١٣/١٢/١٤٣٥ Energy Transformation Reactions Palestine Polytechnic University Department of Environmental Engineering Technology Course: Environment & Biological Diversity • By controlling energy-releasing reactions, organisms are able to use the energy to power activities (reproduction, movement, growth...) • These reactions form biochemical pathways when they are linked to one another. • The products of one reaction are used as the reactants for the next. • All of the chemical reactions in a cell are referred to as the cell’s metabolism. Instructor Dr. Ayman Salah Chapter 7 Energy Transformation Reactions • All living organisms require energy to sustain life. • The source of this energy comes from the chemical bonds of molecules. • Burning organic molecules release energy by breaking chemical bonds.  What are the products of burning? • Living organisms are capable of doing so but in a controlled manner. ١ Energy Transformation Reactions • Living organisms are two types according to the way by which they obtain energy: 1- Autotrophs : "self-feeders (auto means "self," and trophs means "feed"); organisms that make their own food; • Chemoautotrophs: use inorganic substances such as hydrogen sulfide as a source of energy. • Photoautotrophs: convert light energy from the Sun into chemical energy, such as the plants. 2- Heterotrophs: organisms that need to ingest food to obtain energy. ١٣/١٢/١٤٣٥ Energy Transformation Reactions Metabolism • All of the chemical reactions in a cell • Metabolic pathways include two broad types: 1. Catabolic pathways: release energy by breaking down larger molecules into smaller molecules. 2. Anabolic pathways: use the energy released by catabolic pathways to build larger molecules from smaller molecules. • The relationship of anabolic and catabolic pathways results in the continual flow of energy within an organism. Energy Transformation Reactions Metabolism • Two important metabolic pathways: 1- Photosynthesis is the anabolic pathway in which light energy from the Sun is converted to chemical energy for use by the cell • In this reaction, autotrophs use light energy, carbon dioxide, and water to form glucose and oxygen. ٢ Energy Transformation Reactions Metabolism 2- Cellular respiration is the catabolic pathway in which organic molecules are broken down to release energy for use by the cell. • In these reactions, oxygen is used to break down organic molecules, resulting in the production of carbon dioxide and water Energy Transformation Reactions Photosynthesis • Photosynthesis is a process in which light energy is converted into chemical energy. • The overall chemical equation for photosynthesis is: light 6CO2 + 6H2O C6H12O6 + 6O2 • This process occur in the chloroplast of plants ١٣/١٢/١٤٣٥ Energy Transformation Reactions Energy Transformation Reactions The location of photosynthesis • Leaves are the major organs of photosynthesis in plants. • Photosynthetic pigments such as chlorophyll are clustered together on the thylakoid The end products of photosynthesis also can be used to make other organic molecules, such as proteins, lipids, and nucleic acids membranes Energy Transformation Reactions Photosynthesis Photosynthesis occurs in two phases: 1- The light-dependent reactions (Light reactions): light energy is absorbed and then converted into chemical energy in the form of ATP and NADPH. 2- The light-independent reactions (Dark reactions or Calvin cycle): the ATP and NADPH that were formed in phase one are used to make glucose. • Once glucose is produced, it can be joined to other simple sugars to form larger molecules such as starch or used to make other organic molecules. ٣ Energy Transformation Reactions Cellular Respiration • Organic compounds possess potential energy as a result of their arrangement of atoms. • All organisms use glucose (C6H12O6) as a source of energy, except the chemoautotrophs. • Covalent bonds in the sugar glucose contain potential energy • Through a series of enzyme-controlled redox reactions, organisms break the covalent bonds in C6H12O6 and rearrange them into new and more stable configurations (CO2 , water ). ١٣/١٢/١٤٣٥ Energy Transformation Reactions Cellular Respiration • The overall reaction is as follows: • The redox reactions result in the transfer of electrons from glucose to O2. • Glucose is oxidized to 6CO2 and oxygen is reduced to water • From where does energy release? Energy Transformation Reactions Cellular Respiration • When the hydrogen atoms form covalent bonds with oxygen, the shared electron pairs occupy positions closer to the oxygen nuclei than they did when they were part of the glucose molecule. • As electrons (in hydrogen atoms) move from less electronegative carbon atoms in glucose to highly electronegative oxygen atoms, they lose potential energy . • Their energy could be used to phosphorylate ADP molecules, producing higher energy ATP molecules ٤ Energy Transformation Reactions Cellular Respiration • Cellular respiration occurs in two main parts: 1- Glycolysis; anaerobic process • the 6-carbon sugar (glucose) is broken into two smaller 3-carbon molecules of pyruvic acid • 2 ATP are produced. • Hydrogens and their electrons are sent to the electron-transport system (ETS) for processing. 2- Aerobic respiration; includes the Krebs cycle and electron transport Energy Transformation Reactions Cellular Respiration ١٣/١٢/١٤٣٥ Energy Transformation Reactions Cellular Respiration • This is known as aerobic cellular respiration. why? • O2 is not the only possible electron acceptor in the oxidation of glucose in a cell. • Some microorganisms use NO2, SO4, and even Fe+3 as final electron acceptors. • These microorganisms are known as obligate anaerobes -live in environments that contain no O2 Energy Transformation Reactions Cellular Respiration • Living organisms are three types according to their requirements of O2 : 1. Obligate aerobes: require oxygen as the final electron acceptor and cannot survive without it 2. Obligate anaerobes: use something other than O2 as its final hydrogen acceptor. must live in environments that contain no oxygen. 3. Facultative anaerobes: can tolerate aerobic and anaerobic conditions (mostly pathogenic bacteria) ٥ Energy Transformation Reactions Cellular Respiration Anaerobic Cellular Respiration - Fermentation • Organisms use something other than O2 as a final hydrogen acceptor. • The acceptor molecule could be  inorganic; NO2, SO4, CO2, Or  organic molecule such as pyruvic acid. • When organic molecule is the electron accepter the process is called fermentation. • Anaerobic respiration is the incomplete oxidation of glucose Anaerobic Cellular Respiration - Fermentation ١٣/١٢/١٤٣٥ Energy Transformation Reactions Linking Photosynthesis and Cellular Respiration • Photosynthesis and cellular respiration are closely related to one another. • In plants and other autotrophs, both processes may occur within individual cells. • Animals and other heterotrophs undergo cellular respiration, but not photosynthesis. • Heterotrophs require the products of photosynthesis to carry out cellular respiration. • Photosynthesis uses the products of cellular respiration, and cellular respiration uses the products of photosynthesis Linking Photosynthesis and Cellular Respiration ٦ Questions • Are photosynthesis and respiration exact opposites? Explain? • What would happen to humans and most other living organisms on Earth if photosynthesis stopped? • Which contains more free energy: three molecules of CO2 or one molecule of pyrovic acid? Explain. • List two differences between aerobic respiration and fermentation. • Name an organism in which alcoholic fermentation takes place.