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RESPIRATION What is Respiration? Process whereby energy stored in complex organic molecules is used to make ATP. Occurs in living cells. All living organisms need energy to drive their biological processes. All reactions that take place within organism are known collectively asmetabolism: Anabolic – Building large molecules Catabolic – Breaking large molecules into smaller ones. Energy from catabolic reactions is released in the form of heat. This is useful because >>>> Metabolic reactions are controlled by enzymes. Organisms needed to maintain a suitable temperature to allow enzyme actions to proceed at the speed that will sustain life. Metabolic processes that need energy include: Active Transport Moving ions and molecules against the concentration gradient. Cell membranes have sodium-potassium pumps which maintain the resting potential. Secretion Large molecules made in some cells are exported by exocytosis. Endocytosis Bulk movement of large molecules into the cells. Synthesis of large molecules into smaller ones E.g. Proteins to Amino acids, Steroids from Cholesterol, Cellulose from Beta Glucose. (All Anabolic) Replication of DNA and Synthesis of Organelles Movement E.g. Movement of bacteria flagella, eukaryotic cilia and undulipodia. E.g. Muscle contraction E.g. Microtubules motors that move organelles around inside the cell. Activation of Chemicals Glucose is phosphorylated at the beginning of respiration. This is more unstable and can be broken down to release energy. Where does Energy come from? Phooautotrophs Plants, Protoctists (Eukaryotic organism), and some bacteria. Use sunlight energy to make large, inorganic moleculesthat contain chemical potential energy. This chemical potential energy is used by consumers and decomposers (e.g. fungi, animals, and most bacteria). StudyingTeacher Respiration then releases this energy. This energy is used to phosphorylate ADP to make ATP. This phosphorylation also transfers energy to the ATP molecule. ATP – Structure and Role ATP = Phosphorylated Nucleotide Structure of ATP Adenine P P Adenine P Ribose Adenosine Adenosine Monophosphate Adenosine diphosphate Adenosine triphosphate ATP =Universal energy currency Provides immediate source of energy in biological processes Hydrolysed to ADP (adenosine diphosphate) and P (inorganic phosphate). This releases 30.6 KJ energy per mol. Energy is immediately available in small, manageable amounts that will not damage the cell and will not be wasted. Hydrolysis of ATP is coupled with a synthesis reaction, such as DNA replication or protein synthesis, in cells. These synthesis reactions require energy from ATP. Energy can never be created or destroyed, so ENERGY IS NEVER PRODUCED. Respiration RELEASES ENERGY to PRODUCE ATP. Energy released for use by cells to do work HYDROLYSIS ATP ATP Synthase ADP + P CONDENSATION StudyingTeacher Energy released from organic substrate, during respiration GLYCOLYSIS Glycolysis Anaerobic Pyruvate Aerobic LINK REACTION Lactate fermentation(Mammalian) Ethanol fermentation(Yeast) Pyruvate Acetyl CoA CO2 tissue) KREBS CYCLE Lactate CO2 Ethanol + Carbon Dioxide OXIDATIVE PHOSPHORYLATION Coenzymes During glycolysis, the link reaction and Krebs cycle – HYDROGEN ATOMS ARE REMOVED FROM SUBSTRATE MOLECULES OXIDATION REACTIONS. Enzymes are not very good at catalysing oxidation and reduction reactions. Coenzymes are needed to help them carry out the oxidation reactions in respiration. Oxidation and reduction reactions are coupled - when one substrate becomes oxidised, the other becomes reduced. In respiration, the coenzyme becomes reduced so the substrate becomes oxidised.The reduced coenzyme later becomes reoxidised so it can be used again. Coenzymes carry hydrogen ATOMS which later become protons or electrons. (DO NOT SAY THEY CARRY HYDROGEN IONS). NAD – (Nicotinamide Adenine Dinucleotide) Organic, non-protein molecule. Helps dehydrogenase enzymes to carry out oxidation reactions. Accepts two hydrogen atoms with their electrons – REDUCED Loses electrons – OXIDISED Operates during glycolysis, link reaction, krebs cycle, and during the anaerobic and lactate pathways. Coenzyme A (CoA) Accepts acetate to become acetylcoenzyme A to be carried to the Krebs cycle. FAD Tightly bound to the dehydrogenase enzyme that is embedded in the intermembrane. Hydrogen atoms accepted by FAD are passed back into the mitochondrial membrane. StudyingTeacher GLYCOLYSIS Occurs in the Cytoplasm of all living things that respire (Prokaryote and Eukaryote). Four stages: Phosphorylation, Splitting of hexose 1,6-biphosphate, Oxidation of triose phosphate, conversion of triose phosphate to pyruvate. Glucose (6C) One ATP molecule is hydrolysed and the phosphate group released is attached to the glucose molecule at carbon 6 to form glucose 6-phosphate. Glucose molecules are stable and need to be activated before they can split into two. ATP Glucose 6-phosphate Glucose 6-phosphate is changed to fructose 6-phosphate. ATP is hydrolysed and the phosphate group released is attached to the 6-phosphate at Carbon 1. Energy from the hydrolysed ATP molecules activates the hexose sugar and prevents it from being transported out of the cell. Fructose 6-phosphate ATP Activated, phosphorylated sugar = hexose 1,6biphosphate Two hydrogen atoms removed from each triose phosphate molecule. This involves dehydrogenase enzymes which are aided by NAD. (Hydrogen acceptor) Triose phosphate (3C) ATP Reduced NAD Intermediate compound (3C) ATP Pyruvate (3C) Hexose 1,6-biphosphate Each molecule of Hexose 1,6biphosphate is split into two molecules of triose phosphate – Each with one phosphate attached. Two molucules of ADP are phosphorylated to two molecules of ATP (by substrate level phosphorylation). Triose phosphate (3C) ATP Reduced NAD NAD combines with hydrogen atoms, becoming reduced NAD. Two molecules of ATP formed – Substrate level phosphorylation Intermediate compound (3C) ATP Pyruvate (3C) Products of Glycolysis: Two molecules of ATP. Net Gain of ATP = Two molecules. Two molecules of Reduced NAD – will carry hydrogen atoms to inner mitochondrial membranes, and used to generate more ATP during oxidative phosphorylation. Two molecules of Pyruvate – Actively transported into mitochondrial matrix, or changed to lactate or ethanol in cytoplasm (in the absence of oxygen) StudyingTeacher The LINK REACTION and KREBS CYCLE Pyruvate produced during Glycolysis is transported across the outer and inner mitochondrial membrane to the matrix. Link Reaction – Pyruvate to Acetate Krebs Cycle – Acetate oxidised Pyruvate Dehydrogenase removes hydrogen atoms from pyruvate. PyruvateHydrogen Dehydrogenase NAD accepts atoms Pyruvate hydrogenase removes carboxyl group from pyruvate, which eventually becomes CO2 Pyruvate (3C) Reduced NAD removes hydrogen atoms from pyruvate. Acetate from acetyl coenzyme A joins with oxaloacetate to form 6carbon citric acid. 4-carbon compound is further 2H dehydrogenated Reduced NAD and regenerates oxaloacetate. 4C Another molecule of Compound NAD is reduced. 2H CO2 Decarboxylation and dehydrogenation of pyruvate to acetate = enzyme-catalysed reactions CoA accepts Acetate to become Acetyl Coenzyme A. CoA carries Acetate to the Krebs cycle. Acetyl CoA (2C) Oxaloacetate (4C) Coenzyme A is released and becomes available to collect more acetate. Citrate (6C) CO2 Reduced FAD 4-carbon compound is changed into another 4carbon compound. A pair of hydrogen atoms is removed and accepted by the coenzyme FAD, which is reduced. 2H Reduced NAD 4C Compound ATP The pair of hydrogen atoms is accepted by a molecule of NAD, which becomes reduced. 5C Compound 4C Compound The 4-carbon compound is changed into another 4-carbon compound. A molecule of ADP is phosphorylated to produce a molecule of ATP = Substrate level phosphorylation. Citrate is decarboxylated, and dehydrogenated to form a 5carbon compound. 2H CO2 Reduced NAD The 5-carbon compound is decarboxylated and dehydrogenated to form a 4carbon compound and another molecule of reduced NAD One turn of the cycle for each molecule of acetate, which was made from one molecule of acetate – to turns of the cycle Although oxygen is not used in these stages, they won’t occur in the absence of oxygen, so they are aerobic. Other food substrates besides glucose can be respire…..d. Fatty acids are broken down to acetates and enter the Krebs cycle through CoA Amino acids can be deaminated and the rest of the molecule may enter Krebs cycle directly or may be changed to pyruvate or acetate, depending on the type of amino acid. StudyingTeacher Oxidative Phosphorylation and Chemiosmosis Involves electron carriers embedded in the inner mitochondrial membrane, which are folded into cristae, increasing surface area for electron carriers and ATP synthase enzymes. Reduced NAD and reduced FAD are reoxidised when they donate hydrogen atoms, which are split into protons and electrons: Protons Go to the Matrix Flow of protons = chemiosmosis Electron First electron carrier = NADH dehydrogenase. Electrons are passé along a chain of electron carriers and then donated to molecular oxygen – the final electron acceptor. CHEMIOSMOSIS: Flow of hydrogen ions (PROTONS) As electrons flow down the electron transport chain, energy is released and used by coenzymes associated with some of the electron carriers. This energy causes protons to be pumped across the intermembrane space via ion channels (which are associated with ATP synthase enzyme). Protons are always pumped into the intermembrane space because the energy is from electron flow. (Active transport energy is from ATP) This creates a proton gradient = pH gradient, and electrochemical gradient = potential energy build up in intermembrane space. OXIDATIVE PHOSPHORYLATION Formation of ATP by addition of inorganic phosphate to ADP. As protons flow through an ATP synthase enzyme, they drive the rotation of part of the enzyme and join ADP and Pi to form ATP. ATP made before oxidative phosphorylation: 2 molecules during glycolysis by substrate level phosphorylation. 2 molecules made during krebs cycle by substrate level phosphorylation. ATP made DURING oxidative phosphorylation: ATP is made where the reduced NAD and FAD are reoxidised. NAD and FAD provide electrons to electron transport chain, to be used for oxidative phosphorylation. Reduced NAD also provides hydrogen ions that contribute to the build-up of proton gradient for chemiosmosis. Ten molecules of reduced NAD theoretically produces 26 molecules of ATP = One molecules of NAD produces 2.6 molecules of ATP. With ATP made during glycolysis and Krebs cycle, the total yield of ATP molecules, per molecule of glucose respired = 30. THEORETICAL YIELD OF ATP IS RARELY ACHIEVED BECAUSE: Some protons leak across mitochondrial membranes. Some ATP produced is used to actively transport pyruvate to mitochondria. Some ATP is used for the shuttle to bring hydrogen (in the cytoplasm) from reduced NAD made during glycolysis (into mitochondria). StudyingTeacher MITOCHONDRIA Found in Eukaryotic cells. The matrix – LINK REACTION and KREBS CYCLE. Contains the enzymes that catalyse these reactions Contains oxaloacetate that accepts the acetate from the link reaction. Molecules of NAD Mitochondrial DNA – Code for mitochondrial enzymes and other proteins. Mitochondrial ribosomes – where the proteins are assembled. The outer membrane Proteins – channels and carriers – allow passage of pyruvate. Other proteins are enzymes. The inner membrane Different lipid composition to outer membrane and impermeable to most small ions, including hydrogen ions = protons accumulate in intermembrane space = lower pH than the matrix. Folded into cristae for larger surface area. Has electron carriers and ATP synthase enzymes. Electron carriers Protein complexes Arranged in electron transport chain Each electron carrier is an enzyme, which are associated with cofactors (nonprotein haem group that contain an iron atom). Cofactors accept and donate electrons. Iron atoms become reduced by accepting an electron, and oxidised by donating an electron. Electron carriers = oxidoreductase enzymes – involved in oxidation and reduction reactions. Electron carriers – contain enzymes which pump protons into intermembranal space, using energy released from passage of electrons. ATP synthase enzyme Large and protruding from inner membrane into the matrix Stalked particles Allows protons to pass through them – from intermembrane space into matrix (chemiosmosis). StudyingTeacher StudyingTeacher Anaerobic respiration: Electron transport chain cannot function – Krebs cycle and Link reaction stop. Glycolysis becomes the only source of ATP. Glycolysis needs to keep operating – Reduced NAD has to be reoxidised. LACTATE FERMENTATION Occurs in mammalian tissue during vigorous activity. Reduced NAD must be oxidised to NAD. Pyruvate accepts hydrogen from reduced NAD. NAD is now reoxidised and available to accept more hydrogen atoms from glucose. ENZYME LACTATE DEHYDROGENASE catalyses the oxidation of reduced NAD, and the reduction of pyruvate to lactate. Lactate is carried away in the blood from the muscles to the liver. When more oxygen is available lactate may convert back to pyruvate to be used for Link reaction and Krebs cycle. Or recycled to glucose or glycogen. It is NOT the build-up of lactate that causes fatigue, but the reduction in the pH that will reduce enzyme activity. ALCOHOLIC (ETHANOL) FERMENTATION Yeast cells Each pyruvate molecule is decarboxylated (loses carbon dioxide molecule) and becomes ethanal. Enzyme – Pyruvate decarboxylase – has coenzyme thiamine diphosphate attached to it. Ethanal accepts hydrogen atoms from NAD which will become oxidised. The ethanal is reduced to ethanol. Reoxidised NAD will accept more hydrogen atoms from glucose in glycolysis. Yeast = Facultative anaerobe. Can survive without oxygen, and killed when ethanol builds up to 15%. Yeast = Grows faster in AEROBIC conditions. Enzyme names describe its role. E.g. Pyruvate decarboxylase – Removes carboxyl groups from its substrate pyruvate. Respiratory Substrates Is an organic substance that can be used for respiration. More protons = More ATP produced. More hydrogen atoms in a respiratory substrate = More ATP generated when the substrate is respired. More hydrogen atoms per mole of respiratory substance = More oxygen needed to respire that substance. CARBOHYDRATE [Cn(H2O)n] Some mammalian cells e.g. brain cells and red blood cells, only use glucose for respiration. Glycogen in animals and starch in plants hydrolyse to release glucose for respiration. StudyingTeacher Other monosaccharides, such as Fructose and Galactose, can be changed to glucose for respiration. Theoretical maximum energy yield for glucose = 2870kJ (permole) 30.6kJ produce 1 mol ATP Theoretically 1 mol of glucose should produce nearly 94 mol ATP. Actual yield is 30 mol ATP = 32% efficiency Remaining energy is released as heat – maintains suitable body temperature for enzyme-controlled reactions. PROTEIN Excess amino acids can be deaminated by the removal of amine group and conversion to urea. The rest of the molecule is changed to fat or glycogen which is later respired to release energy. When an organism is fasting, starvation or prolonged exercise – the protein from the muscle can be hydrolysed to amino acids, which can be respired. Some amino acids can be converted to pyruvate. Some amino acids can enter directly into the krebs cycle. Protein releases more energy than equivalent masses of carbohydrates. LIPIDS Triglycerides are hydrolysed by lipase to fatty acids and glycerol. Glycerol can be converted to glucose, and respired. Fatty acids cannot be respired. Fatty acids = long-chain hydrocarbons with a carboxylic acid group. In each molecule there is carbons and hydrogen atoms – source of many protons for oxidative phosphorylation so they produce a lot of ATP: Each fatty acid is combined with CoA using energy from the hydrolysis of a molecule of ATP to AMP and two inorganic phosphate. The fatty acid-CoA complex is transported o the mitochondrial matrix where it is broken down into 2-carbon acetyl groups that are attached to CoA. During this breakdown (by the beta-oxidation pathway) reduced NAD ad reduced FAD are formed. The acetyl groups are released from CoA and enter Krebs cycle – forms 3 reduced NAD, 1 reduced FAD, and 1 ATP. The NAD is reoxidised in oxidative phosphorylation producing large amounts of ATP by chemiosmosis. Fats and proteins an only be respired aerobically. They cannot undergo Glycolysis. StudyingTeacher