Chapter 8: Energy and Enzymes: An Introduction to Metabolism PDF

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Chapter 8: Energy and Enzymes: An Introduction to Metabolism A living cell is a dynamic, complex, active, responsive unit What is responsible for all activities in the cell? → Energy and Enzymes! Energy is required to do work ● Growth ● Division ● Pump ions in/out of cell ● Transport vesicles ● Synthesize macromolecules such as DNA, RNA, proteins, and complex carbs ● Tissues such as muscles contract All these activities are considered work, and they require energy. ATP provides energy in a form that all cells can readily use to perform the work of the cell Life Requires Energy ● Chemical reactions take place inside cells and these require energy ● Organisms have two fundamental nutritional needs: 1. Acquiring chemical energy in the form of adenosine triphosphate ATP) 2. Obtaining molecules that can be used as building blocks to make DNA, RNA, proteins, etc. ● How organisms acquire energy is central to life Food = Fuel (any substance used to provide energy)

Metabolism = Catabolism and Anabolism ● Metabolism includes chemical reactions that convert molecules and transfers energy ○ Anabolism: synthesis, the building of molecules from smaller units ○ Catabolism: the breakdown of molecules into smaller units

Potential and Kinetic Energy ● Two types of energy exist ○ Kinetic Energy: energy of motion ■ Thermal Energy: energy of molecules moving ○ Potential Energy: energy that is stored in position ■ Chemical Energy: energy stored in chemical bonds

Laws of Thermodynamics 1. Energy can be transformed from one type to another but total energy remains constant

Potential Energy is stored energy Chemical bonds contain potential energy

ATP Transfers Energy via Phosphate Groups ● Adenosine Triphosphate (ATP) is the energy currency for cells ○ It provides the fuel for most cellular activities ● ATP forms bonds between three negatively charged phosphate groups ○ Negative charges repel each other ○ High-Energy bonds store a large amount of potential energy

Non Spontaneous Reactions Can be Driven Using Chemical Energy ● What source of energy drives cellular reactions? ○ Two Ways: ■ Electron transfer-redox reactions ■ Transfer of a phosphate group - ATP Chemical Reactions Include Energy Transformations: Gibbs Free Energy ΔG ● Measure of the tendency of the system to react or change - Gibbs free energy ● ΔG < 0 or negative = a spontaneous reaction ○ These reactions are exergonic ● ΔG > 0 or positive = a nonspontaneous reaction that requires energy input to occur ○ These reactions are endergonic ● ΔG = 0 = a reaction that is in equilibrium

How Does ATP Drive Endergonic Reactions? ● Both endergonic and exergonic reactions occur in the cell ● Exergonic phosphorylation reactions are coupled to endergonic reactions ● Coupling!

ATP Hydrolysis ● The reaction of ATP with water is exergonic (spontaneous) and releases energy (- ΔG) ● Cells use ATP Hydrolysis for Reaction Coupling ○ ΔG = -7.3 kcal/mol

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Energy liberated can drive a variety of cellular processes

Non Spontaneous Reactions Can be Driven Using Chemical Energy ● Energetic Coupling ○ Between exergonic and endergonic reactions ○ Allows chemical energy released from one reaction to drive another reaction ● ATP Hydrolysis is exergonic and used to couple other reactions Energetic Coupling allows endergonic reactions to proceed using free energy released From exergonic reactions

What Can We Do to Make a Reaction Go Faster? ● Reactions occur when ○ Reactants have enough kinetic energy to reach the transition state (the kinetic energy of molecules is a function of their temperature) ● Thus, reaction rates depend on ○ The kinetic energy of the reactants ○ The activation energy of particular reaction (the free energy of the transition state)

How Enzymes Work ● Most biological chemical reactions occur fast enough only in the presence of an enzyme ● Enzymes are protein catalysts ○ Bring reactants together in precise orientations ○ Make reactions more likely

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Are specific for a single type of reaction

Enzymes Bring Substrates Together ● Help the reactants/substrate molecules to collide in a precise orientation ● Bonds break and form to generate products ● Substrates bind to the enzyme’s active site ● Substrates bind via hydrogen bonding or other interactions with amino acid residues in the active site

Enzymes Lower the Activation Energy ● An unstable intermediate condition called the transition state is formed ● Activation Energy is required to strain substrates’ bonds so they can reach the transition state Factors that Affect Enzyme Activity ● Substrate specificity ● Temperature ● pH Active Site Formation

Key Enzyme Features ● Active site- location where reaction takes place ● Substrate- reactants that bind to active site ● Enzyme-substrate complex formed when enzyme and substrate bind ● Specificity What factors Affect Enzyme Function ● An enzyme’s structure is critical to its function

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Protein structure is dependent on folding Enzyme function is dependent on certain conditions ○ Temperature affects the folding and movement of the enzyme and binding its substrates ○ pH affects the enzyme’s shape and reactivity Each enzyme has optimal temperature and pH

Inhibitors/Activators ● Inhibitors ○ Competitive: bind to the active site of the enzyme and prevent the substrate from binding. They compete with the substrate for the active site. ○ Noncompetitive: bind to a site different from the active site. They slow down the reaction normally catalyzed by the enzyme by altering the enzyme’s shape. ● Activators: increase activity of enzymes...