Chapter 6: How Cells Harvest Chemical Energy6.1 Photosynthesis and cellular respiration provide energy for life- Sun – ultimate source of energyo Photosynthesis – process by which the suns energy is captured- Photosynthesis [in cell’s chloroplasts]o Sunlight + CO2 + H2O  Glucose + O2- Cellular Respiration [in mitochondria of eukaryotic cells]o Glucose + O2  CO2 + H2O + ATP6.2 Breathing Supplies O2 for use in cellular respiration and removes CO2- Respiration – “an exchange of gases” & “aerobic harvesting of energy from food molecules by cells” [aka cellular respiration]- Glucose + O2  CO2 + H2O + ATP6.3 Cellular Respiration banks energy in ATP molecules- Glucose (C6H12O6) – fuel to the cells- Cellular Respiration o 32 ATP molecules for each Glucose o Captures 34% of the energy originally stored in Glucose & the rest is released as heat6.4 The human body uses energy from ATP for all its activities - Kilocalories (kcal) – the quantity of heat required to raise the temperature of 1 kilogram of water by 1oC6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen- Redox Reactions – movement of electrons from one molecule to anothero Oxidation – loss of electrons from a substanceo Reduction – addition of electrons to another substanceo Cellular Respiration  glucose loses hydrogen atoms (e-) as it becomes oxidized to CO2 oxygen gains hydrogen atoms(e-) as it becomes reduced to H2O as the electrons pass from glucoseoxygen they lose potential E- NADH and Electron Transport Chainso NAD+ - coenzyme that accepts e- and becomes reduced to NADHo Energy Staircase Analogy (e- from glucose to oxygen) First step: transfer of e- from an organic molecule to NAD+ NADH delivers these e- to the rest of the staircase in the ETC6.6 Overview: Cellular Respiration occurs in three main stages- Stage1: Glycolysiso “takes energy (-2 ATP) to make energy (4 ATP)”o Occurs in the cytoplasmic fluid of the cello Breaks down glucose into 2 molecules of a 3-carbon compound (pyruvate)o 2 NET ATP- Stage 2: Pyruvate Oxidation & The Citric Acid Cycleo Occurs in the mitochondriao Pyruvate  2-carbon compoundo Citric Acid Cycle – breaks down the glucose to carbon dioxideo 2 NET ATP- Oxidative Phosphorylationo Electron Transport Chain & Chemiosmosiso NADH & FADH2 shuttle e- to an ETC in the inner mitochondrial membraneo As ETC passes e- down the energy staircase, it pumps H+ ions across the inner mitochondrial membrane into the narrow intermembrane space = concentration gradiento In Chemiosmosis the PE of this gradient is used to make ATP6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate- Glycolysis  2 Pyruvate; 2 ATP; 2 NADH; 2 H+o Metabolic pathway (each chemical step leads to the next one)6.8 Pyruvate is oxidized prior to the citric acid cycle- (--COO-) is removed from pyruvate and given off as a molecule of CO2- the 2-carbon compound remaining is oxidized while a molecule of NAD+ is reduced to NADH- Coenzyme A joins with the 2-carbon group to form a molecule called acetyl CoA which then enters the citric acid cycle6.9 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH2 molecules- 2-carbon acetyl group joins a 4-carbon molecule- the resulting 6-carbon molecule goes through a series of redox reactions, while 2 carbon atoms are removed as CO2 & the 4-carbon molecule is regenerated- the first 6-carbon molecule formed in the cycle is citrate- Citric Acid Cycle (2 turns) 2 NET ATP, 6 NADH, 2 FADH2, 4 CO26.10 Most ATP production occurs by oxidative phosphorylation- Electron Transport Chaino Each oxygen atom (1/2 O2) accepts 2 e- from the chain and pick sup 2 H+ from the surrounding solution forming H2Oo 4 main protein complexes & 2 mobile carriers transport electrons between the complexes- Chemiosmosiso The H+ concentration gradient stores PE which drives H+ ions through a channel in ATP synthaseo The ATP synthases built into the inner mitochondrial membrane act like miniature turbineso ADP + P generates ATP6.11 Interrupting cellular respiration can have both harmful and beneficial effects- Rotenoneo Binds with one of the electron carrier molecules in the first protein complex, preventing electrons from passing to the next carrier moleculeo Prevents ATP synthesiso Often used to kill pest insects and fish- Cyanide & Carbon Monoxideo Bind to an electron carrier in the fourth protein complex, where they block the passage of electrons to oxygeno Prevents ATP synthesis- Antibiotic Oligomycino Blocks the passage of H+ through the channel in ATP synthase, preventing cells from making ATP and thereby killing themo Doesn’t hard human cells because it cannot get through our outer layer of dead skin cells- Uncouplerso Make the membrane of the mitochondrion leaky to H+ ionso ATP cannot be made because leakage of H+ through the membrane destroys the H+ often at a higher than normal ratero No ATP made because no gradient exists- Uncoupler-DNPo All steps of cellular respiration run except chemiosmosiso DNP increases metabolic rate, profuse sweating and finally deatho Can be beneficial at times6.12 Review: Each molecule of glucose yields many molecules of ATP- Cells can harvest up to about 34% of the molecules potential energy6.13 Fermentation enables cells to produce ATP without oxygen- Fermentation – a way of harvesting energy that does not require oxygen- Starts with Glycolysis [2 ATP & 2 NADH]- Lactic Acid Fermentationo Regenerate NAD+ by this processo NADH is oxidized to NAD+ while Pyruvate is reduced to Lactate o Lactate is carried in the blood to the liver, where it is converted back to pyruvate and oxidized in the mitochondria of the liver cellso Dairy Industry  cheese & yogurt- Alcohol Fermentationo Yeasts and certain bacteria recycle their NADH back to NAD+ while converting pyruvate to CO2 and ethanolo CO2 provides bubbles in beer and champagneo Bubbles of CO2 generated by bakers yeast causes bread dough to rise- Types of Anaerobeso Obligate anaerobes – require anaerobic conditions and are poisoned by oxygeno Facultative anaerobes – make ATP wither by fermentation or by oxidative phosphorylation Ex. Muscle cells6.14 Glycolysis evolved early in the history of life on Earth6.15 Cells use many kinds of organic molecules as fuel for cellular respiration- Carbohydrates, Fats, Proteins- Fats make excellent cellular fuel because they contain many hydrogen atoms and