Quarter Quiz #3 Prep Metabolism Forms of Energy Laws of thermodynamics 1. Energy cannot be created or destroyed, only changes its form 2. Each time energy is converted, a little is lost to the universe – entropy (entropy is the lost energy) Living is “work” - Cells should organize small molecules into polymers, pump substances across membranes, move or change their shapes, grow and reproduce. o They “work” just to maintain their complex structure. - 2nd law of thermodynamics: order is unstable - Cells are open systems because the energy is exchanged between them and their surroundings. - Cells constantly change. They degrade complex molecules - They have to be rebuilding all the time, which takes a lot of energy Energy must be derived from “outside sources” - Most organisms like plants and photosynthetic organisms gain energy from sunlight (energy entering the ecosystem) - Animals get fuel from eating plants or eating organisms that eat plants. - Chemical energy in organic molecules will be used to generate ATP the energy source that drives most cellular work. Energy is Transduced (Changed in Form) - Ex. Glucose can be broken down so that the energy stored in the carbon-carbon bonds is released and used to produce ATP. o With energy transduction, a little energy is lost in the form of heat (concept of entropy) Metabolism = catabolism and anabolism (The sum of all building up reactions and breaking down reactions) Metabolic Pathways - When large molecules are broken down, it takes a series of rxns to accomplish o Some energy will be released and some will be used to build new molecules. - Exergonic reaction – spontaneous and energy-releasing - The breakdown reaction usually need to be forced by a catalysts or enzymes Enzyme Are Organic Catalysts - The energy that is needed to push a rxn forward is reduced when an enzyme is helping. o The activation energy is higher in uncatalyzed rxn o Lower activation energy in catalysed rxns. - In any chemical rxns there will be a natural repulsion between the electrons in the outer orbitals of the reactants - The orientation of the molecule is often wrong, so that the sides bump together are not the most suitable for making a bond - Only molecules with enough kinetic energy can break bonds and reform bonds to get over the activation energy barrier. Enzyme - Enzymes are usually globular structures which act on much smaller substrates. - Each protein has a unique 3D shape arising from primary, secondary and tertiary protein structure. - On the surface of each enzyme, there is a small area called the active site, which is the key to the enzyme’s specificity (? :/) - Enzymes may also depend on cofactors that are essential for activity o These are special substrates that bind temporarily to a site on the enzyme o The enzyme itself doesn’t change in the chem rxn, it only catalyzes, but the cofactor will change (thus their original form must be restored by other reactions before they can function again. NAD+ And NADH - Enzyme cofactors that are involved in cellular respiration NADP And NADPH - Enzyme cofactors involved in photosynthesis - Energy stored in organic molecules is found in the chemical bonds - If these molecules were to release all their energy at the same time a large amnt of nrg would be lost in the form of heat = spontaneous combustion - Molecules are broken down in a stepwise manner which slowly releases the nrg in a controlled manner. A cell must break he bonds slowly and only a few at a time. So that it is better able to harness the nrg, store it in another form immediately, or it will be lost as heat to the universe. Transducing the Energy - Exergonic – chemical rxns that release nrg - Endergonic – chem rxns that need nrg. o These are often coupled to ensure that the least amnt of nrg is lost as heat. - Cells will use enymes to couple the rxns together o Enzymes that couple the breakdown of C-C bonds with the addition of P to ADP (ADP to ATP) ▪ ^ substrate phosphorylation ▪ Limits the energy lost to the universe, but there will always be a lil nrg lost. - The process of harnessing the energy and storing it is carried out by oxidation and reduction reactions. - The energy has moved around in electrons Electrons from catabolic ( exergonic) reactions are carried by special molecules which work with enzymes (NAD and FAD coenzymes) - The flow of electron from one molecule to another can be thought of as an electrical current. - Each time the electron moved through a different molecule or protein complex, a lil energy is deposited o ^ this energy is used to build molecules and transportations or can be transferred to ATP for short term storage ATP: Biological Energy - The rechargeable batteries of the cell - Source of potential energy - ATP can transfer energy from chem bonds to endergonic reactions occurring in the cell. - ATP carries the energy in the covalent bonds between the phosphates Recharging - ATP must be regenerated - ~90 lbs of ATP every day The energy needed to convert ADP to ATP can come from three distinct sources: 1. Substrate phosphorylation - Taking the energy that is stored in an organic molecule and using to make ATP 2. Oxidative phosphorylation - Movement of electrons down ETC in the inner mitochondrial membrane 3. Photosynthesis - Harnessing the energy of the sun and storing it as ATP Photosynthesis
