Chapter 13 How Cells Obtain Energy from Food PDF

How Cells Obtain Energy from Food Chapter 13 Learning Outcomes  Cellular metabolism is the sum total of catabolic and anabolic reactions; catabolic and anabolic pathways are regulated. o All organisms need to replenish their ATP pools in their cells continuously throug...

How Cells Obtain Energy from Food Chapter 13 Learning Outcomes  Cellular metabolism is the sum total of catabolic and anabolic reactions; catabolic and anabolic pathways are regulated. o All organisms need to replenish their ATP pools in their cells continuously through the oxidation of sugars or fats. o Depending on conditions, cells in plants and animals must determine whether to route key metabolites into anabolic or catabolic pathways  Storage molecules  Feedback Regulation o Glycolysis and the citric acid cycle constitute only a small fraction of the reactions that occur in a cell.  Case study: In animals, the breakdown of food molecules occurs in three stages. o Brief overview of glycolysis, TCA and oxidative electron transport, Fermentative energy production To be able to grow and divide and carry out day-to-day activities, all living cells need energy and organic matter Cellular metabolism is the sum total of all anabolic and catabolic reactions. Metabolism is the sum total of all the chemical (anabolic and catabolic) reactions that occur within the cell(s) of an organism. Catabolic reactions break down large molecules into smaller parts, releasing energy in the process some of that energy will be harnessed by the cell, but some will be lost as heat Anabolic reactions use that energy to add those smaller molecules back together to build useful cellular products – this process requires an energy input, so these reactions will consume the energy produced Catabolic reactions release energy, Anabolic reactions require energy input Catabolic reactions break chemical bonds, releasing energy in the process Energy-releasing reactions are also known as exergonic reactions Anabolic reactions build new chemical bonds, a process which requires energy input Energy-consuming reactions are also known as endergonic reactions Cells use enzymes to speed up metabolic reactions Enzymes are macromolecules that act as catalysts, chemical agents that speed up reactions without being consumed. Enzyme Enzyme A + B -----------------> C A ---------------- > B +C Reactants Product Reactant Products Most cellular enzymes are __________ in nature. Enzymes speed up anabolic reactions as well as spontaneous exergonic catabolic reactions. Enzymes do this by lowering the activation energy. Enzymes lower a reaction’s activation energy Enzyme A + B -----------------> C + D Reactants Products To be able to grow and divide, cells need a constant supply of energy Sugars and fats are a key source of energy for all living organisms. Plants (and many bacteria) can make their own sugars from CO2 (photosynthesis) Animals (and fungi) obtain sugars and other organic molecules that can be transformed into sugars, by eating plants and other organisms (respiration) Are plants capable of respiration? Bacteria are capable of Photosynthesis Aerobic respiration Anaerobic respiration Fermentation! In animals food molecules are broken down in 3 stages All living cells use the controlled, stepwise oxidation of glucose to capture useful energy C6H12O6 + 6 O2 6 CO2 + 6 H2O + 30 ATP What does this chemical reaction represent? The most common energy carrier molecule in the cell is ATP Cells use energy carrier molecules to store energy from catabolic/exergonic reactions, then transfer that energy into anabolic/endergonic reactions – thereby coupling energy-consuming reactions to energy-producing reactions The most common energy carrier molecule in the cell is ATP Glycolysis and the citric acid cycle constitute only a small fraction of the reactions that occur in a cell. Enzyme activity is regulated by a myriad of control mechanisms To balance the activities of these interrelated reactions To allow organisms to adapt swiftly to changes in food availability Enzyme activity can be controlled by covalent modification (example?) Enzyme activity can be positively or negatively regulated. Depending on conditions, plant and animal cells must determine whether to route key metabolites into anabolic or catabolic pathways Active muscle and brain cells depend almost exclusively on glucose for energy. During periods of fasting or intense exercise, glucose gets used up faster than it can be replenished! Feedback regulation allows cells to switch from glucose breakdown to glucose synthesis Gluconeogenesis Mobilization of storage molecules (e.g., glycogen) What is Feedback Regulation? This Photo by Unknown Author is licensed under CC BY-SA Where else have we seen feedback regulation before?  Gluconeogenesis: (Glycolysis reversal) When and how? Builds glucose from pyruvate Most enzymatic reactions in glycolysis are reversible 3 steps (1, 3 and 10) are irreversible! Feedback regulation of phosphofructokinase (step 3) helps decided between glycolysis and ATP blocks enzyme gluconeogenesis ADP activates enzyme GLUCONEOGENESIS GLYCOLYSIS ATP activates enzyme ADP blocks enzyme Glycogen breakdown Glycogen is a branched polymer of glucose Stored as small granules in cytoplasm of liver and muscle cells Synthesis and degradation are regulated by ATP Glycogen Glucose (Glucose)n Glycogen synthetase Glycogen phosphorylase (Glucose)n-1 + Glucose-1-Phosphate Glucose-6-Phosphate GLYCOLYSIS ATP Fats are more important storage material than glycogen …because oxidation of fats releases more energy Fats are stored as water-insoluble droplets in specialized cells called _________ Glucose Glycolysis Fats Fatty acid + Acetyl CoA Kreb’s cycle In animals food molecules are broken down in 3 stages Plants store food too! Plants convert the sugars synthesized by photosynthesis into fats and starch The plant embryo uses this stored food for growth and building material This is why plant seeds (containing the plant embryo) are good sources of food for animals too! Storage fats and starch are stored in chloroplasts Glycolysis Oxidation of Pyruvate to Acetyl CoA Citric Acid Cycle Oxidative Phosphorylation Slide 10 👇🏼  All the carbon atoms of glucose are lost as carbon dioxide: In glycolysis the 6C glucose is broken down to 2 molecules of 3C pyruvate Pyruvate loses 1C to become 2C Acetyl-CoA The 2C’s of acetyl-CoA are lost in Kreb’s cycle CO2 is the most oxidized form of Carbon, thus, cellular respiration involves complete oxidation of glucose. NADH and FADH2 are electron carriers: all the NADH and FADH2 molecules formed during Kreb’s cycle, transfer their electrons to the first complex of the electron transport chain This starts the electron transport It also regenerates NAD+ and FAD, so that Kreb’s cycle can continue The steps of glycolysis can take place in the absence of oxygen but respiration eventually comes to a halt because oxygen is the terminal electron acceptor of the electron transport.