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Aman Singh Yadav, 9453643817, , The mechanism of breaking of C-C bonds of complex molecules, through oxidation within the cell leading to the release of energy for, ATP synthesis is called cellular respiration., ● This energy is used for absorption, transport, movement,, reproduction, breathing etc., ● Ultimate source of food that is respired is photosynthesis., The compounds that are oxidized during respiration are called, respiratory substrates., For ExampleCarbohydrates (most common), Proteins, Fats and Organic acids., The energy released is not used directly but is used to synthesize ATP., When energy is needed, the synthesized ATP is broken down. Hence,, ATP acts as the energy currency of the cell., , Bʀᴇᴀᴛʜɪɴɢ Iɴ Pʟᴀɴᴛs, For respiration, plants take O2 and give out CO2., Plants have stomata & lenticels for gaseous exchange., - Plants need no specialized respiratory organs because, • Each plant part takes care of its own gas-exchange needs. So gas, transport is very limited., • Very low gas exchange as compared to that of animals., • Leaves are adapted for maximum gas exchange during, photosynthesis. During this, O2 is released within the cell., • Most living cells have contact with air. They are located close to the, plant surface., In stems, living cells are organized in thin layers beneath the bark. They, also have lenticels., In leaves, stems & roots, parenchyma cells are loosely packed that, provide interconnected air spaces., , Aman Singh Yadav, 9453643817
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Aman Singh Yadav, 9453643817, , Tʏᴘᴇs Oғ Rᴇsᴘɪʀᴀᴛɪᴏɴ, The cellular respiration may be of two types1. Aerobic Respiration, 2. Anaerobic Respiration, , Aerobic Respiration, The type of respiration in which organisms use oxygen for complete, oxidation of organic food into carbon dioxide water and energy., It starts in cytoplasm and get completed inside the mitochondria., Aerobic respiration yields more energy as a respiratory substrate is, completely oxidized in presence of oxygen., C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy, , Anaerobic Respiration, Anaerobic respiration is a type of cellular respiration where respiration, takes place in the absence or deficiency of oxygen to yield Alcohol or, Lactic acid.The process is also called fermentation., The total sum of ATP molecules produced during anaerobic respiration, or fermentation is very less as compared to aerobic respiration., , Cᴇʟʟᴜʟᴀʀ Rᴇsᴘɪʀᴀᴛɪᴏɴ, It occurs in all living cells and proceeds with the help of enzymes. The, first step of respiration is glycolysis where the substrate is oxidized to, pyruvic acid after which this pyruvic acid enters into Kreb's cycle, (aerobic condition) or fermentation (anaerobic condition)., , Aman Singh Yadav, 9453643817
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Aman Singh Yadav, 9453643817, , Gʟʏᴄᴏʟʏsɪs [EMP Pᴀᴛʜᴡᴀʏ], Glycolysis is the metabolic process that serves as the foundation for both, aerobic and anaerobic cellular respiration. In glycolysis, glucose is, converted into pyruvate., It is the partial oxidation (breakdown) of glucose to 2 molecules of, pyruvic acid (C3H4O3) in the absence of Oxygen., ● It occurs in cytoplasm of all living organisms., ● Its scheme was given by Gustav Embden, Otto Meyerhof & J., Parnas. So it is also known as the EMP pathway., ● In anaerobes, it is the only process in respiration., ● In plants, glucose is derived from sucrose (end product of, photosynthesis) or from storage carbohydrates. Sucrose is, converted to glucose & fructose by an enzyme, invertase., These 2 monosaccharides readily enter the glycolytic pathway., Glucose & fructose are phosphorylated to form glucose-6-phosphate by, the enzyme hexokinase., It is then isomerised to produce fructose-6-phosphate., Subsequent steps of metabolism of glucose and fructose are the same., , Steps of glycolysis:, It includes 10 steps under the control of different enzymes., , Sᴛᴇᴘ I, The first step in glycolysis is the conversion of D-glucose into, glucose-6-phosphate. The enzyme that catalyzes this reaction is, hexokinase., , Sᴛᴇᴘ II, The second reaction of glycolysis is the rearrangement of glucose, 6-phosphate (G6P) into fructose 6-phosphate (F6P) by glucose, phosphate isomerase (Phosphoglucose Isomerase)., Aman Singh Yadav, 9453643817
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Aman Singh Yadav, 9453643817, , Mᴇᴛᴀʙᴏʟɪᴄ Fᴀᴛᴇ Oғ Gʟʏᴄᴏʟʏsɪs, The fate of glycolysis depends upon the availability of oxygen in the cell., , In Presence of Oxygen, , In Absence of Oxygen, , The pyruvic acid enters the, mitochondrion and undergoes, complete oxidation of pyruvic acid to, CO2 and H2O., , The pyruvic acid will undergo, anaerobic respiration, , Fᴇʀᴍᴇɴᴛᴀᴛɪᴏɴ (Aɴᴀᴇʀᴏʙɪᴄ Rᴇsᴘɪʀᴀᴛɪᴏɴ), ● It is the incomplete oxidation of glucose under anaerobic, condition., ● It occurs in many prokaryotes and unicellular eukaryotes., ● It is of 2 types:, Alcoholic fermentation, Lactic acid fermentation, , Alcoholic Fermentation, ● It occurs in Fungi(Yeast) and some higher plants., ● In this type of fermentation the pyruvic acid is converted into, ethanol and carbon dioxide., ● It is completed in two steps, , Sᴛᴇᴘ I, The pyruvic acid is first decarboxylated to acetaldehyde and carbon dioxide., This reaction is catalysed by the enzyme Pyruvic acid decarboxylase., CH3COOH ------------> CH3CHO + CO2, Sᴛᴇᴘ II, , The acetaldehyde is further reduced to ethyl alcohol in presence of, enzyme alcohol dehydrogenase., Aman Singh Yadav, 9453643817
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Aman Singh Yadav, 9453643817, , CH3CHO + NADH + H+ --------> C2H5OH + NAD+, , Lactic Acid Fermentation, ● It occurs in muscle cells., ● In this type of fermentation the pyruvic acid is reduced to Lactic, acid by NADH + H+. This reaction is catalysed by Lactic acid, dehydrogenase, FMN and Zn2+ ions., ● CO2 is not produced here ., , Fermentation, , Drawbacks of fermentation, ● Energy production is limited., ● Less than 7% of the energy in glucose is released and not all of it is, trapped as high energy bonds of ATP., Aman Singh Yadav, 9453643817
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Aman Singh Yadav, 9453643817, , ● Hazardous products (acid or alcohol) are formed., , Aᴇʀᴏʙɪᴄ Rᴇsᴘɪʀᴀᴛɪᴏɴ, It is a complete oxidation of organic substances in the presence of, oxygen releasing CO2, water & energy., - It occurs in mitochondria., - For this, the pyruvate (final product of glycolysis) is transported from, the cytoplasm into the mitochondria., - The crucial events in aerobic respiration are:, ● Complete oxidation of pyruvate by stepwise removal of all the, hydrogen atoms, leaving 3CO2 molecules. It takes place in the, matrix of mitochondria., ● Passing on of electrons removed as part of H-atoms to molecular, O2 with simultaneous synthesis of ATP. It occurs on the inner, membrane of mitochondria., Pyruvate (pyruvic acid) enters the mitochondrial matrix and undergoes, oxidative decarboxylation in the presence of pyruvic dehydrogenase. It, needs coenzymes, NAD+ & Coenzyme A., During this process, 2 NADH molecules are produced from 2 pyruvic, acid molecules., , Acetyl CoA(2C) then enters the tricarboxylic acid (TCA) cycle., , Aman Singh Yadav, 9453643817
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Aman Singh Yadav, 9453643817, , Kreb's Cycle/ Citric Acid Cycle, , Summary equation of Krebs’ cycle:, , Thus, a glucose is broken down to give 6 CO2, 8 NADH+H+, 2 FADH2, and 2ATP., , Importance of Kreb's Cycle, 1. This is the major pathway for the formation of ATP molecules., 2. Many intermediate compounds of this cycle are used in the, synthesis of other biomolecules., , Aman Singh Yadav, 9453643817
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Aman Singh Yadav, 9453643817, , Eʟᴇᴄᴛʀᴏɴ Tʀᴀɴsᴘᴏʀᴛ Sʏsᴛᴇᴍ, &, Oxɪᴅᴀᴛɪᴠᴇ Pʜᴏsᴘʜᴏʀʏʟᴀᴛɪᴏɴ, Electron transport system (ETS) is the metabolic pathway present in the, inner mitochondrial membrane through which electrons pass from one, carrier to another., This is to release and utilize energy stored in NADH+H+ and FADH2, (formed during TCA cycle) by oxidation., ● The electrons are passed on to O2 to form H2O., ● Electrons from NADH are oxidised by an NADH dehydrogenase, (complex I)., ● Electrons are then transferred to ubiquinone (UQ) located within, the inner membrane. Ubiquinone also receives reducing, equivalents via FADH2 (complex II) that is generated during, oxidation of succinate in citric acid cycle., ● The reduced ubiquinone (ubiquinol or UQH2) is the oxidised with, the transfer of electrons to cytochrome c via cytochrome bc1, complex (complex III). Cytochrome c is a small protein attached to, the outer surface of the inner membrane. It acts as a mobile carrier, of electrons between complex III and IV., ● Complex IV (cytochrome c oxidase) contains cytochromes a & a3,, and 2 copper centres., ● When the electrons pass from one carrier to another via complex I, to IV, they are coupled to ATP synthase (complex V) for the ATP, production., , Aman Singh Yadav, 9453643817
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Aman Singh Yadav, 9453643817, , ● In aerobic respiration, the role of oxygen is limited to the terminal, stage. Yet, oxygen is vital since it drives the whole process by, removing hydrogen from the system. Oxygen acts as the final, hydrogen acceptor., , Oxɪᴅᴀᴛɪᴠᴇ Pʜᴏsᴘɢᴏʀʏʟᴀᴛɪᴏɴ, ● In respiration, energy of oxidation-reduction is utilised for the, phosphorylation. So this process is called oxidative, phosphorylation. It is not as photophosphorylation (Here, light, energy is utilised to produce proton gradient for phosphorylation)., ● The energy released during the ETS is utilized to synthesize ATP, by ATP synthase (complex V)., ● ATP synthase has two major components: F 1 & F0 ., ● F1 headpiece (peripheral membrane protein complex): Site for ATP, synthesis from ADP & inorganic phosphate., ● F0 (integral membrane protein complex): It forms a channel, through which protons cross the inner membrane. The passage of, protons is coupled to the catalytic site of the F1 component for ATP, production., , ● For each ATP produced, 2H + passes through F0 from the, intermembrane space to the matrix down the electrochemical, proton gradient., , Aman Singh Yadav, 9453643817
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Aman Singh Yadav, 9453643817, , Tʜᴇ Rᴇsᴘɪʀᴀᴛᴏʀʏ Bᴀʟᴀɴᴄᴇ Sʜᴇᴇᴛ, Net gain of ATP from each glucose molecule is calculated based on the, following assumptions:, • All steps in Glycolysis, TCA cycle & ETS occur sequentially and orderly., • The NADH synthesised in glycolysis is transferred into mitochondria and, undergoes oxidative phosphorylation., • Intermediates in the pathway are not used to synthesise other compounds., • Only glucose is being respired. Other alternative substrates are not entered, in the pathway at any stages., - Such assumptions are not valid because,, ●All pathways work simultaneously and do not take place one after another., ●Substrates enter the pathways and are withdrawn from it as and when, necessary., ● ATP is utilized as and when needed., ● Enzymatic rates are controlled by multiple means., - Such calculations are useful to appreciate the efficiency of the living system, in extraction and storing energy., Net gain of ATP molecules from one glucose molecule, Glycolysis, , 2ATP, 2NADH, , = 2ATP, = 6ATP, , Link Reaction, , 2NADH, , = 6ATP, , Kreb's Cycle, , 6NADH, 2FADH2, 2GTP, , = 18 ATP, = 4ATP, = 2ATP, , Total ATP, Upon oxidation, 1NADH yields 3ATP, and 1FADH2. yields, 2ATP, , = 38 ATP, 2 ATP molecules are spent for transporting 2, NADH molecules formed during glycolysis to, the mitochondria., Hence the net gain = 36 ATP molecules ., , Aman Singh Yadav, 9453643817
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Aman Singh Yadav, 9453643817, , Aᴍᴘʜɪʙᴏʟɪᴄ Pᴀᴛʜᴡᴀʏ, ● Glucose is the favoured substrate for respiration. So, all, carbohydrates are first converted to glucose for respiration.Other, substrates are also respired., ● Fats break down into glycerol & fatty acids. Fatty acids are, degraded to acetyl CoA and enter the pathway. Glycerolis, converted to PGAL and enters the pathway., ● Proteins are degraded by proteases into amino acids. Each amino, acid (after deamination) enters the pathway at some stage in the, Krebs’ cycle or as pyruvate or acetyl CoA., ● The respiratory pathway is generally considered as a catabolic, pathway. But it involves both anabolism (synthesis) and, catabolism, (breakdown). So it is better called as an amphibolic pathway., ● E.g. Fatty acids breakdown to acetyl CoA before entering the, respiratory pathway. But when the organism needs to synthesise, fatty acids, acetyl CoA withdraws from the respiratory pathway., Similarly, during breakdown and synthesis of protein, respiratory, intermediates are involved., , Aman Singh Yadav, 9453643817
