Transcript Enzymes
Energy, Enzymes, and Metabolism Fig. 5-UN1 Amino group Carboxyl group Primary Structure • There are four levels of protein structure: primary, secondary, tertiary, and quaternary. • The peptide backbone consists of repeating units of atoms: N—C—C—N—C—C. • Primary Structure is determined by the specific amino acids that are coded for by the DNA sequence coding its synthesis. Secondary Structure • A protein’s secondary structure consists of regular, repeated patterns in different regions in the polypeptide chain. • This shape is influenced primarily by hydrogen bonds arising from the amino acid sequence (the primary structure). • The two common secondary structures are the a helix and the b pleated sheet. • β Structure • Pleated • Peptide regions are parallel to one another • • • • α Structure Helical Right handed structure R group always points away from the peptide backbone Tertiary Structure • Tertiary structure is the threedimensional shape of the completed polypeptide. • The primary determinant of the tertiary structure is the interaction between R groups and the location of disulfide bridges Quaternary Structure Results from binding and interactions between more than one polypeptide structure Other factors influencing structure – The nature and location of secondary structures – Hydrophobic side-chain aggregation and van der Waals forces, which help stabilize them – The ionic interactions between the positive and negative charges deep in the protein, away from water Effects of the environment in Proteins • Changes in temperature, pH, salt concentrations, and oxidation or reduction conditions can change the shape of proteins. • Chaperonins- proteins that keep other proteins from inappropriately interacting with one another. • This loss of a protein’s normal threedimensional structure is called denaturation. A biological catalyst is any substance that increases the rate of a reaction Catalyst are not themselves used up in the reaction Substrate (sucrose) Enzyme (sucrase) OH Glucose HO Fructose H2O • Some chemical reactions are slow because there is a barrier between the reactants and products • Others require activation energy: – Activation energy (Ea) is energy needed to put molecules in a transition state with a higher energy rate – Heat is typically used in exergonic reactions to increase kinetic energy of molecules and initiate the reaction • Do these problems exist in biological systems? Overcoming Problems • Heat is not a logical solution to increasing energy in reactions in biological systems – • Enzymes: – Bind to reactant substrates at ACTIVE SITE – At active site catalysis occurs – Very specific due to shape and structure of active site • Certain substrates • Certain reactions • Certain environmental conditions Enzyme specificity Induced fit: enzyme shape is caused by the substrate binding Remainder of molecule provides framework of the protein so the active site in the correct position. How an enzyme works • Enzyme is bound to substrate by: – Hydrogen bonding – Ionic bonding – Covalent bonding • These forces hold substrate to enzyme producing an enzyme-substrate complex (ES) • The enzyme-substrate complex generates the product and free enzyme • Enzymes lower the activation energy of the reaction but do not change the ΔG of the reaction • Do not change the equilibrium of the reaction Lowered Activation Energy Enzyme Jobs • At active sites, enzymes and substrates break old bonds and form new bonds • To catalyze a reaction, enzymes will: – Orient the substrate – Cause substrate to be in “distress” – Add positive or negative charges to the substrate Orienting a substrate • In solution- substrate molecules collide randomly • This produces low probability that substrate will be at the correct angle for collision • Enzyme orients the substrates so that reaction is more likely to occur Inducing strain/ distress • The enzyme will cause the structure of the substrate to change • 1. Carbohydrate substrate enters the active site in a strong flattened ring shape ( like an “O”) • 2. Enzyme active site changes the shape to be straight on one end (like a “D”) • 3. This produces a strain on the bonds of the ring making it more reactive with water Producing Charge • R groups of the enzymes’ amino acid chains can make a substrate more chemically active • There are 3 types of interaction: – ACID- BASE CATALYSIS: • Covalent bonds in substrate may be destabilized when H ion transfer occurs between the active site of the enzyme and the substrate – COVALENT CATALYSIS: • R groups interact and temporarily bond with the substrate – METAL ION CATALYSIS: • Metal ion electrons are gained or lost without detaching from protein Energy and Energy Conversions • Remember: – Energy is the capacity to do work – Energy is neither created or lost – Cells must acquire energy from its environment – Energy exists in two forms • Kinetic • Potential Kinetic & Potential Energy • Kinetic Energy– Energy of motion – Does work that alters the state or motion of matter • Potential Energy– Stored energy – Energy of state or position Laws of Thermodynamics • 1st law of thermodynamics• AKA – Principle of Conservation of Energy – Energy put in will be equal to the energy put out. – Energy is conserved – Even though cells are living systems they must obey these rules. – Energy is neither created nor destroyed. – Energy can be transferred and transformed Laws of Thermodynamics • 2nd Law of thermodynamics– Every energy transfer or transformation increases the entropy of the universe – Entropy is defined as the measure of disorder or randomness – Randomness is constantly increasing in the universe Laws of Thermodynamics Free Energy • Portion of a system’s energy that can perform work when temperature is uniform • “Free” for doing work- still costs universe energy Bottom Line: • The QUANTITY of energy in the universe is constant. • The QUALITY of energy is not constant. • In any system: – Total energy = usable energy + unusable energy – In a reaction, increase in entropy causes products to be more random than the reactants Enthalpy (H) • In any system: – Total energy = usable energy + unusable energy H = G + TS H = enthalpy G = free energy T = absolute temperature S = entropy Energy Transfer • Change in systems is measured in calories/joules • ΔG = ΔH - T ΔS • ΔG is positive= free energy is required • Anabolic reactions • ΔG is negative = free energy is released • Catabolic reactions Metabolism • Defined as all of an organisms combined chemical reactions • Two types exist: – Anabolic reactions• Link simple molecules to make more complex ones • Characterized as energy storage reactions • Free energy is required – Catabolic reactions • Break down complex molecules into smaller ones • Characterized as energy releasing reactions • Free energy is released Reaction Relationships • There is a direct relationship between the energy taken in and the energy produced. • Reactions have a tendency to run to completion because of this relationship. • Transfer of energy from catabolism to anabolism = energy coupling • Forward and backward reactions are at the same rate: Equilibrium Exergonic and Endergonic Reactions • Spontaneous reactions Cellular Respiration – Go more than halfway without energy input – EXERGONIC REACTION – neg. ΔG = release energy AB Exergonic • Non-spontaneous reactions Photosynthesis – Need activation energy for reaction to proceed – ENDERGONIC – REACTION – pos. ΔG = consumes energy B A Endergonic Endergonic and Exergonic reactions Hydrolysis of Proteins Synthesis of Proteins Endergonic Reactions • If the surroundings do not supply heat, an endothermic transformation leads to a decrease in the temperature of the system. • If the surroundings do supply heat, an endothermic transformation leads to an increase in the temperature of the system. Exergonic Reactions • Combustion Reactions complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. • Neutralization Reactions Water forming reaction in which an acid and a base or alkali (soluble base) react and produce a salt and water solution (H2O) Coupled Reactions • ATP hydrolysis releases energy ATP + water ADP + Pion + free energy • ATP synthesis consumes energy ADP + Pion + free energy ATP + water ATP Interesting Facts • ATP molecules undergo 10,000 cycles of synthesis and hydrolysis everyday • Cells require more than one million molecules of ATP per second for biochemical activities. Catabolic reaction Anabolic reaction Coupled reactions ADP + Pion Energy in Energy out ATP Accumulation of free energy in cells