BIOL111 Lecture 2 2024 PDF

3/19/24 What you need to know at the end of the lecture n Cells/organisms obey the laws of thermodynamics n Cells need energy to move, to move things across membranes and for che...

3/19/24 What you need to know at the end of the lecture n Cells/organisms obey the laws of thermodynamics n Cells need energy to move, to move things across membranes and for chemical synthesis (i.e. for work) n Cells can’t create energy, so they transform and transfer energy types n Every reaction in a cell increases entropy in the universe (even if it increases order in the cell) n Free energy is energy available to do work n Reactions occur spontaneously if the free energy of the products is lower than that of the reactants (- DG). exergonic reaction. n An endergonic reaction has a + DG value and is non- spontaneous but can occur if coupled with an exergonic reaction. 1 1st Law of Thermodynamics n Energy in the Universe is constant (quantity not quality (type)) n Energy can’t be created or destroyed but it can be transferred or transformed n To do work cells need energy n Transform energy from the sun, from chemicals or from food to enable work 2 1  3/19/24 Types of Energy n Kinetic energy: anything that moves. n Light, electrical, heat n Potential energy: energy related to structure or location n Chemical energy n Proton gradient across a membrane 3 Transforming energy n Food – chemical energy (potential energy) – broken down via a metabolic pathway 4 2  3/19/24 Transforming energy n Food – chemical energy (potential energy) n Used to create a H+ gradient across the membrane of mitochondria (potential energy) (analogous to the water behind the dam) 5 Transforming energy n Food – chemical energy (potential energy) n Used to create a H+ gradient across the membrane of mitochondria (potential energy) n H+ cause ATP synthase to rotate (kinetic energy) (analogous to the water flowing down the waterfall and spinning a water wheel) 6 3  3/19/24 Transforming energy n Food – chemical energy (potential energy) n Used to create a H+ gradient across the membrane of mitochondria (potential energy) n H+ cause ATP synthase to rotate (kinetic energy) n Rotation makes ATP (potential energy) 7 Transforming energy n Food – chemical energy (potential energy) n Used to create a H+ gradient across the membrane of mitochondria (potential energy) n H+ cause ATP synthase to rotate (kinetic energy) n Rotation makes ATP (potential energy) n ATP drives many processes such as muscle contraction (kinetic energy) 8 4  3/19/24 Transforming energy n Sun – light energy (kinetic) n Photosynthesis converts the light energy into sugars (potential energy) 9 Transforming energy n Some prokaryotes n Inorganic compounds (e.g. H2S, NH3, Fe2+- chemical energy n Convert energy in the electrons to chemical energy (ATP) through the electron transport chain or make sugars by reducing CO2 10 5  3/19/24 2nd Law of Thermodynamics n Every energy transfer or transformation increases the disorder (entropy) of the universe n Greater order = lower entropy = greater instability n Higher free energy 11 Free Energy and work n Free energy is essentially a measure of something's stability n Higher free energy (G) = greater instability = greater order = lower entropy (disorder) n Lower free energy = more stability less order – higher entropy n Free energy changes enable work in cells n So look for example at part c. Breaking down glucose to CO2 and H2O results in a free energy change – the released energy enables work 12 6  3/19/24 Free Energy n Free energy (abbreviated as G) n Portion of a systems energy that can perform work when temp and pressure are uniform through the system n As a system changes (e.g. in a reaction) n The change in free energy DG = G (final state) – G (starting state) 13 Free Energy n Let’s work out DG for a reaction Starting state Final state 14 7  3/19/24 Free Energy n Starting state - higher free energy n Final state - lower free energy Starting state Final state 15 Free Energy n Starting state - higher free energy n Final state - lower free energy n Lets put some arbitrary values on these free energies Starting state G = 6 Final state G=2 16 8  3/19/24 Free Energy n The free energy change for the reaction (DG (delta G)) can be calculated subtracting G(starting state) from G(final state) n DG = G(final state) – G (starting state) Starting state G = 6 Final state G=2 17 Free Energy n DG = 2 – 6 = -4 n Negative DGs indicate that a reaction will occur spontaneously n This is an exergonic reaction Starting state G = 6 Final state G=2 18 9  3/19/24 Exergonic reaction 19 Free Energy n If the reaction were to go in the other way?? final state G = 6 starting state G = 2 20 10  3/19/24 Free Energy n If the reaction were to go in the other way?? n DG would be +4 n Reaction would be endergonic final state G = 6 starting state G=2 21 Endergonic reaction 22 11  3/19/24 Entropy n How can cells/organisms develop as highly ordered structures (low entropy) and still increase disorder (high entropy) 23 Entropy n In carrying out reactions some energy is lost as heat, this increases disorder in the surroundings 24 12