CELLULAR RESPIRATION

Cellular Respiration Energy enables life Living organisms efficiently harness energy from the environment, convert it to usable forms, and use it to power the processes of life Almost all organisms use glucose (C6H12O6) as a primary energy source Through a series of redox reactions, organisms break the covalent bonds in the glucose molecule and rearrange them into new configurations. The end result is the release of energy.

C6H12O6 + 6O2  6CO2 + 6H2O + energy Equation for cellular respiration There are 3 main goals of this process To break the bonds between the 6 C atoms in glucose, resulting in 6 CO2 molecules To move H atoms and its electrons from glucose to oxygen forming 6 H2O molecules To trap as much of the free energy released in the process in the form of ATP The entire process occurs in 4 stages so let’s go!

Stage One: GLYCOLYSIS * A ten step process occurring in the cytoplasm Stage Two: PYRUVATE OXIDATION * A one step process occurring in the mitochondria Stage Three: KREB’S CYCLE (a.k.a citric acid cycle) * An eight step process occurring in the mitochondria Stage Four: ELECTRON TRANSPORT CHAIN * A multi-step process occurring in the mitochondria

Ultimate Goal Extract energy from nutrient molecules and store it in the form ATP 2 energy-transfer mechanisms: Substrate Level Phosphorylation Oxidative Phosphorylation

1. Substrate Level Phosphorylation ATP formed in an enzyme catalyzed reaction A phosphate containing compound transfers its phosphate group directly to ADP --- forming ATP

2.Oxidative Phosphorylation ATP is formed indirectly Involves a number of sequential redox reactions, with oxygen being the final electron acceptor It is a more complex process & yields more ATP molecules for each glucose molecule

Oxidative Phosphorylation Begins when NAD+ (nicotinamide adenine dinucleotide, derived from vitamin B3 (niacin)) removes 2 hydrogen atoms (2 protons & 2 electrons) from a portion of the original glucose molecule 2 electrons & 1 proton attach to the NAD+, reducing it to NADH, the remaining proton dissolves into the surrounding solution Catalyzed by dehydrogenase enzyme This reduction occurs in: glycolysis (stage 1) Pyruvate oxidation (stage 2) 3 reactions of the Kreb’s cycle (stage 3)

Pg. 154 Fig 5

Oxidative Phosphorylation Another coenzyme FAD (flavin adenine dinucleotide) performs a function similar to NAD+ FAD is also reduced by 2 H atoms from a portion of the original glucose molecule Its reduced form is FADH2 because all the protons bind directly to the molecule Reduction occurs in the Kreb’s cycle

Oxidative Phosphorylation The reductions of NAD+ to NADH & FAD to FADH2 are energy harvesting reactions that will eventually transfer most of their free energy to ATP molecules The reduced coenzymes act as mobile carriers within the cell, moving free energy from one place to another and from one molecule to another The process by which a cell transfers free energy from NADH & FADH2 to ATP occurs in Stage 4 (Electron Transport & Chemiosmosis)

Homework Section 4.1 Page 168 – 171 # 1, 2, 5, 6