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Chapter 6 Metabolism • You will need to read on the aging process in your textbook • Metabolism: refers to the cell’s capacity to acquire energy and use it to build, store, break apart, and eliminate substance in controlled ways Energy • Potential energy: is the capacity to make things happen, to do work – Measured in kilocalories – Also called chemical energy • Kinetic Energy: is the energy of motion – Heat energy • Heat: transfer of energy from ATP also resulted in the release of another form of energy What can cells do with energy? • Energy from the sun or from organic substances becomes coupled to thousands of energy-requiring processes in cells • Cells use the energy to perform chemical, mechanical, and electrochemical work. How much energy is available? • First law of thermodynamics: states that the total amount of energy in the universe is constant; it can’t be created nor destroyed, it can only change forms – Energy can not be produced by the cell- it can only be borrowed from someplace else – High quality energy is usable – Low quality (such as heat) is released into the universe One way flow energy • Second law of thermodynamics: states that the spontaneous direction of energy flow is from high to low quality forms – Each conversion produces energy (usually heat) that is unavailable for work – Entropy: the measure of disorder Cells and Energy Hills • Energy changes in living cells tend to proceed spontaneously in the direction that results in a decrease in usable energy • Endergonic (“energy in”) reactions require input resulting in products with more energy than reactants – Example: Photosynthesis Continue… • Exergonic (“energy out”) reactions release energy such that the products have less energy than the reactants had – Example: Cellular Respiration ATP couples energy inputs with outputs • ATP is composed of adenine, ribose, and three phosphates – Energy input links phosphate to ADP to produce ATP (phosphorlyation phosphate transfer) – ATP can in turn donate a phosphate group to another molecule, which then becomes primed and energized for specific reactions Continue… • ATP is like currency in an economy – Earning ATP is an exergonic reaction and spending (using) ATP is a endergonic reaction – ADP can be recycled to ATP very rapidly in the ATP/ADP cycle Electrons transfer drive ATP formation • Electrons are transferred in nearly every reaction that harnesses energy for use in the formation of ATP (Oxidation-Reduction Reaction) • In plant cells sunlight energy drives electrons from water molecules to initiate the reactions that will eventually produce carbohydrates • In aerobic respiration, the degradation of glucose release energy that can be transferred to ATP – This actually makes more ATP Participants in Metabolic Reactions • Reactants: are substances that enter a reaction • Products: what is produced from a reaction • Intermediates: are compounds that are formed between the reactant and product. • Energy Carriers: are mainly ATP- usually activate enzymes and other factors Continue… • Cofactors: are small molecules and metal ions that help enzymes by carrying atoms or electrons (EXAMPLE: NAD+) • Transport Proteins: are membrane bound proteins that participate in adjusting concentration gradients that will influence the direction of metabolic reactions What are Metabolic Pathways? • Metabolic Pathways form series of reactions that regulate the concentration of substanceds within cells by enzyme-mediated linear and circular sequences • Biosynthetic pathways, small molecules are assembled into large molecules without the need for energy – Example: Simple sugars assembled into larger complex carbohydrates Continue… • Degradative pathways: large molecules such as carbohydrates,lipids, and proteins, are broken down to form products fo lower energy. – Released energy can be used for cellular work Are Reactions Reversible? • Chemical reactions can proceed from reactants to products, which if they are allowed to accumulate, will be convert back to reactants • The direction of concentrations and the collision of molecules Continue.. • When reaction approaches chemical equilibrium, the forward and reverse raction proceed at equal rates – No net change in concentration – Every reaction has it own ratio of products to reactants at equilibrium No vanishing atoms at the end of the run • The law of conservation of mass states that the total mass of all substances entering a reaction equals the total mass of all products. – This is why we must “BALANCE” a chemical equation by having equal number of atoms of each element on both sides of the arrow. C02 + H20 C6H12O6 + O2 Balance the equation Electron Transfer Chains in the Main Metabolic Pathways • Energy is released from storage molecules (such as glucose) in controlled steps via a series of intermediate molecules – Electrons released during bond breaking are transferred stepwise through the components of electron transport systems located on various cells membranes – Oxidized: Electrons are donated – Reduced: Electrons are gained Continue… • Coenzymes: are large organic molecules such as NAD+, FAD, and NADP+ that transfer protons and electrons from one substrate to another. • Electrons are similar to staircases where the electrons flow down the steps from the top (most energy available) to the bottom (least amount of energy) • The energy is harnessed to move H+ ions which turns establish pH and electric gradient Enzymes • Enzymes helps organisms exist through speeding up chemical reactions • Without enzymes could not process food, build new cells, get rid of old cells, keep your brain working, and to contract muscles • Enzymes increases the rate of reaction by lowering the activation energy (the amount of energy needed to get a reaction going) Enzymes have four features: • 1- speed up a chemical reaction • 2- can be reused • 3- at least some of them, can recognize both reactants and products in order to catalyze a reaction in both directions • 4- very selective about substrates How do enzymes lower energy hills? • Active Site: pockets or crevices where substrates are bound and specific reaction are catalyzed – Increases the rate of reaction by creating a microenvironment that is energetically more favorable for the reaction Transition at the Top of the Hill • Activation Energy brings the reactive chemical groups into alignment so that chemical bonds can be broken, created, and rearranged. • The substrate is brought to its transition state– point where the reaction takes place How Enzyme Work? • Binding energy: energy released from all of the weak interactions • Which helps bring about transition state by four mechanisms: – 1. helping substrate get together – 2. orienting substrate in position to favor a reaction – 3. shutting out water – 4. inducing changes in enzyme shape (induced-fit model) About those cofactors • Cofactors are nonprotein groups that bind to many enzymes and make them more reactive • Inorganic metal ions such as Fe++ also serve as cofactors when assisting membrane cytochrome proteins in their electron transfer in chloroplast and mitochondria Why are enzymes so big? • A large molecule affords structural stability • Extensive folding of polypeptide chains puts amino acids and functional groups in location and orientations that favor interactions with water and substrate How Enzymes Activity Controlled? • Some controls regulate the number of enzyme molecules available by speeding up/slowing down their synthesis • Sometimes enzymes bind to other sites than their active site Continue… • Allosteric enzymes (in addition to active site) regulatory sites where control substances can bind to alter enzyme activity; I fthis control substance is the end product in the enzyme’s metabolic pathway, the feedback inhibition occurs (shutdown) Do Temperature and pH affect Enzymes? • Enzymes operate best within defined temperature ranges – High temperature decreases reaction rate by disrupting the bond that maintain 3-D shape (denaturation occurs) – Most enzymes function best at the pH range of 6 to 8 • Exception: stomach enzyme: Pepsin – Higher or lower pH can disrupt the shape and function Light Up the Night • Fireflies use enzymes (luciferase) to produce light by bioluminescence • Researchers transferred genes for bioluminescence into strains of Salmonella so that the course of infection could be tracked by visualization