Objectives for Exam 2 1 Know the thermodynamic principles governing energy transformations Principle of Conservation of energy Energy can be transferred and transformed but it cannot be created or destroyed Second Law of Thermodynamics Every Energy Transfer or transformation increases the entropy of the universe Entropy is the measure of disorder 2 What are exergonic and endorgonic reactions Exergonic release energy Endergonic absorb energy 3 Know high energy intermediates chemical and physical Chemical ATP ADP NAD NADH FAD FADH Physical building a Chemical gradient through the pump of H ions 4 Know principles of catalytic action 5 Mechanisms of enzymatic action 6 How are enzymes modulated Competative and non competitive inhibitors Feedback Inhibition Cooperative binding Covalent modification 7 Know similarities and differences between oxidative respiration and photosynthesis 8 Starting and end products of various stages of oxidative respiration and photosynthesis 9 Energy balance for each stage of oxidative respiration and photosynthesis Cellular Respiration C6H12O6 6 O2 6 CO2 6 H2O Energy See question 9 See question 9 o Glycolysis First step takes place in the cytoplasm of the cell Anaerobic Does not require oxygen Breaks down a 6 carbon Sugar Glucose into two pyruvate molecules 3 carbon sugar Takes 2 ATP to begin Yields 4 ATP and 2 NADH Net yield of 2 ATP ATP is formed through substrate level Phosphorylation in other words an enzyme phosphorylates ADP into ATP o Preparation for Citric Acid Cycle Krebs cycle Step only takes place in the presence of oxygen Pyruvate diffuses into mitochondrial Matrix Pyruvate is converted into Acetyl CoA 2 carbons Products Per molecule of Glucose 2 acetyl CoA 2 NADH 2 CO2 Citric Acid Cylce AKA Kreb s Cylce o Named a cycle because Oxo acetic acid is used in the first step and regenerated in the last o o o A little energy was used for ATP production via substrate level phosphorylation but most is stored in the form of the reduced NADH H from glycolysis and the Krebs cycle and FADH2 from the Krebs cycle Electron Transport Chain o Where the magic happens o Energy from glucose that was stored in bonds of NADH2 and FADH Electrons are used to create a chemical gradient that will convert potential energy into energy usable by the cell in the form of ATP o The general scenario is as follows Hydrogen atoms bind to hydrogen carriers on the matrix side of the membrane Hydrogen carriers transport hydrogen atoms across the membrane to the intermembrane space Electrons reduce electron carriers on the intermembrane side of the membrane Reduced electron carriers takes electrons back across the inner membrane to the matrix side leaving protons behind in the intermembrane space The cycle repeats with the extraction of the protons from the matrix side to combine into hydrogen atoms with the electrons that have been shuttled back o Reduced NADH H is oxidized by the first component NADH reductase that carries the hydrogens to the other side of the membrane Electrons are picked up by ubiquinone the lipid soluble form of CoQ and transported to the matrix side o On the matrix side enzyme cytochrome c reductase combines electrons with the protons and shuttles hydrogen atoms to the intermembrane space Electrons are shuttled back to the matrix side where they combine with cytochrome c o Electrons from cytochrome c are donated to cytochrome c oxidase which combines electrons with protons shuttles protons to the other side and donates electrons to oxygen the a final electron acceptor In total 3 pairs of H are pumped across per NADH H molecule and 2 pairs of H are pumped across per FADH2 o Pumping of protons results in both a pH gradient and an electrical potential across the inner mitochondrial membrane o o ATP synthase The proton gradient is utilized by the Fo pump of mitochondrial membrane to phosphorylate ADP to ATP This part proton channel part ATP synthetase uses a pair of protons diffusing back to the matrix of a mitochondrion to synthesize an ATP molecule Net Energy Tally o Glycolysis 2 Net ATP substrate level phosphorylation o Citric Acid Cycle 2 ATP Also NADH and FADH that carry the electrons to the ETC for more ATP production also substrate level phosphorylation o ETC 26 28 ATP by oxidative phosphorylation o Total yield is about 30 32 molecules of ATP per molecule of Glucose Photosynthesis 6 CO2 6 H2O light energy C6H12O6 6 O2 o In Chloroplasts of plant cells converts simple molecules and light energy into complex energy holding sugar molecules glucose o Overall reaction is reverse of cellular respiration o Photochemical reactions Light reactions Chlorophyll green pigment inside of chloroplasts that absorbs light energy from the sun Light is absorbed by Photosystem II P680 and Photosystem I An electron is raised to an excited state and accepted by a primary P700 e acceptor The excited electron is passed through protein electron carriers in the electron transport chain and gives off the energy it absorbed from a light photon in PS II which is then used to produce ATP As electrons are passed by cytochrome a protein in ETC cytochrome pumps H ions into the thylakoid lumen contributing to the gradient After ETC PS I accepts the now ground state electron and again excites it by absorbing light energy from a photon The now excited again electron is accepted by another primary acceptor and goes through a second electron transport chain where a protein called NADP reductase harvests energy from the e and stores it into a bond between NADP and H creating a molecule of NADPH ATP formed by the first ETC and NADPH formed by the second is then used in the Calvin Cycle to convert CO2 into glucose or another high energy molecule o Electron Transport Chain 1st ETC Located between PS II and PS I Helps create chemical gradiant of H Produces ATP to be used in Calvin Cycle Located between PS I and ATP synthase Produces NADPH to be used in Calvin Cycle 2nd ETC o Chemiosmosis Process of creating an Chemical Gradiant of H ions and using the potential energy to phosphorylate ADP to ATP ATP Synthase o Carbon Fixation Calvin Cycle Takes place in the stroma of the chloroplast Cycle fixes or reduces carbon dioxide to form glucose Stage 1 Carbon Fixation One CO2 molecule is attached to a 5 carbon sugar RuBP catalyxed by an enzyme called Rubisco This Results in the production of a 6 carbon intermediate that is so unstable that it immediately splits in half to form two molecules of 3
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