Cellular Energetics F2024 PDF

Section 1: Introduction to Cell Biology A The basic building blocks of life B Chemical information (DNA, RNA, making proteins) C Protein Structure and Function D Regulating protein function (phosphorylation and GTP binding) E Cellular Organization: organelles F Pr...

Section 1: Introduction to Cell Biology A The basic building blocks of life B Chemical information (DNA, RNA, making proteins) C Protein Structure and Function D Regulating protein function (phosphorylation and GTP binding) E Cellular Organization: organelles F Prokaryotes, Eukaryotes and cellular evolution G Cellular Energetics H Experimental Methods - Studying gene function For reference reading (optional): Alberts 7e, Chapter 2, pages p 57-62 1  Section 1G: Cellular Energetics 1. Basic review of thermodynamics - Entropy and enthalpy - Gibb’s free energy - Cells are NOT a closed system 2. Transfer of energy between organisms and within cells a) Glucose and other “high energy” molecules b) ATP  Life is driven by energetic processes The laws of thermodynamics tell us that spontaneous reactions are those that either (intuitively): - reduce the enthalpy of the system - increase the entropy (disorder) of the system (or both) Cells are ordered structures that take relatively simple molecules and make them into more complex ones (e.g. DNA), which is both - an increase in enthalpy AND - a reduction in entropy (disorder) how does that happen? 3  Laws of Thermodynamics Law 2: Conversion of potential energy to work is always accompanied by transformation into heat and/or increased entropy Entropy, S: randomness and disorder of the universe increased entropy (+S) = increased disorder = spontaneous decreased entropy (-S) = decreased disorder = non-spontaneous but… -S +S 4  Laws of Thermodynamics Enthalpy, H: energy content (heat) derived from volume, pressure and different types and number of bonds. Intuitively: the heat content of chemical bonds + H: positive enthalpy = increased heat/energy content in a bond = not spontaneous since energy must be transferred into system - H: negative enthalpy = decreased heat/energy content in bond = spontaneous because energy is liberated into the universe -H More energy content C-H C=O Less energy content +H 5  Gibbs Free Energy Gibbs free energy (G) is total energy balance derived from enthalpy and entropy G = H – TS, where T is temperature Kelvin What’s important is change in G between conditions!! DG = DH - TDS S P +DG = increased total energy in system; = not spontaneous; endergonic - DG = decreased total energy in system = spontaneous; exergonic 6 But living organisms are ordered and carry out lots of endergonic reactions! Virus coat Microtubules in Pollen grain proteins sperm flagellum 500 metabolic Energy rich bonds pathways and their interconnections Figure 2-35 Molecular Biology of the Cell (© Garland Science 2008) 7 Figure 2-33 Molecular Biology of the Cell (© Garland Science 2008)  Back to the question: In cells, building macromolecules involves: - an increase in enthalpy AND HOW? - a reduction in entropy (disorder) Cells are NOT a closed system: - intake of molecules into cells from the non-living outside world, metabolism releases (heat) energy - The “fuel” generated (negative DG) from these reactions is COUPLED to other reactions that have a positive DG Fig. 2-16 8  The total ∆G of a series of reactions is the sum of the individual ∆G for each reaction ∆G1 ∆G2 ∆G3 S1 P2 Q3 R4 +100 -75 -75 Dead Living Sources of energy ∆Gnet (S1 to R4) = ∆G1 + ∆G2 + ∆G3 ∆Gnet = -50 Life, despite being ordered, is possible because of the many exergonic reactions that liberate energy to make the whole process exergonic, and thus, spontaneous! 9 Catabolic reactions (release energy) drive anabolic reactions (create order) Catabolism: reactions that Anabolism: reactions that are are highly exergonic (increase endergonic (decrease disorder disorder and/or liberate and/or “store” energy in bonds) – energy) – spontaneous. not spontaneous Breakdown of molecules like Synthesis of complex molecules sugars and lipids like proteins and nucleic acids 10 Photosynthesis provides an “unlimited” source of energy Photosynthesis involves conversion of energy: 1) First from electromagnetic energy TO high energy electrons 2) Then, from high-energy electrons to chemical bonds The energy provided for generation of new chemical bonds allows formation of complex molecules (e.g. glucose) Fig 2-17 11  “High energy” molecules are made by plants and then consumed by other living organisms e.g. glucose Fig. 2-18 12 In many living cells, there is a common energy “currency” molecule Catabolism: Energetically favourable reactions can be coupled to “regenerating” an activated energy carrier molecule Anabolism: Energy carrier molecules are “consumed” to allow otherwise unfavourable reactions to take place Fig. 2-31 13 Adenosine triphosphate (ATP) is the common energy “currency” molecule Fig 2-33 14  Section 1G Summary: Cellular Energetics Cells need a constant source of energy to survive Mostly all energy comes from sunlight and photosynthesis Other organisms (other than plants) obtain energy from plant-made molecules Catabolic reactions are energetically favourable (negative DG), and many generate ATP or other energy carrier molecules Anabolic reactions are energetically unfavourable (positive DG) unless coupled to a reaction involving ATP or other energy carrier molecule (which makes the overall DG negative) Cells use adenosine triphosphate (ATP) as energy currency 15