Molecular Cell Biology BS101 Lecture Notes PDF

MOLECULAR CELL BIOLOGY BS101 LECTURE LIST 17. Cellular activities. Enzymes and the regulation of enzyme activity 18. Introduction to cellular respiration 19. Glycolysis in the cytosol 20. Mitochondria 1: citric acid cycle 21. Mitochondria 2: oxidative phosphorylation...

MOLECULAR CELL BIOLOGY BS101 LECTURE LIST 17. Cellular activities. Enzymes and the regulation of enzyme activity 18. Introduction to cellular respiration 19. Glycolysis in the cytosol 20. Mitochondria 1: citric acid cycle 21. Mitochondria 2: oxidative phosphorylation 22. Regulation of respiration and integration with cell metabolism LEARNING OBJECTIVES Explain the role of glycolysis and the citric acid cycle in supporting biosynthetic (anabolic) pathways. Outline the key metabolic degradative (catabolic) pathways that connect with glycolysis and the citric acid cycle. Explain the processes alcohol fermentation and lactate (lactic acid) fermentation. Distinguish between fermentation and cellular respiration The Versatility of Catabolism Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration Glycolysis accepts the products from a wide range of carbohydrates including starch, glycogen, and several disaccharides Proteins that are used for fuel must be digested to amino acids and their amino groups must be removed  Fats are digested to glycerol (used to produce compounds needed for glycolysis) and fatty acids Fatty acids are broken down by beta oxidation and yield acetyl CoA, NADH, and FADH2 (carried out in the mitochondrial matrix) An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate Concept 10.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways  Proteins Carbohydrates Fats Figure 10.19_1 Amino Sugars Glycerol Fatty acids acids © 2018 Pearson Education Ltd.  Proteins Carbohydrates Fats Figure 10.19_2 Amino Sugars Glycerol Fatty acids acids GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate  Proteins Carbohydrates Fats Figure 10.19_3 Amino Sugars Glycerol Fatty acids acids GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Acetyl CoA  Proteins Carbohydrates Fats Figure 10.19_4 Amino Sugars Glycerol Fatty acids acids GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Acetyl CoA CITRIC ACID CYCLE © 2018 Parson Education Ltd.  Proteins Carbohydrates Fats Figure 10.19_5 Amino Sugars Glycerol Fatty acids acids GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Acetyl CoA CITRIC ACID OXIDATIVE CYCLE PHOSPHORYLATION  Protein Deamination Examples Serine Pyruvate Acetyl CoA Citric acid cycle NH3 α-ketoglutarate Aspartate Oxaloacetate Citric acid cycle Glutamate Glutamate α-ketoglutarate Citric acid cycle NH3  Proteins Carbohydrates Fats Figure 10.19_5 Amino Sugars Glycerol Fatty acids acids GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Acetyl CoA CITRIC ACID OXIDATIVE CYCLE PHOSPHORYLATION Metabolism of fats Fatty acids are broken down via beta-oxidation in the mitochondria matrix. Each lipid hydrocarbon chain combines with co- enzyme A. Reactions generate FADH2 and NADH. Reaction cleaves 2 carbons as acetyl-CoA to go into the Citric Acid/Krebs cycle. This is repeated for every 2 carbons in the chain. No need to remember full details of diagram. Biosynthesis (Anabolic Pathways) The body uses small molecules from food to build its own molecules such as proteins These small molecules may come directly from food, from glycolysis, or from the citric acid cycle Biosynthesis (Anabolic Pathways) Dihydroxyacetone phosphate (DHAP – intermediate in glycolysis) can be used to synthesise fats (triacylglycerols) Pyruvate can be used to produce glucose (gluconeogenesis) Acetyl CoA can be used to synthesise fatty acids (in the cytosol) However, mammals CANNOT synthesise glucose from fatty acids Anabolic pathways are highly endergonic and require significant use of ATP © 2018 Pearson Education Ltd. Concept 10.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen Most cellular respiration depends on electronegative oxygen to ‘pull’ electrons down the transport chain Without oxygen, the electron transport chain will cease to operate In that case, glycolysis couples with anaerobic respiration or fermentation to produce ATP Concept 10.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen, continued… Anaerobic respiration uses an electron transport chain with a final electron acceptor other than oxygen, for example, sulfate Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP  Types of Fermentation Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis Two common types are alcohol fermentation and lactic acid fermentation a) Alcohol fermentation b) Lactic acid fermentation Figure 10.17 Fermentation Types of Fermentation, Continued In alcohol fermentation, pyruvate is converted to ethanol in two steps: 1. The first step releases CO2 from pyruvate 2. The second step produces NAD+ and ethanol from pyruvate Alcohol fermentation by yeast is used in brewing, winemaking, and baking Figure 10.17a Fermentation (Part 1: Alcohol) a) Alcohol fermentation Types of Fermentation, Continued In lactate fermentation, pyruvate is converted to lactate in a single step: 1. Pyruvate is converted to lactate, producing NAD+ from NADH This process occurs when the body's circulatory and respiratory systems can't supply oxygen to muscles fast enough to maintain aerobic respiration. The result is a buildup of lactic acid in the muscles, which can cause pain, tiredness, and cramps. Some bacteria (lactic acid bacteria) break down sugars in foods to produce lactic acid, can be used to preserve food and add flavour. Figure 10.17b Fermentation (Part 2: Lactic Acid) b) Lactic acid fermentation Comparing Fermentation with Anaerobic and Aerobic Respiration All use glycolysis (net ATP = 2) to oxidise glucose and harvest the chemical energy of food In all three, NAD+ is the oxidising agent that accepts electrons during glycolysis  Comparing Fermentation with Anaerobic and Aerobic Respiration, Continued The processes have different mechanisms for oxidizing NADH to NAD+ In fermentation, an organic molecule (such as pyruvate or acetaldehyde) acts as a final electron acceptor In cellular respiration, electrons are transferred to the electron transport chain Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule Comparing Fermentation with Anaerobic and Aerobic Respiration, Continued-1 Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2 Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes Figure 10.18 Pyruvate as a Key Juncture in Catabolism