BIOL 213 1st Edition Lecture 12 Outline of Last Lecture I Electron transport chain of cellular respiration a Review of main points b The steps c What if O2 were removed d Redox potential e Electron transfer between molecules f II Proton gradient Net ATP yield for cellular respiration a 30 ATP per 1 glucose III Photosynthesis a Chloroplast b Two stages c Chlorophyll d Electron transport Outline of Current Lecture I Carbon fixation a 3 CO2 9 ATP 6 NADPH Rubisco 1 G3P II Overview of photosynthesis and its interaction with cellular respiration a A brief review of all the steps III Comparing the proton gradients of mitochondria and chloroplasts IV Endosymbiotic theory a Mitochondria These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute b Chloroplasts Current Lecture I II Carbon fixation a This is the second step of photosynthesis b It is called the Calvin cycle c It takes place in the chloroplast stroma i Similar to how the Krebs cycle takes place in the mitochondrial matrix d CO2 is reduced to sugar molecules so that energy created by photosynthesis can be transported throughout the plant in a stable form of energy e The energy ATP and NADPH created in the first stage is used to drive the reduction of CO2 f Because no light is used to directly drive this step carbon fixation continues in the dark until all of the ATP and NADPH has been used i This is a good reason why the plant can t just use the ATP created in the first step no ATP is created when it s dark yet the plant still needs energy when it s dark g One cycle of the Calvin cycle produces one glyceraldehyde 3 phospate G3P molecule i 3 molecules of CO2 1 carbon are reduced to 1 molecule of G3P 3carbon ii This is done by the enzyme ribulose bisphosphate carboxylase Rubisco 1 This is most likely the most abundant protein on Earth iii G3P can be converted to multiple molecules in the cytosol and can then be used in glycolysis h Carbon fixation is very energetically expensive i It costs the cell 6 ATP and 6 NADPH to reduce 3 CO2 molecules to 1 G3P and another 3 ATP to regenerate the necessary molecules for the cycle to happen again ii For a total of 1 9 ATP 2 6 NADPH a 1 NADPH 3 ATP therefore 6 NADPH 18 ATP for a total of 27 ATP iii A lot of the energy is wasted it escapes as heat and other byproducts Overview of photosynthesis and its interactions with cellular respiration a In step one energy from light as a photon excites an electron from photosystem II which is transported down various proteins to photosystem I b Where it is again excited and transported down proteins to NADP to create NADPH i NADP is the final electron acceptor like O2 is in cellular respiration III IV c As the electron is transported down the chain of proteins a proton gradient is created which drives ATP synthase to make ATP d The ATPs and NADPH created in step 1 are used to drive step 2 carbon fixation e 9 ATP and 6 NADPH total are used to reduce 3 CO2 to 1 G3P by Rubisco f G3P is converted into sucrose and other high energy molecules in the cytosol that are transported around the plant g These molecules can be used in glycolysis to make pyruvate when the cell needs energy h The pyruvate is then transported to the mitochondrial matrix where it is oxidized to acetyl CoA i Acetyl CoA goes through the Krebs cycle where it is completely oxidized to CO 2 j NADH created in the Krebs cycle takes electrons to the electron transport chain where ATP is created via oxidative phosphorylation and O2 is oxidized to H2O Comparing the proton gradients of mitochondria and chloroplasts Both Mitochondria Chloroplast Use membranes to create pH gradients Pumped across inner membrane Pumped across thylakoid membrane Have ATP synthase BUT THEY RE NOT IDENTICAL ATP flows from the intermembrane space to the matrix ATP flows from the thylakoid space to the stroma Lower pH more H in intermembrane space Lower pH more H in thylakoid space Endosymbiotic theory a Mitochondria i Billions of years ago a bacteria cell that was able to go through aerobic respiration was engulfed by an anaerobic ancestral eukaryote ii This benefited both cells in that the eukaryotic was able to utilize aerobic respiration and the bacteria was protected so the bacteria wasn t broken down by the eukaryote iii Eventually over millions of years the bacterial cell changed into the mitochondria we recognize today iv A more fun version 1 Once upon a time a long time ago a little bacteria cell that was able to go through aerobic respiration was engulfed by an old ancestor of eukaryotic cells 2 This old ancestor was amazed by the aerobic respiration because he had only ever gone through anaerobic respiration 3 The little bacteria cell was amazed at how much protection he got when he was inside the old eukaryotic ancestor 4 The old eukaryotic ancestor told the little bacteria that he could stay and that he would provide him with protection if the little bacteria shared his aerobic respiration 5 The two agreed and they lived happily ever after b Chloroplast i These are thought to have formed the same way ii A photosynthetic bacteria like cyanobacteria was engulfed by a eukaryotic cell 1 All eukaryotic cells now contained mitochondria 2 A cyanobacteria has inner membranes similar to the thylakoid membrane of chloroplasts iii It was beneficial to both cells because the eukaryote was able to utilize sunlight and the bacteria was protected iv Eventually over time the bacteria changed to a chloroplast c Research 4 pieces of evidence that support the Endosymbiotic theory