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Transcript
Cellular Respiration By the end of this class you should understand: • The major processes that living things use to make energy • The relationship between photosynthesis and cellular respiration • The key differences between aerobic and anaerobic processes • The three steps of eukaryotic cellular respiration What is needed to make ATP? • ADP (nucleic acid) and phosphate – There is plenty of this in the cell already since it gets reused a lot • Energy source (carbohydrate, protein, lipid) • Oxygen (for aerobic respiration only) – Anaerobic respiration requires no oxygen Which cells do this? • All cells need energy • All cells with mitochondria perform complete cellular respiration (aerobic) • Cells with no mitochondria (i.e. red blood cells, most prokaryotes) can only perform anaerobic respiration or fermentation Complete Cellular Respiration C6H12O6 + 6O2 6CO2 + 6H2O + ATP Technically a Combustion Reaction: C6H12O6 + 6O2 6CO2 + 6H2O + Heat Photosynthesis in Reverse! • Water is split into O2 to extract electrons • Electron transport chain creates proton gradient • Glucose is broken down with enzymes to make 3-carbon sugar (glycolysis) • 3-carbon sugar enters Krebs cycle, is broken down into CO2 – Used by ATP synthase • Products of Krebs cycle are ATP and electron carriers • ATP and electron carriers are used up • Electron carriers power electron absorbing CO2 making transport chain which creates 3-carbon sugar in the proton gradient Calvin Cycle – Used by ATP Synthase • 3-carbon sugars made • Electrons are dumped onto O2 into glucose to make water Fermentation • Breakdown of sugar is nearuniversal to living things • Many different chemical pathways available • Anaerobic pathways (lacking oxygen) include producing ethanol and lactic acid – How do you think your beer was made? – Yogurt also made this way Glycolysis • Fermentation typically takes place with no oxygen • Most eukaryotes (and a few aerobic prokaryotes) use oxygen to complete metabolism of sugar • The first step is glycolysis, or breaking down the sugar with enzymes, into pyruvate Human Fermentation • If no oxygen is present, pyruvate buildup in cell can become toxic • Pyruvate is instead converted to lactic acid • Lactic acid enters bloodstream and creates the “burning” feeling in your muscles Krebs Cycle • The Krebs Cycle is an enzymatic process • Aerobic: requires oxygen to keep running – If no oxygen, no electron carriers available • Reactant: 1 Acetyl CoA – Pyruvate is converted to Acetyl CoA first • Product: 3 CO2 Krebs Cycle • Performed in the mitochondria • Produces ATP and high-energy electrons • Produces the CO2 that we breathe out – CO2 exits cell and dissolves into blood until we breathe it out at the lungs Electron Transport Chain • Electrons are pushed one by one through a transport chain • As the electron moves, its energy is used to pump hydrogen ions into a special reservoir – Sort of like using energy to pump water to a lake above a dam • As the hydrogen ions are released back, they turn a “water wheel” that makes ATP Electron Transport Chain • Each of these structures pulls a little more tightly on the electron • The final recipient of the electron is oxygen, which makes water • This means the entire chain is aerobic Electron Transport Chain • The energy in the electron does work to create a gradient of hydrogen ions • The hydrogen ions move down their gradient through an ATP Synthase enzyme • This enzyme creates ATP when turned by hydrogen ions – This is called chemiosmosis – This step makes a LOT of ATP (overall total for 1 glucose molecule: ~34 ATP) ATP Synthase Cellular Respiration Summary Cellular Respiration Summary: • Glucose – is broken down by glycolysis to • Pyruvate – which enters the Krebs cycle and becomes • CO2 – which leaves, but the released electrons power the • Electron Transport Chain – which makes fat stacks of ATP – oxygen absorbs the electrons to become water Alternative Energy • This is the main sequence of energy for metabolizing glucose – All organisms with mitochondria perform this type of cellular respiration • Most organisms have alternatives as well – Humans can convert fat into Acetyl CoA through a process called beta oxidation – One fat molecule can provide hundreds of ATP! Part 2: Open Question Time! • First exam is tomorrow! Yaaay…