Topic 3.7: Cell Respiration

1. Topic 3.7: Cell Respiration

2. Assessment Statements • 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 • 3.7.4: Explain that, during aerobic respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP

3. Cell Respiration is used by all cells to produce ATP • Organic Molecules contain energy in their molecular structures • Each covalent bond in a glucose, amino acid, or fatty acid represents stored chemical energy • Burning wood—release stored chemical energy • Rapid oxidation is not controlled by enzymes and results in the breaking of many, many covalent bonds in a very short period of time

4. Cell Respiration is used by all cells to produce ATP • Cells break down (or metabolize) their organic nutrients by way of slow oxidation • The ultimate goal of releasing energy in a controlled way is to trap the released energy in the form of ATP molecules

5. Glycolysis is the first step in the cell respiration process • Glucose enters a cell through the plasma membrane and floats in the cytoplasm • An enzyme modifies the glucose slightly, then a second enzyme modifies this molecule even more • This is followed by an entire series of reactions which ultimately cleave the 6 carbon glucose into two 3 carbon molecules (each called pyruvate)

6. Glycolysis is the first step in the cell respiration process • Energy • 2 ATPs molecules needed to begin glycolysis • 4 ATP’s are formed during glycolysis • Net Gain of 2 ATP’s • http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_glycolysis_works.html

7. Some cells use anaerobic respiration for ATP production • “cell respiration” refers to a variety of biochemical pathways that can be used to metabolize glucose • All pathways begin with glycolysis • The breakdown of organic molecules for ATP production in an anaerobic way called fermentation • Alcoholic Fermentation • Lactic Acid Fermentation

8. Alcoholic Fermentation • All organisms use glycolysis to begin the cell respiration sequence. Yeast uses Alcoholic Fermentation! • Yeast cells take in glucose from their environment and generate a net gain of two ATP by way of glycolysis

9. Alcoholic Fermentation • The organic products of glycolysis are always two pyruvate molecules. • Yeast then converts both of the 3 carbon pyruvate molecules into ethanol • The carbon is given off in a carbon dioxide molecule • Both the ethanol and carbon dioxide that are produced are waste products to the yeast and are simply given off into the environment

10. Lactic Acid Fermentation • Sometimes organisms that use aerobic respiration sometimes find themselves with not enough oxygen • If the person’s exercise rate exceeds their capability of supplying oxygen, then at least some of the glucose entering into cell respiration will follow the anaerobic pathway called lactic acid fermentation

11. Lactic Acid Fermentation • Pyruvate is converted into a 3 carbon molecule called lactic acid • No production of Carbon Dioxide • The only benefit is serves is that it allows glycolysis to continue with the small gain of ATP generated.

12. Aerobic cell respiration is the most efficient pathway • Cells that have mitochondria use an aerobic pathway for cell respiration • This pathway also begins with glycolysis and thus a net gain of two ATPs are generated as well as two pyruvate molecules • The two pyruvate molecules now enter a mitochondrion and are further metabolized

13. Aerobic cell respiration is the most efficient pathway • Each pyruvate first loses a carbon dioxide molecule and becomes a molecule known as acetyl-CoA • Each acetyl-CoA enters into a series of reactions called Krebs Cycle • During this series of reactions, two more carbon dioxide molecules are produced from each original pyruvate that entered • The Krebs cycle series of reactions is a cycle because each time it returns to the molecule that once again reacts with another incoming acetyl-CoA molecule

14. Aerobic cell respiration is the most efficient pathway • The Krebs cycle series of reactions is a cycle because each time it returns to the molecule that once again reacts with another incoming acetyl-CoAmolecule • Aerobic cell respiration breaks down a glucose molecule and the end-products are carbon dioxide and water

15. Aerobic cell respiration is the most efficient pathway • Aerobic respiration is much more efficient because it completely oxidizes the glucose and does not leave any by products • Some ATP is directly generated during the Krebs cycle and some is indirectly generated through a later series of reactions directly involving oxygen