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Cellular Respiration

Cellular Respiration. Objectives. 3.6.0 – Introduction to metabolism (review) 3.6.1 – Review enzyme kinetics and ATP production. 3.7.1 – Define cell respiration

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Cellular Respiration

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  1. Cellular Respiration

  2. Objectives • 3.6.0 – Introduction to metabolism (review) • 3.6.1 – Review enzyme kinetics and ATP production. • 3.7.1 – Define cell respiration • 3.7.2 – State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP. • 3.7.3 – Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP.

  3. Introduction to metabolism Energy needs of living things Autotrophs Get energy from the sun or chemicals Producers Heterotrophs Get energy from consuming food Consumers Herbivores Carnivores Detritivores Saprotrophs Get energy from consuming dead material Decomposers

  4. Metabolic pathways alter molecules in a series of steps. • Enzymes selectively accelerate each step. • Catabolic pathways release energy by breaking down complex molecules to simpler compounds. • Anabolic pathways consume energy to build complicated molecules from simpler compounds. Introduction to metabolism Metabolism is the sum of chemical reactions in a body. • Metabolic pathways alter molecules in a series of steps. • Catabolic pathways release energy by breaking down complex mole- cules to simpler compounds. • Anabolic pathways consume energy to build complicated molecules from simpler compounds. • Enzymes selectively accelerate each step. Metabolic pathway

  5. Introduction to metabolism Organisms transform energy. • Energy is the capacity to do work - to move matter against opposing forces. Energy is also used to rearrange matter. • Kinetic energy is the energy of motion - ex: photons, heat. • Potential energy is the energy matter possesses because of its location or structure. • Chemical energy is a form of potential energy in molecules because of the arrangement of atoms. ATP

  6. Introduction to metabolism Energy can be converted from one form to another. • Ex: as a boy climbs a ladder to the top of the slide he is converting his kinetic energy to potential energy. • As he slides down, the potential energy isconverted back to kinetic energy. • It was the potential energy in the food he had eaten earlier that provided the energy that permitted him to climb up initially.

  7. Introduction to metabolism • Cellular respiration and other catabolic pathways unleash energy stored in sugar and other complex molecules, which were created during photosyn- thesis, an anabolic path- way. • CO2 + H2O ⇄ C6H12O6 +O2 Anabolism Photosynthesis → → → Catabolism ←←← Respiration

  8. Introduction to metabolism Anabolic reactions (building molecules) are endergonic (or endothermic) – ones that absorb energy. • Ex: the overall reaction of photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2 • Through this reaction, energy from the sun has been put into the chemical bonds of a sugar molecule. The sugar has more energy than the CO2 and H2O.

  9. Introduction to metabolism Catabolic reactions (breaking molecules) are exergonic (or exothermic) – ones that release energy. • Ex: the overall reaction of cellular respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O • Through this reaction energy in the sugar is been made available to do work in the cell. The products (CO2 and H2O) have less energy than the reactants.

  10. Introduction to metabolism Exergonic vs. endergonic reactions Respiration - Photosynthesis - energy released for work energy gained from the sun

  11. Introduction to metabolism The energy created by respiration is used to do work. • A cell does three main kinds of work: • Mechanical work: beating of cilia, muscle contraction • Transport work: pumping substances across membranes • Chemical work: driving ender- gonic reactions such as the synthesis of polymers from monomers.

  12. Introduction to metabolism In most cases, the immediate source of energy that powers cellular work (coupling exergonic reactions to endergonic reactions) is ATP (adenosine triphosphate).

  13. Introduction to metabolism • Energy from respiration (burning food with O2) is used to add a PO4- group to ADP. • When energy is needed by a cell, the PO4- group is removed, and the energy is released. • The energy traveled from the sun, to the plant, to the animal. Exergonic→ ← Endergonic

  14. Enzyme review Most chemical reactions do not occur spontaneously in our bodies at 98.6o F – we’re too cold. Enzymes are proteins that assist our metabolism. • Substrates are held in the active site by weak hydrogen bonds and ionic bonds. Within the active site, chemical bonds are stressed, and ATP provides the little energy needed to start the chemical reaction.

  15. Enzyme kinetics An enzyme is a catalytic protein. • A catalyst is a chemical agent that changes the rate of a reaction without being consumed by the reaction. • Enzymes speed up metabolic reactions by lowering energy barriers. Ex: In a match head, S + O2→ SO2 + energy, but the reaction is not spontaneous – friction must be applied to give some initial energy for combustion. friction In a match head: S + O2→ SO2 + energy

  16. Catabolic reactions Remember: Catabolic reactions (breaking molecules) are exergonic (or exothermic) – ones that release energy. • Ex: the overall reaction of cellular respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O • Through this reaction 686 kcal have been made available to do work in the cell. The products have 686 kcal less energy than the reactants. • The released energy is used to make ATP.

  17. Catabolism is coupled to ATP production The catabolism of food is coupled to synthesis of ATP, which is the molecule that powers our bodies. Energy from food Exergonic→ ← Endergonic

  18. What is cell respiration? Cell respiration is the controlled release of energy from organic compounds in cells to form ATP. • It encompasses different reactions under different circumstances. • Anaerobic respiration: no oxygen • Glycolysis • Fermentation • Aerobic respiration: with oxygen • Citric acid cycle

  19. Glycolysis Glycolysis (Greek: sugar destruction) is the first step in cell respiration. • An ancient process - occurs in all cells on Earth. • Takes place in the cytoplasm. ⇒ • Does not require oxygen. Remember: only eukaryotic cells have mitochondria.

  20. Glycolysis • Glucose is broken down into pyruvate. • Yields a small amount of ATP – only 2 molecules. 2 ATP must be used to activate the glucose; then 4 ATP are pro- duced – enough to power only a small cell. BUT without NAD+, the pathway stops.

  21. Fermentations Fermentation allows NAD+ to be regenerated, which allows glycolysis to continue. • Two anaerobic pathways: • Alcoholic fermentation • Lactic acid fermentation Sole function of fermentation is to regenerate NAD+, but there are many side benefits.

  22. Alcoholic fermentation Pyruvate is converted in the cytoplasm into ethanol and CO2; no more ATP, but NAD+ is regenerated. • The process is present in yeast and some bacteria. • Humans use this process to make bread, wine, & beer. • CO2 makes bread rise. • Ethanol forms when CO2 is removed from pyruvate. • Also important now as a bio-fuel (gasoline substitute).

  23. Alcoholic fermentation • Yeast are critical for bread, beer, and wine production. Beer production line Winery fermenters

  24. Alcoholic fermentation Production of bio-fuels Ex: from starch in corn seeds

  25. Lactic acid fermentation Muscle cells switch from aerobic to lactic acid ferment-ation so ATP is still produced when O2 is scarce. • Ex: athletes such as those running a marathon. • The NAD+ must be regenerated to make more ATP. • The waste product, lactate, causes muscle fatigue, but ultimately it is converted back to pyruvate in the liver.

  26. Lactic acid fermentation Pyruvate is reduced directly by NADH to lactic acid. • Lactic acid fermentation by some fungi and bacteria is used to make cheese & yogurt. The “bite” of these products is due to the lactic acid.

  27. Aerobic Cell Respiration

  28. Objectives • 3.7.4 – Explain that, during aerobic cell respiration, pyru- vate can be broken down in the mitochondrion into CO2 and H2O with a large yield of ATP. • C.3.3 – Draw and label a diagram of a mitochondrion; ex- plain the relationship between its structure and its function. • C.3.7 – Analyze data relating to respiration.

  29. Aerobic cell respiration Remember: glycolysis is the first step in both aerobic and anaerobic respiration. • It’s an ancient process (>3 byo), • It’s found in all cells (cytoplasm), • It converts glucose into 2 pyru- vates with a net production of only 2 ATP. More than ¾ of the original energy in glucose is still present afterglycolysis. • This energy can be captured in the process of aerobic respiration.

  30. Aerobic cell respiration With oxygen, pyruvate can be broken down further to yield much more energy. • In the mitochondria, pyruvate is completely oxidized to CO2 and H2O. • There is a large yield of ATP – 34 more than glycolysis. Most of the energy within the bonds of sugar is made available.

  31. Mitochondrial structure Mitochondria have a double membrane; membrane ridges are called the cristae, and the soupy space between them is called the matrix. They also have their own DNA and ribosomes.

  32. Mitochondrial structure Mitochondrial structure is related to its function. • They were once free-living bacteria (the theory of endosymbiosis). • The outer membrane is thought to be the host’s, from the original endocytosis; the inner is bacterial. • They need a lot of membrane surface area since this is where the enzymes for respiration are located. • More space for more energy production.

  33. Aerobic cell respiration The 3 stages of cell respiration: • Glycolysis occurs in the cytoplasm. • Breaks 1 glucose into 2 molecules of pyruvate; forms 2 NADH and 2 ATP. • The Krebs cycle occurs in the mitochondrial matrix. • Degrades pyruvate to CO2; forms 2 NADH & 2 ATP. • NADH passes electrons to the electron transport chain on the mitochondrial membrane. • Electrons eventually combine with O2 to form water. • In the process, 34 more ATP are produced, and NAD+ is regenerated to be used in glycolysis.

  34. Aerobic cell respiration No oxygen With oxygen

  35. Aerobic cell respiration In the Krebs cycle pyruvic acid from glycolysis is degraded to 3 CO2, which are breathed out. • Two ATP and several NADH are made through enzyme actions from each pyruvate

  36. Aerobic cell respiration NADH, made in the Krebs cycle in the matrix of the mito-chondria (its cytoplasm) carries the electrons produced when pyruvate is broken down into CO2 to the inner mitochondrial membranes (the cristae). • The electrons are passed from one molecule to another and give up some energy at each step. • This energy is used to pump hydrogen (H+) across the membrane, building up a high concentration inside.

  37. Aerobic cell respiration NADH, made in the Krebs cycle in the matrix of the mito-chondria (its cytoplasm) carries the electrons to the inner mitochondrial membranes (the cristae). • The H+ can only exit by diffusion through a protein called ATP synthase. • The protein is like a turbine in a dam; the H+ spin the protein and ADP +P → ATP.

  38. Aerobic cell respiration The electron transfer chain • Energy in the NADH (the electrons from glucose) pump H+ into the cristae, building up a thousand-fold concentration difference. • These diffuse out through ATP synthase making ATP. • Aerobic respiration yields 38 ATP vs. 2 from glycolysis alone. The electrons eventually get picked up by oxygen, hydrogens follow, making H2O (water).

  39. Respiration poisons Some poisons interrupt cell respiration. • Cyanide decouples electron transport: electrons can’t reach oxygen and back-up. No NAD+ is available for glycolysis, and creatures run out of ATP and die.

  40. An Analysis of respiration data Biosphere 2, an enormous greenhouse built in the Arizona desert, has been used to study 5 different ecosystems. It is a closed system, so measurements can be made under controlled conditions. The effects of different factors, including changes in CO2 concentration in the greenhouse, were studied. The data shown below were collected over the course of 1 day in January. • Identify the time of day when the sun rose. • Identify the time of minimal CO2 concentration. • What was the CO2 concentration at that time?

  41. An Analysis of respiration data • Determine the maximum difference in CO2 conc. over the 24-hr period. • What is the relationship between CO2 concentration and light intensity? • Suggest reasons for changes in CO2 conc. during the 24-hr period.

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