Chapter 9 and 10
Chapter 9 and 10 BSCI105
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L Loss of hydrogen atoms oxidation C HlZOo Shira Clements BSC105 Chapter 9 Cellular Respiration and Fermentation Catabolic Pathways and Production of ATP Cell degrades the complex molecules into simpler ones to use the potential energy in bonds energy is used as work or heat Fermentation catabolic process that degrades sugars or organic fuels without the use of oxygen Cellular Respiration includes both of the following o Aerobic respiration catabolic pathways where oxygen is consumed with other fuels Organic compounds 02 yields C02Water Energy C6H1206 602 yields 6H20 Energy ATP heat Glucose is fuel for cells Breakdown is exergonic free change of 686kcal o Anaerobic respiration makes chemical energy without 02 prokaryotes do it Redox Reactions Transfer of one or more elections fro one reactant to another Loss of electrons from one oxidation addition of electrons to one reduction 0 Xe39 Y yields X Ye39 X becomes oxidized when Y becomes reduced more negaUve Electron donor reducing agent and electron acceptor oxidizing agent Therefore it always goes together Energy state of electron changes as hydrogen with electrons are transferred to oxygen Oxidation of glucose transfers electrons to lower energy state liberating energy that becomes available for ATP synthesis Can be in covalent reactions doesn t have to involve complete transfer of electrons just more negative or more positive The more electronegative the more energy you need to for redox reaction to occur 0 Redox reaction that moves electrons closer to oxygen releases chemical energy that can be put to work Activation energy holds back the electron ood from energy yielding foods to lower energy state energy being released all at once is not conducive for work so glucose and other organic molecules are broken down by steps at key steps electrons are stripped from glucose along with a proton all together a hydrogen atom which are then passed to an electron carrier coenzyme NAD ATP 6C02 l 6H2O l Energy l Gain of hydrogen atoms j reduction Glucose NAD can easily be oxidized NAD or reduced NADH making it the perfect carrier 0 As an electron acceptor NAD acts as an oxidizing agent 0 Traps electrons from glucose and other organic molecules through enzymes of dehydrogenases which removes a pair of hydrogen atoms 2 e and 2 protons from substrate glucose which oxidizes it One proton is released as H ion into surrounding solution and 2 e and one proton is delivered by the enzyme to NAD which then neutralizes it and becomes NADH which stores some energy to make ATP when electrons fall down energy gradient from NADH to oxygen The electrons lose very little of their potential energy during this transfer Electron Transport Chain ETC number of molecules proteins usually in the inner membrane of mitochondria used to break the fall of electrons into several energy 139 7 releasing steps Top is high energy from NADH and 5 s l bottom is low energy going to 02 with addition of H to 232quot g 3 make water a Creates an exergonic reaction of 53 kcalmol by steps W of Cellular Respiration ging of energy from glucose by three metabolic stages catabolic a GElycolysis in cytosol a z o Begins the process of breaking down glucose into two pyruvate Pyruvate oxidation and citric acid cycle o in mitochondria for eukaryotes cytosol for prokaryotes gt o the pyruvate is brought there and is oxidized by Acetyl CoA which then enters citric acid cycle where glucose is then turned into C02 represents oxidized fragments of oxidized molecules 0 some redox reactions occur making NAD into NADH via dehydrogenases Oxidative phosphorylation electron transport chain and chemiosmosis o Accepts electrons from breakdown of products of rst stages and passes them from molecule to next and at the end the they are combined with molecule 02 and H ions making water 0 Energy released is stored in mitochondria and is used to make ATP from ADP which is called oxidative phosphorylation powered by redox reactions of ETC 0 Inner membrane is site of ETC and chemiosmosis in eukaryotes but in plasma membrane for prokaryotes processes that together make oxidative phosphorylation accounts for 90 of ATP synthesis in respiration Glycolysis and citric acid cycle can make ATP through substrate level phosphorylation enzyme transfers a phosphate group from substrate molecule organic ratelevel Glycoly i e Pyruvate Subslt phosphoryl molecule generated as an intermediate during catabolism of glucose to ADP instead of adding inorganic phosphate to ADP like oxidative phosphorylation For every glucose molecule made into C02 and HZO cell makes up to 32 molecules of ATP each with 73 kcalmol of free energy Glycolysis ln cytosolcytoplasm Harvest chemical energy by oxidizing glucose into 2 pyruvates 6 C is split up into 2 3C sugars and are oxidizedrearranged to form two pyruvates Energy investment stage 2 ADP Pi makes 2 ATP which is used to start reaction Energy payoff stage 4 ATP is produced by substrate level phosphorylation and 2NAD is reduced to 2NADH by glucose acting as the reducing agent giving up electrons Occurs even when 02 is not there 2ATP 2RDP m Net glucose yields 2 pyruvate 2H20 333 km 0 4ATP form 2ATP used yields 2 ATP lata o 2 NAD 4e 4H yields 2NADH 2H r 2 ADP EN ERG INVESTMENT 2 ADP 2 ATP 2ATP Citric Acid Cycle Krebs Cycle WWW ln mitochondria 39l One pyruvate enters the cycle at a time so double results at end two get cellular respiration of one glucose molecule Oxidation of pyruvate to acetyl coenzyme A Acetyl CoA before citric acid 0 Pyruvate s carboxyl group C00 is oxidized and is given off at C02 0 NAD turns into NADH because of the electrons from acetate the remains of pyruvate CH3COO39 o CoA contains sulfur and attaches to acetate forming acetyl CoA which will give the acetyl group to citric acid eyele and joinsgwith oxaloacetate to form citrate in rst step mil For each acetyl group o Pyruvate is broken down to 3 C02 including the one f o 1 ATP is produced by substrate level phosphorylation o 3 NAD is reduced to 3NADH which is energy also 0 7 o 1 FAD is reduced to FADH2 which is energy also CYTOSOL Transport protein quotg k T Electron Transport Chain in inner membrane of mitochondrial439 o NADH and FADH2 enters and goes from protein to proteins ghd lets out free energy after each drop the proteins go between reduced and oxidized as they accept and free electrons reduced 3 I electron transport system I when NADH or FADH2 come to them but as they let them go they are oxidized again FADH2 enters at a lower point because it holds less energy They let out H and form and H gradient 0 Last electron acceptor of the chain is 02 which picks up pair of hydrogen ions and forms H20 Chemiosmosis turns the free energy into ATP 0 In the inner membrane of the mitochondria there are a lot of ATP synthase enzyme that makes ATP from ADP and Pi works like reverse ion pump It uses energy from existing ion gradient to power ATP synthesis power source for it is the difference in the concentration if H in opposite sides of inner mitochondrial membrane ow of H through this enzyme powers ATP generation It is a rotor motor spins and makes the product The H has tendency to move back across the membrane by diffusing down its gradient and the ATP synthase is the only place where they can do so and it uses the exergonic ow of H to drive the phosphorylation of ADP Energy in H gradient across membrane couples the redox reactions of ETC to ATP synthesis the H gradient is called proton motor force o It is an energy coupling mechanism that uses energy stored in the form of an H gradient across a membrane to drive cellular work Makes between 2628 ATP Without pull from 02 at end of oxidative phosphorylation it would cease Production of ATP without 07 Anaerobic Respiration ETC is used o It uses other very electronegative molecules in place of 02 and then it can build up which then builds up a protonmotive force to produce ATP and then H25 is produced instead of H20 Fermentation harvests chemical energy without cellular respiration 0 Extension of glycolysis because it generates little ATP without oxygen rather it uses substrate level phosphorylation Must be suf cient supply of NAD to accept the electrons during the oxidation step of glycolysis otherwise it would deplete because there would be no oxidizing agent Transfer electrons from NADH to pyruvate instead of transferring electrons to ETC 0 Alcohol Fermentation pyruvate converted to ethanol in two steps Releases carbon dioxide from pyruvate which is converted to 2C compound acetaldehyde That is then reduced by NADH to ethanol which generates supply of NAD needed for glycolysis o Lactic Acid Fermentation pyruvate is reduced directly by NADH to form lactate with no release of C02 Muscle cells make ATP through this when 02 is scarce Excess lactate goes into liver where it is converted back to pyruvate 0 Only 2 molecules of ATP are produced just like glycolysis Obligate anaerobes only fermentation of anaerobic respiration can t survive with 02 Facultative anaerobes can make enough ATP to survive on just fermentation Pyruvate is needed in all processes Glycolysis and Citric acid cycle are major intersections of the cell s catabolic Emmanabolic pathways l Catabolic breaks down and uses for energy Anabolic helps with molecules structure not everything is used for energy and comsume ATP 0 Helps convert some kinds of molecules to others that we need lntermiediate compounded generated by glycolysis Dihydroxyscetone phosphate can be converted to one of the major precursors of fats if we eat too much than diet can hold then we store it as fat 7 ack really helps with cellular respiration The anabolic pathways that creates certain things will be switched off if there is too much of it o The end product of anabolic pathway inhibits the enzyme that catalyzes an earlier step in the pathway o Catabolism as well if cell is working hard and ATP concentrations 9 y it begins to drop respiration speeds up When there is plenty of a Li ATP respiration slows down allowing the organic molecule to focus on the other functions 39 Phosphofructokinase is considered a peacemaker because it is the enzyme that catalyzes the third step in glycolysis which commits the substrate to nishing the the glycolytic pathway can speed up or slow down based on the feedback o It is an allosteric enzyme with receptor sites for inhibitors or activators inhibited by ATP but activated by AMP which is derived from ADP Becomes active when ATP is being converted to ADP faster than the synthesis of ATP Also inhibited by citrate rst step in citric acid cycle Chapter 10 Photosynthesis Photosynthesis in a nutshell chloroplasts of plants capture light energy and convert it to chemical energy that is stored in sugar and other organic molecules Nourishes entire world 0 Organism gets organic compound it uses for energy and carbon skeleton by one of 2 ways Autotrophs self feeders sustain themselves without eating other things that are derived from other living things but can be a source for others 0 Produce their organic molecules from C02 and other raw inorganic materials from the environment 0 Plants are because they just get water and nutrients from the soil and C02 from air speci cally photoautotrophs because they use light also to synthesize organic molecules Heterotrophs get organic compounds from other organisms consumers Animals eat other living things Dependent on photoautotrophs for food and 02 byproduct of photosynthesis Photosynthesis probably originated from bacteria s molecules in plasma membrane which is now known as a chloroplast in a eukaryotic cell Chloroplasts site of photosynthesis Make the plant green from chlorophyll in the thylakoid and found mostly in mesophyl leaf s interior tissue 0 C02 enters leaf and 02 exits by pores called stomata and water is absorbed through veins of leaf Stroma liquid in chloroplast thylakoids separates the stroma from the thylakoid space within these sacs each stack of sacs is called granum Light energy absorbed by chlorophyll drives the synthesis of the organic molecules Process of Photosynthesis 6C02 12H20 light energy yields C6H1206 602 6H20 Opposite of cellular respiration 02 given off from plants is derived from H20 not C02 chloroplast splits the water into H and oxygen Redox Reaction 6C02 oxidizing agent becomes reduced into C6H1206 6H20 reducing agent is oxidized to 602 Electrons increase potential energy as they move from water to sugar it requires energy which means it is endergonic and this energy is provided through light It is two processes light reactions photo part and Calvin cycle synthesis part Light reactions water is split providing H ions and giving of 02 as a by product Light absorbed by chlorophyll causes transfer of electrons and H ions to NADP acceptor extra phosphate in this compared to NAD Use solar power to reduce NADP to NADPH by adding a pair of electrons with H generate ATP by photophosphorylation adding a ADP light energy is now converted to chemical energy in form of APH and ATP quotll Occurs in thylakoids 39 On outside of thylakoids NADP and ADP pick up electrons and phosphate and then NADPH and ATP are released into stroma Calvin cycle can be referred to as dark reaction don t need light C02 from air into organic molecules present in chloroplast carbon xation Reduces xed carbon to carbohydrate by addition of electrons and this reducing power is provided by NADPH The ATP and NADPH is needed for the synthesis to occur 0 Occurs in stroma Nature of Sunlight Light is electromagnetic energy that travels in waves 0 Distance between the two crests is called wavelength from less than a nm to more than a km and the entire range is known as electromagnetic spectrum 0 Visible light between 380nm and 750 nm can be recognized o Photons discrete particles in light the shorter the wavelength the greater energy of each photon Pigment substances that absorb visible light and each absorb different wavelength o If it absorbs all colors it appears black If it re ects all colors it appears white 0 The color you see is re ected back while the pigment absorbs the shorter wavelengths 0 Light can perform work in chloroplasts only if it is absorbed there What happens when chlorophyll and other pigments absorb light is elevated to an orbital where it has more potential energy which went from ground state Colors with absorbed wavelengths disappear but energy cannot disappear When a molecule absorbs a photon one molecules electrons to excited state the only photons absorbed are those whose energy is exactly equal to the energy difference between ground and excited state making each pigment have a unique absorption spectrum The electron can t remain in excited state for long since it is unstable and generally drop right back down to ground state releasing excess energy as heatphotons 0 When photons are given off there is an afterglow uorescent Photosystem A reaction center complex associated with light harvesting complexes Chlorophyll and other organic molecules are organized into a photosystem converts light energy into chemical energy Reaction center complex organized association of proteins holding a special pair of chlorophyla molecule 0 Contains a molecule capable of accepting electrons and becoming reduced primary electron acceptor pair of chlorophyll a molecules are special because of their environment able to use energy from light to boost electron to higher energy but also to transfer it to the primary electron acceptor Light harvesting complex various pigment molecules chlorophyll a chlorophyll b carotenoids bound to proteins 0 Number and variety of pigment molecules helps photosystem harvest light over bigger surface area and act as antenna for reaction center complex 0 When pigment molecule absorbs light the photon is passed along from molecule to molecule until it is passed into reaction center complex Transfer of photon from reaction center chlorophyll a pair to primary electron acceptor is rst step of light reactions Excited then primary electron acceptor catches it which happens in structured environment of chloroplast redox reaction Thylakoid is populated by two types of photosystems that cooperate in the light reactions of photosynthesis photosystem II and photosystem I 0 Reaction center of chlorophyll a in P5 is known as P680 because it is best at absorbing light with wavelength of 680 o Chlorophyll at reaction center complex of PSI is known as P700 because it is best at absorbing light with wavelength of 700 0 They have different proteins associations which effects electron distribution which accounts for slight differences in light absorbing properties Linear Electron Flow Light drives synthesis of ATP and NADPH by energizing the two photosystems but a ow of electrons through the photosystems and other components in thylakoid is necessary Steps 1 Photon hits pigment in PS and an e is boosted to higher energy level and as this fails another e in a nearby pigment is excited repeats until it reaches P680 and an electron pair of chlorophylls is exc ed 2 E is transferred from excited P680 which is now known as P680 strongest oxidizing agent to primary electron acceptor 3 Enzyme catalyzes split of water into H 2 e and O atom The e are supplied one by one to P680 H go into thylakoid lumen and O combines with another 0 to make 02 4 Each photoexcited electron is passed from primary electron acceptor of PS to PSI via ETC made up of proteins which is exergonic 5 ETC provides energy for synthesis of ATP and H are pumped into thylakoid lumen helping with proton gradients that is used in chemiosmosis 6 Light energy has been transferred via light harvesting complex pigments to the PSI reaction center complex exciting an electron of the P700 pair of chlorophyll a which was then transferred to PSl s primary electron acceptor making it P700 a holemissing something allowing it to act as an electron acceptor accepting an electron that reaches the bottom of the ETC gets more electronegative as it gets toward bottom and source for electrons is water from P5 7 Redox reactions occur when pass from primary acceptor down second ETC through protein Fd no proton gradient so no ATP 8 NADP reductase enzyme catalyzes transfer from Fd to NADP and made into NADPH by two electrons NADPH is higher energy than water and e more readily available for Calvin cycle Removes H from stroma Cyclic Electron Flow only uses P5 in certain cases 0 electrons cycle back from Fd to cytochrome complex whi makes ATP via chemiosmosis and then to P700 LOW no production of NADPH no release of 02 but it generat ATP MITO CHDMDRHON STRUC TUIRE Comparison of chemiosmosis in mitochondria and chloroplasts is explanipen space p I U Membrane r eron this c in CHLORDF LAST STRU E quotPURE Summary of light reaction electron ow pushes electron from water low state of energy to NADPH stored as high state of energy and this current drives production ofmg TP 02 is byproduct low Hf concentration cymchmme complex V Plhotosystem ii Photosystem I dillF Li thil u afgi INIALIIJP1L H THYLAKOlID SPACE high Hquot eon santrationj To Calvin Cycle Thylakoid memb ra ne ATP STRDMA synthase low H concentration Calvin Cvcle uses chemical energy of ATP and NADPH to reduce C02 to sugar anabolic builds carbohydrates from smaller and consumes energy Carbon enters in form of C02 and leaves as sugar Spends ATP as energy source and consumes NADPH as reducing power for adding high energy electrons to make sugar Carbohydrate produced directly is glyceraldehyde 3phoshphate G3P for synthesis of one Calvin cycle must happen three times xing 3 C02 molecules Phase 1 Carbon Fixation gets each C02 molecules by attaching it to ve carbon sugar RuBP which is catalyzed by rubisco most abundant protein which makes a very unstable 6C which then splits in half forming two 3phosphoglycerate for each C02 Phase 2 Reduction each 3phosphoglycerate gets phosphate group from ATP making it 1 3bisphoglycerate then a pair of electrons from NADPH reduces that and makes it lose a phosphate group which then becomes G3P same sugar from glycolysis when glucose is split So 6 G3P are formed for all three C02 Phase 3 regeneration of the C02 acceptor RuBP the carbon skeleton of ve molecules of G3P are rearranged into three molecules of RuBP by spending three more molecules of ATP and RuBP is now prepared for more C02 Net synthesis of one G3P consumes 9 molecules of ATP and 6 NADPH but light reaction regenerates ATP and NADPH GBP made from Calvin cycle is string material for for metabolic pathways that synthesize other organic compou CFLWN C I39CLE 39 SharHiued 7 739 intermediate 2 50 D O 3Phosphuglycelraie 3amp0 GQOQ Flibluloge lbisphospham 6 DLQ OPE 1EeBisphoaphaglyceralle i Importance of Photosynthesis from photons to food light reaction capture solar energy and make ATP and transfer electrons from water to NADP to form NADPH The Calvin cycles uses the ATP and NADPH to produce sugar and carbon dioxide Energy that enters chloroplasts as sunlight becomes sotred as chemical energy in organic compounds Sugar gives entire plant chemical energy and carbon skeleton for production of organic molecules in cell half of organic material is consumed as fuel for cellular respiration Responsible for oxygen in atmosphere Makes billions and billions of carbohydrates