Chapter 6 04 20 2014 ATP adenosine triphosphate Organisms classified according to energy and carbon source Phototrophs energy from sunlight o Autotrophs carbon from CO2 plants o Heterotrophs carbon from organic compounds Chemotrophs energy from chemical compounds o Autotrophs carbon from CO2 o Heterotrophs carbon from organic compounds animals Metabolism chemical reactions that convert molecules into other molecules and transfer energy to living organisms Catabolism break down molecules into smaller units produces ATP o Macromolecules carbohydrates proteins fats nucleic acids Anabolism build molecules from smaller units and requires ATP o Subunits sugars amino acids fatty acids nucleotides Chemical energy is a form of potential energy C C and C H bonds electrons far away from atoms store chemical potential energy Carbohydrates lipids and proteins fuel molecules ATP is cell s energy currency Chemical energy of ATP is held in phosphate bonds Adenine Ribose Adenosine 1 phosphate Adenosine 5 monophosphate AMP 2 phosphates Adenosine 5 diphosphate ADP 3 phosphates Adenosine 5 triphosphate ATP First Law of Thermodynamics energy is conserved Energy changes from one form to another total amount always stays the same Second Law of Thermodynamics disorder tends to increase Energy available to do work decreases disorder increase Energy loss due to entropy often in the form of heat Chemical Reactions Gibbs free energy G amount of energy available to do work G is positive products have more free energy than reactants net input of energy is required to drive reaction Not Spontaneous requires energy endergonic Anabolic reactions have G require ATP Less disorder S More chemical energy in bonds H G is negative reactants have more free energy than products energy is released and available to do work Spontaneous releases energy exergonic Catabolic reactions have G release ATP More disorder S Less chemical energy in bonds H Enthalpy H total amount of energy Entropy S degree of disorder G H ST Hydrolysis of ATP release energy ATP H2O ADP Pi o Exergonic reaction releases energy ADP contains less chemical potential energy in its bonds than ATP Hydrolysis of ATP release chemical energy allows ATP to drive chemical reactions Non Spontaneous Reactions G for forward and reverse reactions have same absolute value Coupling of non spontaneous reaction to a spontaneous one drive non spontaneous reaction as long as net G is negative Energetic coupling spontaneous reaction drives non spontaneous one provides thermodynamic driving force of a non spontaneous biochemical reaction Most common reaction w energetic coupling hydrolysis of ATP ADP is an energy acceptor and ATP is and energy provider Enzymes o G more negative than that of ATP hydrolysis give phosphate group to ADP o G less negative than that of ATP hydrolysis receive phosphate group from ATP by energetic coupling Catalysts substances that increase rate of reaction catalysts are usually proteins called enzymes Enzymes reduce activation energy of reaction Transition state intermediate stage between reactants and products highly unstable has large amount of free energy o To reach transition state reactant must absorb energy from o All reactions require input of energy energy barrier o Activation energy energy input necessary to reach o Lower the energy barrier faster reaction higher barrier surroundings transition state slower reaction o Enzymes reduce activation energy by stabilizing transition state and decreasing free energy changes path of reaction between reactants and products but not starting or end point Enzymes form a complex with reactants and products o Reactant substrate o Substrate first forms complex with enzyme o In complex substrate is converted to product o Complex dissociates releasing enzyme and product Enzyme folds into 3D shape bring particular amino acids close to each other to form active site o Active site is portion of enzyme that binds substrate and converts it to product o Enzymes reduce activation energy by positioning 2 substrates to react aligning their reactive chemical groups Enzyme activity can be influenced o Inhibitors decrease activity of enzymes Common synthesized naturally by plants and animals many drugs to treat infections cancer Irreversible inhibitors form covalent bonds with enzymes irreversibly inactive them Reversible inhibitors form weak bonds with enzymes easily dissociate from them Competitive inhibitors bind to active site of enzyme prevent binding of substrate compete with substrate for active site of enzyme often structurally similar to substrate reduce affinity of enzyme for substrate can be overcome by increasing concentration of substrate Non competitive inhibitors have structure very different from substrate bind to enzyme at different site from active site no change in affinity of enzyme for its substrate slows down reaction by altering shape of enzyme and reducing activity o Activators increase activity of enzymes o Allosteric enzymes in cell regulated by activators and inhibitors reaction Negative feedback final product inhibits first step of the Allosteric enzyme bind to activators and inhibitors at sites that are different from active site result in change in shape and activity of enzyme Catalyze key reactions in metabolism usually found at near start of metabolic pathway or crossroads between 2 metabolic pathways o Cofactor substance that associates with an enzyme and plays a key role in its function o Metallic cofactors bind to diverse proteins including those used in DNA synthesis nitrogen metabolism and transport of electrons for cellular respiration and photosynthesis Metal ions catalyze chemical reactions by themselves Chapter 7 Cellular Respiration 04 20 2014 Series of catabolic reactions convert energy stored in fuel molecules into chemical form that can be readily used in cells Aerobic respiration occur in presence of oxygen o Oxygen consumed CO2 and H2O produced o Stage 1 glucose fatty acids or amino acids are partially broken down and some energy is release Glucose breaks down to pyruvate glycolysis Stage 2 Pyruvate converted to molecule acetyl coenzyme A acetyl CoA CO2 is produced o Stage 3 citric acid cycle acetyl CoA broken down more CO2 released electron carriers Stages 1 3 chemical energy transferred to ATP and o Stage 4 oxidative phosphorylation electron carriers donate their high energy electrons to an electron transport chain respiratory chain Electron transport chains transfer
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