EXAM III Study Guide PART 1
EXAM III Study Guide PART 1 Bsci105
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This 13 page Study Guide was uploaded by Trang Le on Tuesday November 10, 2015. The Study Guide belongs to Bsci105 at University of Maryland taught by Dr. Alewall in Summer 2015. Since its upload, it has received 160 views. For similar materials see Intro to biological sciences in Biological Sciences at University of Maryland.
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Date Created: 11/10/15
CELLULAR RESPIRATION The energy stored in organic molecules of food ultimately comes from the sun. Respiration breaks this down and generates ATP to fuel biochemical processes. Fermentation: a catabolic process of partially degrading sugars or other organic molecules in anaerobic (without oxygen) environment. The most effective anabolic pathway is aerobic respiration (requires oxygen). Summary of this: (Organic compounds) + O >2CO + H 02+ Ene2gy. This process is exergonic. Cellular respiration oxidizes carbohydrates, producing CO , H O 2nd A2P. Catabolic pathways yield energy from redox reactions: transfer of one or more e from one reactant to another. Overall oxidation reaction of glucose in respiration: C H O 6+ 12 6 O 2> 6 CO 2 6 H O 2 Energy An example to explain redox reaction: The reducing agent is oxidized and the oxidizing agent is reduced. Oxidation=(partial) removal of electrons. Reduction=(partial) acceptance of electrons. Because of the different electronegativities of O2 and CO2, C partially loses electrons and O partially gains electrons in this example. Glucose is broken down in a series of steps, in which most includes transfer of e. H+ are not transfer directly to oxygen, but to an e acceptor first, a coenzyme called NAD+, which functions as oxidizing agent during respiration. e loses very little potential energy when being turned from glucose to NAD+. NAD+ + 2 H > NADH + H+ (NAD picks up H Oxidized + Reduced > Reduced Oxidized (hydride ion) FAD + 2 H. > FADH2 (FAD picks up 2H.) Energy Stored in NADH and FADH are Used to Pro2uce ATP in Stages. Each pair of hydrogen atoms produces a maximum of 3 ATP/NADH, 2 ATP/FADH2. Electron transport chain: consist mostly of proteins, built into inner membrane of mitochondria in eukaryotic cells. e removed from glucose are shuttled by NADH to the "top" (higher energy end), travelled to the "bottom", where oxygen captures these and combine with H+ to form water. e go down through a series of redox reactions, and on the way to oxygen release ATP > exergonic. The stages of cellular respiration has three major steps (image below). Oxidative Phosphorylaton produces ATP Oxidative phosphorylaton: enzymes donate an inorganic phosphate to ADP. Substrate level phosphorylaton: substrates donate an inorganic P to ADP. Conversion of Glucose to Pyruvate in Glycolysis (exergonic): + + C 6 O12 26 + 2 ADP + 2 P > 2C H O +i2NADH + 2H3+ 4 A3 + 2 H O 2 (Glucose) (pyruvate) (Glycolysis) Upon entering mitochondria, pyruvate is converted to acetyl CoA. Pyruvate's carboxyl group is removed and given off CO2. The remaining 2 carbon fragment is oxidized to form acetate (CH COO). 3 CO2 released; keto group converted to carboxyl/NAD is reduced; acetyl group reacts with CoA to form acetyl CoA. The Citric acid cycle Acetyl CoA + 3NAD+ + FAD + ADP + Pi > 2 CO2 + CoA + 3NADH + 3 H+ + FADH2 + ATP (must double the number of molecules for each because one glucose molecule requires two turns of the citric acid cycle). Citric acid cycle: (1) Acetyl coA adds twocarbon acetyl group to oxaloacetate, producing citrate. (2) Citrate is turned into its isomer, isocitrate, by removal of one water molecule and add another. (3) Isocitrate is oxidized, reducing NAD+ to NADH, lose a CO2 molecule. (4) Another CO2 is lost, and resulting compound is oxidized, reduce NAD+ to NADH > Succinyl CoA. (5) CoA is displaced by a phosphate group that is transferred to GDP and form GTP which is similar to ATP but can be used to make ATP. (6) Succinate oxidation: 2 H are transferred to FAD+, forming FADH . (2) Succinate > Fumarate; addition of a water molecule. (8) Fumarate > Malate. the substrate is oxidized, forming NADH and regenerate oxaloacetate. <repeat cycle> Catabolism of fats and proteins also involves glycolysis and citric acid cycle. In fermentation, NADH produced in glycolysis is reoxidized by transferring electrons to pyruvate (muscle) and/or Acetaldehyde, a product of pyruvate (produce ethanol). Phosphofructokinase is a major regulator of cellular respiration: Energy flow in respiration and oxidative phosphorylation Glycolysis and the TCA cycle oxidize glucose producing NADH, FADH2 and ATP (by substrate level phosphorylation) Electrons from NADH and FADH2 are transferred to electron transport chain Protons are pumped across inner mitochondrial membrane as electrons move along electron transport chain At the end of the electron transport chain, electrons are transferred to O2, producing H2O The proton gradient generated is used to drive synthesis of ATP by ATP synthase (chemiosmosis) Pyruvate (Cytoplasm) AcetylCoA (Mitchondrion) Conversion. Some reactions to consider: Glucose + 2 NAD+ + 2 ADP + 2 Pi 2 Pyruvate + 2 NADH + 2 H+ + 2 ATP + 2 H2O <Glycolysis>; 2 Pyruvate + (2 ATP) + 2 NAD+ + 2 H2O 2 AcCoA + 2 CO2 + 2 NADH + 2 H+ + (2 ADP + 2Pi) <Acetyl CoA>; 2 AcCoA + 6 NAD+ + 2 ADP + 2 Pi + 2 FAD + 2 H2O 4 CO2 + 2 CoA + 6 NADH + 6 H+ + 2 ATP + 2 FADH2 <Citric acid cycle>. How mitochondria convert energy stored in NADH and FADH to2ATP. Oxidative Phosphorylation: Electron transport chain removes protons and electrons from NADH, FADH ; 2 Electrons are used to reduce O 2to H2O; Protons create electrochemical gradient across inner mitochondrial membrane; Electrochemical gradient drives formation of ATP from ADP, Pi (chemiosmosis) by ATP synthase. PHOTOSYNTHESIS The flow of energy and molecules in photosynthesis is in many ways are the opposite of what occurs in cellular respiration (eg energy source, energy flow, direction of proton movement). Other aspects are similar (eg electron transport chain) Proteins involved in photosynthesis are found in membranes of thylakoid sacs The reactions that require light (light reactions) occur in two stages, located in Photosystem II and Photosystem I. Synthesis of carbohydrates (dark reactions) does not require light and occurs in the Calvin cycle. Autotrophs: Can obtain organic molecules through photosynthesis without eating other organisms. Photoautotroph: organisms that use light as the source of energy to synthesize organic molecules (plants, algae). Chloroplasts are found mainly in mesophyll, a tissue in the interior of leaves. CO2 enters and leaves through pores called stomata. In thykaloid membranes are chlorophyll, the green pigment that gives leaves their green color. Photosynthesis: 6CO + 12H2O + Ligh2 energy C H O + 6O +66H12.6CO is 2 2 2 reduced while water is oxidized to become oxygen. Oxygen given off from plants come from water, not carbon dioxide. Plants split water molecules as source of e from H atoms, releasing oxygen as byproduct. Photosynthesis has 2 steps: light reaction and Calvin cycle. Light reactions: convert solar energy into chemical energy. Drive e and H ions to an acceptor called NADP+ forming NADPH. Also use a process called photophosphorylation, generating ATP using chemiosmosis. This occurs in chloroplast. Occur in the stroma, Calvin cycle begins with adding CO2 from air to organic molecules in a process called carbon fixation. It then reduces the fixed carbon to form carbohydrate (Glyceraldehyde3P) by addition of e. This requires energy from ATP, thus ATP is oxidized into ADP and Pi, and this goes back to Light reactions (figure above). Synthesis of carbohydrate in stroma (NOT require light) A photosystem: a reactioncenter complex associated with Lightharvesting complexes. How a photosystem harvests light: A photon (molecule of solar energy) strikes a pigment molecule in a lightharvesting complex, the energy is passed from molecule to molecule until it reaches reactioncenter complex. Here, an excited e from the special pair of chlorophyll a molecules is transferred to the primary e acceptor. Photosystem II (PS II) and photosystem I (PS I) Energy of electrons excited in PS II make ATP; energy of electrons excited by PS I make NADPH. Light drives the synthesis of ATP and NADPH through linear electron flow: Absorption of photon by pigment molecule in PSII excites electron in the molecule; Energy (in the form of excited electrons) is passed along other pigment molecules to a P680 dimer where it excites two electrons. These electrons are passed to the primary PSII acceptor, converting each P680 monomer to P680+; An enzyme splits water and two electrons pass to the P680+ dimer; Both excited electrons move along electron transport chain to PSI, enabling ATP synthesis; Absorption of light excites 2 electrons in P700 dimer which pass to PSI primary acceptor, creating P700+. These electrons pass along a second electron transport chain, enabling reduction of NADP to NADPH; P700 is regenerated by accepting electrons from the first electron transport chain. Proton Gradient Used to Drive ATP Synthesis (1) Water is split by PS II on the side of the membrane facing thykaloid space. (2) Plastoquinone (Pq) transfers e to cytochrome complex, 4 protons are moved across membrane into thykaloid space. (3) A H ion is removed from stroma when it's taken up by NADP+. The diffusion of H+ from thykaloid space back to stroma along H+ concentration gradient powers ATP synthase. These reactions require light, and store energy in ATP which move to Calvin cycle.
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