LO29-细胞内代谢.docx

X Hello and welcome! In this online session,you will learn about cellular metabolism in the module:Metabolism. Page 1/44 School of Biological Sciences Learning Objectives At the end of the session,you should be able to: Describe the variety of ways cellular metabolic pathways may be organised....

X Hello and welcome! In this online session,you will learn about cellular metabolism in the module:Metabolism. Page 1/44 School of Biological Sciences Learning Objectives At the end of the session,you should be able to: Describe the variety of ways cellular metabolic pathways may be organised. Distinguish between catabolic and anabolic metabolism. Recognise the patterns connecting the metabolism of different macromolecules. Explain why compartmentalisation of metabolic pathways is necessary and distinguish between that at the levels of organelles and organs. Categorise the metabolic types found among living things based on the sources of energy,electron and carbon they can make use of. School of Biological Sciences In this LO,you will be introduced to the concept of cellular metabolism, which refers to how cells utilise various molecules to acquire, transform and store energy,and use that energy to do work. These functions are accomplished by thousands of reactions occurring in and around the cells of an organism, be it prokaryotic or eukaryotic. All the reactants,products,intermediates,enzymes -in other words,all the components involved in metabolism -are crowded in a small cell with an aqueous space of about 1000 μm³(or less for prokaryotes).Yet,they work in a highly coordinated and regulated manner. In the previous LO,we started our examination of metabolism from the extracellular digestion of foodstuff in the gastrointestinal system. You have learnt that complex food materials are broken down to comparatively simple molecules during extracellular metabolism. These are then transported through the epithelial cells of the Gl tract into the cellular environment. Within the cells,the processes and reactions classified as cellular metabolism start. School of Biological Sciences Within a cell,it is often possible to identify groups of reactions which always occur in specific sequences relative to each other. Such a sequence of reactions generally serves the purpose of producing a specific product from a given substrate. These sequences are what we refer to as "metabolic pathways". Most of the reactions in a metabolic pathway require enzymes for catalysis. For example,glycolysis is a metabolic pathway where glucose is the substrate from which the product pyruvate is produced through a sequence of 10 reactions,as shown in the figure here. Hence,it is unavoidable to show reactions when discussing metabolic pathways as examples.Do note that you are NOT expected to memorise them. Page 5/44 INANYANG TTCHNOLOCICAI UNTVERSTTY Within a cell,it isc of reactions which sequences relativt Such a sequence( the purpose of prc a given substrate. These sequences "metabolic pathw: Most of the reactit require enzymes f For example,glyco where glucose is tl product pyruvate sequence of 10 re. here, Hence,it is unavol discussing metabo note that you are N( them. Glucose (Substrate) Glucose 6 Phosphate Fructose Phosphate Fructose1. nate Dihydroxyacetone Phosphi 2(Glyceraldehyde 3 Phosphate) 2(1.3 Bisphosphoglycerate) 2(3 Phosphoglycerate) 2(2 Phospho glycerate) 2 Phosphoenolpyruvate 2 Pyruvate (Product) 1 2 3 4 5 6 7 8 9 10 In a metabolic pathway,the product of one reaction acts as the reactant (substrate)of the next reaction.Depending on how the reactions are arranged,a metabolic pathway can be classified as linear,branched, cyclic,or spiral. Select on each orpe given below to view how the reactions are arranged in that type of metabolic pathwey. Linear ① Branched ① Cyclic ① Spiral ① School of Biological Sciences In a metabolic pathway,the product of one reaction acts as the reactant (substrate)of the next reaction.Depending on how the reactions are arranged,a metabolic pathway can be classified as linear,branched,cyclic,or spiral. Select on each type given below to view how the reactions are arranged in that type ef metabolic pathwey. Branched Linear Pathway A三>B三>c>DE > F An example of a linear pathway is glycolysis,which was shown in the previous page. Page 6/44 School of Biological Sciences In a metabolic pathway,the product of one reaction acts as the reactant (substrate)of the next reaction.Depending on how the reactions are arranged,a metabolic pathway can be classified as linear,branched,cyclic,or spiral. Select on each orpe given below to view how the reactions are arranged in that type of metabolic pathwey. Linear ① Branched Branched Pathway (convergent) E>G >| Cyclic ① Spiral ① Branched Pathway (divergent) A三>日 A branched pathway can either be convergent or divergent,as shown. School of Biological Sciences In a metabolic pathway,the product of one reaction acts as the reactant (substrate)of the next reaction.Depending on how the reactions are arranged,a metabolic pathway can be classified as linear,branched,cyclic,or spiral. Select on each orpe given below to view how the reactions are arranged in that type of metabolic pathwey. A cyclic pathway is arranged in a circular manner,generating a product (e.g.H)that can be fed back to be the substrate to start the next cycle with an injection of new A. School of Biological Sciences In a metabolic pathway,the product of one reaction acts as the reactant (substrate)of the next reaction.Depending on how the reactions are arranged,a metabolic pathway can be classified as linear,branched,cyclic,or spiral. Select on each orpe given below to view how the reactions are arranged in that type of metabolic pathwey. remaining the same product. Page 6/44 A given metabolic pathway can also be classified based on the overall biochemical purpose,as either catabolic or anabolic. Catabolism means "breaking down"while anabolism means "building up". Select on each tab to know more about each type of metabolic pathwey. Catabolic Pathway ④ Anabolic Pathway ④ 部 NANYANG TECHNOLOGICAL UNIVERSITY School of Biological Sciences A given metabolic pathway can also be classified based on the overall biochemical purpose,as either catabolic or anabolic. Catabolism means "breaking down"while anabolism means "building up". each tab to know about each type of metabolic pathway ules Catabolic Pathway ④ es Catabolic pathways are pathways in which large molecules are broken down to smaller molecules, accompanied by a release of energy. Energy is generally stored in the form of ATP,NADH,NADPH,or FADHz. Catabolic pathways are generally oxidative pathways. Example:Glycolysis is a catabolic pathway in which glucose (6 carbon atoms)is oxidised to form two smaller molecules of pyruvate (3 carbon atoms)along with the production of ATP and NADH. Page 7144 School of Biological Sciences A given metabolic pathway can also be classified based on the overall biochemical purpose,as either catabolic or anabolic. Catabolism means "breaking down"while anabolism means "building up". Select on eoch tab to know more about each type of metabolic pathwey. Anabolic pathways are biosynthetic pathways,meaning small molecules are used to produce larger molecules by spending energy which is available from molecules like ATP and NADH. Anabolic pathways are generally reductive pathways. Example:Gluconeogenesis-an anabolic pathway in which pyruvate (3 carbon atoms)is used to form glucose (6 carbon atoms). Anabolic Pathway ④ MoYecules School of Biological Sciences A given metabolic pathway can also be classified based on the overall biochemical purpose,as either catabolic or anabolic. Catabolism means "breaking down"while anabolism means "building up". Select on eoch tab to know more about each type of metabolic pathwey. Anabolic pathways are biosynthetic pathways,meaning small molecules are used to produce larger molecules by spending energy which is available from molecules like ATP and NADH. Anabolic pathways are generally reductive pathways. Example:Gluconeogenesis-an anabolic pathway in which pyruvate (3 carbon atoms)is used to form glucose (6 carbon atoms). Now let us try to discern the beautiful pattern in overall cellular metabolism as shown here.Observe the relationship of the pathways with each other. Glutamate Urea cfrme 0mine cycle Argìnno Arǎning Saeciute Acnoooatyl-CoA Gnct Pywate 1.The catabolic pathways are convergent as shown in red, … Phenylalanine lsoleucine Alanine Phospholipidis Glucose ●Carbohydrates ●Amino Acids ●Lipids Acetyl-CoA …and anabolic pathways are divergent as shown in blue. Acetyl-CoA ● Carbohydrates ● Amino Acids ●Lipids Oxaloacetate Mevalomate Fafy Acids riacylglycerot Pyruvate Acepartate Cholestero CDP-Diacylgyicerol Caratenoid Glucose Arginine Mormone Cholesteryiesters Phospholipids Gyicogen 2.Some pathways are cyclic e.g.the tri-carboxylic acid (TCA)cycle and the urea cycle. Carbamoyl- Phosphate Glutamate Urea citrulline Fumarate TCA cycle Oxaloacetate Pyruvate 2.Some pathways are cyclic e.g.the tri-carboxylic acid (TCA)cycle and the urea cycle. Carbamoyl- Phosphate Urea Citrulline Urea cycle Arginino Succinate Oxaloacetate Pyruvate 3.All catabolic pathways shown here converge to an important metabolite acetyl CoA.Acetyl CoA has an acetyl group that is attached covalently with a coenzyme A molecule. Glycogen Phenylalanine Triacylglycerols Starch Sucrose lsoleycine Alanine Glucose Serine Leucine ●Carbohydrates ●Amino Acids Pyruvate Fattyacids ●Lipids Acetyl-CoA 和 NANYANG TECHNOLOGICAL UNIVERSITY School of Biological Sciences 3.All catabolic pathways shown here converge to an important metabolite acetyl CoA.Acetyl CoA has an acetyl group that is attached covalently with a coenzyme A molecule. Coenzyme A molecule 出。 A Acetyl group Acetyl CoA School of Biological Sciences 4.CoAstands for coenzyme A.It is a common non-protein molecule required by many enzymes,primarily to catalyze reactions that can transfer an acetyl group from one compound to another. Coenzyme A molecule H-6 Acetyl group Acetyl CoA Page 10/44 4.CoA stands for coenzyme A.It is a common non-protein molecule required by many enzymes,primarily to catalyze reactions that can transfer an acetyl group from one compound to another. Oxaloacetate L NAD 0 CH₂-( C Pyruvate- Coenzyme A HS-CoA NADH C H Acetyi CoA 0 CH₇--( s-caA citrate OH- -oo Coenzyme A HS-CoA 5.From acetyl CoA,anabolic pathways diverges,meaning acetyl CoA becomes the starting molecule for the TCA cycle and for many anabolic pathways. ● Carbohydrates ● Amino Acids ●Lpids TCA cycle Acetoacety-CoA Oxaloacetate Mevalonate Fatty Acids acylglycerols Cholesterol Carotenoid Gucose Homones Cholesterylesters Gyicogen 部 NANYANG TECHNOLOGICAL UNIVERSITY School of Biological Sciences When discussing metabolism,it is inevitable to show reactions or refer to the names of metabolic pathways. While we do NOT expect you to memorise them for this module,you should familiarise yourself with the names of some common metabolic pathways as they are mentioned. Metabolic Pathway Purpose Glycolysis Glucose is broken down to pyruvate TCA Cycle or Kreb Cycle Acetyl CoA is oxidized to CO₂ Glycogenolysis Glycogen is broken down to glucose Glycogenesis Glycogen is synthesized from glucose Fatty Acid Oxidation Fatty acids are oxidized sequentially to form acetyl CoA Fatty Acid Synthesis Fatty acids are synthesized sequentially from acetyl CoA Amino Acid Oxidation Surplus amino acids (beyond the needs of protein synthesis) are degraded to ammonia and a-keto acid Urea Cycle Toxic ammonium ion (formed during amino acid oxidation)is removed Page 11/44 部 NANYANG TECHNOLOGICAL UNIVERSITY School of Biological Sciences Try to observe the flow of sequence of reactions to gain an awareness of the purpose of the pathway, Metabolic Pathway Purpose Glycolysis Glucose is broken down to pyruvate TCA Cycle or Kreb Cycle Acetyl CoA is oxidized to CO₂ Glycogenolysis Glycogen is broken down to glucose Glycogenesis Glycogen is synthesized from glucose Fatty Acid Oxidation Fatty acids are oxidized sequentially to form acetyl CoA Fatty Acid Synthesis Fatty acids are synthesized sequentially from acetyl CoA Amino Acid Oxidation Surplus amino acids (beyond the needs of protein synthesis) are degraded to ammonia and a-keto acid Urea Cycle Toxic ammonium ion (formed during amino acid oxidation)is removed Page 11/44 School of Biological Sciences Prokaryotic organisms are made of simple cells having very little subcellular structures. Almost all metabolic pathways in prokaryotes occur in the cytoplasm,with some occurring across the cell membrane. than in prokaryotes. A more sophisticated organisation for metabolism can therefore be achieved in a eukaryotic cell through the use of organelles such as mitochondrion,chloroplast, endoplasmic reticulum,nudeus and so on as compartments. This feature of cellular compartmentalisation allows cells to develop strategies of metabolic regulation through physical separation accorded by the organelle structures. > < sembnis alpue810 ayi Aq popia)DE uoneiedas jojsAyd y8nouyp uonejnSau 3lloqou jo se/Sanens dojanap oi slia?smolle gdulo3 Agjr?jo aam 州 州 doV ON a DD pi ovN vo)-any HOVN, QvN aCV 面 mmoV 0w aeAnuAd avw wavt 山 QvN 0502n9 310AdVXOdd SKeMed 3loqeiaWJO uonesileiuauJedoD ALISSHAIN1 IVDDGTONHD1 ONVANVNI INANYANG TTCHNOLOCICAI UNTVERSTTY Compartmentalisation Of Metabolic Pathways EUKARYOTE o NAD Nudeus NAD AcetylCoA ADP Pyruvate NAD NADH* Cytoplasm Mitochondria This feature of cellular compartmelil allows cells to develop strategies of metabollc regulation through physical separation accorded by the organelle structures. > 部 NANYANG TECHNOLOGICAL UNIVERSITY School of Biological Sciences Inside cells,organelles have evolved to do specific metabolic function; Similarly cells have evolved into various types to form tissues and organs to perform specific metabolic functions. For some metabolic pathways,it can even be that they occur exclusively in specific organs and tissues. Thus the metabolic work load for the entire organism is divided among the organs. For example,skeletal muscles must move,so they should not be very heavy -hence it should not be used for storage. However,it must be supplied continuously with energy to “power”the movement. An organ which does not need to move should take responsibility for this storage of energy,e.g.the liver. 13/44 部 NANYANG TECHNOLOGICAL UNIVERSITY School of Biological Sciences Glucose (Carbohydrate) To help you see how cellular metabolism is coordinated and compartmentalised within a cell, we shall discuss the example of cellular respiration. Oxygen Cellular respiration is a metabolic process by which the chemical energy of organic substrates such as glucose is converted to the energy currency of ATP and reducing powers such as NADH,NADPH and FADH₂ It is a universal process occurring both in eukaryotes and in prokaryotes. Using glucose as the carbohydrate,the process can be summarised as: C₄ H₂O₆+6O₂>6CO₂+6H₂O+(free energy+heat) Where part of the free energy is coupled to formation of ATP molecules.Thus,respiration can be described as a catabolic process where glucose is fully oxidised to CO,with liberation and storage of free energy Page 17/44 Cellular respiration does not occur in one step. It is comprised of three metabolic pathways occurring in four phases: Glycolysis Pyruvate oxidation —Tricarboxylic acid (TCA)cycle —Electron transfer (transport)chain (ETC)coupled to ATP synthesis. In eukaryotic cells,these phases do not occur in one compartment (as do in prokaryotic cells cytoplasm)but at three cellular locations (cytoplasm, mitochondrial matrix,and inner mitochondrial membrane). The four phases of cellular respiration:glycolysis,pyruvate oxidation,the TCA cycle,and election transfer and ATP synthesis,are illustrated below: etspbum Gvcovss PRWATEQRIDATDW m Eketren trente and AIP eyrthet Q NANYANG TECIINOIOGICAI UNTVERSTTY GLUCOSE ADP GLUCOSE-6 Phosphate FRUCTOSE-6 Phosphate ATP ADP FRUC¹O⁵E-1.6 Biphosphate AAe Cytoplasm 2(Glyceraldehyde-3) Phosphate 2 NAD C 2.NADH Cedrene e 2ADP 2(1-3- 2AIP Biphosphoglycerate) GLYCOLYSIS 2(2-Phosphoglycerate) meee 2(Phospheenolpyuvate) 2(3-Phosphoglycerate 2ADP 2ATP 2(Pyruvate) Dihyroxyacetone .Phosphate Cell membrane NANYANG NRsm Cytosol intermembrane Space H* Pyruvate oxidation CO₂ School o!Biological Sciene OXIDATION NAD NADH tuction Mitochondrial Matrix CenymeA(CoA) Acetyl group AcetyICoA Pyruvate Dehydrogenase NANYANG NRsm a-Ketoglutarate a-Ketoglutarate dsbuthrceenase NAD Dhyarsfnsw NADH NAD* GDP+Pi< GTP FAD Mitochondrial Matrix whe* FADH Dahyeheemsg Oxaloacetate Acetyl-CoA NANYANG (CAI Electron transfer and ATP synthesis NAD' MITOCHONDRIAL MATRIX Cemplek 1 e FD FADH ATP rYnthare INTERMEMBRANE SPACE CYTOPLASM School of Biological Sciences Glycolysis is the metabolic pathway which converts a glucose molecule to two pyruvate molecules in the cytoplasm through a series of ten reactions catalysed by ten enzymes. Along the way,two molecules of NAD+are reduced to NADH.In addition,two molecules of ADP are phosphorylated to two molecules of ATP. Thus,the net reaction of glycolysis for glucose is: C₆ H1₂O₆+2ADP+2Pi+2NAD⁴->2C₃ H₄O₃(Pyruvate)+2ATP+2NADH+2H⁴+2H₂O NANYANG 螃歌微常 Cytosol Intermembrane Space H' Pyruvate Oxidation co, School o!Biologital Science PYRUVATE OXIDATION NAD+ NADH luctien He+ Mitochondrial Matrix oinymeA(CoA) Acetylsroup AcetylCoA Pyruvate Dehydrogenase The product of glycolysis:pyruvate,can be channeled to one of the 4 options of metabolism below.This is Pyruvate Co₂ Acetyi-CoA Further Oxidation Pyruvate Oxidation: Pyruvate forms acetyl CoA.This happens in plants,animals, bacteria,under aerobic condition. Page 21/44 NADH NAD* Lactate Lactate fermentation: Pyruvate forms lactate.This happens in red blood cells, highly active muscles, bacteria,under oxygen limiting (anaerobic) conditions. CO₂ Acetaldehyde NADH NAD° Ethanol Ethanol fermentation: Pyruvate forms ethanol.This happens in yeast and some bacteria under anaerobic conditions. Glucose Gluconeogenesis: Pyruvate goes into anabolic pathway to form back glucose. School of Biological Sciences The oxidation of pyruvate to produce acetyl-CoA is a crucial reaction in the second phase of cellular respiration that"commits"the pyruvate to enter into the third phase. A pyruvate molecule is transported from the cytoplasm to the mitochondrial matrix.There,one of the three carbon atoms of pyruvate is cleaved and released as CO2. The outcome of this reaction is that pyruvate is oxidized (by losing two electrons and two protons),NAD+is reduced and the remaining acetyl group is attached to CoA,forming acetyl-CoA. NANYANG 螃歌微常 Cytosol Intermembrane Space H' Pyruvate Oxidation co₂ School o!Biological Science PYRUVATE OXIDATION NAD+ NADH luctien He+ Mitochondrial Matrix oinymeA(CoA) Acetylsroup AcetylCoA Pyruvate Dehydrogenase Pyrwate DAyenoserse Page 22/44 School of Biological Sciences The TCA cycle,also called the citric acid cydle or the Kreb's cycle,is a cyclic pathway that consists of several reaction steps which are mostly oxidative in nature,and occurs in the mitochondrial matrix. The cyde"starts"with the 2-carbon acetyl group of acetyl-CoA combining with a 4-carbon molecule (oxaloacetic acid,OAA)resulting in a 6-carbon molecule,citric acid (TCA). The resulting citrate in the first reaction of the cycle undergoes a sequence of oxidative reactions whereby two carbon molecules are oxidized to COz and the OAA molecule is regenerated.This completes one turn of the cycle and allows another turn to start. NANYANG NRsm Intermembrane Space Succinyl-CoA Suednyl-CoA D-isocitrate Citate Mitochondrial Matrix yoen FADH, Dnhansomsg Oxaloacetate NAD' Malate Fumarate Acetyl-CoA School of Biological Sciences If we do an accounting of the input and the output of the TCA cycle from 1 glucose molecule,we will need to count 2 cycles because 1 glucose generates 2 pyruvate molecules and hence 2 acetyl coA (to enter the cycle twice). The inputs and outputs for two turns of the cycle are shown in the table below. Note that both ATP and reducing powers are(NADH,FADH2)generated as a result of these 2 turns of TCA. INPUT OUTPUT 2 Acetyl groups 4 CO₂ 6 NAD* 6 NADH+H+ 2 FAD 2FADH₂ 2GDP+2Pi 2 ATP School of Biological Sciences If we do an accounting of the input and the output of the TCA cycle from 1 glucose molecule,we will need to count 2 cycles because 1 glucose generates 2 pyruvate molecules and hence 2 acetyl coA (to enter the cycle twice). The inputs and outputs for two turns of the cycle are shown in the table below. Note that both ATP and reducing powers are(NADH,FADH2)generated as a result of these 2 turns of TCA. INPUT OUTPUT 2 Acetyl groups 4 CO₂ 6 NAD* 6 NADH+H+ If we do an accounting of the input and the output of the TCA cycle from 1 glucose molecule,we will need to count 2 cycles because 1 glucose generates 2 pyruvate molecules and hence 2 acetyl coA(to enter the cycle twice). The inputs and outputs for two turns of the cycle are shown in the table below. Note that both ATP and reducing powers(NADH,FADH)are generated as a result of these 2 turns of TCA School of Biological Sciences In this final phase of cellular respiration,NADH and FADHz molecules are oxidised,releasing electrons. The free energy generated from oxidation of NADH and FADHzis used to make more ATP. The phase is divided into three parts:electron transfer chain,formation of proton gradient,and finally ATP synthesis. The electron transfer chain (ETC) NANYANG Use of proton gradient and ATP synthesis Any concentration gradient is a potential source of free energy which can be coupled with endergonic processes. In mitochondria,the proton gradient created by the ETC across its inner membrane is dissipated through a protein complex in an amazingly ingenious way,and the released free energy is captured to synthesise ATP from ADP and Pi.This protein complex is called the ATP synthetase. .3.Use of proton gradient and ATP synthesis CYTOPLASM When we consider the metabolic type of an organism,its three primary requirements need to be examined. ENERGY SOURCE The form of energy that get transterred from the environment into the organism ELECTRON SOURCE Compound used by the organism to (ultimately generate its reducing powers (reductants),such as NADH and FADH? CARBON SOURCE Used to build up the physical body 部 NANYANG TECHNOLOGICAL UNIVERSITY School of Biological Sciences For example,in animals,organic materials such as carbohydrates can be the source of all three requirements, achieved through the overall reaction shown below; CH₂O(carbohydrates)+O₂>CO₂+H₂O As seen in the process of cellular respiration,the organic material carbohydrates satisfies all three requirements in the following ways: Energy in the form of chemical potential energy: the oxidation of carbohydrates generates energy as ATP. Electron source:the oxidation of (i.e.transfer of electrons from)carbohydrates produce reducing powers in the form of NADH and FADHz. Carbon source:breakdown of carbohydrates to smaller units generates a pool of carbon sources that can be drawn upon to make metabolic intermediates and various biomolecules. 部 NANYANG TECHNOLOGICAL UNIVERSITY School of Biological Sciences In photosynthetic organisms,the three requirements are coming from different sources. In green plants,for example,the requirements are satisfied by overall reaction shown below: CO₂+H₂O(in the presence of light)>CH₂O (carbohydrates)+O₂ Energy in the form of light:the source of energy that oxidises water in order to generate energy as ATP is light and also fix CO₂ . —Electron source:H₂O is the source of electrons needed to produce NADPH (the UGHT ENERGY SOURCL reducing power found primarily in plants). Carbon source:COzis fixed into organic compounds to become metabolic intermediates and for making various biomolecules of the plant body. co₂ CARBON SOURCE Based on the combination of these three primary requirements that define the metabolic types,organisms There aretwo major groups: Autotrophs and Heterotrophs. Select each group to understand its defining features: Autotrophs ① Heterotrophs ① Smpleingests moleoule UGHT— CHEMICAL— SWPLENORGAHC WoLicuS H₂O- CO₂- ,Macromolecules · ENERGV Metabolic Work< M -CHEMICAL coMPuKGG HO →simple inget molecdes School of Biological Sciences Based on the combination of these three primary requirements that define the metabolic types,organisms There are two major groups: Autotrophs and Heterotrophs. 中/ZE ə&ed —O) sajoapou 一O²H 51n5310W 3INV98ONI 31dWIS -TVDIW3HD 1H9N Kiod (3)seM) sojpoojou'ɔjue8jout sydonolazaH pue sydonoinv :sdno18 lofeu omy ale aləyl "sdnoi8qns pue sdno18 oui payissepaie susjue8lo'sadAɔioqeaw aup auyəp yeyp sjuaweinbai Kuewyd aaiyr asoyr yo uoneuiquoɔayp uo pasea NNANG Photoautotrophs Photoautotrophs use energy from sun light to produce the energy currency ATP and to convert water (electron source)and carbon dioxide (carbon source)from the air into glucose by a process called Photosynthesis.From glucose,other intermediates are further generated for biosynthesis. Examples of photoautotrophs are:plants,algae,photosynthetic protists and cyanobacteria. NANYANG Chemoautotrophs Chemoautotrophs use energy from chemical compounds to produce ATP and reducing power,through a process called Chemosynthesis.The chemical reactions involve making use of simple inorganic compounds such as Hz,H₂S,NH₃and Fe++as electron sources,leading to their oxidation. Examples of chemoautotrophs are:Some extremophiles such as bacteria and archaea found inside or near active volcano,hydrothermal vents in sea floor,hot water springs. School of Biological Sciences Based on the combination of these three primary requirements that define the metabolic types,organisms are classified into groups and subgroups. There are two major groups: Autotrophs and Heterotrophs. Based on the combination of these three primary requirements that define the metabolic types,organisms are classified into groups and subgroups. There are two major groups: Autotrophs and Heterotrophs. UGHT ¹ Macromolecules- CHEMICAL COAPLEX ORGANIC MOLECULES H₂O( O₂ wiode HETE Simple organic inorganic molecules (waste) Some Heterotrophs are versatile enough to use light together with chemical compounds.These heterotrophs, called photoheterotrophs,use light as energy source and rely on chemical compounds as electron and carbon sources. Examples of photoheterotrophs are: Purple photosynthetic bacteria -they use light as a source of energy,while using inorganic hydrogen,sulfide and/or sulfur as electron sources. Pitcher plant (found in tropical regions)-these plants are capable of normal photosynthesis using light,COzand water and are partially photoautotrophs.However,they are also carnivorous,feeding on small insects,hence taking on photoheterotrophic metabolism. NANYANG Chemoheterotrophs Chemoheterotrophs make use chemical compounds for all three requirements -energy, electrons,and carbon,as depicted in the process of cellular respiration.Examples of chemoheterotrophs are:parasites,most bacteria,all fungi,most protozoa,and all animals (including humans). In this section,you need to take home the following messages: 1.Cellular metabolism in living organisms consists of a complex network of metabolic pathways. 2.The chemistry of life is organised into metabolic pathways,which may have linear,branched,cyclic or looped arrangements 3.Compartmentalisation of metabolic pathways in organelles and sharing them among the organs are two important features of metabolism in eukaryotic organisms. School of Biological Sciences In this section,you need to take home the following messages: 4.Cellular respiration demonstrates how metabolism is coordinated within a cell, with metabolic pathways distributed into 4 phases and occurring at different sites (cytoplasm,mitochondrial matrix, inner membrane and intermembrane space). 5.The metabolism of organisms is classified according to how the three requirements of energy,electron source and carbon source are fulfilled. 6.They can be broadly classified as autotrophs or heterotrophs,and further sub-classified into Photoautotrophs/Chemoautotrophs and Photoheterotrophs/Chemoheterotrophs respectively.