An Introduction to Metabolism Chapter 6

Metabolism The totality of an organism’s chemical reactions. Metabolic Pathway: begins w/ a specific molecule, it is modified by enzymes until the end product is created Catabolic: breaking down (degradative) C6H12O6 + 6O2  6CO2 + 6 H2O + energy (ATP + heat) Anabolic: Consume energy (build materials) synthesis of protein from amino acids Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Starting molecule Product

Forms of Energy Potential: energy of position or structure Chemical energy: stored in chemical bonds Kinetic: movement perform work, by moving matter Heat or thermal energy: random movement of particles KMT Light energy Energy animation.swf Energy changed to heat is not usable (to do work) by living organisms http://www.greenscreen.org/articles_sr/energy/images_potential_kinetic_energy/potential_kinetic.jpg

Thermodynamics 2nd Law 1st Law Every E transfer or transformation increases the entropy (randomness) of the universe Energy lost as heat is only usable if it is warming the organism, most goes to waste Living systems increase entropy of surroundings 1st Law E can be transferred and transformed but neither created nor destroyed Photosynthesis and eating are huge energy transfers! 1st Law 2nd Law

Free Energy Enthalpy: Change in energy in a system Entropy: Measure of disorder of a system Free Energy (G): Energy available to do work Random molecular motion (heat) can’t be recovered to do work = NOT USEFUL Enthalpy –Temp (change in entropy) - G is spontaneous, increases entropy of the universe +G is non spontaneous, decreases entropy of universe (requires input of energy)

Free Energy: ΔG = ΔH- TΔS Free energy = enthalpy (total energy) change- temperature x entropy change - ΔG are spontaneous, is exergonic: cellular respiration + ΔG are endergonic: photosynthesis ΔG = ΔGfinal – ΔGinitial a negative result is spontaneous since less free energy exists in the products! Reaching equilibrium means death, no work being done http://iws.collin.edu/biopage/faculty/mcculloch/1406/outlines/chapter%206/Ra74.JPG

Biological sources of Free Energy ATP ATP is a high-energy molecule: when it breaks down into adenosine diphosphate (ADP) and inorganic phosphate (Pi), it releases free energy that can be used to drive biological processes Proton Motive Force Movement of H+ ions across a membrane creating an electrochemical gradient

Cellular work Mechanical work – movement (Cilia & Flagella) Transport work – molecules across membranes against concentration gradients Chemical work – endergonic chemical reactions Cells use exergonic reactions to drive endergonic reactions 9 + 2 Microtubule arrangement Na+/K+ pump Photosynthesis

ATP Structure Ribose sugar bonded to adenine w/ 3 phosphates attached to the sugar Phosphates can be broken off by hydrolysis Phosphorylation: The inorganic phosphate is then transferred to other molecules (changes the reactivity of the other molecule). ENERGY is released ΔG = -7.3 Kcal/mol ATP + H20  ADP + Pi Adenine Phosphate groups Ribose

Fig. 8-10 + ∆G = +3.4 kcal/mol Glutamic acid Ammonia Glutamine NH2 NH3 + ∆G = +3.4 kcal/mol Glu Glu Glutamic acid Ammonia Glutamine (a) Endergonic reaction 1 ATP phosphorylates glutamic acid, making the amino acid less stable. P + ATP + ADP Glu Glu NH2 P 2 Ammonia displaces the phosphate group, forming glutamine. NH3 + + P i Glu Glu Figure 8.10 How ATP drives chemical work: Energy coupling using ATP hydrolysis (b) Coupled with ATP hydrolysis, an exergonic reaction (c) Overall free-energy change

ATP Cycle & Regeneration of ATP from ADP The E to rephosphorylate ADP to become ATP comes from the cell’s catabolic reactions. ΔG = + 7.3 kcal/mol ATP H2O http://library.thinkquest.org/C006669/media/Biol/img/atp_cycle.gif Energy for cellular work (endergonic, energy-consuming processes) Energy from catabolism (exergonic, energy-releasing processes) ADP + P i

Progress of the reaction Enzymes: Enzymes: Speed up reactions that happen anyway: CATALYST Enzyme Animation.swf Enzymes are: Proteins, usually end in ase: sucrase, lactase, catalase, pepsin (huh?) Enzymes: Lower activation energy, The E necessary to start a rxn Enzymes: DO NOT change the ΔG Progress of the reaction Products Course of reaction without enzyme Reactants with enzyme EA EA with is lower ∆G is unaffected by enzyme Free energy Figure 8.15

Enzymes & Substrates Substrate: Molecule that enzyme acts on Enzyme-substrate complex: Enzyme bound to the reactant it works on Active Site: Area on the enzyme where the substrate binds Induced Fit: The enzyme changes shape to hold the substrate with weak bonds (H bonds or Ionic bonds) How it works: Template to bring substrates together “stretches” substrate and stresses its bonds Changes environmental conditions of substrate

Conditions that affect Enzyme Activity pH: pH’s that are too high or too low denature the protein (enzyme), most work in pH of 6-8 (pepsin is an exception in stomach pH of 2) Temperature: Enzymes have an optimal temperature, above this the protein denatures Cofactors: inorganic substance bound to enzyme for enzyme to work Coenzyme: organic molecule required for enzyme to function

Enzyme Inhibition Competitive Inhibition: Noncompetitieve Inhibitors Bonds to active site, prevents substrate from binding Reversible: mimic substrate Irreversible: CO + hemoglobin Noncompetitieve Inhibitors bind to enzymes and change the conformation of the active site so a substrate can no longer bind. http://www.yellowtang.org/images/competitive_inhibit_c_la_784.jpg

Allosteric Regulation Allosteric regulation occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another site

Enzyme Regulation Feed back inhibition – turns off a metabolic pathway when enough product has accumulated Products act as allosteric inhibitors when in excess. When the products are used up the enzyme is no longer inhibited and free to catalyze more reactions. http://www.life.illinois.edu/bio100/lectures/s97lects/16GeneControl/lac_operon_ind.GIF

Enzyme Concept Check Inhibition pathways Allosteric Pathways Describe the Vocabulary word in each box, and give an example of that pathway. To summarize, describe how enzymes affect the activation energy and the ΔG of a reaction.