(kilo ) or heat energy (kilo ) C. Organisms carry out conversions between potential energy and kinetic energy 1. Potential energy is energy;

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1 I. Biological work requires energy A. Energy is the to do work B. Energy is expressed in units of work (kilo ) or heat energy (kilo ) C. Organisms carry out conversions between potential energy and kinetic energy 1. Potential energy is energy; Kinetic energy is energy of II. Two laws of thermodynamics govern energy transformations A. The total energy in the universe does not change 1. First law of thermodynamics=law of of energy a. The total energy of a closed system remains b. Biological systems are systems c. Organisms can only convert energy to other forms B. The entropy of the universe is 1. In most energy conversions, energy is lost as 2. Second law of thermodynamics a. As energy is converted from one form to another, the total amount of (S) increases in the universe -due to an expanding universe; will decrease once universe retracts b. Entropy may be defined as an increase in disorder or III. Metabolic reactions involve energy transformations A. Metabolism of an organism includes anabolic and catabolic pathways 1. includes synthetic pathways 1

2 2. includes reactions in which molecules are degraded B. is the total potential energy of a system 1. Bond energy is the amount of energy required to break a molecular bond 2. Enthalpy (H) is the total bond energy 3. Enthalpy is often referred to as the heat content of the system C. energy is energy that is available to do cellular work 1. Is expressed in kilojoules or kilocalories as G 2. G is related to entropy 3. H = G + TS a. H is enthalpy, T is the absolute temperature (Kelvin scale), S is entropy b. As the temperature increases, entropy D. Chemical reactions involve changes in free energy 1. The capital Greek letter delta ( ) is used to refer to changes between initial and final states 2. G = H - T S E. Free energy during an exergonic reaction 1. The total free energy of a system in the final state is less than the total free energy in the original state 2. reactions have a - G 3. Exergonic reactions release and are reactions 4. These reactions still require energies F. Free energy during an endergonic reaction 1. An endergonic reaction is one in which there is a in free energy 2

3 G. Free energy changes depend on the concentrations of reactants and products 1. Reactions proceed to a state of dynamic equilibrium 2. Cellular reactions are typically never at equilibrium -always pulling products away to other reactions to keep system going H. Cells drive endergonic reactions by coupling them to reactions 1. Coupled reactions may drive thermodynamically unfavorable endergonic reactions 2. In energy coupling, one must look at the total G of both reactions 3. Endergonic reactions are coupled with exergonic reactions a. the breakdown of ATP is a good example IV. Adenosine triphosphate (ATP) is the energy currency of the cell A. The ATP molecule has three main parts 1. Nitrogen containing base ( ) 2., a pentose sugar 3. 3 phosphate groups in a series B. ATP energy through the of a phosphate group -called phosphorylation 1. The bonds linking the three phosphate groups may be broken by a. These reactions have a large - G (-7.6 kcal/mole) b. ATP is hydrolyzed to form and P i c. This reaction may be coupled with an endergonic reaction d. reactions occur when the phosphate group is transferred to another molecule 3

4 C. ATP links exergonic and endergonic reactions 1. Phosphorylation is coupled to endergonic processes D. The cell maintains a very high of ATP to ADP 1. The actual free energy of ATP under cellular conditions is -10 to -12 kcal/mole 2. The ratio of ATP to ADP is about 10:1 3. ATP cannot be stockpiled 4. A resting human uses about 100 lbs. per day of ATP, but the amount present at any given time in the entire body is less than a gram (0.03 oz.) 5. Each second, approximately 10 million molecules of ATP are made and recycled V. Cells transfer energy by redox reactions A. Oxidation is the of electrons; reduction is the of electrons 1. Oxidation involves the loss of energy; reduction is the gain of energy B. Most electron carriers carry hydrogen atoms 1. Electron carriers transfer energy 2. Electrons energy as they are transferred between acceptors 3. Nicotinamide adenine dinucleotide, (NAD + ) is a common hydrogen acceptor in respiratory and photosynthetic pathways 4. Nicotinamide adenine dinucleotide phosphate (NADP + ) is involved in photosynthesis 5. Flavin adenine dinucleotide (FAD) is involved in cellular respiration 6. Cytochromes are proteins containing iron and are also electron carriers VI. Enzymes are chemical regulators A. Enzymes are catalysts that speed the rate of chemical reactions 1. Not all organic catalysts are proteins, some nucleotide-based molecules function as enzymes as well, e.g. ribozyme 2. Enzymes that catalyze specific chemical steps allow for cellular control B. All reactions have a required energy of 4

5 C. An enzyme the activation energy needed to initiate a chemical reaction 1. Enzymatic action has no effect on the overall energy D. An enzyme works by forming an - complex 1. Enzymes have at least one three-dimensional area, known as the site or active sites 2. The current model of enzymatic action is the - model a. The active site is not rigid, but binding of the substrate to the active site involves changes in both the enzyme and typically) the substrate b. The enzyme and substrate form an ES or enzyme-substrate complex c. After binding to the substrate, the product is released, and the enzyme can be E. Most enzyme names end in ase 1. Sucrase is an enzyme that reacts with sucrose 2. Other enzymes have older names ending in zyme 3. Enzyme names such as pepsin and trypsin give no clues (totally clueless) as to their function F. Most enzymes are 1. Because of the binding at the active site 2. But lipases react with a variety of G. Many enzymes require cofactors 1. Many enzymes are composed of a protein (an ) and a cofactor 2. cofactors include elements such as Mg, Ca, Fe, Cu, Zn, and Mn 3. Organic non-protein cofactors bind with the enzyme forming a coenzyme 5

6 a. Coenzymes are typically transfer agents b. NADH, NADPH, and FADH 2 are coenzymes c. ATP is a coenzyme d. Coenzyme A is important in cellular respiration 4. Most vitamins are coenzymes or are parts of coenzymes H. Enzymes are most effective at conditions 1. Each enzyme has an optimal a. In the human body, the optimal temperature for enzymes is near body temperature ( C) b. High temperature protein enzymes 2. Each enzyme has an optimal a. In the human body, the optimal ph for most enzymes is between ph and (not in the tummy (1.5 to 2.5) :p b. A suboptimal ph protein enzymes I. Enzymes are organized into teams in metabolic pathways 1. Enzymes often work in sequences or J. The cell regulates enzymatic activity 1. The amount of enzyme produced can control the rate of a reaction; this is typically accomplished by mechanisms 2. Allosteric enzymes have a receptor site to which allosteric regulators bind -allosteric means other than the active site a. Some allosteric regulators are of the enzyme; others are of the enzyme K. Enzymes can be inhibited by certain chemical agents 1. Reversible inhibition may be competitive or noncompetitive 6

7 a. Reversible competitive inhibition involves a molecule that is structurally similar to the normal i. The inhibitor binds to the active site temporarily b. Reversible noncompetitive inhibition involves binding at a site other than the active site (allosteric) temporarily 2. Irreversible inhibitors permanently the enzyme a. Examples: nerve gases, heavy metals b. Some drugs are enzyme inhibitors i. Examples include sulfa drugs and penicillin which are used to combat bacterial infections ii. Insecticides such as DDT, malathion and parathion act by inhibiting enzymes L. Enzyme Cooperativity a. If an enzyme has multiple subunits and it is in its inactive configuration, just one substrate binding to one active site makes all the active sites become active for other substrate b. very efficient M. Many household items use enzymes 1. Proteolytic (protein-busting) enzymes are found in laundry detergents and stain removers 2. Meat tenderizers are enzymes that pre-digest meat (yuck!) a. must sit for a while on the meat; otherwise the temperature of cooking will denature the tenderizer, since it is a protein as well N. Enzyme Expression and Temperature 1. In Siamese cats an enzyme affects coat color a. only functional in cooler, peripheral parts of body b. body is light, but appendages, ears, and tails are darker 2. In seals, dark pigment in hair active only at lower temperatures a. at birth, baby seals are born with a white coat, since is warm in mother s uterus b. after birth, hair grows dark, as skin cools 7