BIOLOGICAL SCIENCE FIFTH EDITION Freeman Quillin Allison 9 Lecture Presentation by Cindy S. Malone, PhD, California State University Northridge © 2014 Pearson Education, Inc. Roadmap 9 In this chapter you will learn how Cells make ATP starting from sugars and other high potential energy compounds by examining by examining How cells produce ATP when How cells produce ATP when oxygen is present 9.1 oxygen is absent looking closer at Glycolysis 9.2 Pyruvate oxidation 9.3 focusing Citric acid cycle 9.4 on Electron transport Fermentation and chemiosmosis 9.5 9.6 © 2014 Pearson Education, Inc. ▪ All organisms use glucose to build fats, carbohydrates, and other compounds ▪ Cells recover glucose by breaking down these molecules – Glucose is used to make ATP through cellular respiration or fermentation ▪ Cellular respiration produces ATP from – A molecule with high potential energy—usually glucose © 2014 Pearson Education, Inc. ▪ Each of the four steps of Energy conversion cellular respiration Photosynthesis consists of – A series of chemical Energy storage reactions Starch, glycogen, fats (synthesized from glucose) – A distinctive starting molecule Energy use – Characteristic set of products Cellular Respiration Fermentation © 2014 Pearson Education, Inc. ▪ Carbon atoms of glucose are oxidized to form carbon dioxide ▪ Oxygen atoms in oxygen are reduced to form water C6H12O6 6 O2 6 CO2 6 H2O energy glucose oxygen carbon water dioxide ▪ Glucose is oxidized through – A long series of carefully controlled redox reactions ▪ The resulting change in free energy is used to – Synthesize ATP from ADP and Pi ▪ These reactions comprise cellular respiration © 2014 Pearson Education, Inc. ▪ Cellular respiration is – Any set of reactions that produces ATP – In an electron transport chain ▪ Cellular respiration has four steps: 1. Glycolysis – Glucose is broken down to pyruvate 2. Pyruvate processing – Pyruvate is oxidized to form acetyl CoA © 2014 Pearson Education, Inc. 3. Citric acid cycle – Acetyl CoA is oxidized to CO2 4. Electron transport and chemiosmosis – Compounds reduced in steps 1–3 are oxidized in reactions leading to ATP production © 2014 Pearson Education, Inc. Figure 9.2 1. Glycolysis 2. Pyruvate 3. Citric Acid Cycle 4. Electron Transport and Occurs in: Processing Oxidative Phosphorylation Cytoplasm of eukaryotes and Inner membrane of mitochondria Matrix of mitochondria or cytoplasm of prokaryotes prokaryotes or plasma membrane of prokaryotes What goes in: What comes out: © 2014 Pearson Education, Inc. ▪ Energy and carbon – Are two fundamental requirements of cells – Need high-energy electrons for generating chemical energy – In the form of ATP – Are a source of carbon-containing molecules – For synthesizing macromolecules ▪ Metabolism includes – Thousands of different chemical reactions that are either catabolic pathways or anabolic pathways © 2014 Pearson Education, Inc. ▪ Catabolic pathways – Involve the breakdown of molecules and production of ATP – Often harvest stored chemical energy to produce ATP ▪ Anabolic pathways – Result in the synthesis of larger molecules from smaller components – Often use energy in the form of ATP © 2014 Pearson Education, Inc. ▪ For ATP production, cells – First use carbohydrates – Then fats – And finally proteins ▪ Proteins, carbohydrates, and fats can all furnish substrates for cellular respiration © 2014 Pearson Education, Inc. ▪ Enzymes remove the amino groups from proteins – The remaining carbon compounds are intermediates – These compounds are used in glycolysis and the citric acid cycle ▪ Enzymes break down fats – To form glycerol – Enters the glycolytic pathway – To form acetyl CoA – Enters the citric acid cycle – To remove the amino groups from proteins © 2014 Pearson Education, Inc. Figure 9.3 Carbohydrates Fats and phospholipids Proteins Catabolic pathways Anabolic pathways Glycogen Pathway for synthesis Substrates for amino Phospholipids Fats or starch of RNA, DNA acid synthesis © 2014 Pearson Education, Inc. ▪ Molecules found in carbohydrate metabolism are used to synthesize macromolecules such as – RNA – DNA – Glycogen or starch – Amino acids – Fatty acids – And other cell components © 2014 Pearson Education, Inc. ▪ About half the required amino acids can be synthesized from citric acid cycle molecules ▪ Acetyl CoA is the starting point in the synthesis of fatty acids ▪ Fatty acids can be used to build phospholipid membranes or fats ▪ Intermediates in glycolysis can be oxidized to start the synthesis of the sugars in ribo- and deoxyribonucleotides © 2014 Pearson Education, Inc. ▪ Nucleotides are building blocks used in RNA and DNA synthesis ▪ Pyruvate and lactate can be used in the synthesis of glucose © 2014 Pearson Education, Inc. Figure 9.4 Lipid Carbohydrate metabolism metabolism Nucleotide metabolism Amino acid metabolism © 2014 Pearson Education, Inc. ▪ Glycolysis is – A series of 10 chemical reactions – The first step in glucose oxidation ▪ All of the enzymes needed for glycolysis are found in the cytosol ▪ In glycolysis – Glucose is broken down into two molecules of pyruvate – The potential energy released is used to phosphorylate ADP to ATP © 2014 Pearson Education, Inc. ▪ Glycolysis consists of – An energy investment phase – An energy payoff phase ▪ In the energy investment phase – 2 molecules of ATP are consumed – Glucose is phosphorylated twice – Forming fructose-1,6-bisphosphate © 2014 Pearson Education, Inc. ▪ In the energy payoff phase – Sugar is split to form two pyruvate molecules – 2 molecules of NAD+ are reduced to NADH – 4 molecules of ATP are formed by substrate-level phosphorylation (net gain of 2 ATP) © 2014 Pearson Education, Inc. Figure 9.5 All 10 reactions of glycolysis occur in the cytosol Dihydroxyacetone phosphate What goes in: Enzyme Glucose Glucose- Fructose- Fructose- 6-phosphate 6-phosphate 1,6-bisphosphate Glycolysis begins with an energy-investment phase: 2 ATP 2 ADP What comes out: Glyceraldehyde-3-phosphate The “2” indicates that fructose-1,6- bisphosphate has been split into two 3-carbon sugars (only one is shown) 1,3-Bisphosphoglycerate 3-Phosphoglycerate 2-Phosphoglycerate Phosphoenolpyruvate Pyruvate During the energy-payoff phase, 4 ATP are produced for a net gain of 2 ATP © 2014 Pearson Education, Inc. ▪ Substrate-level phosphorylation occurs when – ATP is produced by the enzyme-catalyzed transfer of a phosphate group from an intermediate substrate to ADP – ATP is produced in glycolysis and the citric acid cycle ▪ Oxidative phosphorylation occurs in – An electron transport chain – A proton gradient provides energy for ATP production – The membrane protein ATP synthase uses this energy to phosphorylate ADP to form ATP © 2014 Pearson Education, Inc. Figure 9.6 ATP ADP Enzyme Phosphorylated substrate © 2014 Pearson Education, Inc. ▪ Feedback inhibition occurs – When an enzyme in a pathway is inhibited by the product of that pathway ▪ Cells that are able to stop glycolytic reactions – When ATP is abundant ▪ Can conserve their stores of glucose for – Times when ATP is scarce © 2014 Pearson Education, Inc. ▪ During glycolysis, high levels of ATP inhibit – The enzyme phosphofructokinase – This enzyme catalyzes one of the early reactions ▪ Phosphofructokinase has two binding sites for ATP: 1. The active site – Where ATP phosphorylates fructose-6-phosphate – Resulting in the synthesis of fructose-1,6-bisphosphate 2. A regulatory site © 2014 Pearson Education, Inc. ▪ High ATP concentrations cause – ATP to bind at the regulatory site – Changing the enzyme’s shape – Dramatically decreasing the reaction rate at the active site ▪ In phosphofructokinase: – ATP acts as an allosteric regulator © 2014 Pearson Education, Inc. Figure 9.7 ATP at When ATP binds here, the regulatory reaction rate slows dramatically site Fructose-6- phosphate ATP at at active site active site © 2014 Pearson Education, Inc. ▪ The mitochondrial matrix – Is inside the inner membrane – But outside the cristae © 2014 Pearson Education, Inc. Figure 9.8 Cristae are sacs of inner membrane joined to the rest of the inner membrane by short tubes Matrix Cristae Inner membrane Intermembrane space Outer membrane 100 nm © 2014 Pearson Education, Inc. ▪ Pyruvate processing is – The second step in glucose oxidation – Catalyzed by the enzyme pyruvate dehydrogenase – In the mitochondrial matrix ▪ In the presence of O2: – Pyruvate undergoes a series of reactions, results in the product molecule acetyl coenzyme A (acetyl CoA) © 2014 Pearson Education, Inc. ▪ During these reactions – Another molecule of NADH is synthesized – One of the carbon atoms in pyruvate is oxidized to CO2 Pyruvate Acetyl CoA © 2014 Pearson Education, Inc. ▪ Pyruvate processing is – Under both positive and negative control ▪ Abundant ATP reserves inhibit the enzyme complex – Large supplies of reactants – Such as acetyl CoA and NADH ▪ Low supplies of products stimulate the enzyme complex – Such as ATP © 2014 Pearson Education, Inc. ▪ The third step of glucose oxidation – The acetyl CoA produced by pyruvate processing enters the citric acid cycle – Located in the mitochondrial matrix – Each acetyl CoA is oxidized to two molecules of CO2 ▪ Some of the potential energy released is used to 1. Reduce NAD+ to NADH 2. Reduce flavin adenine dinucleotide (FAD) to FADH2 – Another electron carrier 3. Phosphorylate GDP to form GTP – Later converted to ATP © 2014 Pearson Education, Inc. ▪ A series of carboxylic acids – Are oxidized and recycled in the citric acid cycle ▪ Citrate (the first molecule in the cycle) is formed from – Pyruvate