Cellular Respiration & Fermentation Food as Fuel Cellular Respiration & Fermentation

Harvesting stored energy Energy is stored in organic molecules carbohydrates, fats, proteins Heterotrophs eat these organic molecules  food digest organic molecules to get… raw materials for synthesis fuels for energy controlled release of energy “burning” fuels in a series of step-by-step enzyme-controlled reactions We eat to take in the fuels to make ATP which will then be used to help us build biomolecules and grow and move and… live! heterotrophs = “fed by others” vs. autotrophs = “self-feeders”

Harvesting stored energy Glucose is the model catabolism of glucose to produce ATP glucose + oxygen  energy + water + carbon dioxide respiration + heat C6H12O6 6O2 ATP 6H2O 6CO2  + Remember, catabolism is the breakdown of a large molecule. By breaking down the bonds in glucose, we release energy. That energy can then be used to form ATP, which can be used in different endergonic reactions that occur in the cell. fuel (carbohydrates) COMBUSTION = making a lot of heat energy by burning fuels in one step RESPIRATION = making ATP (& some heat) by burning fuels in many small steps ATP ATP glucose enzymes O2 O2 CO2 + H2O + heat CO2 + H2O + ATP (+ heat)

Overview Respiration: a way of releasing energy from food by breaking bonds of organic molecules Aerobic respiration: requires O2; 3-step process: Glycolysis TCA cylce (Kreb’s Citric Acid Cycle) Cytochrome chain (Electron Transport Chain) Anaerobic respiration (fermentation): doesn’t require O2 Alcoholic fermentation: yields alcohol; performed by yeasts Lactic acid fermentation: yields lactic acid; performed by muscle cells

Thermodynamics 1st law: Energy is neither created nor destroyed; it just changes form 2nd law: Over time, the amount of useful energy will transform into useless energy

Thermodynamics Exergonic reactions Endergonic reactions ∆G is negative spontaneous Endergonic reactions ∆G is positive

Thermodynamics Catalysts ∆G does NOT change Reaction requires less activation energy and occurs faster

Thermodynamics Coupled Reactions: energy released from an exergonic reaction can be used to drive an endergonic reaction.

Thermodynamics Coupled Reactions This shows the nature of coupled reactions, not a true example. Notice that the energy from one event can power another.

Hydrolysis of ATP The high-energy bond between the 2nd and 3rd is A LOT! Reason: the phosphate group is a bulky molecule… so when you pack them close together, it takes a lot of energy to bond them. So when ATP is hydrolyzed, all of that energy is released (∆G=-7.3 kcal/mol). It’s like stuffing luggage full of sweaters and winter jackets. Imagine stuffing it to more than maximum capacity and trying to close it. What do you think will happen when you open it? Clothes everywhere! (or maybe that just happens in cartoons, but you get the idea.) The energy harvested from ATP hydrolysis can be used to drive endergonic reactions.

Phosphorylation Transfer of a phosphate group Substrate-level phosphorylation Oxidative phosphorylation

Phosphorylation Substrate-level phosphorylation: a compound that already has a phosphate group transfers Pi onto ADP Enzyme-mediated Exergonic Remember that when you go from a high-energy molecule to a lower-energy molecule, it releases energy. Therefore, exergonic!

Phosphorylation (substrate-level) Phosphoenolpyruvate (PEP) forces phosphate onto ADP, making ATP

Phosphorylation Oxidative phosphorylation: adding a phosphate ion directly to ADP endergonic The transport of just two electrons through the electron transport chain generates enough free energy in the form of electrochemical gradient to drive the synthesis of one molecule of ATP. The synthesis of ATP necessitates the dissolution of the electrochemical gradient, however, since the whole process is driven by positive hydrogen ions (protons) flowing back into the matrix space from the intermembrane space. The ETC maintains the electrochemical gradient by continuing to generate hydrogen ions.

Oxidation/Reduction + – + + Oxidation: lose electrons or hydrogen atoms; exergonic Reduction: gain electrons or hydrogen atoms; endergonic loses e- gains e- oxidized reduced + – + e- + e- e- oxidation reduction redox

Where the electrons go, the energy goes

Coenzymes Chemicals that attach to enzymes to make them work VITAMINS are coenzymes NAD (nicotinamide adenine dinucleotide) FAD (flavin adenine dinucleotide) Carry the substrates to the enzymes; recycled over and over again.

Cofactors are chemicals that help activate proteins Cofactors are chemicals that help activate proteins. Coenzymes are a type of cofactor.