Introduction to Cellular Catabolism

Packet #25Chapter #9Introduction to Cellular Catabolism

Laws of ThermodynamicsLaws of ThermodynamicsEnergy is defined as the capacity to do work and takes a number of formsLight; heat; chemicalThe 1st law of thermodynamicsEnergy cannot be created or destroyed but changed from one form into another.When scientists used the term that energy is lost, they are simply stating that it (energy) has been converted into a form which cannot be usefully available for a particular purpose.The 2nd law of thermodynamicsAll natural processes tend to proceed in a direction which increases the randomness or disorder of a system.All natural processes tend to high entropy.MetabolismEnergy & Chemical Reactions IThe summation of chemical reactions, via the use of enzymes, that occur within living organisms is called metabolism.Metabolism is divided is divided into two groupsAnabolismCatabolismDo not forget the role of enzymes in these chemical reactions5Energy & Chemical Reactions IIThe reactions that make up these processes may either be termed exogonic or exergonic.ExogonicChemical reactions that release energyExergonicChemical reactions that absorb free energy.Do not forget the role of enzymes in these chemical reactions6Entropy & Living OrganismsLiving organisms maintain low entropy by taking their chemical energy in the form of food.This food is converted into a form of energy called ATP.ATPFunctions of ATPIn a metabolically active cell, up to 2 million molecules of ATP are required every second. The ATP is used for a variety of purposes.Anabolic processesActive TransportMovementActivating reactantsChemicals often require the addition of phosphate groups from ATP to make them more reactivePhsophorylation of glucose at the beginning of glycolysis.SecretionATP provides energy for the secretion of cell products.ATP & Energy YieldsAdenosine triphosphate (ATP) is the form in which energy is temporarily stored from the breakdown of glucose.The removal of the final phosphate, when changing ATP to ADP, releases 30.6 kJ mol-1 of energy.ATP + H2O -> ADP + phosphate + 30.6 kJ

The removal of the next phosphate yields the same amount of energy.The amount of ATP produced during anaerobic respiration is small. For instance, in alcoholic fermentation, glycolysis yields two molecules of ATP directly and two hydrogen atoms. However, the hydrogen atoms do not enter the electron transfer system as they are used to form the alcohol. The total yield is therefore only two ATPs or 61.2 kJ of energy from a potential of nearly 300kJ for the complete oxidation of a glucose molecule. The process is therefore only about 2% efficient.10RespirationTypes of RespirationGaseous ExchangeExternal respiration (Organ SystemRespiratory System)Processes involved in obtaining oxygen needed for respiration and the removal of gaseous waste such as carbon dioxide.Cellular RespirationInternal/tissueBiological processes which take place within living cells that release energyRevisit of the Hiearchy12Cellular RespirationCells require a constant supply of energy to generate and maintain the biological order that keeps them alive.The energy is derived from the chemical bond energy in food molecules.Sugars, such as glucose, are particularly important fuel molecules.Animal cells obtain sugars, and other molecules such as starch that are converted to sugars by eating other organisms.HeterotrophsTypes of Cellular RespirationAerobic RespirationThe oxidation of glucose to produce energy via the use of oxygen.Sugar molecule is broken down and oxidized to CO2 and H2O.Energy is derived from the chemical bond energy stored in the sugar.Anaerobic RespirationProduction of energy without the use of oxygen.Aerobic Cellular RespirationCellular respiration is a complex metabolic process of over 70 reactions that can be divided into three stagesGlycolysisKrebs Cycle (Tricarboxylic acid cycle)Electron transfer systemChemiosomosisElectron Carrier MoleculesBefore discussing the stages, it is necessary to mention a group of substances that are employed throughout cellular respiration

16Electron (Hydrogen) CarriersElectron (Hydrogen) carriers are also known as acceptor molecules.Electrons are collected by electron carriers molecules and passed to electron carriers at lower energy levels.The electrons are at lower energy levels.The energy released, as the electrons move to lower energy levels, is used to form ATP from ADP.17Electron (Hydrogen) Carriers IIThe electrons are initially part of a hydrogen atom.Hydrogen coming directly, or indirectly, from glucose.Hydrogen atom eventually splits into a proton and an electron.

The reason why electron carriers are sometimes known as hydrogen carriers is because hydrogen atoms, before split apart, carries the electrons with them. NAD when reduced to NADH carries the hydrogen atom that contains the electrons. Furthermore, NAD acts a coenzyme because they are essential to dehydrogenase enzymes that catalyze the removal of hydrogen atoms.18Electron (Hydrogen) CarriersExamplesNicotinamide adenine dinucleotideNADNicotinamide adenine dinucleotide phosphateNADPFlavine adenine dinucleotideFADCytochromesRespiratory QuotientsRespiratory QuotientsA respiratory quotient (RQ) is a measure of the ratio of carbon dioxide evolved to the oxygen consumed:RQ = CO2 evolved / O2 consumedFor a hexose sugar, such as glucose, used during cellular respiration, it can be seen from the equationC6H12O6 + 6O2 6CO2 + 6H2OThe ratio is 6CO2/6O2 = 1.0For a fat such as steric acid, RQ = 0.7Other RQsMalate = 1.33Proteins = 0.9 (varies slightly based on particular protein)The Role of Vitamin BVitamin BThe group of vitamins, called vitamin B, plays a major role in cellular respirationparticularly by acting as coenzymes.Found in green and leafy vegetables.

Vitamin BVitaminRole in Cellular RespirationB1ThiamineInvolved in formation of some Krebs cycle enzymes; forms part of ACOAB2RiboflavinForms part of the hydrogen carrier FADB3Niacin (nicotinic acid)Forms part of the coenzyme NAD and NADP; forms part of ACOAB5Pantothenic acidForms part of ACOA