How Cells Harvest Chemical Energy Cellular respiration is the process by which energy is harvested by cells from sugar Requires Oxygen (O2) Releases Carbon Dioxide (CO2) , water (H2O) and a large amount of ATP All of our cells harvest chemical energy (from food)

Cellular Respiration stores energy in ATP molecules A cell uses energy to build and maintain its structure, transport materials, manufacture products, move, grow and reproduce Cellular respiration involves mainly sugars, but other organic compounds can be broken down (nearly all the equations you’ll see use glucose as the representative food molecule) Our bodies require a continuous supply of energy just to stay alive

Organisms use energy from ATP for all its activities Breathing Heart pumping Maintaining body temperature Thinking, dreaming

Organisms use energy from ATP for all its activities Above and beyond the energy we need for body maintenance, cellular respiration provides energy for voluntary activities The amount of energy it takes to perform these activities are expressed as kilocalories (a “calorie” on a nutritional label actually equals 1 kilocalorie) A kilocalorie is the quantity of heat required to raise the temperature of 1L water by 1 ̊C

Energy consumed by various activities (kilocalorie consumed per hour) Running 979 Dancing 510 Bicycling 490 Swimming 408 Walking 245 Sitting 28

Cellular Respiration Cellular respiration occurs in 3 stages C6H12O6 + 6O2 + 38ADP +38P→ 6H2O + 6CO2 + 38ATP Cellular respiration occurs in 3 stages Glycolysis Citric Acid Cycle The Electron Transport Chain (Oxidative Phosphorylation) All of these steps occur in and around the mitochondria in eukaryotic cells

High-energy electrons NADH High-energy electrons carried by NADH NADH FADH2 and GLYCOLYSIS OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) Pyruvate CITRIC ACID CYCLE Glucose Pyruvate Cytoplasm Inner mitochondrial membrane CO2 CO2 34 ATP 2 ATP 2 ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation

Cellular Respiration – Glycolysis What two words do you see immediately in the word “glycolysis”? Glycolysis literally means the “splitting of sugar” Glycolysis begins with a molecule of glucose (6-Carbon sugar) and ends with 2 molecules of pyruvate (a 3-Carbon compound) Requires the initial input of 2 ATP molecules

Glycolysis Glucose (C6H12O6)+ 2ATP  2 Pyruvate Glycolysis is a multi-step pathway, which utilizes at least 6 different enzymes in a metabolic pathway that is anaerobic (without oxygen) In the later stages of glycolysis, 4 ATP molecules are synthesized using the energy given off during the chemical reactions; net gain of 2 ATP Additionally, 2 hydrogen atoms are removed from the molecules that are formed as glucose is converted into pyruvate. These hydrogen atoms are picked up by the coenzyme NAD to form NADH (2 total) which are used during the Electron Transport Chain

Glycolysis http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_glycolysis_works.html

The Citric Acid Cycle (aka “The Krebs Cycle”) As pyruvate is formed at the end of glycolysis, it is transported from the cytoplasm into a mitochondrion The pyruvate is converted into 2 molecules of acetate which also produces 2 molecules of CO2 and 2 molecules of NADH The Citric Acid Cycle breaks down acetate in the mitochondrial matrix The Citric Acid Cycle produces 2 ATP molecules plus 6 NADH and 2 FADH (another coenzyme)

The Electron Transport Chain The Electron Transport Chain is oxygen-driven and produces the largest amount of ATPs in the entire cellular respiration process For every glucose molecule that enters glycolysis, there is a total net production of 38 ATPs by the end of the Electron Transport Chain The many folds of the mitochondrial inner membrane enlarge its surface area, providing space for thousands of copies of the Electron Transport Chain occurring at once, producing many ATP molecules

Electron Transport Chain A group of 3 integral proteins and 2 membrane coenzymes associated with the inner mitochondrial membrane called the electron transport chain (ETC) creates a H+ gradient between the intermembrane space and the matrix of the mitochondria using the H of from NADH and FADH2 that accumulate in the mitochondrial matrix as products of glycolysis and the Krebs cycle 3 (integral) enzyme complexes of the ETC remove the H from NADH and FADH2 (oxidized back to NAD+ and FAD+) in the matrix

ETC and Oxidative Phosphorylation FADH FAD+

NADH and the Electron Transport Chain NADH is oxidized by Enzyme complex 1 of the ETC The H that is removed by Enzyme complex 1 is split into an electron (e-) and a proton (H+) The e- is passed from the beginning to the end of the ETC and energizes the 1st, 2nd and 3rd Enzyme complexes along the way Once energized, each enzyme complex pumps a free proton from the mitochondrial matrix into the intermembrane space (3 total)

FADH and the Electron Transport Chain FADH is oxidized by Enzyme complex 2 of the ETC The H that is removed by Enzyme complex 2 is split into an electron (e-) and a proton (H+) The e- is passed to the end of the ETC and energizes the 2nd and 3rd Enzyme complexes along the way Once energized, each enzyme complex pumps a free proton from the mitochondrial matrix into the intermembrane space (2 total)

ATP Synthase ATP synthase is an integral membrane protein in the inner mitochondrial membrane that has 2 functions: it acts as a H+ channel allows H+ to diffuse down its gradient from the intermembrane space into the matrix it acts as an enzyme uses the energy that is released by the diffusion of H+ to synthesize ATP from ADP and P This type of ATP synthesis is called oxidative phosphorylation because, this process requires the oxidation of NADH and FADH

ATP Synthesis During Oxidative Phosphorylation For each NADH that is oxidized, 3H+ are pumped into the intermebrane space and the allowed to diffuse back into the matrix through ATP synthase. Each H+ that diffuses through ATP synthase provides enough energy to synthesize 1 molecule of ATP Therefore each NADH oxidized provides enough energy to synthesize 3 molecules of ATP Since 10 molecules of NADH are made between glycolysis and the Citric Acid cycle, 30 molecules of ATP are made once all 10 NADH are oxidized 10 NADH x 3 ATP = 30 ATP

ATP Synthesis During Oxidative Phosphorylation For each FADH that is oxidized, 2H+ are pumped into the intermebrane space and the allowed to diffuse back into the matrix through ATP synthase. Each H+ that diffuses through ATP synthase provides enough energy to synthesize 1 molecule of ATP Therefore each FADH oxidized provides enough energy to synthesize 2 molecules of ATP Since 2 molecules of FADH are made between glycolysis and the Citric Acid cycle, 4 molecules of ATP are made once all 2 FADH are oxidized 2 FADH2 x 2 ATP = 4 ATP

Formation of Water After the electrons arrive to the last enzyme complex of the ETC they are transferred to atoms of oxygen in the mitochondrial matrix this makes oxygen especially negative In the matrix, these oxygen atom are combined with the H+ that have diffused back into the matrix from the intermembrane space to form water (H2O) the protons become “reunited” with their electron

Fermentation enables cells to produce ATP without oxygen In the absence of oxygen, ATP may still be produced via a process called fermentation Fermentation is the process of deriving energy from organic compounds such as carbohydrates in the absence of oxygen Cellular respiration always begins with glycolysis; the presence or absence of oxygen will then determine whether cellular respiration or fermentation will follow

Fermentation Remember, glycolysis results in the formation of 2 3-carbon pyruvate molecules from 1 6-carbon glucose molecule, and 2 ATP molecules are released When oxygen is lacking, certain organisms (such as yeasts) can convert pyruvate into ethyl alcohol and CO2 which removes electrons and allows continuous ATP production Yeasts are able to perform this process because they have the necessary enzyme to convert pyruvate into ethyl alcohol

Fermentation continued… In muscle cells, another type of fermentation takes place When muscle cells contract too quickly (e.g., strenuous exercise), they rapidly use up their oxygen supply, which slows ATP production Muscle cells, however, have the ability to produce a small amount of ATP through glycolysis in the absence of oxygen = lactic acid fermentation

The muscle cells convert glucose to pyruvate, and then an enzyme in the muscle cells converts pyruvate into lactic acid, releasing 2 ATP molecules Lactic acid is toxic and must be removed by the liver (& converted back to pyruvate); heavy breathing after exercise helps restore oxygen back to the muscle cells