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Chapter Six Energy and Metabolism I. Energy A. Energy: Kinetic & Potential Energy, Chemical Energy B. Two Law of Thermodynamics Term: Entropy C. ATP Structure & Function – Exergonic & Endergonic Reactions – Coupled Reactions D.Enzymatic Reactions (E + S ---> E•S ---> E + P) – Factors that Affect Enzymatic Reactions I. Energy (pg. 105) A. Sun = Ultimate source of all energy; (e.g. radiant energy) – Living things cannot maintain organization, grow, repair, or reproduce w/o constant input of ENERGY – ENERGY = Capacity to do Work • Two major categories of energy: – KINETIC = energy of motion (e.g. mechanical energy) – POTENTIAL = stored energy (e.g. chemical energy) • Potential energy is stored in the chemical bonds of molecules (e.g. ATP & glucose) • When chemical bonds are broken, energy is released • Provides energy for cellular work Kinetic – Movement of muscles (mechanical work) – Movement of molecules across PM (transport work) – Synthesis (dehydration) chemical reactions (chemical work) • Calorie - a measure of energy – Amount of heat required to raise the temperature of 1 g of water by 1º C – 1 Calorie = 1000 calories = 1 kilocalorie • Oxidation-reduction reactions transfer electrons while bonds are made or broken. – OXIDATION = when an atom or molecule losses an electron – REDUCTION = when an atom or molecule gains an electron • Oxidation and reduction reactions (redox reactions) always take place together and play a critical role in the flow of energy through biological systems. B. Two laws of thermodynamics: (pg. 105-106) • Thermodynamics = study of energy transformations 1. Law of Conservation – Energy cannot be created nor destroyed but can be changed from one form to another – EXAMPLE: (chemical) (mechanical) POTENTIAL KINETIC Gas in car Car moves Glucose → ATP Cell work 2. Energy cannot be changed from one form to another without a loss of usable energy. When energy is transformed, only some of the energy is converted into a usable form for cell work. Most of the energy is “lost” from the system as heat. (NOTE: Heat is not a usable form of energy for cellular work; however, it can be used to warm our body.) – EXAMPLE: HEAT POTENTIAL KINETIC Gas in car Car moves Hood of car gets hot Glucose → ATP Cell work Heat generated helps maintain body temperature HEAT HEAT • CONCEPTS: – Potential energy can be converted into kinetic energy and vise versa – Conversion of energy is NOT efficient (cells about 40% efficient; better than machines) – As energy conversions occur, most energy is changed into heat – Living things continually lose heat (energy) to the environment; therefore, a constant input (solar energy) is required • Heat gives disorder to the system • Amount of disorder in system is measured as amount of ENTROPY • Universe as a whole has increasing disorder C. ATP Structure & Function (pg. 107) – ALL CELLS use ATP for energy - common currency of energy – Review Structure of ATP (nucleotide): ribose sugar; adenine nitrogen base; 3 P groups + High energy bond Adenosine Triphosphate ATP Adenosine Diphosphate ADP + Phosphate P – Just enough energy is released when ATP → ADP + P so little energy is wasted – Consumption and regeneration of ATP of entire pool of ATP occurs about once each minute. • Exergonic & Endergonic Reactions (pg. 108) • Metabolism - Sum of all the chemical reactions occurring in the cell • Two types of chemical reactions as they relate to energy 1. Endergonic - Chemical reactions that require an input of energy – Building up of molecules - forming bonds – Synthesis (e.g. dehydration) reactions – EXAMPLES A+B→C INPUT Energy ADP + P → ATP PS: CO2 + H2O → (CH2O)n + O2 Solar Energy • Exergonic - Chemical reactions that release energy – Breaking down of molecules - breaking bonds – Degradation (e.g. hydrolysis) reactions – EXAMPLES A→B+C OUTPUT Energy ATP → ADP + P CR: (CH2O)n + O2 → CO2 + H2O 36 – 38 ATP Molecules • Concept: • Coupled Reactions (pg. 89) - occur in the same place at the same time • Energy released from exergonic reactions can be used to drive the endergonic reactions. A→B+C OUTPUT Energy INPUT A+B→C D. Enzymatic Reactions (pg. 109) – Enzymes speed up chemical (metabolic) reactions. – Without enzymes, chemical reactions within cells would occur too slowly. E Organic catalyst Speeds up chemical Rx Protein (can be denatured) Lowers E of A Specific for substrate Contains active site where substrate fits Usually ends in -ase S Reactant E•S complex Induced Fit Model E Unchanged P Formed as a result of chemical Rx • Enzyme - Speeds up chemical reactions by lowering the energy of activation • Energy of Activation - Energy needed to start a chemical reaction • Active Site - Place on the enzyme where the substrate(s) fit • Induced Fit Model - Model that explains how the active site of the enzyme alters slightly to accommodate the substrate; Helps achieve an optimum E•S fit and facilitates the enzyme reaction *NOTE: Not all enzymes are proteins. Some reactions are catalyzed by RNA. Ribozymes are RNA with enzymatic abilities (Ribosomes) • Enzymes are specific and can only react with a certain substrate AND are usually named by adding (–ase) to the substrate name. – Substrate: Urea Enzyme: Urease – Substrate: lactose Enzyme: lactase • CONCEPT: – It takes many different kinds of enzymes to catalyze all the reactions within cells. However, cells do not make to make large quantities of each because – enzymes are unchanged (not consumed) during the chemical reaction – are used over and over again • Factors that Affect Rate of Reactions: (*denatures) p. 110-112 – Maximum Rate occurs when there is enough substrate available to fill the actives sites of all enzyme molecules most of the time 1. Substrate concentration - ↑ sub. Conc = ↑ rate (to a point) 2. Temperature * - ↑ rate = ↑ rate to a point (Optimal temp 35-40°C) 3. pH * - optimal pH varies per enzyme; adjust pH = ↑ rate 4. Cofactors / Coenzymes • As enzymes are needed to be present for reactions to occur, also cofactors and/or coenzymes may need to be present in order for enzymes to function properly. – Cofactors: Inorganic ions • Examples: Metal ions such as Cu, Zn, Fe – Coenzymes: Organic non-protein molecules • Cells make coenzymes from our dietary intake of vitamins • Examples: NAD+, FAD, CoA 5. Inhibitors (pg. 112) • Competitive inhibition – Inhibitor competes with substrate for Active Site Bad • Non-Competitive inhibition – Inhibitor sets in Allosteric Site in vicinity of active site causing a change in the Active Site of the enzyme Good • Feedback inhibition - Method in which cells control amount of product being made B-ase A-ase C-ase D-ase B C D A E Binds to Allosteric Site NOTE: Inhibitions are usually reversible. But in the cases of poisons, they can be irreversible. ** OVERVIEW: Factors that affect rate vs. maximizing the rate of reactions** Product acts as Temporary inhibitor