Metabolism and Energy SBI4U1

All chemical reactions change matter and energy in cells What is Metabolism? All chemical reactions change matter and energy in cells Via metabolic pathways Metabolic Pathways: multiple chemical reaction catalysed by enzymes Function to break down energy rich compounds like glucose for energy

Catabolism: breaking down to smaller compounds to release energy Anabolism: building larger molecules using energy

Energy Some physics terms... Energy: capacity to do work Kinetic Energy: energy of motion Potential Energy: stored energy

The weight has potential energy as it is suspended in the air. Once it is dropped the potential energy is transformed to kinetic energy. Potential energy is converted to kinetic energy in living cells, this is how molecules are moved into and out of cells in active transport.

Bond Energy: the amount of energy required to break or form a chemical bond Energy released from rxns in living things can be thermal, the movement of molecules, contraction of a muscle, or the emission of light.

Laws of Thermodynamics 1st Law of Thermodynamics Law of conservation of energy Energy cannot be created or destroyed, but it can be transformed from one type into another and transferred from one object to another.

2nd Law of Thermodynamics Transformation of potential energy into heat, or random motion. During any process, the universe tends toward disorder. Entropy (S): a measure of disorder

ordered (less stable)disordered (stable) Energy transformation convert matter from: ordered (less stable)disordered (stable) This law only applies to closed systems. Organisms are open systems and therefore highly ordered. Energy is used to decrease randomness

Free Energy (G): energy from a chemical rxn available to do work “G” is = to the energy contained in chemical bonds, called enthalpy. Enthalpy (H): total energy of a thermodynamic system

G = H – TS In a chemical rxn, the bonds of reactants are broken and the products form new bonds. For chemical rxns under constant temperature, pressure and volume the change in free energy can be determined by: ΔG = ΔH -TΔS

ΔG can predict the spontaneity of a rxn. If ΔG is + Products > free energy than reactants Bond energy, H, is higher Entropy, S, is lower Not spontaneous Endergonic (absorb energy) E.g. photosynthesis

ΔG>O; energy absorbed

If ΔG is – Products < free energy than reactants Bond energy, H, is lower Entropy, S, is higher Spontaneous Exergonic (release energy) E.g. Cellular respiration

ΔG<O; energy released

Thermodynamics and Metabolism Spontaneous rxn do not always occur Must be initiated w/ energy (EA) E.g. Combustion rxn In cells, energy from catabolic rxns initiate anabolic rxns The energy is ATP Enzymes catalyse the rxn and lower EA

Hydrolysis of ATP 3rd phosphate group detached an exothermic rxn ATP  adenosine triphosphate ADP  adenosine diphosphate 3rd phosphate group detached an exothermic rxn H2O is added High energy bond breaks releasing energy ATP ADP

Coupled Rxns Spontaneous exergonic rxns release ATP and drive endergonic rxns The rxns are coupled Hydrolysis and synthesis of ATP is cyclical Phosphorylation = addition of phosphate

Electron Carriers Redox rxns are coupled rxns Recall: LEO goes GER Electrons carry energy (reducing power) Reduced = less energy Oxidized = more energy Electron carriers are compounds in cells that transfer electrons From high energy compounds to low energy compounds

E.g. NAD+ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) These are oxidized forms NADH and FADH2 are reduced forms They play a role in cellular respiration

How the NAD+ Works http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::525::530::/sites/dl/free/0072464631/291136/nad.swf::nad.swf

Things You Should Know... Metabolic Pathways Catabolism vs. anabolism Bond energy 1st and 2nd Law of Thermodynamics Entropy, Enthalpy, Free Energy Endergonic vs. Exergonic Hydrolysis of ATP Coupled Rxns Electron Carriers