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Lecture 4

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Biology 1002B
Tom Haffie

Lecture 4: Energy and Enzymes Independent Study Outcomes: Isolated, closed and open systems. • Isolated System: does not exchange matter or energy with its surroundings. (e.g. thermos) • Closed System: can exchange energy, but not matter, with its surroundings. (e.g. earth- releases heat energy, but no matter) • Open System: both energy and matter can move freely between the system and the surroundings. (e.g. the ocean) First law of thermodynamics • First Law of Thermodynamics: energy can be transformed from one form into another or transferred from one place to another, but it cannot be created or destroyed. (Principle of the conservation of energy) -Photosynthesis is a good example of first law, you can take photon of light and convert it to chemical energy. Second law of thermodynamics • Second Law of Thermodynamics: the total disorder of a system and its surrounding always increases. o Systems will move spontaneously toward arrangements with greater disorder—greater entropy • Cells only able to convert 40% of potential energy in glucose into a form useable for metabolism; heat is lost to environment • Unusable energy produced during energy transformations results in an increase in the disorder or randomness of the universe • Entropy: randomness or disorder. What is meant by the phrase "it takes energy to maintain low entropy" (section 4.1e) • It takes energy to maintain low entropy o i.e. need car mechanic to fix car when it starts breaking down • living cells have ability to create ordered structures or of less ordered starting materials • living cells are open systems • living things bring in energy and matter and use them to generate order out of disorder o most of food we eat is to maintain our cells in their highly ordered state o cell components (proteins, organelles) become damaged and constantly need repair or replacements  by synthesis of proteins, carbohydrates, lipid molecules • living things give off heat and metabolic byproducts (CO2) that are much les ordered, and increase the disorder/entropy of surroundings. Lecture Outcomes: Photons from the sun (light), they represent low entropy energy, because photosynthetic organisms can transform those photons from low entropy and then produce low entropy energy (glucose, proteins, nucleic acids…) meaning of potential, kinetic, chemical energy, closed, open vs. isolated systems, First Law of Thermodynamics, Second Law of Thermodynamics, entropy, spontaneous reaction, enthalpy (H), DH, exothermic, endothermic, Gibbs Free Energy, exergonic, endergonic, DG, catalyst, rate of reaction, energy of activation (EA), transition state, kinetic stability, active site, catalytic cycle Why life does not go against the second law. • 2 law of Thermodynamics- disorder of system+ surroundings increase • cells are highly ordered, but…. o cells are open systems; exchange energy and matter with surroundings o cells use energy to maintain order (low entropy) >> entropy could be explained as energy spreading, dispersal. Why life needs to consume energy - You need huge amounts of calories because entropy causes things to break down, so house keeping proteins have to be translated continually or the body will die. • cells emit lots of heat; this increases disorder of surroundings • huge amounts of energy in allows maintenance of low entropy Components of Gibbs Free Energy equation • It is the energy available to do work • ∆G = ∆H -T∆S • ∆ free energy= ∆ enthalpy (is it +endo/or –exothermic?)- temperature( ∆ entropy “is it + more disorder/or – less disorder”) Reactions tend to be spontaneous ((-ΔG)) means that it doesn’t need energy to proceed “spontaneous /or do I need energy to do so?)) • enthalpy is potential energy o could be biosynthetic pathway, or breakdown of molecule in the cell o endothermic (+) o exothermic (-) • entropy is disorder o more disorder (+) o less disorder (-) • free energy o enerdergonic (+ G) o exergonic (- G) Whether or not a given reaction will be spontaneous, given DG • Reactions tend to be spontaneous (-∆G; exergonic) when… 2 things happen o Reaction is exothermic ( energy is released, and entropy increases e.g. glucose will spontaneously break down) o Products are more disorder (entropy goes up)  Eg. 1: fermentation of glucose to ethanol  Melting of ice room temp. is spontaneous; driven by massive change “increase” in entropy  gas and liquid are more disordered than a solid (entropy) • some spontaneous reactions can take billions of years Role of enzymes in endergonic vs. exergonic reactions • Enzymes can increase rate of spontaneous reaction by 10 -10 20 • Why does life require enzymes? o Without enzymes, the
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