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Essential idea: Cell respiration supplies energy for the functions of life. Topic 2: Molecular Biology 2.8 Respiration Nature of Science Assessing the ethics of scientific research—the use of invertebrates in respirometer experiments has ethical implications. (4.5) Understandings 2..8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP. 2.8.U2 ATP from cell respiration is immediately available as a source of energy in the cell. 2.8.U3 Anaerobic cell respiration gives a small yield of ATP from glucose. 2.8.U4Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose. Applications and Skills 2.8.A1 Application: Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking. 2.8.A2 Application: Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions. 2.8.S1 Skill: Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer. Key Terms Summary of Energy Reactions: Energy Reactions Photosynthesis Light Energy --> Chemical energy sunlight 6CO2 + 6H2O ----> C6H12O6 + 6O2 chlorophyll Respiration Chemical Energy --> Chemical energy C6H12O6 + 6O2 ----> 6CO2 + 6H2O + Heat ADP + P Occurs in green plant cells ATP Occurs in all living cells Energy for life Every living cell in your body needs energy. The average adult has about 50 million million cells – that’s a lot of energy! energy Where does all this energy come from? In body cells, the energy needed for life comes from the chemical energy stored in glucose. What is needed for releasing energy? Burning is a chemical reaction in which energy is released in the form of heat. What other substance is needed for energy to be released from this fuel? fuel oxygen ? Respiration In respiration, carbohydrates like glucose (fuel) are broken down to provide energy for the body. This must occur in a controlled manner in order for the body to capture the energy in a usable form. What is breathing? DON’T GET THESE MIXED UP What is aerobic respiration? Respiration is the process used by the body’s cells to release the chemical energy stored in glucose. When oxygen is involved in this energy-releasing process, it is called aerobic respiration. What do you think aerobic means? aerobic = ‘with oxygen’ Aerobic respiration is an efficient process that generates enough energy to supply the whole body. Our bodies perform aerobic respiration most of the time, as long as the supply of oxygen remains high enough. Respiration is the process by which organisms extract the energy stored in complex molecules and use it to generate adenosine triphosphate (ATP). What is this ‘Useable Form of Energy? In this way they obtain energy to fuel their metabolic pathways. ATP provides the immediate source of energy for biological processes such as active transport, movement and metabolism. ATP Adenosine triphosphate adenine ATP contains a sugar (ribose), a base (adenine) and three phosphate groups. ribose phosphates When ATP is hydrolysed to form ADP and inorganic phosphate, 30.5 kJ of energy are released. + ATP + H 2O ADP + 30.5 kJ inorganic phosphat e Biological systems transfer the energy in glucose to ATP because unlike glucose… Why ATP? glucose ATP ATP releases its energy instantly in a single reaction. The hydrolysis of ATP releases a small amount of energy, ideal for fuelling reactions in the body. Types of Respiration During aerobic respiration, a respiratory substrate, e.g. glucose, is split in the presence of oxygen to release carbon dioxide and water. A large number of ATP molecules are produced, releasing the energy from the glucose. C6H12O6 + 6 O2 6 CO2 + 6 H2O + 36 ATP In anaerobic respiration, glucose is converted (in the absence of oxygen) to either lactate or ethanol. The ATP yield is low. C6H12O6 2 C2H5OH + 2 CO2 + 2 ATP ethanol C6H12O6 2 C3H6O3 + 2 ATP lactate Where Does Respiration Occur? Respiration occurs in all living cells. In eukaryotes the early stages of respiration occur in the cytoplasm. The later stages of respiration are restricted to the mitochondria. Mitochondria contain highly folded inner membranes that hold key respiratory proteins (including the enzyme that makes ATP) over a large surface area. Mitochondria provide an isolated environment to maintain optimum conditions for respiration. Mitochondria have their own DNA and ribosomes, so can manufacture their own respiratory enzymes. The structure of the mitochondria An overview of respiration Respiration in detail………… Cell respiration occurs in 3 main stages: 1. Glycolysis 2. Krebs Cycle Transport 3. Electron Glycolysis means “splitting of sugar” A six-carbon sugar (glucose) is broken into two three-carbon molecules of pyruvate, which still hold most of the energy of glucose. This occurs in the cytoplasm and does not require oxygen. There is a net yield of two ATP molecules. The first stage of respiration: glycolysis The stages of glycolysis The fate of pyruvate Krebs cycle Counting carbons For each molecule of glucose, glycolysis produces: Keeping track of the products 2× 2× 2× For each molecule of glucose, the link reaction produces: 2× 2× 2× For each molecule of glucose, Krebs cycle generates: Keeping track of the products 4× 6× produced by redox reactions 2× produced by redox reactions 2× produced by substrate-level phosphorylation produced by decarboxylation The NADH and FADH2 contain the potential energy originally locked in glucose. This energy is now transferred to ATP by oxidative phosphorylation in the electron transport chain. The electron transport chain Understanding the ETC How much ATP is produced? Process ATP in ATP produced glycolysis 2 4 2 link reaction 0 0 0 Krebs cycle 0 2 (per glucose) Net ATP out 2 (per glucose) Via the electron transport chain and chemiosmosis, each NADH can yield 2.5 ATP and each FADH2 1.5 ATP. From one molecule of glucose, glycolysis yields 2 NADH, the link reaction yields 2 NADH and the Krebs cycle yields 6 NADH and 2 FADH2. 10 × 2.5 = 25 ATP from NADH 2 × 1.5 = 3 ATP from FADH2 total = 2 + 2 + 25 + 3 = 32 ATP overall The theoretical yield of 32 ATPs for each glucose molecule is rarely achieved. In fact respiration is only about 32% efficient. Efficiency of aerobic respiration Some protons leak across the mitochondrial membrane, so not all are available to generate ATP via chemiosmosis. Some ATP is used up moving pyruvate into the mitochondria by active transport. Some ATP is used up moving hydrogen from reduced NAD made during glycolysis into the mitochondria. Some energy is lost as heat. This heat helps to maintain a suitable body temperature for enzyme-controlled reactions. Adaptations of mitochondria Evidence for chemiosmosis The theory of chemiosmosis states that the energy in a chemical gradient established by electron movement is used to generate ATP. matrix Evidence includes: The proton gradient across the inner membrane can be measured as it corresponds to a pH gradient. Isolated ATP synthase enzymes can produce ATP using a proton gradient even if no electron transport is occurring. Chemicals that block the ETC inhibit the formation of a proton gradient and prevent ATP synthesis. Respiratory rate The respiratory rate is the rate at which an organism converts glucose to CO2 and water. It can be calculated by measuring an organism’s rate of oxygen consumption. Studies on simple animals often use a respirometer. Respirometers measure the change in gas volume in a closed system. Any change is due to the respiratory activity of the study organisms. Potassium hydroxide or soda lime is used to absorb the carbon dioxide produced, meaning any changes in volume are due to oxygen consumption. The respirometer Respirometer experiments Other substances as well as glucose can be respired. Different respiratory substrates release different amounts of energy. Respiratory substrates Respiratory substrate carbohydrate Mean energy value (kJ g-1) 15.8 lipid 39.4 protein 17.0 The difference in the relative energy values of these respiratory substrates is due to the amount of hydrogen atoms present in each one. If more hydrogen atoms are available to reduce coenzymes, more energy can subsequently be generated in the electron transport chain. Respiratory quotient (RQ) is the ratio of the volume of carbon dioxide produced to the volume of oxygen used in the same period of time. Respiratory quotient RQ = volume of CO2 given out volume of O2 taken in RQ gives an indication of the respiratory substrate being respired and whether respiration is aerobic or anaerobic. Type of respiration Substrate RQ anaerobic glucose >1 aerobic carbohydrate 1.0 protein approx. 0.9 lipid approx. 0.7 Respiration calculations Anaerobic Respiration Anaerobic respiration: Without oxygen Partial breakdown of glucose molecule Minimal release of energy: 1 glucose 2ATP Occurs in 2 stages: 1. Glycolysis (occurs in the cytoplasm) 2. Fermentation (occurs in the cytoplasm) Glycolysis: Glucose Pyruvate + 2ATP During fermentation: 1. In animals: Pyruvate Lactic acid 2. In plants and yeast: Pyruvate Ethanol + CO2 Anaerobic respiration is useful to the body when energy is needed in a hurry. The problems with anaerobic respiration glucose lactic acid energy There are two problems with anaerobic respiration: Anaerobic respiration releases much less energy from glucose compared to aerobic respiration. Lactic acid is a poisonous waste product. Why is anaerobic respiration not the best way to get energy from glucose? Lactic acid is the product of anaerobic respiration and is harmful because it can stop muscles from doing their job. Why is lactic acid so harmful? If lactic acid builds up in muscle cells, it stops muscles from contracting and relaxing and they become fatigued. The muscles ache and the body experiences cramp, which forces the body to stop what it is doing and rest. Why can anaerobic respiration only be carried out for short periods of time? After anaerobic respiration, the body is in recovery and must get rid lactic acid. Recovery and getting rid of lactic acid glucose lactic acid energy The body is now at rest but the breathing rate and heart rate remain high. Why does this happen? Oxygen is needed to get rid of lactic acid by turning it into carbon dioxide and water. lactic acid oxygen carbon dioxide water Why do the breathing and heart rates return to normal after a few minutes of recovery? During aerobic respiration, muscles get energy Oxygen debt – build up from glucose by ‘paying’ for it with oxygen. glucose oxygen carbon dioxide water energy During anaerobic respiration, muscles get energy from glucose but do not ‘pay’ for it with oxygen. glucose lactic acid energy This means that an oxygen debt is created. When and how is this oxygen debt ‘paid off’? The oxygen debt caused by Oxygen debt – pay off anaerobic respiration is paid off during the recovery period after exercise. It is the oxygen needed to get rid of lactic acid that pays back the oxygen debt. lactic acid oxygen carbon dioxide water oxygen to pay back ‘oxygen debt’ When is the oxygen debt completely paid off? Anaerobic respiration: word equation activity Revision Questions: 1. Write a chemical equation for the process of aerobic respiration. 2. Draw a diagram of the mitochondria and label the parts. 3. Explain why it is possible that the products of anaerobic respiration in animal and plant cells results in different products even though they both start with Pyruvate. 4. Define cell respiration. 5. List the differences between aerobic and anaerobic respiration. 6. Define autotroph and heterotroph in terms of energy and respiration (will need to look this up). Anaerobic and Muscles Aerobic Vs Anaerobic Uses of Anaerobic Respiration Summary Glossary What’s the keyword? Multiple-choice quiz