BES 107: Introduction to Cell Biology: Metabolism & Bioenergetics - PDF

BES 107 Introduction to Cell Biology Part 6 – METABOLISM & BIOENERGETICS Campbell’s Biology Chapter 8 Winter 2025 Sophon Bailey All figures are from Campbell’s Biology, © 2021 Pearson Pre...

BES 107 Introduction to Cell Biology Part 6 – METABOLISM & BIOENERGETICS Campbell’s Biology Chapter 8 Winter 2025 Sophon Bailey All figures are from Campbell’s Biology, © 2021 Pearson Press, unless otherwise attributed. Course content, digital or otherwise, created and/or used within the context of the course is to be used solely for personal study, and is not to be used or distributed for any other purpose without prior written consent from the content author(s). LEARNING OBJECTIVES Apply the principles of thermodynamics to chemical reactions in the cell Define the free energy of a chemical process and distinguish exergonic and endergonic reactions Understand the principles that govern the interconversion of light energy, chemical energy, and work Describe the energetics of metabolic pathways and the ways biological systems use the energy equivalence of ATP to perform work Understand the role of enzymes as catalysts to increase the rate and specificity of chemical reactions in the cell Identify different modes of regulation of enzymes that are used to control and coordinate cellular metabolism 2 METABOLISM The totality of all chemical reactions within a cell or organism An emergent property of life that arises from orderly interactions between molecules G re e k ‘m e ta b o le ’: c h a n g e  © 2017 Roche Interactive Pathways Campbell’s Biology © 2021 Pearson Press http://biochemical-pathways.com/ M ETABOLIC Metabolic pathways are visualized as a sequence of chemical reactions Pathways are interconnected and in a constant dynamic steady state of homeostasis PATHWAYS 4 THERMODYNAMICS Metabolism transforms matter and energy, subject to the laws of thermodynamics 1. Conservation of energy –energy can be transferred and transformed but not created or destroyed 2. Energy always moves from high to low - Every transfer or transformation of energy increases the entropy of the universe 5 Campbell’s Biology © 2021 Pearson Press  Campbell’s Biology © 2021 Pearson Press ENERGY Most biological systems are generally concerned with the transformation of chemical energy to kinetic energy TRANSFORM ATION Photosynthesis (next unit) is concerned with transformation of kinetic energy (from light) into chemical energy 6 ENTROPY AND ORDER Biological systems appear to increase order (lowers entropy) in violation of the 2nd law › Chemicals, macromolecules, organelles, cells, and tissues are more ordered than their respective component parts Cells, organisms, and ecosystems areopen systems Local increases in order are permitted so long as entropy of the universe increases 7 Campbell’s Biology © 2021 Pearson Press FREE ENERGY Gibbs free energy How do we determine if a reaction can proceed according to the laws of thermodynamics? Josiah Gibbs Free energy describes the thermodynamics of any process ∆𝐺 = ∆𝐻 − 𝑇∆𝑆 › If the increase in entropy at a given temperature (TΔS) is greater than the temperature (K) energy required (ΔH) the process is spontaneous Enthalpy (energy) » ΔG < 0 spontaneous (exergonic) Entropy » ΔG > 0 not spontaneous (endergonic) 8 Campbell’s Biology © 2021 Pearson Press FREE ENERGY CHANGE Spontaneous reactions are allowed thermodynamically –does not mean they will occur quickly or without acatalyst 9 Campbell’s Biology © 2021 Pearson Press Free energy can also be estimated from the difference in total free energy between the final and initial conditions ΔG = GPRODUCTS – GREACTANTS For chemical reactions this is the difference between products and reactants 10  RESPIRATION H OH Glucose oxidation HO is a central HO + O2 → 6CO2 + 6 H2O reaction in cell metabolism glucose Glucose breakdown is highly exergonic C6H12O6 + O 2 → 6CO2 + 6 H2O ΔG = –2870 kJ/mol 11 KEY POINTS Metabolism is the sum total of reactions that transform matter and energy subject to the laws of thermodynamics 1. Energy can be transferred or transformed but must always be conserved 2. The entropy of the system must always increase Biological systems convert light energy to chemical energy, and chemical energy into kinetic energy  work Biology creates local decreases in entropy, but overall increases in entropy Free energy (ΔG) describes whether a reaction is likely to proceed spontaneously › Negative ΔG is an exergonic reaction and can proceed spontaneously › Positive ΔG is endergonic and cannot proceed spontaneously 12  DISEQUILIBRIUM A closed system at equilibrium can no longer to work Metabolism is an open system and never reaches equilibrium Closed system in equilibrium Metabolism is generally a steady state with a high amount of flux or flow through reactions in disequilibrium 13 Campbell’s Biology © 2021 Pearson Press  REVERSABILITY H OH HO O Metabolic processes H HO H H are reversible H OH OH In different conditions cells can redirect or reverse Gluconeogenesis flow through Glycolysis Anabolism Catabolism pathways (building up) (breakdown) requires energy releases energy Catabolic pathways are generally exergonic, anabolic pathways are CO2 + H2O endergonic 14  light energy ENERGY CURRENCY (photoautotrophs) chemical energy (heterotrophs) ATP (adenosine triphosphate) acts as a standard currency of energy in the cell 15 Campbell’s Biology © 2021 Pearson Press  ATP HYDROLYSIS ATP acts as a currency by hydrolysis to ADP (adenosine diphosphate) or AMP (adenosine monophosphate) ATP hydrolysis is exergonic (ΔG = –30 kJ/mol) The excess energy from ATP hydrolysis can be used to perform work in the cell 16 Campbell’s Biology © 2021 Pearson Press  Campbell’s Biology © 2021 Pearson Press HOW DOES ATP ATP is often hydrolyzed to form reaction intermediates Phosphorylated intermediates can be more reactive and helps PERFORM WORK? make and otherwise endergonic reaction exergonic 17  OTHER FORMS OF WORK ATP can drive other processes in the cell Hydrolysing ATP can produce kinetic energy to transport solutes or drive motor proteins by altering the shape of proteins 18 Campbell’s Biology © 2021 Pearson Press Campbell’s Biology © 2021 Pearson Press Spontaneous reactions do not proceed quickly or easily due to the ACTIVATION ENERGY requirement of activation energy Catalysts are some component that affects the reaction by lowering activation energy without being consumed in the reaction  19 biological catalysts are enzymes SUBSTRATE SPECIFICITY Enzymes-substrate (E-S) interactions are required for catalysis to occur E-S interactions must be: › Specific –binds only the desired substrate › Sensitive –binds substrate at low concentrations › Reversible –must be able to release products 20 Campbell’s Biology © 2021 Pearson Press  ENZYM ES Bind specific substrates Align substrates in active site for optimal reaction Lower E A by bringing substrates into close proximity Induced fit strains substrates to promote reaction Reversibility releases product leaving enzyme unchanged 21 Campbell’s Biology © 2021 Pearson Press ENZYME REGULATION Metabolic pathways must be regulated to control and redirect resources asneeded Allosteric sites are sites on enzyme that will bind a ligand other than the substrate › Allosteric activators increase activity of an enzyme › Allosteric inhibitors decrease activity of an enzyme 22 Campbell’s Biology © 2021 Pearson Press FEEDBACK INHIBITION Allosteric inhibitors can include products of a metabolic pathway Allosteric inhibition by an end product allows the pathway to quickly respond to changes in product levels Regulated an early enzyme prevents accumulation of unwanted intermediates 23 Campbell’s Biology © 2021 Pearson Press  COVALENT REGULATION Enzymes can be regulated by covalent modification with phosphate › Phosphorylation transfers Pi from ATP to a site on an enzyme by akinase › Dephosphorylation hydrolyzes Pi from the enzyme by a phosphatase Covalent regulation requires energy (ATP)and additional enzymes but is explicitly controlled by the cell › Commonly used during signal transduction from extracellular receptors Becker’s World of the Cell, 9e © 2016 Pearson Education Inc, 24 Jeff Hardin and Gregory Bertoni KEY POINTS Metabolism is an open system with continuous, steady state of flux Metabolic pathways operate in two general directions › Anabolic (biosynthesis) –build biomolecules from smaller components, requires energy › Catabolic (breakdown) –degrades biomolecules to simpler components, recovers energy ATP hydrolysis to ADP is an exergonic process that is used as an energy currency to drive otherwise endergonic reactions › Catabolic reactions convert chemical energy to ATP › Anabolic reactions consumeATP Enzymes are catalysts that allow reactions to occur under the conditions of the cell › Specific, sensitive, reversible › Lowers the activation energy of a reaction, but does not change the ΔG of reaction Enzyme regulation ties the activity of metabolic pathways to the conditions of the cell › Allosteric activators and inhibitors are used to provide negative feedback or positive regulation of a pathway › Covalent regulation allows signaling processes to control metabolic pathways 25