* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download ATP
Fatty acid synthesis wikipedia , lookup
Magnesium in biology wikipedia , lookup
Biosynthesis wikipedia , lookup
Butyric acid wikipedia , lookup
Signal transduction wikipedia , lookup
Size-exclusion chromatography wikipedia , lookup
Photosynthesis wikipedia , lookup
Mitochondrion wikipedia , lookup
Electron transport chain wikipedia , lookup
Phosphorylation wikipedia , lookup
Basal metabolic rate wikipedia , lookup
Microbial metabolism wikipedia , lookup
Fatty acid metabolism wikipedia , lookup
Light-dependent reactions wikipedia , lookup
Photosynthetic reaction centre wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Oxidative phosphorylation wikipedia , lookup
Citric acid cycle wikipedia , lookup
Chapter 16 Respiration Cellular (internal or tissue) Respiration - the metabolic processes within cells which release energy from glucose. Gaseous Exchange - the processes involved in obtaining the oxygen for respiration and the removal of gaseous wastes. Cellular Respiration can be divided into 3 stages: 1 glycolysis 2 Krebs (tricarboxylic acid) cycle 3 Electron (hydrogen) transport system 16.1 Adenosine triphosphate (ATP) ATP is the short-term energy store of all cells. It is easily transported and is therefore the universal energy carrier. Computer graphics representation of ATP 16.1.1 Structure of ATP Adenine + P AMP + P ADP + P ATP P=inorganic phosphate = H3PO4 16.1.2 Importance of ATP The energy stored in ATP is released when ATP is hydrolysed by enzymes into ADP Further hydrolysis of ADP into AMP releases a similar quantity of energy BUT hydrolysis of AMP releases much less energy than the other two The energy is stored in the molecule as a whole, although the breaking of the bonds initiates its release AMP & ADP may be reconverted to ATP by adding phosphate group(s) through the process called phosphorylation, e.g. 1.Photosynthetic phosphorylation - occurs during photosynthesis in chlorophyll containing cells 2.Oxidative phosphorylation - occurs during cellular respiration in all aerobic cells The addition of each phosphate molecule requires 30.6 kJ of energy. If less than this, energy cannot be stored as ATP but lost as heat. ATP is a means of transferring free energy from energy-rich compounds to cellular reactions requiring it. It is by far the most abundant and the most important energy transferring compound used by cells. 16.1.3 Uses of ATP An active cells may use as many as 2 million molecules of ATP every second ! ATP is a source of energy for: 1. Anabolic processes - build up macromolecules from component units, e.g. polysaccharide from monosaccharides, proteins from amino acids and DNA replication 2. Movement - e.g. muscle contraction, ciliary action and spindle formation in cell division 3. Active transport- move materials against a concentration gradient e.g. Na/K pumps 4. Secretion - form vesicles necessary in cell secretions 5. Activation of chemicals - make chemicals more reactive, e.g. phosphorylation of glucose 16.2 Glycolysis Break down glucose into 2 molecules of pyruvate (pyruvic acid), 2ATP & 2H atoms It occurs in all cells. In anaerobic respiration it is the only stage of respiration Stages of glycolysis: (in the cytoplasm) Stages of glycolysis: (in the cytoplasm) Each glucose molecule produces two molecules of glycerate 3-phosphate The energy yield is a net gain of 2 ATP and 2 pairs of H atoms Each pair of H atoms gives 3 ATP Total number of ATP is 8 Krebs Cycle 16.3 Krebs (tricarboxylic acid) cycle (in the mitochondrion) Majority of the energy from glucose is locked up in the pyruvate. Pyruvate enters the mitochondria and in the presence of oxygen, they are broken down into water and carbon dioxide. A total of 4 pairs of H atoms and 1 ATP are produced: 3 pairs of H atoms give 9 ATP 1 pair of H atoms give 2 ATP Total number of ATP = 38 3 pairs of H atoms give 9 ATP 1 pair of H atoms give 2 ATP 9 + 2 + 1 = 12 ATP + 3 ATP = 15 ATP 3ATP x 2 = 6 ATP + 2ATP (glycolysis) = 8 ATP 8 + 15x2 = 38 ATP 16.3.1 Importance of Krebs Cycle 1. It brings about the degradation of macromoelcules 2. It provides the reducing power for the electron transport system 3. It is an interconversion centre for making fatty acids, amino acids, chlorophyll, etc. 16.4 Electron transport system The electron transport system is the means by which energy from the Krebs cycle, in the form of hydrogen atoms, is converted to ATP The H atoms attached to the H-carriers NAD & FAD are transferred to a chain of other carriers at progressively lower energy levels. As the H atom pass from one carrier to the next, the energy released is used to produce ATP. The series of carriers is called the respiratory chain. The carriers include: NAD (nicotinamide adenine dinucleotide), FAD (Flavine adenine dinucleotide, coenzyme Q and iron-containing proteins (cytochromes) Oxidative phosphorylation: generation of ATP by H atoms in an electron transport system in which H atoms link with O atoms to form water. Oxygen is necessary as the final H acceptor. In its absence, anaerobic glycolysis can continue to provide energy for the cell. Cyanide poisons the enzyme cytochrome oxidase to stop aerobic respiration. 16.4.1 Mitochondria and oxidative phosphorylation Mitochondria are present in all eukaryotic cells. Highly active cells have numerous large mitochondria packed with cristae, e.g. Liver cells – for driving chemical reactions inside the body Striated muscles – muscle contraction Sperm tails – provide energy to propel the sperm Nerve cells – numerous mitochondria are present to provide energy needed for synapses to function Intestinal epithelial cells – mitochondria beneath the microvilli to release energy for the absorption of digested food by active transport Inner membrane of the mitochondrion is folded to form cristae which are lined with stalked particles for oxidative phosphorylation while the enzymes of the Krebs Cycle are mostly found in the matrix of the mitochondrion. Portions of a mitochondrion matrix Outer membrane Intermembrane space Inner membrane Stalked particle Intermembrane space The synthesis of ATP according to the chemi-osmotic theory of Mitchell 16.5 Anaerobic respiration Obligate anaerobes: Organisms must respire anaerobically, they die in the presence of oxygen Facultative anaerobes: Organisms respire aerobically, but can carry out anaerobic respiration if lack of oxygen Without oxygen, H atoms accumulate and prevent glycolysis to continue. H atoms are accepted by the pyruvate formed at the end of glycolysis to give either alcohol or lactate, in a process called fermentation. 16.5.1 Alcoholic fermentation pyruvate ethanal + CO2 ethanal + 2H (from NAD+) ethanol 16.5.2 Lactate fermentation pyruvate + 2H (from NAD+) lactic acid (lactate) Lactic acid can be oxidised by oxygen to release energy OR resynthesized into carbohydrate OR excreted Examples: muscles during heavy exercise, baby during & immediately following birth Oxygen Debt: Lactic acid causes muscle fatigue, Oxygen debt is the extra oxygen to remove all the lactic acid after heavy exercise to CO2, H2O or glucose in the liver, and To replenish the depleted stores of ATP & oxygen in the tissue 16.6 Comparison of energy yields Aerobic Respiration: Two sources 1 direct phosphorylation 2 indirect oxidative phosphorylation of hydrogen ions from glucose breakdown TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers No. of Total No. ATP of ATP molecules molecules Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers No. of Total No. ATP of ATP molecules molecules Glycolysis Pyruvate acetyl CoA Krebs Cycle Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers Glycolysis 2NADH2+ No. of Total No. ATP of ATP molecules molecules Pyruvate acetyl CoA Krebs Cycle Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers Glycolysis 2NADH2+ No. of Total No. ATP of ATP molecules molecules Pyruvate 2NADH2+ acetyl CoA Krebs Cycle Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers Glycolysis 2NADH2+ No. of Total No. ATP of ATP molecules molecules Pyruvate 2NADH2+ acetyl CoA Krebs Cycle 3 NADH2+ x 2 1 FADH2+ x 2 Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers Glycolysis 2NADH2+ No. of Total No. ATP of ATP molecules molecules 2x3=6 Pyruvate 2NADH2+ acetyl CoA Krebs Cycle 3 NADH2+ x 2 1 FADH2+ x 2 Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers Glycolysis 2NADH2+ 2x3=6 Pyruvate 2NADH2+ acetyl CoA 2x3=6 Krebs Cycle No. of Total No. ATP of ATP molecules molecules 3 NADH2+ x 2 1 FADH2+ x 2 Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers Glycolysis 2NADH2+ 2x3=6 Pyruvate 2NADH2+ acetyl CoA 2x3=6 Krebs Cycle No. of Total No. ATP of ATP molecules molecules 3 NADH2+ x 2 6 x 3 = 18 1 FADH2+ x 2 2 x 2 = 4 Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers No. of Total No. ATP of ATP molecules molecules Glycolysis 2NADH2+ 2x3=6 2 Pyruvate 2NADH2+ acetyl CoA 2x3=6 Krebs Cycle 3 NADH2+ x 2 6 x 3 = 18 1 FADH2+ x 2 2 x 2 = 4 Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers No. of Total No. ATP of ATP molecules molecules Glycolysis 2NADH2+ 2x3=6 2 Pyruvate 2NADH2+ acetyl CoA 2x3=6 0 Krebs Cycle 3 NADH2+ x 2 6 x 3 = 18 1 FADH2+ x 2 2 x 2 = 4 Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers No. of Total No. ATP of ATP molecules molecules Glycolysis 2NADH2+ 2x3=6 2 Pyruvate 2NADH2+ acetyl CoA 2x3=6 0 Krebs Cycle 3 NADH2+ x 2 6 x 3 = 18 1 x 2 1 FADH2+ x 2 2 x 2 = 4 Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers No. of Total No. ATP of ATP molecules molecules Glycolysis 2NADH2+ 2x3=6 2 Pyruvate 2NADH2+ acetyl CoA 2x3=6 0 Krebs Cycle 8 3 NADH2+ x 2 6 x 3 = 18 1 x 2 1 FADH2+ x 2 2 x 2 = 4 Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers No. of Total No. ATP of ATP molecules molecules Glycolysis 2NADH2+ 2x3=6 2 8 Pyruvate 2NADH2+ acetyl CoA 2x3=6 0 6 Krebs Cycle 3 NADH2+ x 2 6 x 3 = 18 1 x 2 1 FADH2+ x 2 2 x 2 = 4 Total ATP 38 TABLE 16.1 ATP yield during aerobic respiration of one molecule of glucose Respiratory process No.of reduced H No.of ATP carrier molecules molecules formed formed from reduced H carriers No. of Total No. ATP of ATP molecules molecules Glycolysis 2NADH2+ 2x3=6 2 8 Pyruvate 2NADH2+ acetyl CoA 2x3=6 0 6 Krebs Cycle 3 NADH2+ x 2 6 x 3 = 18 1 x 2 1 FADH2+ x 2 2 x 2 = 4 24 Total ATP 38 The total of 38 ATP produced represents the maximum possible yield; the actual yield may be different depending upon the conditions in any one cell at the time. For example, the NADH + H+ in glycolysis may enter the mitochondria in two, indirect ways. This may give only 4 ATP instead of 6 ATP. Total ATP = 36 Efficiency = energy by glycolysis & Krebs Cycle / glucose molecule = 40 % Anaerobic Respiration: All NADH + H+ are not available for oxidative phosphorylation. Only 2 ATPs are released. Efficiency = 2% BUT energy is locked up in lactate or ethanol 16.7 Alternative respiratory substrates Sugars are not the only material which can be oxidised by cells to release energy. Both fats and proteins may, in certain circumstances, be used as respiratory substrates, without first being converted to carbohydrate. 16.7.1 Respiration of fat FAT fatty acids + glycerol Glycerol glyceraldehyde 3-phosphate 16.7.1 Respiration of fat FAT fatty acids + glycerol Glycerol glyceraldehyde 3-phosphate glycolysis 16.7.1 Respiration of fat FAT fatty acids + glycerol Glycerol glyceraldehyde 3-phosphate glycolysis Fatty acids broken into parts of 2-C compound - 2C 16.7.1 Respiration of fat FAT fatty acids + glycerol Glycerol glyceraldehyde 3-phosphate glycolysis Fatty acids broken into parts of 2-C compound acetyl CoA in mitochondria. 16.7.1 Respiration of fat FAT fatty acids + glycerol Glycerol glyceraldehyde 3-phosphate glycolysis Fatty acids broken into parts of 2-C compound acetyl CoA in mitochondria Fat oxidation produces a lot of H atoms which release ATP through the electron carrier system. It is twice as much as energy as the same mass of carbohydrates. 16.7.2 Respiration of protein Protein is only used in cases of starvation. Proteins amino acids carbohydrate + amino group 16.7.2 Respiration of protein Protein is only used in cases of starvation. Proteins amino acids carbohydrate + amino group aspartic acid oxaloacetate glutamic acid -ketoglutarate alanine pyruvate 16.8 Respiratory quotients (not required) R.Q. = CO2 evolved / O2 consumed a measure of the ratio of carbon dioxide evolved by an organism to the oxygen consumed, over a certain period For glucose oxidation: R Q = 1 C6H12O6 + 6O2 6CO2 + 6H2O + energy For fat oxidation: RQ 1 For protein oxidation: R Q = 0.9 Organisms rarely, if ever, respire a single food substance, nor are substances always completely oxidized. Experimental R Q values therefore do not give the exact nature of the material being respired. Most resting animals have R Qs between 0.8 and 0.9 (a mixture of carbohydrate & fat metabolism, assuming proteins are only respired during starvation).