Energy & Metabolism Matter – anything that has mass and takes ups space Energy - capacity to do work or bring about change Matter is a form of energy [ E=mc 2 ] > 4 billion kg of matter per second are converted into energy in the sun Energy is expressed as units of work – kilojoules (kJ) or as heat energy – kilocalories (kcal)

Energy and Metabolism Energy flows as heat energy from an object with a higher temperature to an object with lower temperature Cells are too small to have regions with different temperatures, so biologists talk about work energy (kJ) Organisms carry out conversions between potential energy (stored/position) and kinetic energy (motion) Chemical energy is PE stored in chemical bonds

Thermodynamics Thermodynamics – study of energy and its transformation ◦First Law: energy cannot be created or destroyed. It can only be transferred or converted from one form to another. ◦Mass/energy present 14 billion years ago =today’s mass/energy ◦Organisms can’t create own energy – have to capture it from the environment and transform it into a form used for biological work

Thermodynamics Second law – When energy is converted from one form to another, some usable energy (energy available to do work) is converted to heat. Heat is the KE of randomly moving particles. This heat – the random motion of particles- cannot do work. Amount of usable energy in the universe decreases over time Energy is constant, but usable energy is decreasing

Thermodynamics Less-usable energy is more diffuse and disorganized. Entropy (S) is a measure of this disorder. Organized usable energy has low entropy. Disorganized energy (i.e. heat) has high entropy. As a result of 2 nd Law, the cell’s net energy conversion is about 40% efficient. Organisms maintain a high degree of organization, why don’t they “wind down?”

Organisms are open systems. They exchange energy and materials with the environment. Organization is maintained through a constant input of energy. ◦Plants do photosynthesis ◦Animals eat

Metabolism Metabolism is the sum of all chemical activities in an organism. ◦Anabolism – complex molecules made from simpler substances ◦Catabolism – larger molecules broken down into smaller ones ◦These are complementary processes. ◦Catabolism results in overall release of energy ◦Anabolism requires overall input of energy

Metabolism In order to talk about how much usable energy is available to a cell, we talk about Enthalpy (H) – total PE of a system, Entropy (S) – disorder and Free Energy (G) – energy available to do work in biochemical reactions G = H – T(S) As entropy of a system increases, the amount of free energy decreases.

When we measure the temperature difference of a process, we are measuring the enthalpy (PE) change of the system. If ΔT is +, then heat has been released from the system, ΔH is – (exothermic) If Δ T is -, then heat has been absorbed by the system, ΔH is + (endothermic)

Metabolism Exergonic reactions release energy. This means that the products have less free energy than was present in the reactants. The free energy of the system (energy available to do work) decreases and ∆G is considered to be negative. (ΔG = - ) Endergonic reactions absorb energy, the products have more free energy than the reactants, the free energy of the system increases and ∆G is positive. (ΔG = +)

Metabolism - ∆G (exergonic) means that the reaction occurs without input of additional energy +∆G (endergonic) means that the reaction requires input of energy to proceed In organisms, endergonic reactions are coupled with exergonic reactions.

Free energy Diffusion is exergonic. Diffusion goes down a concentration gradient. There is PE in a concentration gradient. Cell uses energy to produce this concentration. A region with a high concentration is more ordered (has lower entropy)than a region with low concentration. As particles move around randomly, they become more disordered (they now have higher entropy). As they have gain higher entropy, they have less free energy. This is exergonic and the energy released can be used for cellular work.

Chemiosmosis ∆G depends on concentration of reactants and products. Any process that increases randomness (increases entropy) can do work because free energy is increased: ∆G = ∆H – T∆S As S (randomness) increases, ∆G becomes more negative. -∆G = exergonic Exergonic means it is free energy- releasing. This means that energy is made available to the cell to do work. Formation of ATP through chemiosmosis is an example of use of H+ ion concentration this way.

LEO the lion goes GER Loss of electrons = Oxidation Gain of electrons = Reduction Many energy conversions in a cell involve electron transfers from one substance to another. A transfer of an electron involves the transfer of the energy of that electron. 4 Fe + 3 O 2 ---> 2 Fe 2 O 3 4 Fe ---> 4 Fe e - (iron is oxidized) 3 O e - ---> 6 O 2- (oxygen is reduced)