Lecture 5 - Sept 13 - Metabolism PDF

Review of proteins and nucleic acids Describe the four levels of protein structure. Describe enzyme action. Compare and contrast DNA and RNA. Explain the role of ATP in cell metabolism. 1 Human Anatomy & Physiology Sept 13 Metabolism...

Review of proteins and nucleic acids Describe the four levels of protein structure. Describe enzyme action. Compare and contrast DNA and RNA. Explain the role of ATP in cell metabolism. 1 Human Anatomy & Physiology Sept 13 Metabolism Lecture 5 [email protected] Office Hours (2RC056) Mondays 11am to 1pm or by appointment 2 Human Anatomy & Physiology Sept 13 OpenStax 24.1 Metabolism Tortora 25.1 Metabolism is the sum of all biochemical reactions inside a cell involving nutrients. Copyright © 2020 by John Wiley & Sons, Inc. All rights reserved. 3 Human Anatomy & Physiology Sept 13 OpenStax 24.1 Nutrient processing Tortora 25.1 Food is digested in the gastrointestinal tract and absorbed nutrients enter the blood to reach cells. Within cells, nutrients can either be used in ___________ pathways to build complex molecules or broken down through ___________ pathways to produce energy (typically in the form of ATP). 4 Human Anatomy & Physiology Sept 13 OpenStax 24.1 Oxidation-Reduction reactions Tortora 25.1 Oxidation reactions involve the gain of oxygen or loss of hydrogen atoms (and their electrons). Oxidation-reduction (redox) reactions involve oxidized substances losing electrons and reduced substances gaining electrons. Mnemonic: LEO the lion says GER LEO = lose electrons, oxidized GER = gain electrons, reduced OIL RIG (oxidation is losing, reduction is gaining) 5 Human Anatomy & Physiology Sept 13 OpenStax 24.1 Capturing energy from food Tortora 25.1 Glucose is an energy-rich, highly reduced molecule (many hydrogen atoms). You can oxidize it into lower-energy, highly oxidized compounds (many oxygen atoms or double-bonds) to release energy. When we metabolize glucose with oxygen: Glucose (C6H12O6) is oxidized to carbon dioxide (CO2) Oxygen (O2) is reduced to water (H2O) Released energy is used to make ATP 6 Human Anatomy & Physiology Sept 13 OpenStax 24.1 Capturing energy from food Tortora 25.1 Wood is mostly made of the carbohydrate cellulose and the protein lignin. When wood burns in a fire: Wood is oxidized to carbon dioxide (CO2) Oxygen (O2) is reduced to water (H2O) Energy is released as heat and light. The energy released in a fire would be dangerous inside living cells. We use a complicated system of enzymes and coenzymes to safely capture most of the energy and convert it into ATP. 7 Human Anatomy & Physiology Sept 13 OpenStax 24.1 Redox enzymes and coenzymes Tortora 25.1 Redox reactions are catalyzed by enzymes that usually require a B vitamin coenzyme. Two important coenzymes act as hydrogen (or electron) acceptors in oxidative pathways. Nicotinamide adenine dinucleotide (NAD+) is derived from niacin (Vitamin B3) and can be reduced into NADH + H+. Flavin adenine dinucleotide (FAD) is derived from riboflavin (Vitamin B2) and can be reduced into FADH2. 8 Human Anatomy & Physiology Sept 13 OpenStax 24.1 Adenosine triphosphate (ATP) Tortora 25.1 ATP is used by all known forms of life to power chemical reactions. 1. ATP very briefly holds chemical energy. 2. ATP transfers that chemical energy into an enzyme to power a chemical reaction. By releasing that energy, ATP (adenosine triphosphate) turns into ADP (adenosine diphosephate). 3. ADP then gets recharged into ATP to be used for a new chemical reaction. 9 Human Anatomy & Physiology Sept 13 OpenStax 24.2 ATP synthesis Tortora 25.2 Two mechanisms are used to make ATP from energy that is released during cellular respiration: In substrate-level phosphorylation, chemical bonds are broken and energy from reactants is used to phosphorylate ADP into ATP. This does not require oxygen. When done with glucose, this is glycolysis. In oxidative phosphorylation, energy from food creates a proton gradient (electron transport chain) that is used to attach phosphates to ADP. This requires oxygen as the final electron acceptor. 10 Human Anatomy & Physiology Sept 13 OpenStax 24.2 Overview of cellular respiration Tortora 25.3 Copyright © 2021 by John Wiley & Sons, Inc. All rights reserved. 11 Human Anatomy & Physiology Sept 13 OpenStax 24.2 Substrate-level phosphorylation Tortora 25.2 In substrate-level phosphorylation, a high-energy phosphate group is transferred from a phosphorylated molecule to ADP. This normally occurs twice in glycolysis and once in the citric acid cycle (Krebs cycle) per molecule of glucose. This process does not require ____________. 12 Human Anatomy & Physiology Sept 13 OpenStax 24.2 Oxidative phosphorylation Tortora 25.2 Energy from food is used to pump protons (H+) across the inner mitochondrial membrane, creating a H+ concentration gradient. As H+ flow back through ATP synthase enzyme, energy from this flow is used to phosphorylate ADP into ATP. Oxidative phosphorylation requires oxygen for the final step in the electron transport chain. 13 Human Anatomy & Physiology Sept 13 OpenStax 24.2 Oxidation of glucose Tortora 25.3 Glucose is our “________________”. Glucose is catabolized via the following reaction: C6H12O6 + 6O2 → 6H2O + 6CO2 + 30 ATP + heat glucose oxygen water carbon dioxide Complete glucose catabolism requires three pathways: 1. Glycolysis and formation of acetyl CoA 2. Citric acid cycle (Krebs cycle) 3. Electron transport chain (ETC) and oxidative phosphorylation 14  pages 922-933 15 Human Anatomy & Physiology Sept 13 OpenStax 24.2 Glycolysis Tortora 25.3 Also called the glycolytic pathway, this involves a 10-step pathway that occurs in the cell cytoplasm. Glycolysis is ______________; it takes place despite the presence or absence of oxygen. One glucose molecule (6C) is broken into two ________________ molecules (3C). Glucose loses 4 hydrogens, which are now bound to 2 molecules of NAD+, producing 2 NADH + 2 H+. Net gain of 2 ATP (makes 4 but costs 2 to start). 16 Human Anatomy & Physiology Sept 13 OpenStax 24.2 Glycolysis (continued) Tortora 25.3 Because the supply of NAD+ is limited, NADH must donate its accepted hydrogen atoms to become NAD+ again to be free to pick up more H+ so glycolysis can continue. If no oxygen is present, NADH returns its hydrogen to pyruvic acid, forming ___________, which allows NAD+ to continue to act as an electron acceptor. Once enough oxygen is available within the cell, lactic acid is oxidized back to pyruvic acid and enters aerobic pathways. 17 Human Anatomy & Physiology Sept 13 OpenStax 24.2 Citric acid cycle (Krebs cycle) Tortora 25.3 This occurs in mitochondrial matrix, fueled by pyruvic acid from glucose breakdown and fatty acids from fat breakdown. Pyruvic acid must be actively transported into mitochondria because it is a charged molecule that cannot diffuse across the mitochondrial membrane. Once inside mitochondria, pyruvic acid enters transitional phase where each pyruvic acid is converted to acetyl coenzyme A (acetyl CoA), if oxygen is available. 18 Human Anatomy & Physiology pages Citric acid cycle (Krebs cycle) 927-928 If oxygen is available, pyruvic acid is converted to acetyl coenzyme A. Copyright © 2021 by John Wiley & Sons, Inc. All rights reserved. Pyruvic acid loses a C as CO2 and two H atoms as it enters the mitochondria. The 2C molecule formed (acetic acid) is attached to coenzyme A to produce acetyl CoA (2 for every molecule of glucose), which enters the citric acid (Krebs) cycle. Hs are transferred to NAD+ to produce NADH + H+. 19 Human Anatomy & Physiology Sept 13 OpenStax 24.2 Electron transport chain Tortora 25.3 In the electron transport chain, energy from NADH and FADH2 move H+ from the mitochondrial matrix to the inter-membrane space. H+ diffuse back to through an enzyme, ATP synthase, which phosphorylates ADP to ATP as the H+ diffuses. Copyright © 2021 by John Wiley & Sons, Inc. All rights reserved. 20 Human Anatomy & Physiology Sept 13 OpenStax 24.2 ATP from cellular respiration Tortora 25.3 21 Human Anatomy & Physiology Sept 13 OpenStax 24.2 Storing sugar for later Tortora 25.3 ________________ is a process that forms glycogen (the animal carbohydrate storage product) from glucose. Because ATP cannot be used to store energy for long periods of time, high cellular ATP inhibits glycolysis. Instead, glycogen synthase catalyzes the attachment of glucose into a chain of glycogen. This process occurs mostly in the liver and skeletal muscle. 22 Human Anatomy & Physiology Sept 13 OpenStax 24.2 Releasing previously stored sugar Tortora 25.3 _________________ is a process that breaks down glycogen (animal glucose polysaccharide). When blood glucose levels drop, cells can respond by breaking down glycogen into glucose molecules. In most body cells, glycogen is broken down to glucose but kept inside the cell, so it can be used for glycolysis to generate ATP. In the liver, glycogen is broken down to glucose and transported to the blood, so it can be used by all tissues in the body. 23 Human Anatomy & Physiology Sept 13 OpenStax 24.2 Making sugar out of protein or fat Tortora 25.3 _________________ is a process that forms glucose from non-glucose molecules, such as glycerol or amino acids, to maintain blood glucose when dietary sources and glucose reserves begin to be depleted. Gluconeogenesis protects the body, especially the nervous system, from the damaging effects of hypoglycemia (low blood sugar). 24 © 2016 Pearson Education, Inc. 25 After today’s lecture, you should be able to: Define metabolism and explain how catabolism and anabolism differ. Define oxidation and reduction and indicate the importance of these reactions in metabolism. Indicate the role of coenzymes in cellular oxidation reactions. Explain the difference between substrate-level phosphorylation and oxidative phosphorylation. Summarize important events and products of glycolysis, the citric acid cycle, and electron transport. Define glycogenesis, glycogenolysis, and gluconeogenesis. 26