Energy and Metabolism Unit 5

Biology, Sixth Edition Chapter 6, Energy and Metabolism Organisms and Energy What is energy? Ability to do work Organisms use energy to: Build structure Carry out ongoing functions, e.g.: Transcription Movement Secretion Reproduce

Potential and Kinetic Energy Biology, Sixth Edition Chapter 6, Energy and Metabolism Potential and Kinetic Energy Potential energy is stored energy. Kinetic energy is energy in action or motion. When the archer releases the arrow, potential energy stored in the bow drives the arrow forward with a pulse of kinetic energy. Some energy is lost as heat. Friction creates heat as the string internally rubs, as the arrow flies through air, etc. Cells store potential energy as chemical energy, and use kinetic energy as chemical energy

Metabolism Metabolism – sum of all the chemical reactions that occur in the body 2 components Anabolism – synthesis of complex molecules in living things Catabolism – breaking down on complex molecules in living things Anabolism and Catabolism are linked in living things!

Laws of Thermodynamics First Law The law states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed. Second Law In any cyclic process the entropy will either increase or remain the same. Entropy – is the degree of disorder in a system

What is the ultimate source of energy? Free Energy Free energy is energy that is available to perform work. It’s what metabolism is all about. It can be represented mathematically. What is the ultimate source of energy?

Gibbs Free Energy Equation Enthalpy is the heat of the system Entropy is the degree of disorder

Biology, Sixth Edition Chapter 6, Energy and Metabolism

Endergonic vs. Exogonic Reactions Reactions that require energy input are called endergonic; if they need heat, they are endothermic If a reaction releases energy it is exergonic; if the energy is released as heat, it’s exothermic.

Biology, Sixth Edition Chapter 6, Energy and Metabolism ATP Adenosine triphosphate It is a nucleotide 3 parts Nitrogen base (adenine) Ribose (5C sugar) 3 phosphate groups Energy of ATP is in these bonds Hydrolysis (adding water) breaks this bond making ADP + Pi This is called phosphorylation

Biology, Sixth Edition Chapter 6, Energy and Metabolism Role of ATP ATP is the common currency of energy in the cell. It provides energy because the phosphates are unstable (lots of ‘-’ charges; they mutually repel each other) These phosphate bonds are sometimes called “high energy” bonds. ATP’s terminal phosphate can be added to a reactant This is called phosphorylation. This process releases ATP Thus ATP is broken down into ADP + Pi

Energy Released by the Hydrolysis of ATP is Coupled to Other Reactions Biology, Sixth Edition Chapter 6, Energy and Metabolism Energy Released by the Hydrolysis of ATP is Coupled to Other Reactions

Biology, Sixth Edition Chapter 6, Energy and Metabolism Another class of "high energy/low stability" molecules involves the reduction of certain compounds.  For example, the addition of two electrons and a proton to nicotinamide adenine dinucleotide (NAD+) leads to the formation of the high energy/unstable molecule NADH. The energy carried by NADH and FADH2 is used to drive a number of cellular reactions, it can also be used to generate ATP.

Biology, Sixth Edition Chapter 6, Energy and Metabolism Similarly, the addition of two electrons and two protons to flavin adenine dinucleotide (FAD) leads to the formation of FADH2, which has high energy and low stability FAD FADH2

NAD+ / NADH & Oxidation / Reduction Reactions Biology, Sixth Edition Chapter 6, Energy and Metabolism NAD+ / NADH & Oxidation / Reduction Reactions Reduction is the addition of electrons. Results in increased energy content Very common in metabolism e.g., NAD+ NADH e.g., FAD FADH2 Oxidation is the loss of electrons. e.g., NADH NAD+ e.g., FADH2 FAD Oxidation and reduction are often coupled as redox reactions. OILRIG

Biology, Sixth Edition Chapter 6, Energy and Metabolism Enzymes Enzymes are protein catalysts that enormously speed up reactions. They often have an “-ase” ending to their name. e.g., hexokinase, catalase, peptidase, mutase They are not themselves changed and are the same before and after a reaction. Enzymes: Lower the activation energy: this is the MOST important characteristic Do not add or remove energy from a reaction Do not change the equilibrium for a reaction Are reused over and over

Biology, Sixth Edition Chapter 6, Energy and Metabolism Enzymes Lower EA Activation energy (Ea) is the energy required to break the bonds to begin the reaction

The Enzyme-Substrate Complex Biology, Sixth Edition Chapter 6, Energy and Metabolism The Enzyme-Substrate Complex Substrates are the reactant(s) upon which the enzyme acts Enzymes form a noncovalent complex with their substrates called the enzyme-substrate complex (ES complex) at the active site When the ES complex breaks up it releases product The induced fit model: The enzyme conforms to the shape of the substrate, and/or the substrate conforms to the shape of the enzyme; this induces strain in the substrate structure

Hexokinase and Induced Fit Biology, Sixth Edition Chapter 6, Energy and Metabolism Hexokinase and Induced Fit

Biology, Sixth Edition Chapter 6, Energy and Metabolism A Catalytic Cycle ES Complex substrates enzyme product -> now available to catalyze again enzyme

Biology, Sixth Edition Chapter 6, Energy and Metabolism Enzymes: Components Some enzymes are only a protein, but many have other components: Apoenzyme -- the protein part Cofactor(s) -- an inorganic component, often an ion such as Ca2+ or Mg2+ Apoenzyme + cofactor = the active enzyme Organic cofactors are called coenzymes: Vitamins ATP, NADH Coenzyme A

Biology, Sixth Edition Chapter 6, Energy and Metabolism Enzyme Specificity Enzymes fall into broad general classes, but in most cases themselves catalyze specific reactions. Type of enzyme Function Oxidoreductases Redox reactions Transferases Transfer of a functional group from donor to acceptor Hydrolases Hydrolysis reactions Isomerases Conversion from one isomer to another Ligases Joins two molecules together Lyases Double bond formation/breakage

Enzymes are Very Sensitive Biology, Sixth Edition Chapter 6, Energy and Metabolism Enzymes are Very Sensitive Each enzyme has an optimal temperature, pH, and ionic strength Human enzymes are optimized to work at body temperature (37OC) while enzymes from thermophilic bacteria are optimally active at much higher temperatures Certain body enzymes are most active at the pH of a given body compartment: Pepsin’s optimum pH matches that of the stomach (acidic) Trypsin’s optimum pH is basic, like the upper intestine

Biology, Sixth Edition Chapter 6, Energy and Metabolism So… High temperatures rapidly denature enzymes and this is not reversible If pH is altered, enzymes become inactive and is not reversible

Biology, Sixth Edition Chapter 6, Energy and Metabolism Enzyme Inhibition Two types: Competitive: Inhibitor binds at the active site Noncompetitive: Inhibitor binds at a site distant from the active site

Biology, Sixth Edition Chapter 6, Energy and Metabolism Allosteric Control Biology, Sixth Edition Chapter 6, Energy and Metabolism If a substance binds to an allosteric site (another region besides the active site), the conformation of the active site is changed and this affects enzyme activity

Enzyme Regulation is Very Important Biology, Sixth Edition Chapter 6, Energy and Metabolism Enzyme Regulation is Very Important Imagine a series of enzyme-mediated reactions, which is the way biological chemistry really works. The products or reactants of any of the reactions can have effects on the enzymes involved in that reaction, or enzymes involved in other reactions. If an enzyme is ‘turned off’ (e.g., lowered affinity for reactants) by its products, we say it is ‘feedback inhibited’. If it is ‘turned on’ by some other products, it can be stimulated. The homeostatic balance of living systems is regulated in this manner.

Example of Feedback Inhibition Biology, Sixth Edition Chapter 6, Energy and Metabolism Example of Feedback Inhibition