Cell Respiration

1. Cell Respiration IB Topic 3.7

2. Cell respiration is used by all cells to produce ATP • Every living cell must carry out cell respiration • Converts energy into a form that can be used within the cell • Cells require energy for: • Synthesizing large molecules like DNA, RNA, and proteins • Pumping molecules or ions across membranes by active transport • Moving things around inside the cell, such as chromosomes, vesicles or in muscle cells the protein fibers that cause muscle contraction

3. Cell respiration is used by all cells to produce ATP • The energy for these processes is supplied by ATP (adenosine triphosphate) • When ATP is split into ADP (adenosine diphosphate) and phosphate, energy is released Cell respiration ADP + phosphate ATP Active cell processes

5. Cell respiration is used by all cells to produce ATP • ATP cannot usually be absorbed through the plasma membrane • So, every cell must produce its own supply • Organic compounds containing energy are broken down by enzymes • Very controlled • So that as much as possible of the energy released can be used to form ATP from ADP • Cell respiration defined as the controlled release of energy from organic compounds to form ATP

6. What is cell respiration? • A: taking air into the lungs • B: removing carbon dioxide from the lungs • C: Use of ATP in cells • D: Controlled release of energy in cells

7. Glycolysis • Cell respiration can release energy form a variety of organic compounds, but carbohydrates and lipids are the usual substrates • If glucose is being used, almost all organisms begin cell respiration the same way • Before we get to the process, think about what the word means … • Glyco = sugar • Lysis = split

8. Glycolysis • Overview: • A chain of reactions takes place in the cytoplasm of the cell • Converts glucose to pyruvate • This chain of reactions is called glycolysis

9. Glycolysis – Deeper Look • Glucose enters the cell through the plasma membrane (into the cytoplasm) • An enzyme modifies the glucose (slightly) • A second enzyme modifies the molecule even more • Followed by a series of reactions (biochemical …) • Which you do not need to know • Ultimately, the reactions cleave the 6-carbon glucose molecule into 2, 3-carbon molecules called pyruvate

10. Glycolysis – A Deeper Look (cont.) • Some of the covalent bonds in the glucose were broken • Some of the energy that was released from the breaking of these bonds was used to form a small number of ATP molecules • 2 ATP molecules are needed to get the reaction started • A total of 4 ATP molecules are produced • So there is a net gain of 2 ATP molecules

11. Glycolysis – Recap • No oxygen is used in glycolysis • A small amount of ATP is produced • If no oxygen is available, then this is the only ATP that can be produced • Anaerobic conditions • Alcoholic fermentation • Lactic acid fermentation

12. What are the products of glycolysis? • A: glucose • B: glucose and ATP • C: ATP and pyruvate • D: glucose, ATP, and pyruvate

13. Glycolysis Animation & Quiz • http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_glycolysis_works.html

14. Let’s check in … • Cell respiration  variety of biochemical pathways that metabolize glucose • All of the pathways start with glycolysis • Common to all organisms • Some organisms derive all of their ATP completely without oxygen (anaerobic) • Also called fermentation • Two main anaerobic pathways • Alcoholic fermentation • Lactic acid fermentation

15. Alcoholic Fermentation • Yeast – common, single-celled fungus that uses alcoholic fermentation for ATP generation • Use glycolysis • Produce 2 net ATP molecules • Produce 2, 3-carbon pyruvate molecules • Yeast then converts the pyruvate molecules to ethanol • Ethanol is a 2-carbon molecule • So a carbon molecules is “lost” • Given off as carbon dioxide • Baking – helps dough rise • Ethanol is drinking alcohol

16. Alcoholic fermentation CO2 Glycolysis (net gain 2 ATP) Pyruvate 3C Ethanol 2C Glucose 6C

17. Which substances are produce by yeast in anaerobic cell respiration? • A: carbon dioxide and lactate • B: carbon dioxide and ethanol • C: Lactate and ethanol • D: carbon dioxide, lactate, and ethanol

18. Lactic Acid Fermentation • Organisms that use aerobic respiration sometimes find themselves in a metabolic situation where they cannot supply enough oxygen to their cells • Example: a person pushing beyond their physical limits; their pulmonary & cardiovascular systems supply as much oxygen to their cells as is physically possible • If a person’s exercise rate exceeds their capability of supplying oxygen, then some of the glucose entering the cell respiration will follow lactic acid fermentation

19. Lactic Acid Fermentation (cont.) • Low-oxygen setting (not a normal setting) • Excess pyruvate molecules are converted into lactic acid molecules • Lactic acid molecules • 3-carbon molecules • No production of carbon dioxide • What’s the benefit? • Allows glycolysis to continue with the small gain of ATP generated in addition to the ATP which is being generated through aerobic respiration

20. Lactic Acid Fermentation Glycolysis (net gain 2 ATP) Pyruvate 3C Lactate 3C (Reaction reversible when oxygen available) Glucose 6C Aerobic pathway

21. If a blood sample from a person contains a high concentration of lactate, what is the conclusion? • A: the person has been drinking too much milk and ingested large amounts of lactose • B: the person is lactose intolerant and should change to drinking lactose-free milk • C: the person has eaten live yogurt, containing bacteria that have carried out anaerobic cell respiration • D: the person has exercised vigorously and carried out anaerobic cell respiration

22. Summary Equations • Cell Respiration = glucose  pyruvate • Occurs in almost all organisms • Aerobic or anaerobic respiration • Lactic Acid Fermentation =pyruvate  lactate • Occurs in humans • Occurs in some bacteria • Anaerobic respiration • Alcoholic Fermentation = pyruvate  ethanol + CO2 • Occurs in yeast • Anaerobic respiration ADP ATP

24. Aerobic Cell Respiration • The most efficient pathway • Takes place in the mitochondria • Begins with glycolysis • 2 net ATP & 2 pyruvate molecules • Enter the mitochondrion • Further metabolized

25. Aerobic Respiration – A Deeper Look • Each pyruvate first loses a carbon dioxide molecule • Becomes a molecule called acetyl-CoA • Each acetyl-CoA enters into a series of reactions called the Krebs cycle • During this series, two more CO2 molecules are produced from each original pyruvate that enter • See Figure 3.24 in your textbook (page 82)

27. Aerobic Respiration – A Deeper Look • Some ATP is directly generated during the Krebs cycle • Some ATP is indirectly generated through a later series of reactions directly involving oxygen • Aerobic respiration breaks down (completely oxidizes) a glucose molecule and the end product are carbon dioxide and water • In most organisms, carbon dioxide is a waste product that must be excreted • The water is useful – in humans, about ½ a liter of water is produced per day • Some desert animals never have to drink water and eat only dry foods because cell respiration supplies almost all their water needs

28. What is the main source of energy in aerobic cell respiration? • A: oxygen • B: ATP • C: Heat • D: organic compounds

29. Why is aerobic respiration more effective than anaerobic respiration? • Anaerobic respiration does not completely oxidize the glucose molecule • Ethanol and lactic acid are generated because they represent portions of the original glucose that were not oxidized • Aerobic respiration leaves no such by-products • Aerobic respiration results in a much higher yield of ATP

30. Khan Academy – Helpful Link/Tutorial • https://www.khanacademy.org/science/biology/cellular-respiration/v/introduction-to-cellular-respiration

31. Cell Respiration – Khan Academy