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BIOL 130
Heidi Engelhardt

Thermodynamics: relationship b/w forms of energy and heat - 1st law of thermodynamics: energy can be transferred and transformed, but not destroyed or created nd - 2 law of thermodynamics: energy tends to spontaneously disperse, from being ordered to disordered -> disorder=entropy, the disorder of the universe can only increase Energy: capacity to do work Potential energy: stored in bonds (location), top of hill (location) *formation of bonds is favorable, energy required to break bonds* *breaking old bonds to form new bonds that require less energy can free the energy from the old bonds since the energy required to break the old bonds is less than the energy released* Reactions occurring in an isolated cell of constant volume and temp. can cause disorder in 2 ways: - changes in bond energy in reacting molecules can realease heat, disordering the environment - molecules can be broken to increase entropy in the cell, or by disrupting interaction that prevents bond rotation Exergonic reactions: Products are less ordered than reactants and have lower potential energy. Heat released. Endergonic: Products more ordered than reactants, higher potential energy, heat absorbed. Gibbs free energy: - predicts spontaneity of rxns (can occur w/o the addition of external energy) - DOES NOT predict reactions rates - predicts chemical equilibria - provides basis for coupled rxns -> allows energetically unfavorable rxns to occur - reaction is spontaneous if g is negative (ie. Products have lower energy than reactants -> rxn is favorable and occurs alone) -g= exergonic, +g=endergonic -standard free energy is free energy under certain conditions (ie. 1M concentration reactants) - biologically, require non favorable reactions to occur to produce more complex molecules from simpler ones (ie. H2O, CO2 -> atp) so, we couple more favorable reactions together. Overall free energy is sum of coupled rxns. (ie. Glucose + fructose -> sucrose driven by atp -> adp, 5.5 kcal+ (-7.3 kcal) = -1.8 kcal) -Rates of spontaneous rxns depend on how fast molecules are moving (temp.), how crowded they are (concentration), bc the right molecules’ bonds must break before a new one forms (the right molecules must collide) -> we need a biological system to make rxns occur quicker under physiological conditions of ph, temp, concentration. - enzymes catalyze (control speed of) favorable rxns (spontaneous) Rxns require a “push” to get started (activation energy) (ie. Making new bonds may first require breaking/weakening of existing bonds) Enzymes are biological catalysts (catalysts change rate of rxn but is not consumed, ie. 1 molecule of carbonic anhydrase in red blood cells can catalyze 1 million+ rxns per sec!) Enzymes bind substrate(reactants) to its active site w/ non-covalent bonds (allows for perfect position for interaction), activation energy lowered, enzyme changes shape, products are released and enzyme reverts to original shape. *specific enzyme for each reaction (lock and key model), energy lvl of products is different than substrates -> reduces affinity for active site Enzymes need to bind cofactors to help catalyze rxns -> non-protein (ie. Metal ions, coenzymes -> organic molecules * many vitamins are parts of coenzymes) *coenzymes are changed during rxn, must be regenerated to complete catalytic cycle Enzyme activity must be regulated based on the needs of the cell -> regulatory molecules bind to an enzyme and changes its reactivity (inhibitors decrease activity, activators increase activity) Two types of regulation: allosteric and competitive Competitive inhibitor: competes with substrate to bind to enzyme’s active site, can be overcome by increasing substrate concentration Non-competitive inhibitor: Binds to allosteric site on enzyme, changes its shape, substrate can no longer be catalyzed by the enzyme (allosteric activation) *Allosteric inhibition changes shape and allows reaction to proceed Regulation of enzyme activity can be result of covalent modification of enzyme by functional group (ie. Phosphorylation at –OH containing side chains) (STUDY FURTHER) Examples of enzyme inhibitors: • many environmental toxins work by inhibiting enzymes • DDT, many other pesticides inhibit key enzymes in nervous system • penicillin irreversibly inhibits an enzyme in the synthesis of the bacterial cell wall (transpeptidases) • blocks active site of enzyme bacteria need to make their cell walls • HIV produces an enzyme (protease) which is required for the activation of other viral proteins • inhibitor of this protease is a potent drug against AIDS last but not least: • selective inhibition and activation of enzymes by molecules naturally present in the cell are essential mechanisms for metabolic control - need to be reversible Cellular Respiration - Cells obtain energy from carbs (sugar) by oxidizing it to CO2 and H2O, energy is transported and stored in activated carrier molecules (ATP and NADH, contain one or more high energy content bonds) for later use ATP- phosphate group carried in high energy linkage NADH, NADPH, FADH2- electrons and hydrogens carried in high energy linkage Acetyl CoA- Acetyl group carried in high energy linkage Unactivated carrier molecules readily accept a hydride atom (H-, 2 electrons and a proton) and donate it. (NAD+, FAD, NADP+) ****As glucose is oxidized, carrier molecules are reduced and thus, store energy for later use*** Catabolism: breakdown of complex molecul
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