* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download File - Ms. Richards IB Biology HL
Radical (chemistry) wikipedia , lookup
Fatty acid metabolism wikipedia , lookup
Basal metabolic rate wikipedia , lookup
Nicotinamide adenine dinucleotide wikipedia , lookup
Mitochondrion wikipedia , lookup
Phosphorylation wikipedia , lookup
NADH:ubiquinone oxidoreductase (H+-translocating) wikipedia , lookup
Metalloprotein wikipedia , lookup
Photosynthesis wikipedia , lookup
Adenosine triphosphate wikipedia , lookup
Electron transport chain wikipedia , lookup
Photosynthetic reaction centre wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Light-dependent reactions wikipedia , lookup
Microbial metabolism wikipedia , lookup
Citric acid cycle wikipedia , lookup
Topic 8 Metabolism, cell respiration, and photosynthesis 8.2 Essential idea: Energy is converted to a usable form in cell respiration 8.2 Cell respiration Understandings • Cell respiration involves the oxidation and reduction of electron carriers • Phosphorylation of molecules makes them less stable • In glycolysis, glucose is converted to pyruvate in the cytoplasm • Glycolysis gives a small net gain of ATP without the use of oxygen • In aerobic respiration pyruvate is decarboxylated and oxidized and converted into acetyl compound and attached to coenzyme A to form acetyl coenzyme A in the link reaction • In the Kreb cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating carbon dioxide • Energy is released by oxidation reactions is carried to the cristae of the mitochondria by reduction of NAD and FAD • Transfer of electrons between carriers in the electron transport chain in the membrane of the cristae is couple to proton pumping • Oxygen is the final electron acceptor • In chemiosmosis protons diffuse through ATP synthase to generate ATP • Oxygen is needed to bind with the free protons to maintain the hydrogen gradient, resulting in the formation of water • The structure of the mitochondrion is adapted to the function it performs 8.2 Cell respiration Applications and Skills: • Application: Electron tomography used to produce images of active mitochondria • Skill: Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation reactions occur • Skill: Annotation of a diagram of a mitochondrion to indicate the adaptations to its function Cellular Respiration: Harvesting Chemical Energy • This is the part of biology that deals with recycling the ATP used in cellular work. All living organisms use ATP for: 1. Transport work- by phosphorylating membrane proteins 2. Mechanical work- phosphorylating motor proteins 3. Chemical work- energizing other molecules (unstable phosphorylated intermediates) ATP and Cellular Work Cellular Respiration • ATP is obtained or recycled in all organisms, including plants, in the catabolic processes of fermentation (without oxygen= anaerobic) and cellular respiration • Most efficient catabolic pathway is cellular respiration, in which oxygen is consumed as a reactant along with the organic fuel • Most of cellular respiration takes place in the mitochondria Overall Process • Organic compounds + Oxygen Carbon dioxide + Water + Energy • For convenience we usually start with glucose, but can use lipids, proteins and other carbohydrates • C6H12O6 + 6 O2 6 CO2 + 6H2O + Energy • Glucose is oxidized and oxygen is reduced Oxidation-Reduction • Always coupled • Chemical reactions which involve a partial or complete transfer of electrons from one reactant to another • Oxidation: partial or complete loss of e- from a substance; e- donor is the reducing agent • Reduction: partial or complete addition of e- to another substance; eacceptor is an oxidizing agent Methane Combustion: Oxidation and Reduction Methane Combustion 1. Covalent electrons of methane are equally shared because carbon and hydrogen have similar electronegativities 2. As methane reacts with oxygen to form carbon dioxide, electrons shift away from carbon and hydrogen to the more electronegative oxygen 3. Since electrons lose potential energy when they shift closer to the more electronegative atoms, redox reactions that move electrons closer to oxygen release energy • Look back at the equation for cellular respiration and note: 1. Valence e- of carbon and hydrogen lose potential energy as they shift toward electronegative oxygen 2. Released energy is used by cells to produce ATP 3. Carbs – fats: excellent energy stores, because they are rich in C to H bonds • Electrons “fall” from organic molecules to oxygen during cellular respiration. • The “fall” of electrons is stepwise, via NAD+ and an electron transport chain Oxidation vs. Reduction Oxidation Addition of oxygen atoms Removal of H atoms Loss of e- from a substance Reduction Removal of oxygen atoms Addition of H atoms Addition of e- to a substance NAD+ • Co-enzyme which acts as an e- acceptor for the hydrogens stripped from glucose • Nicotinamide adenine dinucleotide- found in all cells, assists enzymes in e- transfer during redox • Functions as an oxidizing agent by trapping e- from food Dehydrogenases • Remove a pair of hydrogen atoms (2 e- and 2 protons) from substrate • Deliver the two electrons and one proton to NAD+ • Release the remaining proton into the surrounding solution. • High energy e- transferred from substrate to NAD+ and then passed down the electron transport chain to oxygen, powering ATP synthesis in a process called oxidative phosphorylation NAD: Electron Shuttle Oxidizing agent when it is reduced Electron Transport Chain • Convert some of the chemical energy extracted from food to a form that can be used to make ATP • Composed of electron-carrier molecules built into the inner mitochondrial membrane • Accept energy-rich e- from reduced coenzymes (NADH and FADH2) and pass down chain to oxygen. Water is formed • Energy is released in a controlled stepwise fashion. E- transfer is exergonic Electron Transport: Controlled release of energy Overview of Cell Respiration Glycolysis • Glyco-lysis splitting of glucose • Catalyzed by enzymes in the cytoplasm • Glucose is partially oxidized and a small amount of ATP is produced • Accomplished without the use of oxygen • Is part of both aerobic and anaerobic respiration Glycolysis Overview Glycolysis • Energy investment phase: 2 phosphate groups from ATP are added to a molecule of glucose to form a hexose biphosphate Glycolysis • Stage 2 Lysis: The hexose biphosphate is split to form two molecules of triose phosphate. Glycolysis • Stage 3 Oxidation: 2 molecules of NAD+ are reduced to 2 NADH and 2H+ so the triose phosphate is oxidized • The energy is used to add another phosphate group to each triose • NADH can enter the electron transport chain in the mitochondria and be used to produce more ATP in the process called oxidative phosphorylation Glycolysis • Stage 4 ATP Formation: Two phosphate groups are removed from the two trioses and passed to ADP to form ATP • So 4 ATPs are generated for a net gain of 2 ATPs • ATP is produced by a process called substrate-level phosphorylation because an enzyme transfers a phosphate group from a substrate (organic molecule generated by the sequential breakdown of glucose) to ADP Substrate Level Phosphorylation Glycolysis End of Glycolysis • A 6-Carbon compound has been turned into 2 3-Carbon compounds called pyruvate (or oxopropanoate) • Glucose has been oxidized • Glycolysis also yields 2 water molecules for each glucose Hexose biphosphate Lysis 2 triose phosphate molecules Oxidation ATP Formation Link Reaction • Pyruvate oxidation and the formation of acetyl • Acetyl is a 2-Carbon compound aka ethanol • Occurs after pyruvate molecules are translocated from the cytosol into the mitochondrion by carrier proteins in the mitochondrial membrane • Involves the removal of a molecule of carbon dioxide • Oxidizes 2 carbon fragment to acetate while reducing NAD+ to NADH 2 per glucose Link Reaction • Attaches coenzyme A to the acetyl group, forming acetyl CoA • This bond is unstable, making acetyl (ethanol) very reactive • It is acetyl CoA that enters the Krebs Cycle The Link Reaction: oxidative decarboxylation The Kreb Cycle • Explicated by German-British scientist Hans Krebs • Also called citric acid cycle or tricarboxylic acid cycle • Oxidation of the remaining acetyl fragments to CO2 • Energy from this exergonic process is used to reduce coenzymes NAD+ and FAD (both electron carrier molecules) and to phosphorylate ATP (once again through substrate level phosphorylation) Entry into the Krebs cycle (Citric Acid Cycle): 2 C + 4C = 6C Kreb Cycle • A 2-carbon acetyl group bonds to the 4-carbon oxaloacetate to form the 6-carbon citrate • The 6-C compound loses CO2 and becomes a 5-C compound • 5-C compound is oxidized and NAD+ is reduced • Another CO2 is removed • 4 C compound is oxidized and NAD+ is reduced 6C – 1CO2= 5 C 5C - 1CO2= 4 C Kreb Cycle • A molecule of ATP is formed • Co-enzyme FAD is reduced to FADH2 • Another NAD+ is reduced and oxaloacetate is regenerated to begin this cycle again Hydrogen-carrying coenzymes: NAD and FAD The starting material is regenerated and we go around again! Kreb Cycle Summary Krebs cycle results per glucose • 2 molecules of pyruvate are oxidized • 2 ATPs by substrate level phosphorylation • 6 NADH and 2 FADH2 • Starting material is regenerated • Electron transport chain couples electron flow down the chain to ATP synthesis Electron Transport Chain • Most molecules of ATP are produced during oxidative phosphorylation • The reduced coenzymes NADH and FADH2 link glycolysis, the link reaction, and the Krebs cycle to oxidative phosphorylation by passing their e- down the electron transport chain to oxygen • This exergonic transfer of e- is coupled to ATP synthesis Electron Transport Chain Cristae • Movement of electrons through progressively more electronegative molecules down to oxygen Electron Transport Chain • Made of electron carrier molecules embedded in the inner mitochondrial membrane • Each successive carrier in chain has a higher electronegativity than the carrier before it, so that the e- are pulled down hill to oxygen • Most carriers are proteins bound to nonprotein cofactors which alternate between reduced and oxidized states as they accept and donate electrons • As molecular oxygen is reduced, it also picks up 2 protons from the medium. For every 2 NADHs, one O2 is reduced to 2 water molecules • FADH2 also donates e- but at a lower energy level • Chain does not make ATP directly • It generates a proton gradient across inner mitochondrial membrane which stores potential energy that can be used to phosphorylate ADP Chemiosmosis Oxidative Phosphorylation • The electron transport chain (oxidative because of oxygen’s pull on e-) • Combines with the flow of H+ through ATP synthase called chemiosmosis (phosphorylation because ATP is made with the energy) • To give the process of Oxidative Phosphorylation The Energy-Coupling Mechanism • The exergonic e- flow from the oxidation of food is used to pump H+ across the inner mitochondrial membrane from the mitochondrial matrix to the intermediate space • The energy from the flow of electrons is used to set up a gradient of pH (H+) • The pH of the intermembrane space is 1 to 2 pH units lower that the matrix but same as cytosol ATP Synthase • H+ can leak back across the inner membrane at specific sites since the membrane’s phospholipid bilayer is impermeable to H+ and prevents diffusion back • This specific site is a protein complex embedded in the mitochondrial membrane – ATP Synthase • ATP Synthase is the enzyme that makes ATP ATP Synthase • ATP Synthase uses the potential energy stored in a proton gradient to make ATP by allowing H+ to diffuse down the gradient back across the membrane • Protons diffuse through ATP synthase complex which causes phosphorylation of ADP • H+ gradient is called proton-motive force to emphasize gradientpotential energy ATP Synthase: Converts H+ gradient into ADP Electrochemical gradient • Has a concentration gradient of protons • Has a voltage across the membrane because of a higher concentration of positively charged protons on one side • Tends to drive protons across the membrane back into the matrix Chemiosmosis Cell Respiration Review Oxidation of organic nutrients in the absence of oxygen • Anaerobic fermentation • Glycolysis oxidizes glucose to pyruvate • The oxidizing agent is NAD+, not oxygen • Net production of ATP = 2 • In fermentation, pyruvate is reduced and NAD+ is regenerated with no additional ATP produced Alcohol Fermentation • Alcohol fermentation- pyruvate is converted to ethanol in two steps 1. Loses CO2 acetaldehyde 2. NADH is oxidized to NAD+ and acetaldehyde is reduced to ethanol • Common in bacteria and yeast in anaerobic conditions Fermentation: Regenerating NAD+ Lactic Acid Fermentation • NADH is oxidized to NAD+ and pyruvate is reduced to lactate • Commercially important products include cheese and yogurt • Occurs when O2 is scarce in human muscle cells which switch from aerobic respiration to lactic acid fermentation • Lactate accumulates, carried to liver, converted back to pyruvate when O2 available Lactic Acid Fermentation Branching off point for pyruvate Oxidation of other organic compounds • Glycolysis and Krebs cycle connect to many other metabolic pathways • Complex molecules such as fats, proteins, disaccharides and polysaccharides must be hydrolyzed to simpler molecules or monomers that can enter the intermediate reaction of glycolysis or Krebs if they are to be oxidized to make ATP Fats • Rich in hydrogens and high energy e• Fats are digested into glycerol and fatty acids. Glycerol can be converted to an intermediate of glycolysis • Most of the energy in fats is in fatty acids which can be converted into acetyl Co-A by beta oxidation • Can then enter the Krebs cycle Proteins and fats in cell respiration: Central role of Acetyl CoA Carbohydrates and Proteins • Notice that complex carbohydrates would be hydrolyzed to glucose • Proteins are hydrolyzed to amino acids. Excess amino acids are enzymatically converted to intermediates of glycolysis and Krebs cycle. Common intermediates are pyruvate, acetyl Co-A • Conversion process deaminates amino acids and the resulting nitrogenous wastes are excreted Feedback and Control of cellular respiration • 1st on-off switch occurs in glycolysis. Enzyme phosphofructokinase is inhibited by ATP and stimulated by ADP. ATP is allosteric inhibitor of this enzyme • It is also sensitive to the concentration of citrate. Helps to synchronize the rates of glycolysis and Krebs cycle A 8.2.1 Electron tomography used to produce images of active mitochondria • Used to obtain a three dimensional model of active mitochondria • Tomography is technique that images sections through the body using X-rays or ultrasound • This has shown that cristae are connected with the intermembrane space between the inner and outer membranes by narrow openings • When the mitochondria is active the volume and shape of cristae change S 8.2.1 Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation reactions occur S 8.2.1 Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation reactions occur S 8.2.1 Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation reactions occur Where does decarboxylation occur? S 8.2.1 Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation reactions occur S 8.2.1 Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation reactions occur S 8.2.2 Annotation of a diagram of a mitochondrion to indicate the adaptations to its function • Structure and function in organisms is closely related • It is a result of natural selection and is called adaptation