Test #1Energy – The Capacity For Work • Work = force X distance • Bioenergetics – flow and exchange of energy within a living system • First law of thermodynamics – matter cannot be created nor destroyed, but transforms from one form to another without being depleted • Energy system in the body o Chemical energy mechanical energy + heat o Body does not produce, consume, or use up energy; instead it transforms it from one state into another as physiologic systems undergo continual change.Potential and Kinetic Energy • Potential energy – bound energy (i.e. macronutrient before releasing its stored energy in metabolism.) o Releasing potential energy transforms into kinetic energy of motion• Biosynthesis – specific building block atoms of C, H, O, and N become activated and join other atoms and molecules to synthesize important biologic compounds and tissues Energy Releasing and Energy-Conserving Processes • Exergonic – any physical or chemical process that releases (frees) energy to its surroundings (“downhill process”) o G = H – TS G = free energy H = enthalpy (potential energy within a molecule’s chemical bonds) S = energy unavailable due to randomness T = absolute temperature (deg C + 273) • Endergonic – store or absorb energy (“uphill”) proceeds with an increase in free energy for biologic work • Changes in free energy occur when bonds in reactant molecules form new product molecules with different bonding o ΔG = ΔH – TΔS• Second law of thermodynamics – the tendency of potential energy to degrade to kinetic energy of motion with a lower capacity for work (i.e. increased entropy)o Entropy – the inertia that makes a thermodynamic process more likely to occur; the higher the entropy the higher the disorder o The entropy of an isolated system never decreases because isolated systems spontaneously evolve towards thermodynamic equilibrium Interconversions of Energy• Even under favorable conditions, the net flow of energy in the biologic world moves toward entropy, ultimately producing the LOSS of potential energy o The entire system always shows a net increase in energy entropy • Forms of energy o Chemical (fossil fuel, oil burner) o Mechanical (hydroelectric generating plant)Test #1o Heat (solar panels) o Light (sun) o Electrical (electrical energy) o Nuclear (reactor) Examples of Energy Conversions • Photosynthesis and respiration – represent the most fundamental examples of energy conversion in living cells • Photosynthesis – sun (gamma radiation radiant energy) pigment of chlorophyll absorbs radiant energy (synthesizes glucose from CO2 and H2O) release of O2• Endergonic process (+ΔG)o Solar energy coupled with photosynthesis powers the animal world with food and oxygen • Respiration – exergonic reaction (reverse of photosynthesis) –ΔGo Glucose + 6O2 6CO2 + 6H2O + ATPBiologic Work in Humans • Mechanical work muscle contraction o Directly convert chemical energy into mechanical energy o i.e. cilia or contractile elements to facilitate cell division (non-obvious mechanical work) • Chemical work synthesizes cellular molecules o Maintenance and growth; continuous synthesis of cellular components takes place as others break down• Transport work concentrates substances in the intracellular and extracellular fluids o Active transport describes energy-requiring process Factors that Affect the Rate of Bioenergetics • Enzymes and coenzymes greatly alter the rate of energy release during chemical reactions • Types: o Oxidoreductases – catalyze oxidation-reduction reactionss where the substrate oxidized is regarded as hydrogen or electron donor • i.e. dehydrogenases, oxidates, oxygenases, reductases, peroxidases, hydroxylases o Transferases – catalyzes the transfer of a group from one compound (donor) to another (acceptor) • i.e. kinases, transcarboxylases, transaminases o Hydrolases – catalyzes reactions that add water• i.e. esterasess, phosphatases, peptidases o Lyases – catalyze ractions that cleave C-C, C-O, C-N, and other bonds by other means than by hydrolysis or oxidation • i.e. synthases, deaminases, decarboxylasesTest #1o Isomerases – catalyze reactions that rearrange molecular structure• i.e. isomerases and epimerases o Ligases – catalyze bond formation between two substrate molecules with concomitant hydrolysis of the diphosphate bond in ATP or a similar triphosphate • i.e. pyruvate carboxylase Enzymes as Biologic Catalysts • Enzymes – highly specific and large protein catalysts that accelerate the forward and reverse rates of chemical reactions without being consumed or changed in the reactions o Reduce the required activation energy (energy input to initiate reaction) o For an uncatalyzed reaction to proceed, the reactant must have a HIGHER free energy level than the product Fun fact: Without enzyme action, the complete digestion of a breakfast meal might take 50 years!o Enzymes are not altered in reactions and may be reusedo A single mitochondria may contain up to 10 billion enzyme moleculeso Lock-and-key mechanism – ensures that the correct enzyme “mates” with its specific substrate to perform a particular function; conformational change in enzyme will then occur Mode of Action • Enzyme turns on where its active site joins in a “perfect fit” with the substrates’ active site o Forms enzyme-substrate complex Coenzymes • Some enzymes remain dormant unless activated by coenzymeso Coenzymes – nonprotein organic substances facilitate enzyme action by binding the substrate with specific enzyme • Enzyme inhibitors – substances inhibit enzyme to slow rate of reaction o Competitive inhibitors – resemble the structure of a normal substrate for an enzyme, bind to enzyme’s active site but the enzyme cannot change them; blunts intreraction with real substrate o Noncompetitive inhibitor – do not resemble enzyme’s substrate and do not bind to its active site; they bind to enzyme at site other than active site (changes enzyme’s structure and ability to catalyze reaction) Hydrolysis • Splits bonds by adding H+ and OH- to reaction byproducts • Digestion of starches and disaccharides Condensation (or I like to call it dehydration) • Reactions of hydrolysis can occur in opposite direction • Structural components of nutrients bind together in condensation reaction to form more complex
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