Exam # 2 Study Guide Chapters: 6 – 8 Chapter 6: Energy and Metabolism. Terms and Definitions: - Catalyst: substance that speeds up a chemical reaction by lowering the activation energy. What is Metabolism? -Metabolism is the sum of all biochemical reactions in a cell. It includes two types of reactions, anabolism and catabolism. -Anabolic reactions: require energy to build up molecules (dehydration). -Catabolic reactions: break down molecules and release energy (hydrolysis). What is “Activation Energy”? Activation energy is the extra energy needed to destabilize existing chemical bonds and initiate a chemical reaction. The rate of exergonic reaction depends on the activation energy and it can be increased by (1) increasing the energy of reacting molecules or (2) by lowering activation energy. What are enzymes? What are their functions? -Enzymes are agents that carry out most of the catalysis in living organisms. -Most enzymes are proteins that may be found in the cytoplasm or attached to cell membranes and organelles. -They alter the activation energy of a reaction. -An enzyme consists of active sites (pockets for substrate binding) so that when it binds to a substrate it becomes an ‘enzyme-substrate complex’. What do enzyme cofactors do? -cofactors are chemical components that assist enzyme function. These can be metal ions that are often found in the active site participating directly in catalysis. -Cofactors are called coenzymes if they are nonprotein organic molecules. Vitamins are example of coenzymes. What is the role of inhibitors? What is the difference between their types? BIO 183 1st Edition-Inhibitors are substances that bind to enzymes and decrease their activity. -There are 2 types: -competitive: compete with substrates for active sites. -noncompetitive: bind to enzymes on allosteric sites (other than active sites), which affect the shape of enzymes so that they can bind to substrates. What is a biochemical pathway? -A biochemical pathway is a sequence of reactions that occur in the cell. It is the organizational unit of metabolism. -In such pathways, the product of one reaction becomes the substrate for the next. Figure 1. Biochemical pathway What is a feedback inhibition? -Feedback inhibition is when the end-product of a biochemical pathway binds to an allosteric site on the enzyme that catalyzes the first reaction in the pathway. -It shuts down pathway so raw materials and energy are not wasted.What are the major factors that affect the function of an enzyme? -Temperature -pH -substrate concentration -Salt concentration -inhibitors Chapter 7: How Cells Harvest Energy. Terms and Definitions: - Electrochemical gradient: is a gradient of electrochemical potential, usually for an ion that can move across a membrane. - ATP: Adenosine triphosphate is used to power most of the cell’s activities. - ATP synthase: is the enzyme that synthesizes ATP using energy from a proton gradient (H+). - NAD: nicotinamide adenosine dinucleotide acts as a cofactor that helps enzyme catalysis. What is the difference between Autotroph and Heterotroph? Organisms can be classified based on how they obtain energy: -Autotroph: able to produce their own organic molecules through photosynthesis. -Heterotroph: live on organic compounds produced by other organisms. What is a ‘Redox reaction’? What is the difference between fermentation, Aerobic, and Anaerobic respiration? Redox reaction is the pair of oxidation (electron loss) and reduction (electron gain) reactions. Oxidation-reduction reactions play a role in the flow of energy through biological systems. For example, cells use NAD+ as a cofactor to carry out redox reactions. NAD+ accepts 2 electrons and 1 proton to become NADH. NADH can then donate electrons to other molecules. At the end of the process, high-energy electrons from the initial chemical bonds lose much of their energy and are transferred to a final electron acceptor. -Aerobic respiration: is when the final acceptor is oxygen. -Anaerobic respiration: is when the final acceptor is an inorganic molecule other than oxygen. -Fermentation: is when the final acceptor is an organic molecule.How do electrons transport work? ATP is generated when electrons transfer from one energy level to another. Energy is released each time electrons fall to lower energy levels in steps. What are the types of electron carriers? Electron carriers are used in energy metabolism. Different forms of these carriers can be used. 1. Soluble carriers: move electrons from one molecule to another. 2. Membrane-bound carriers: form a redox chain. 3. Carriers: move within membrane. These carriers can be reversibly oxidized or reduced. NAD+ is one of the most important electron and proton carrier. How is ATP synthesized? ATP is synthesized by two different mechanisms: 1. Substrate-level phosphorylation: -ATP is formed by transferring a phosphate group directly to ADP from a phosphate-bearing intermediate or substrate. -A molecule of phosphoenolpyruvate (PEP) possess a high-energy phosphate bond similar to the bonds in ATP. When a phosphate group from PEP is transferred to ADP, the energy in the bond is conserved and ATP is created. 2. Oxidative phosphorylation: -ATP is synthesized by the enzyme ATP synthase using energy from a proton (H+). -This gradient is formed by high-energy electrons from the oxidation of glucose passing down an electron transport chain. Depleted energy from electrons are then donated to oxygen. -The cell carries out a series of enzyme-catalyzed reactions that remove energetic electrons.These electrons are then used in an electron transport chain and passed to the intermembrane space. -Since it is an aerobic respiration, the final acceptor is O2, and the resulting proton gradient provides energy for ATP synthase to phosphorylate ADP to ATP. What are the stages for glucose oxidation? 1. Glycolysis: -Occurs in the cytoplasm. -Consists of 10-step biochemical pathway. -Converts glucose (6 Carbons) to 2 pyruvate (3 Carbons). -Produces 2 ATP molecules for each pyruvate by substrate-level phosphorylation. -Reduces NAD+ to 2 NADH for each pyruvate. Recycling NADH to continue respiration by: a. Aerobic respiration: -Produces ATP -O2 is the final electron acceptor b. Fermentation: -occurs when O2 is not available