Bio121_F24_Energy and Enzymes_Student (2) PDF

Energy + Electrons + Enzymes = *Metabolism* Campbell Biology Sections 8.1-8.5 Professor Andrea Greiff Bio 121 – Cell Biology 1 Objectives We’ve talked about macromolecul...

Energy + Electrons + Enzymes = *Metabolism* Campbell Biology Sections 8.1-8.5 Professor Andrea Greiff Bio 121 – Cell Biology 1 Objectives We’ve talked about macromolecules and how they are “put together” We’ve discussed a number of enzymes, so far Now we are going to start exploring metabolism by looking at energy transfer, reactions, and how enzymes make life possible for the cell This will lay the foundation for discussing photosynthesis and cellular respiration in the next few weeks 2  Nuclear fusion in the sun gives off Energy Flow is energy in the form of light Continuous Plants collect light energy Use CO2 and H2O (given off by animals) to convert light to chemical energy (macromolecules) + O2 Free that chemical energy by breaking bonds in macromolecules Use that energy to do work for the cell Animals consume plants to gain energy in the form of macromolecules Use O2 (given off by plants) to break bonds in macromolecules Releases energy to be used to do work Animals give off CO2 and H2O (byproducts of combustion) that are used by plants 3  Energy Flow In the Biosphere Energy transfer reactions are not perfectly efficient, and some energy is lost as heat Flow of matter accompanies flow of energy in the biosphere: Energy enters the biosphere as light without matter Energy leaves the biosphere as heat without matter Within the biosphere, energy exists as the chemical bonds in matter 4  Electrons are the “Currency” of Energy Energy in matter is contained in chemical bonds Chemical bonds are formed by the sharing or transfer of electrons Oxidation is the process of losing electrons Gives off energy Oxidized compound becomes more positive Reduction is the process of gaining http://redoxreactionsavi.weebly.com/uploads/5/3/4/9/53498209/212078579.gif electrons Requires energy OIL-RIG (oxidation is loss, reduction is gain) Reduced compound becomes more negative LEO-GER (lose electrons oxidation, gain electrons reduction) 5 Slide modified from Dr. K Strand  REDOX Reactions REDOX reactions couple reduction of one molecule to oxidation of another In this figure, electrons (energy) are being transferred from molecule A to molecule B REDOX terminology: Reducing agent: molecule losing electrons Oxidizing agent: molecule gaining electrons Reduced molecule: gained electrons Oxidized molecule: lost electrons 6 Slide modified from Dr. K Strand  In Cells, Protons Come With Electrons When Transferring Energy 1e- + 1p+ = hydrogen (H) Protons are often written as H+ , so 1e- + 1H+ = hydrogen (H) A proton is usually received with an electron in biochemical REDOX reactions, so follow the H Carbon is gaining H ∴ being reduced Oxidation is loss of + e- H+ (= H) Oxygen is losing H ∴ being oxidized and gives off energy Reduction is gain of e- + H+ (= H) and requires energy input 7 Slide modified from Dr. K Strand Question 1 Fill in the blanks: Energy enters the biosphere as _________ and leaves as ________. While in our biosphere, energy is stored in _______________ and is transferred as __________. A molecule that has lost electrons is __________. A molecule that has gained electrons is __________.  Energy transfer in living things = Metabolism Anabolic reactions build things Form bonds between atoms and small molecules to build bigger molecules Bonds store energy Catabolic reactions break things down Break bonds in bigger molecules to make small molecules Releases energy stored in bonds  Chemical Reactions Either Use or Release Energy Type of reaction? Anabolic or catabolic? Forming bonds or breaking bonds? Using energy or releasing energy? 10 Slide modified from Dr. K Strand  Chemical Reactions Either Use or Release Energy Type of reaction? Anabolic or catabolic? Forming bonds or breaking bonds? Using energy or releasing energy? 11 Slide modified from Dr. K Strand  Free energy in metabolism Free Energy (G): the amount of stored energy High G Large, ordered, many bonds storing energy Catabolic Anabolic reactions reactions -ΔG +ΔG Low G Smaller pieces, less ordered, fewer bonds storing energy  Changes in Free Energy of Metabolism The change in free energy (ΔG) is dependent on enthalpy (ΔH), entropy (ΔS), and the temperature the reaction is taking place at ΔG = ΔH – TΔS ΔG in units of cal/mol 13 Slide modified from Dr. K Strand  Enthalpy and Entropy: Heat and Randomness in Systems Enthalpy (H): the amount of heat in Entropy (S): the amount of disorder a system or randomness in a system Measured as a change in enthalpy: ∆H Measured as a change in entropy: ∆S + ∆H - ∆H - ∆S + ∆S https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Thermo http://www.theunrealtimes.com/2013/05/09/bjp-creates-guinness- dynamics/Fundamentals_of_Thermodynamics/Enthalpy_Changes_in_Reactions 14 record-for-maximum-entropy-after-confirmation-by-scientists/  Metabolism: Exothermic and Endothermic Reactions Exothermic: Heat energy released (-ΔH) Entropy increased in system (+ΔS) Energy stored in bonds released (-ΔG) Ex: Catabolic reactions Endothermic: catabolic anabolic reactions reactions Heat energy required (+ΔH) Entropy decreased in system (-ΔS) Energy stored as bonds formed (+ΔG) Ex: Anabolic reactions Modified from: 15 Slide modified from Dr. K Strand Question 2 For each type of reaction, fill in the actions (exothermic/endothermic, making/breaking bonds) and energetics (is the sign of each positive or negative) Type of reaction Endothermic or Making or breaking Enthalpy (∆H) Entropy (∆S) Free Energy (∆G) exothermic? bonds? Anabolic Catabolic  Activation Energy Both endothermic and exothermic reactions need energy input to proceed This energy input is called the activation energy (EA) Reactants absorb energy from their environment until they reach EA Absorbed energy makes reactants’ structure unstable At EA, the bonds are unstable enough to break Often this energy comes from heat Cells cannot heat up to make reactions happen Would not be able to control which reactions happen when 17  Enzymes Reduce Activation Energy Enzymes are catalysts that: Lower the activation energy by bringing reactants close together Increase the rate of reactions Remain unchanged and are reused 18 Slide modified from Dr. K Strand  Cells use enzymes to reduce amount of activation energy (EA) needed to make a reaction proceed http://ib.bioninja.com.au/higher-level/topic-8-metabolism- High Low EA EA cell/untitled-6/activation-energy.html 19 Slide modified from Dr. K Strand Enzymes Reduce Activation Energy By Bringing Reactants Close Together Without an enzyme: reactants have to gain enough energy (EA) to be reactive AND bump into each other With an enzyme: the protein holds the reactants close together in a favorable conformation to react Reactants still have to gain energy (EA) to react, but not as much Reactants still have to bump into the enzyme 20 Question 3 Enzymes increase the rate of chemical reactions by decreasing which measure of energy? a) Entropy b) Activation energy c) Enthalpy d) Free energy Cells can regulate when/where reactions happen by: Controlling when/where an enzyme is produced: Transcription and Translation Controlling the activity of the enzyme: Regulation by activators and inhibitors Regulation of enzymes by inhibitors and activators https://www.khanacademy.org/science/biology/energy-and-enzymes/enzyme- regulation/a/enzyme-regulation Bioninja.com 22  Characteristics of Enzymes: Active Site Most enzymes are proteins Specific amino acids within protein enzymes interact with substrate Not always adjacent Brought together by folding to form the active site Many have cofactors or coenzymes Cofactors: small inorganic molecules, often metal ions, required for enzyme function Coenzymes are small organic molecules, often vitamin derivatives, that help enzymes do their job 23  Common examples of coenzymes (and REDOX) In photosynthesis and cellular respiration we’ll Oxidized Coenzyme Reduced Coenzyme see examples of coenzymes shuttling energy NAD+ NADH + H+ Shuttle energy by gaining or losing electrons NADP NADPH (REDOX) FAD FADH2 Enzymes add energy to a molecule by transferring it from (oxidizing) their coenzyme Enzymes remove energy from a molecule by transferring it to (reducing) their coenzyme Example at right: isocitrate is oxidized to alpha-ketoglutarate by breaking a bond to release CO2 Breaking a bond releases energy (e- + H+) Isocitrate-dehydrogenase + + transfers the released + energy (e + H ) to NAD reducing it to NADH + H  Characteristics of Enzymes: Temperature Effects Temperature effects: Reaction rate usually increases with increase in temperature until the denaturing temperature is reached Optimal temperature reflects the environment the enzyme is active in Fun fact: fever is thought to work by denaturing (unfolding) the enzymes of the pathogen 25  Characteristics of Enzymes: pH Effects and Other Factors pH effects: Most enzymes are only active within a narrow pH range (3-4 pH units) Optimal pH reflects the environment the enzyme is active in Other factors: Activators and inhibitors change enzyme activity Ionic strength affects proteins Concentration of substrate, product, activators, inhibitors 26 Question 4 Which of these are ways cells can control enzymes (and the reactions they catalyze)? Choose all that apply. a) Heating up to increase reaction rate b) Adjusting their pH to favor an enzyme c) Production of the enzyme (transcription and translation) d) Production of activator and inhibitor molecules  Enzymes Increase Reaction Rate Without enzymes, reactions needed for survival would take too long to carry out in the dilute, aqueous, temperate environment most organisms inhabit http://nptel.ac.in/courses/122103039/module5/lec34/1.html 28