CHAPTER 6 Energy, Enzymes, and Metabolism

CHAPTER 6Energy, Enzymes, and Metabolism

Energy and Energy Conversions • Energy is the capacity to do work • Potential energy is the energy of state or position; it includes energy stored in chemical bonds • Kinetic energy is the energy of motion • Potential energy can be converted to kinetic energy, which does work.

Energy Conversion figure 06-01.jpg Kinetic Potential

First Law of Thermodynamics • Energy cannot be created or destroyed.

Second Law of Thermodynamics figure 06-03.jpg • In a closed system, the quantity of energy available to do work decreases and unusable energy increases • Usable energy = free energy (G) • Unusable energy = product of entropy (S) and absolute temperature (T) • Total energybefore transformation = enthalpy (H)

Energy and Energy Conversions • Organisms are open systems that are part of a larger closed system (universe)

Energy and Energy Conversions • Changes in free energy, total energy, temperature, and entropy are related DG =DH – TDS • Exergonic reactions • Release free energy • Have a negativeDG • Entropy increases, enthalpy decreases • Spontaneous • Endergonic reactions • Take up free energy • Have a positiveDG • Entropy decreases, enthalpy increases • Non-spontaneous

Reactions figure 06-05.jpg

Energy and Energy Conversions • G determines equilibrium point • Exergonic reactions • Equilibrium lies toward completion • Endergonic reacitons • Reaction will not occur without input of energy G-1-P  G-6-P G=-1.7kcal/mol

ATP - an energy currency in cells Hydrolysis of ATP releases free energy. ATP: Transferring Energy in Cells

ATP: Transferring Energy in Cells • Reaction Coupling • couples exergonic and endergonic reactions

Coupling Reaction figure 06-10.jpg Glutamate

Enzymes: Biological Catalysts • Rates of reactions are independent ofDG • Determined by the activation energy • Catalysts speed reactions by lowering the activation energy

Enzymes: Biological Catalysts • Highly specific for their substrates • Active site • determines specificity • where catalysis takes place • enzyme–substrate complex • Domains

In the active site, the substrate is induced into a transition state Transition state temporary substrate configuration Inducing & stabilizing thetransition state decreases activation energy & increases reaction rate Enzymes: Biological Catalysts

Catalytic Mechanisms figure 06-15.jpg Lysozyme

Molecular Structure Determines Enzyme Function • Induced Fit • Enzyme conformation alters upon substrate binding

Enzymes: Biological Catalysts • Substrate concentration affects the rate of an enzyme-catalyzed reaction

Molecular Structure Determines Enzyme Function • The active sites of many enzymes contain special reactive molecules which mediate the chemical catalysis

Metabolism and Enzyme Regulation • Metabolic pathways • Upstream downstream sequence of reactions • Product of one reaction is a reactant for the next • Regulation of enzymes • Feedback inhibition • Downstream products inhibit upstream enzymes

Enzyme Regulation - Competitive Inhibition • Succinate  fumarate  malate  OAA • Build up of OAA inhibits succinate dehydrogenase

Enzyme Regulation - Competitive Inhibition • Thr  a-Ketobutyrate   Ile • Buildup of Ile inhibits threonine dehydratase

Enzyme Regulation - Suicide Inhibitors figure 06-20.jpg • Inhibitor reacts with amino acids in the active site permanently inhibiting the enzyme • PMSF inhibits serine proteases such as trypsin

Metabolism and Enzyme Regulation • Allosteric enzymes, • reaction rate v substrate concentration is sigmoidal

Enzyme Regulation figure 06-23.jpg • Allosteric inhibitors bind to sites different from the active site • Multiple catalytic subunits may interact cooperatively

Enzyme Regulation • End product of pathway may inhibit upstream allosteric enzymes

Enzyme Regulation • pH and temperature affect enzyme activity

CHAPTER 6 Energy, Enzymes, and Metabolism