aerobiosis 1

8/10/2019 Aerobiosis 1

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Respiration


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Importance of Respiration and EnergyRespiration : a process of breaking down of foodmolecules with the liberation of energy in the form of ATP.Energy required for various activities :

1)In anabolic reactions (building or synthesis ofsubstances)

2) Active transport

3)Contraction of muscles4)Transmission of impulse5)bioluminescence


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Energy Carrier : ATP

Structure of ATP


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Energy Carrier : ATP ATP is a nucleotide consisting adenine , ribose andthree phosphate joined by covalent bonds. ATP is hydrolysed into adenosine diphosphate (ADP)

and inorganic phosphate, energy is released. (30.6 kJ).This reaction is a hydrolysis reaction and requires water.The enzyme ATPase catalyses this reaction.


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Energy Carrier : ATP


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Energy Carrier : ATP The process of adding inorganicphosphates to ADP is known asphosphorylation . ATP can be produced in three different ways

a) Substrate-level phosphorylation.b) Oxidative phosphorylation.c) Photophosphorylation.


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Substrate level phosphorylationThe formation of a bond between ADP and phosphateby directly transfering a phosphate group from a high-

level molecule to ADP to form ATP.eg.a) PGAL + ADP PGA + ATPb) GTP + ADP creatine + ATPc) creatine phosphate + ADP creatine

+ ATP


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Substrate level phosphorylationCharacteristics:a) it is catalysed by a transferase

(phosphorylase)b) it does not require oxygenc) it can occur in cytoplasm, nucleus or

mitochondrion


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Substrate-level phosphorylation:Some ATP is made by direct enzymatic transfer of a phophate group from asubstrate to ADP. The phosphate donour in this case is PEP, which isformed during glycolysis


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Oxidative phosphorylationIs the formation of ATP from ADP and phosphateusing the energy comes from the oxidation of organicmolecules during respiration.Oxygen is requiredOccurs inside the mitochondria (at the innermembrane), which involves the electron transport

system


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Photophosphorylation ATP is made using energy from

light.


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Energy Carrier : NADH NADH is a reduced form of NAD +

NAD+ is a dinucleotide (made from 2 nucleotides).It consist of adenine, 2 ribose, 2 phosphate,nicotinamide and a H atom.

NAD+

is derived from the vitamin niacin or B 3 Niacin can be obtained from meat, wholemeal bread, yeast extract and liver.3 ATP molecules are formed for every NADH that

enters the ETC


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Energy Carrier : NADH


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Energy Carrier : FADH 2 FADH2 is a reduced form of FAD.It consist of riboflavin (vitamin B 2), adenine, 2

phosphate and 2 hydrogen atoms.2 ATP molecules are formed for every FADH 2 thatenters the ETC.


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Energy Carrier : FADH 2


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Types of respiration

Aerobic respiration (aerobiosis) andanaerobic respiration ( anaerobiosis) Aerobic respiration occurs in livingcells in the presence of oxygen. Anaerobic respiration occurs in livingcells in the absence of oxygen .


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Aerobic respirationFour stages:1) Glycolysis

2) The link reaction (linkingglycolysis to the Krebs cycle)

3) Krebs cycle4) Electron transport system


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The link - the formation of acetyl CoA

When oxygen is available, pyruvate is transported intothe matrix of mitochondrion from the cytoplasmPyruvate (3C) is decarboxylated (removal of carbondioxide) and oxidised (removal of hydrogen atoms) toform a two-carbon acetate (2C)


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The link


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The formation of acetyl Co-AThe acetate combines with coenzyme A to form a two-carbon acetylcoenzyme A which then enters into theKrebs cycleTwo acetyl CoA molecules are formed from oneglucose molecule


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Krebs cycle/ Tricarboxylic cycle/ Citric acid

cycle Acetyl CoA (2C) combines with oxaloacetate (4C) toform citrate (6C)Citrate rearranges to form isocitrate (6C)Isocitrate is oxidised to form oxalosuccinate (6C).NAD+ is reduced to become NADHOxalosuccinate (6C) is decarboxylated (loses a CO 2)and is converted to -ketoglutarate


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Second oxidative-decarboxylation of -ketoglutaratetakes place and produces succinyl coenzyme A (4C),CO2 and NADHSubstrate level phosphorylation takes place. SuccinylCo-A is converted succinate (4C). The energy releasedis used for phosphorylation of GDP to form GTP.GTP transfers its phosphate group to ADP forming ATP


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Succinate is oxidised to fumarate (4C), two hydrogenatoms are transferred to FAD (flavin adenine

nucleotide) to form FADH 2 Fumarate becomes hydrated by addition of water isconverted to malate (4C)Malate is oxidised regenerating oxaloacetate (4C), andNAD+ is reduced to NADH.


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Formation of NADH, FADH 2, GTP and ATP Duringthe Kreb Cycle.

NADH is produced in 3 reactions when hydrogen atomis removed from the intermediate duringdehydrogenation catalysed by dehydrogenase.NAD+ acts as coenzyme to accept the hydrogen atom.FADH2 is produced when succinate is dehydrogenatedto fumarate catalysed by succinate dehydrogenase.


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Formation of NADH, FADH 2, GTP and ATP

During the Kreb Cycle. FAD is the prosthetic group of succinatedehydrogenase and acts as a cofactor to accept 2hydrogen atoms.GTP is formed at substrate-level phosphorylation fromGDP and inorganic phosphate when an intermediatereleases energy catalysed by an enzyme.

ATP can be formed from GTP with the help oftransferase. The phosphate group is transferred on ADP to form ATP. (substrate-level phosphorylation )


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Electron transport systemIt is a functional unit consisting of coenzymes in whichH+ and electrons are transferred from one coenzyme toanother and finally accepted by oxygen to form water At certain stage when the electron is transferred fromone coenzyme to another, enough energy is given out

to form ATPOne NADH + H + can form 3 ATP whereas one FADH 2 can form 2 ATP


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Electron transport system/ chain


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ChemiosmosisElectrons released by the oxidation of substrate in thematrix flows down the electron transport chainThe energy released is used to pump H + from thematrix into the intermembrane space. This builds up atransmembrane electro-chemical protons (H +)gradient


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The inner membrane of the mitochondrion isimpermeable to hydrogen ions. The gradient forces

hydrogen ions to diffuse through the ATP synthase.The potential energy is used to synthesise ATP from ADP and P i


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Role of NADH, FADH2, and ATP Synthase

in ETCThe role of FADH2 is to pass thehydrogen atom to the Second electroncarrier ( cytochrome reductase ) of ETCand 2 ATP can be produced.FAD is formed and can be used toaccept hydrogen atom for succinatedehydrogenase .


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Role of NADH, FADH2, and ATP Synthase

in ETC

The role of ATP synthase is acting as

enzyme to catalyse the formation of ATP from ADP and inorganicphosphate when hydrogen ion diffuse

across it in the cristae.


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The electron transport system uses high-energy electronsfrom the Krebs cycle to convert ADP into ATP


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ATP synthesis by chemiosmosis using the energy released in theElectron transport system


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The maximum ATP yield for cellular respiration in a eukaryotic cell


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Respiratory inhibitorsCyanide

is a competitive inhibitorBinds strongly to the ferric Fe3 + component ofcytochrome a 3 present in the cytochrome oxidase.Inhibits the terminal transfer of electron to oxygen.The whole process of oxidative phosphorylationcannot take place, so it prevents the formation of ATP


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Carbon monoxideIs a toxin gas.

combines tightly with haemoglobin. Once attached,the haemoglobin cannot carry oxygen, this leads tohypoxia ( a fall in partial pressure of oxygen in arterialblood) When no oxygen is carried to the cells, no oxidativephosphorylation can take place.Haemoglobin has a higher affinity for carbonmonoxide compared to oxygen.


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AnaerobiosisBreakdown of glucose with the production of energy inthe absence of oxygenTwo types: in plants and in animals


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Anaerobiosis in plants and yeast


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Anaerobiosis in muscle


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After anaerobic respiration, the lactic acid is convertedin the liver to form glucose or glycogen through theCori cycleThe oxygen needed to break down the lactic acid isknown as the oxygen debt


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Use of fermentation in industryFor production of alcoholic beveragesFor production of vinegar (ethanoic acid)

Used in making bread and spongy cookiesFor production of cheese and yoghurtFor production of monosodium glutamate (MSG)

aerobiosis 1

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