Ch 9- Cellular Respiration How do we get the energy we need? – Food – What in food gives us the energy we need? Cellular Respiration- process that releases energy by breaking down food molecules in the presence of oxygen – Made up of glycolysis, Krebs cycle, and the electron transport chain Equation for cellular respiration – 6 O₂+ C₆H₁₂O₆→ 6 CO₂+ 6 H₂O + Energy

Main Stages of Cellular Respiration Each stage captures some of the chemical energy available in food molecules and uses it to produce ATP Glycolysis- process in which one molecule of glucose is broken in half, producing two molecules of pyruvic acid- 3-carbon compound Glycolysis needs 2 ATP molecules to begin process What happens during glycolysis? – 2 molecules of pyruvic acid, 2 molecules of ATP, and 2 molecules of NADH are produced One of reactions of glycolysis removes 4 high energy electrons and passes them to NAD⁺-electron carrier – Each NAD⁺ accepts a pair of high energy electrons and transfers them to other molecules – Allows energy from glucose to be passed to other pathways in cell Cellular Respiration

Fermentation Releases energy from food molecules by producing ATP in the absence of oxygen What happens during fermentation? – NADH is converted back to NAD⁺ by passing high energy electrons back to pyruvic acid – Allows glycolysis to produce steady supply of ATP Anaerobic 2 main types of fermentation- alcoholic fermentation and lactic acid fermentation

Alcoholic fermentation- uses pyruvic acid and NADH to produce ethyl alcohol, carbon dioxide and NAD⁺ – Used by yeasts and few other microorganisms Lactic Acid- uses pyruvic acid and NADH to produced lactic acid and NAD⁺ – Produced in muscles during rapid exercise when body cannot supply enough oxygen to tissues – Unicellular organisms produce lactic acid as waste, as result prokaryotes are used in array of food production

Sec 2- Krebs Cycle and Electron Transport 90% of chemical energy still available in glucose after glycolysis, locked up in high energy electrons of pyruvic acid Oxygen is required for final steps of cellular respiration- aerobic

Krebs Cycle Oxygen must be present Also known as Citric Acid Cycle During cycle, pyruvic acid is broken down into carbon dioxide in a series of energy extracting reactions Citric Acid Production – Pyruvic acid enters mitochondrion, carbon is removed forming CO₂, electrons are removed, changing NAD⁺ to NADH – Coenzyme A joins the 2 carbon molecule, forming acetyl- CoA. Acetyl- CoA adds the 2 carbon acetyl group to a 4- carbon compound forming citric acid

Energy Extraction – Citric acid is broken down into 5-carbon compound and then into 4-carbon compound – 2 more molecules of CO₂ are released and electrons join NAD⁺ and FAD, forming NADH and FADH₂, one molecule of ATP is generated – Energy output from one molecule of pyruvic acid= 4 NADH, 1 FADH₂, and 1 molecule of ATP CO₂ released is source of all carbon dioxide we breathe ATP produced in Krebs cycle is used for cellular activities

Electron Transport Chain Krebs cycle generates high energy electrons that are passed to NADH and FADH₂ Electrons are passed from carriers to electron transport chain Uses high energy electrons from Krebs cycle to convert ADP to ATP Takes place in mitochondrion Steps of Electron Transport Chain – High energy electrons passed along chain from one carrier protein to next. At end of chain, enzyme combines these electrons with hydrogen ions and oxygen to form water – Oxygen serves as final acceptor, it is essential for getting rid of low energy electrons and hydrogen ions-the wastes of cellular respiration

Every time 2 high energy electrons transport down chain, energy is used to transport hydrogen ions across the membrane Inner membrane of mitochondria contain protein spheres called ATP synthases, as H⁺ ions escape through channels, into these proteins, ATP synthases spin and grab a low energy ADP and attaches a phosphate, forming high energy ATP On average, each pair of high energy electrons produces 3 molecules of ATP from ADP

Totals Glycolysis produces 2 ATP molecules Krebs cycle and Electron Transport Chain produce roughly 36 ATP molecules, 18 times more than glycolysis