of high energy electrons into the electron transport chain. Note: Almost 90% of the ATP generated in cellular respiration is made by oxidative phosphorylation OXIDATIVE PHOSPHORYLATION Most ATP production occurs by oxidative phosphorylation. Electrons from NADH and FADH2 are passed down the electron transport chain to O2, which picks up H+ to form water. • During electron transport along the chain, electron carriers which alternate between reduced & oxidized states by accepting & donating electrons. Energy released by these redox reactions is used to pump H+ into the intermembrane space. In chemiosmosis, the H+ gradient drives H+ back through ATP synthase complex in the inner membrane, synthesizing ATP. FERMENTATION: ANAEROBIC HARVESTING OF ENERGY Fermentation enables cells to produce ATP without oxygen. • harvests chemical energy without using electron transport chain. NAD+ is recycled from NADH as pyruvate is reduced to lactate (lactic acid fermentation) or alcohol and CO2 (alcohol fermentation). Note: An electron transport chain is used in anaerobic respiration but not in fermentation. Anaerobic respiration: has electron transport chain, but the final electron acceptor is other than oxygen. Chapter 6 CELLS USE MANY KINDS OF ORGANIC MOLECULES AS FUEL FOR CELLULAR RESPIRATION Carbohydrates, fats, and proteins from food can all be used as fuel for cellular respiration. Monomers of these molecules enter glycolysis or the citric acid cycle at various points. Note: Fats contain many hydrogen atoms and thus many energy-rich electrons. Chapter 6 ORGANIC MOLECULES FROM FOOD PROVIDE RAW MATERIALS FOR BIOSYNTHESIS Cells use intermediates from cellular respiration and ATP for biosynthesis of other organic molecules. Metabolic pathways are often regulated by feedback inhibition. e.g. If ATP accumulates in a cell, it inhibits an early enzyme in glycolysis, slowing down respiration. Chapter 6 YOU SHOULD NOW BE ABLE TO 1. Compare the processes and locations of cellular respiration and photosynthesis. 2. Provide the overall chemical equation for cellular respiration. 3. Explain how the energy in a glucose molecule is released during cellular respiration. 4. Explain how redox reactions are used in cellular respiration. 5. Compare the reactants, products, and energy yield of the three stages of cellular respiration. 6. Compare the reactants, products, and energy yield of alcohol and lactic acid fermentation. 7. Explain how carbohydrates, fats, and proteins are used as fuel for cellular respiration. PHOTOSYNTHESIS: Using light to make food Note: Photoautotroph Tropical forest plants Kelp, a large alga Cyanobacteria (photosynthetic bacteria) Note: Does the oxygen come from carbon dioxide or water? PHOTOSYNTHESIS Conversion of sunlight energy to the chemical energy stored in sugar provides food and O2 for almost all living organisms. Photoautotrophs use the energy of sunlight to convert CO2 and H2O to sugar O2. • Autotrophs: “Self-feeders”. Organisms that produce their own organic molecules for energy and carbon skeletons. Producers. • Heterotrophs: Organisms that live on compounds produced by other organisms. Consumers. Chapter 7 PHOTOSYNTHESIS OCCURS IN CHLOROPLASTS Chloroplasts are surrounded by a double membrane and contain stacks of thylakoids and a thick fluid called stroma. • The thylakoid membrane house much of the machinery that converts light energy to chemical energy, which is used in the stroma to make sugar. Chlorophyll is a light-absorbing pigment built into the thylakoid membrane that plays a central role in converting solar energy to chemical energy. Chapter 7 PHOTOSYSTEMS CAPTURE SOLAR ENERGY In the thylakoid membrane, chlorophyll molecules are organized along with other pigments and proteins into photosystems. Chapter 7 TWO PHOTOSYSTEMS COOPERATE IN THE LIGHT REACTIONS Electrons are removed from water, passed from photosystem II to photosystem I, and accepted by NADP+, reducing it to NADPH. Two photosystems connected by an electron transport chain generate ATP and NADPH. Chapter 7 Note: • Light energy absorbed by the two photosystems drives the flow of electrons from water to NADPH. • The electron transport chain helps to produce the concentration gradient of H+ across the thylakoid membrane, which drives H+ through ATP synthase, producing ATP. • Because the initial energy input is light (“photo”), this chemiosmotic production of ATP is called photophosphorylation. Chapter 7 PHOTOSYNTHESIS OCCURS IN TWO STAGES, WHICH ARE LINKED BY ATP AND NADPH The light reactions in thylakoids convert light energy to chemical energy, producing ATP and NADPH split water, releasing O2. The Calvin cycle in the stroma forms sugar from CO2 (Carbon fixation), using ATP for energy and NADPH for reducing power produced from the light reaction. Light-independent reactions The cycle returns ADP, and Pi, and NADP+ to the light reactions. Note: • Solar energy • Using carbon from CO2, electrons from NADPH, and energy from ATP, the cycle constructs G3P (glyceraldehyde-3-phosphate), which is used to build glucose and other organic molecules. Cellular respiration Other organic compounds Chapter 7 YOU SHOULD NOW BE ABLE TO 1. Explain how plants produce oxygen. 2. Explain how photosystems capture solar energy. 3. Explain how the electron transport chain and chemiosmosis generate ATP, NADPH, and oxygen in the light reactions. 4. Review the overall process of the light reactions and the Calvin cycle, noting the products, reactants, and locations.