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Cellular Respiration STAGE 1: Glycolysis 2005-2006 What’s the point? ATP The Point is to Make ATP! 2005-2006 Glycolysis • Breaking down glucose – “glyco – lysis” (splitting sugar) glucose pyruvate 2x 3C 6C – most ancient form of energy capture • starting point for all cellular respiration – inefficient • generate only 2 ATP for every 1 glucose – in cytosol • why does that make evolutionary sense? 2005-2006 Evolutionary perspective • Life on Earth first evolved without free oxygen (O2) in atmosphere – energy had to be captured from organic molecules in absence of O2 • Organisms that evolved glycolysis are ancestors of all modern life – all organisms still utilize glycolysis 2005-2006 You mean, I’m related to them?! SEE H.O. E SEE H.O F NOTES!!! Stage I – Glycolysis 1). One glucose molecule is phosphorylated by 2 ATP molecules . ( formed from previous glucose molecules). In addition to this phosphorylation, the structure of the glucose molecule is altered slightly (It is now primed for a split into (2) 3-C compounds) This converts the glucose into a compound called fructose diphosphate. (symbolized as P - FRUCTOSE - P ) 2). The fructose diphosphate is then split in half to form 2 molecules of a substance called glyceraldehyde phosphate. ( P - GAL & GAL - P ) 3. EACH GLYCERALDEHYDE PHOSPHATE WILL UNDERGO THE FOLLOWING CHANGES: A). 2 H atoms are released from each molecule (total = 4 H atoms). Each pair of H atoms is picked up by an NAD+ (total = 2 NAD+). The H atoms are transported to the H / e´ T.C. and used to form ATP. B). Another phosphate is added to each glyceraldehyde. The phosphate is taken from phosphoric acid, (already present). The substance formed is glyceraldehyde diphosphate ( P - GAL - P ) 4). 2 phosphates are removed from each glyceraldehyde diphosphate molecule. (T= 4 phosphates). Each phosphate is added to an ADP forming 4 ATP. The structure of each remaining molecule is altered again, forming a pyruvic acid molecule (pyruvate). Energy accounting of glycolysis 2 ATP 2 ADP glucose pyruvate 2x 3C 6C 4 ADP 4 ATP • Net gain = 2 ATP – some energy investment (2 ATP) – small energy return (4 ATP) • 1 6C sugar 2 3C sugars 2005-2006 All that work! And that’s all I get? Is that all of the energy that there is? Not a lot of energy… – for 1 billon years+ this is how life on Earth survived • only harvest 3.5% of energy stored in glucose • slow growth, slow reproduction Heck of a way to make a living! In addition…by the end of Glycolysis, two additional products have been formed: • 2 pyruvic acid molecules which will enter Stage II • 2 NADH + H + which will travel to the H / e´ T.C. to form ATP. Where does the supply of NAD+ come from? glucose + 2ADP + 2Pi + 2 NAD+ 2 pyruvate + 2ATP + 2NADH • NADH must be about to give its H to another molecule • without regenerating NAD+, energy production would stop NADH 2005-2006 Problem solved with options! 1. anaerobic respiration (absence of oxygen) • ethanol fermentation • lactic acid fermentation 2. aerobic respiration NADH Ex. Anaerobic ethanol fermentation • Bacteria, yeast pyruvate ethanol + CO2 3C beer, wine, bread NADH at ~12% ethanol, kills yeast 2C NAD+ Animals, some fungi pyruvate lactic acid 3C NADH 3C NAD+ cheese, yogurt, anaerobic exercise (no O2) 2005-2006 1C Pyruvate is a branching point Pyruvate O2 O2 fermentation Kreb’s cycle mitochondria 2005-2006 Glycolysis summary endergonic invest some ATP exergonic harvest a little more ATP & a little NADH 2005-2006 Another View OVERVIEW OF GLYCOLYSIS 1 2 3 6-carbon glucose (Starting material) 2 ATP P P 6-carbon sugar diphosphate P P 6-carbon sugar diphosphate P 3-carbon sugar phosphate P 3-carbon sugar phosphate P 3-carbon sugar phosphate NADH P 3-carbon sugar phosphate NADH 2 ATP 2 ATP 3-carbon pyruvate Priming reactions. Priming reactions. Cleavage reactions. Then, the six- Glycolysis begins with the addition of carbon molecule with two phosphates energy. Two high-energy phosphates is split in two, forming two threefrom two molecules of ATP are added to carbon sugar phosphates. the six-carbon molecule glucose, producing a six-carbon molecule with two phosphates. 2005-2006 3-carbon pyruvate Energy-harvesting reactions. Finally, in a series of reactions, each of the two three-carbon sugar phosphates is converted to pyruvate. In the process, an energy-rich hydrogen is harvested as NADH, and two ATP molecules are formed. Any Questions?? 2005-2006