10/1/2012 10/1/2012 10/1/2012 Life Needs Energy • Recall that living organisms are built of complex structures • Building complex structures that are low in entropy is only possible when energy is spent in the process • The ultimate source of this energy on Earth is the sunlight 10/1/2012 Central Importance of Glucose • Glucose is an excellent fuel – Yields good amount of energy upon oxidation – Can be efficiently stored in the polymeric form – Many organisms and tissues can meet their energy needs on glucose only • Glucose is a versatile biochemical precursor – Bacteria can use glucose to build the carbon skeletons of: • • • • All the amino acids Membrane lipids Nucleotides in DNA and RNA Cofactors needed for the metabolism Four Major Pathways of Glucose Utilization • When there’s plenty of excess energy, glucose can be stored in the polymeric form (starch, glycogen) • Short-term energy needs are met by oxidation of glucose via glycolysis • Pentose phosphate pathway generates NADPH that is used for detoxification, and for the biosynthesis of lipids and nucleotides • Structural polysaccharides (e.g in cell walls of bacteria, fungi, and plants) are derived from glucose 10/1/2012 Glycolysis: Importance • Glycolysis is a sequence of enzyme-catalyzed reaction by which glucose is converted into pyruvate • Pyruvate can be further aerobically oxidized • Pyruvate can be used as a precursor in biosynthesis • In the process, some of the oxidation free energy in captured by the synthesis of ATP and NADH • Research of glycolysis played a large role in the development of modern biochemistry – Understanding the role of coenzymes – Discovery of the pivotal role of ATP – Development of methods for enzyme purification – Inspiration for the next generations of biochemists Glycolysis: Overview • In the evolution of life, glycolysis probably was one of the earliest energy-yielding pathways • It developed before photosynthesis, when the atmosphere was still anaerobic • Thus, the task upon early organisms was how to extract free energy from glucose anaerobically? •The solution –Activate it first by transferring couple of phosphates to it –Collect energy later form the high-energy metabolites of the activated glucose 10/1/2012 10/1/2012 Laws of Thermodynamics Apply to Living Organisms • Living organisms cannot create energy from nothing • Living organisms cannot destroy energy into nothing • Living organism may transform energy from one form to another • In the process of transforming energy, living organisms must increase the entropy of the universe • In order to maintain organization within the themselves, living systems must be able to extract useable energy from the surrounding, and release useless energy (heat) back to the surrounding 10/1/2012 10/1/2012 10/1/2012 10 10/1/2012 11 10/1/2012 Feeder Pathways for Glycolysis 12 10/1/2012 Under Anaerobic Conditions, Animals Reduce Pyruvate to Lactate • During strenuous exercise, lactate builds up in the muscle • The acidification of muscle prevents its continuous strenuous work • The lactate can be transported to liver and converted to glucose there Under Anaerobic Conditions, Yeast Ferments Glucose to Ethanol • Both steps require cofactors – Mg++ and thiamine pyrophosphate in pyruvate decarboxylase – Zn++ and NAD+ in alcohol dehydrogenase 13 10/1/2012 Gluconeogenesis: Precursors for Carbohydrates • Notice that mammals cannot convert fatty acids to sugars Glycolysis vs Gluconeogenesis • Glycolysis occurs mainly in the muscle and brain • Gluconeogenesis occurs mainly in the liver 14 10/1/2012 Summary In this chapter, we learned about: • Glycolysis, a process by which cells can extract a limited amount of energy from glucose under anaerobic conditions • Gluconeogenesis, a process by which cells can use a variety of metabolites for the synthesis of glucose • Pentose phosphate pathway, a process by which cells can generate reducing power (NADPH) that is needed for the biosynthesis of various compounds 15 ... NADPH that is used for detoxification, and for the biosynthesis of lipids and nucleotides • Structural polysaccharides (e.g in cell walls of bacteria, fungi, and plants) are derived from glucose... acids Membrane lipids Nucleotides in DNA and RNA Cofactors needed for the metabolism Four Major Pathways of Glucose Utilization • When there’s plenty of excess energy, glucose can be stored in the... energy in captured by the synthesis of ATP and NADH • Research of glycolysis played a large role in the development of modern biochemistry – Understanding the role of coenzymes – Discovery of