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Unit L Energy and Respiration

Unit L Energy and Respiration. What is Energy?. In science, the ability to do work Energy = force x distance Measured in Joules 1J = 1N x 1m 1 kJ = 1000J. Energy has many forms. Kinetic contraction of muscle fibres Chemical energy stored in food Heat energy lost to surroundings

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Unit L Energy and Respiration

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  1. Unit L Energy and Respiration

  2. What is Energy? • In science, the ability to do work • Energy = force x distance • Measured in Joules • 1J = 1N x 1m • 1 kJ = 1000J

  3. Energy has many forms • Kineticcontraction of muscle fibres • Chemicalenergy stored in food • Heatenergy lost to surroundings • Soundvibrations of vocal cords • Lightenergy trapped by photosynthesis • Electricalimpulses transmitted along a neurone

  4. Chemical Energy • Energy is transferred from one form to another • Energy is never created or destroyed (the law of conservation of energy) • All chemicals contain energy within their bonds • This energy is transferred during a chemical reaction

  5. Combustion of ethanol • C2H5OH + 3O2 2CO2 +3H2O • Products contain less energy than reactants • 1400kJ per mole released as heat • Exergonic reaction – releases energy • Exothermic reaction – releases heat • Many metabolic processes are Endergonicandneed energy to drive them, e.g. protein synthesis • Respiration releases energy for processes which require it.

  6. ATP • Combustion reactions release energy as heat • Too much heat would damage cells • Intermediate source of chemical energy, ATP • Adenosine triphosphate • Phosphorylated nucleotide • Has universal role of immediate energy source in cells • Cannot be transported or stored • Must be made continuously

  7. Structure of ATP

  8. ATP ATP + H2O ADP + Pi Hydrolysis releases 30.6 kJ per mole A metabolically active cell may require up to 2million ATP molecules every second

  9. Formation of ATP • ATP Animation • Formation of ATP

  10. Uses of ATP 1) Anabolic processes (building macromolecules from components) - formation of polysaccharides - protein synthesis - DNA replication 2) Movement - muscle contraction - ciliary action - spindle movement in cell division

  11. Uses of ATP 3) Active transport (movement of molecules against the concentration gradient) - ion pumps 4) Secretion - formation of vesicles 5) Activation of chemicals(making chemicals more reactive) - phosphorylation of glucose at start of glycolysis

  12. Metabolic Pathways • A series of reactions in a cell • Product of one reaction is substrate for next • Each reaction catalysed by a specific enzyme A enzyme 1 B enzyme 2 C enzyme 3 D enzyme 4 E • Enzymes often arranged close to one another bound to membranes in cells • Multi-enzyme complex

  13. Advantages of Metabolic Pathways • Direct conversion may require a large amount of energy • Intermediates may be useful products or form the start of other metabolic pathways • Final products may act as inhibitors – feedback or end product inhibition • Allosteric inhibitor

  14. Anabolic or Catabolic Anabolic reactions - involve build up of small, simple molecules into larger ones - require energy input - protein synthesis and photosynthesis Catabolic Reactions - break down of large molecules into smaller ones - release energy - hydrolysis of starch

  15. Co-factors and Co-enzymes Inorganic ions – combine with enzyme or substrate making E-S complex form more easily e.g. salivary amylase and Cl- ions Prosthetic groups – non protein organic co-factors permanently attached to an enzyme e.g. catalase has organic haem group Co-enzymes – small non protein organic molecules which binds temporarily with enzymes when it forms E-S complex and acts as a carrier e.g. NAD (nicotinamide adenine dinucleotide)

  16. NAD Nicotinamide adenine dinucelotide • Works with dehydrogenaseenzymes which catalyse removal of hydrogen • Accepts H atoms and passes to another carrier • In cell exists as NAD+ • Carries hydrogen as NADH and a proton 2H 2H+ + e- NAD+ + 2H+ +2e- NADH + H+

  17. Structure of NAD

  18. Redox Oxidation Reduction Addition of oxygen Removal of oxygen Removal of hydrogen Addition of hydrogen Removal of electrons Addition of electrons

  19. Anaerobic Respiration • Four stages • 1) Glycolysis 6C glucose 2 x 3C pyruvate • 2) Links Reaction 3C pyruvate 2C acetyl CoA • 3) Kreb’s Cycle 2C acetyl CoA CO2 • 4) Electron Transport Chain Most ATP made here

  20. Overview of Aerobic Respiration

  21. Glycolysis • “Sugar splitting” • Takes place in cytosol • Glucose is phosphorylated (requires ATP) • Phosphorylated glucose split into 2 triose phosphate molecules • Triose phosphate loses phosphate group to ADP making ATP • Trioseoxidised by losing H atoms to co-enzyme NAD

  22. Glycolysis

  23. Overall • Pyruvate (pyruvic acid) formed • ATP produced • Reduced NAD made (NADH + H+) • 2ATP used for phosphorylation • 4 ATP made during glycolysis • Net gain of 2ATP • Reduced NAD passes into electron transport chain and can generate 6ATP per glucose • Glycolysis

  24. Overall

  25. Link Reaction • If oxygen available pyruvate enters matrix of mitochondria • Each pyruvate is decarboxylated and loses C as CO2 • 2C fragment = acetyl group • Picked up by coenzyme A • Oxidised by NAD 2C +CoA + NAD+ acetyl CoA + CO2 + NADH + H+ • Acetyl Co A enters Kreb’s cycle

  26. The Link Reaction

  27. Mitochondria

  28. Mitochondria

  29. Structure and Function • Rod shaped structure with double membrane • Outer membrane - permeable to nutrient molecules, ions, ADP and ATP due to presence of porins • Inner membrane site of electron transport chain and permeable only to CO2, O2 and H2O. Cristae, folds on inner surface which increase surface area for ATP production. • Matrix – mixture of enzymes for ATP production, mitochondrial ribosomes, tRNA and DNA.

  30. Kreb’s Cycle • Tricarboxylic acid or citric acid cycle • Involves 2 types of reaction Decarboxylation • Catalysed by decarboxylase enzymes • Involves removal of C atoms from intermediates and formation of CO2 Dehydrogenation • Oxidation of intermediate followed by removal of H atoms, catalysed by dehydrogenaseenzymes • Hydrogen taken up by acceptor molecules NAD and FAD (flavinadeninedinucleotide)

  31. Kreb’s Cycle Cont’d • 2C Acetyl CoA combines with a 4C compound to form a 6C compound • 6C compound undergoes a series of reactions eventually losing 2C to regenerate the 4C compound • The C atoms are lost as CO2 • The 6C compound is oxidised by removal of H atoms • H atoms pass to hydrogen acceptor molecules 3 molecules of reduced NAD and 1 molecule of reduced FAD (FADH2) • 1 ATP synthesised

  32. Kreb’s Cycle

  33. Electron Transport Chain C6H12O6 + 6O2 6CO2 + 6H2O The story so far: • Glucose has been used up in glycolysis • CO2 was produced in the Link Reaction and Kreb’s cycle • But we have not yet seen the use of O2 or production of water • These happen in the electron transport chain (ETC)

  34. Electron Transport Chain • Electrons from NADH or FADH2 are passed through a chain of carrier molecules • At the end of the chain molecular oxygen is reduced to water • Electron transport is coupled to the formation of ATP from ADP and Pi • The 2 processes occur simultaneously • Electron carriers are large protein complexes on the inner membranes of mitochondria arranged in order of electron affinity • flavoproteins, quinones and cytochromes

  35. Electron Transport Chain • Start of chain NADH + H+ NAD+ + 2H+ + 2e- • Electrons are passed from carrier to carrier down the chain • At the end of the chain molecular oxygen accepts electrons and protons produced from oxidation of NADH at the start 1/2O2 + 2H+ + 2e- H2O • This takes places at the final electron carrier cytochromeoxidase

  36. Electron Transport Chain • As electrons pass along the chain they lose energy • This energy is used to pump protons through the inner mitochondrial membrane setting up a concentration gradient. • As protons re-enter ATP synthasesuse their energy to make ATP from ADP and Pi. • Mitchell’s chemiosmotic theory • Oxidative phosphorylation

  37. Summary of Respiration Source of ATP How Many Molecules? Glycolysis 2 2 x NADH + H+ (glycolysis) 6 (or 4) 2 x ATP in Kreb’s 2 2 x NADH + H+ (Link) 6 6 x NADH + H= (Kreb’s) 18 2 x FADH2 (Kreb’s) 4 Total 38 (or 36) • Overview of Respiration

  38. Efficiency • Car engine 20% efficient • Complete combustion of o2 releases 2870 kJ • 38 moles ATP = 38 x 30.6 = 1162.8 kJ • 1162.8/2870 x 100 = 40% efficiency

  39. Which part of respiration? ATP produced CO2 formed 6C into 3C Mitochondria NAD reduced to NADH + H+ • ETC animation and quiz

  40. Anaerobic Respiration • Used by organisms in O2 deficient environments or to maintain supplies of ATP when temporarily deprived of O2 • e.g bacteria in stagnant water • e.g muscles during continuous exercise • Different processes in yeast and mammals.

  41. Yeast • Single celled fungus found on surface of fruits C6H12O6 2C2H5OH + 2CO2 • Glycolysis takes place as normal 2ATP 2ADP + Pi Glucose 2 x pyruvate NAD NADH + H+

  42. Anaerobic Respiration in Yeast • Pyruvate is then decarboxylated forming CO2 and ethanal • Ethanal is reduced to ethanol by NADH + H+ • Regeneration of NAD+ enables glycolysis to continue • Only 2 ATP produced as NADH + H+ doesn’t enter mitochondria for oxidative phosphorylation

  43. Muscles • During vigorous exercise not enough O2 for anaerobic respiration • Pyruvate is converted to lactate CH3COCOO- + NADH + H+ CH3CHOHCOO- +NAD+ • Lactate is 3C compound • No decarboxylation • CO2 not produced • Build up causes muscle fatigue. • After exercise oxidised in liver to pyruvatethen respired aerobically to CO2 and H2O

  44. Oxygen Debt • Oxygen needed to fully oxidise the lactate produced during anaerobic repiration

  45. Respiration of other Substrates

  46. Energy from other Substrates • Hydrolysis of polymers e.g. starch/glycogen into glucose • Fructose/galactose chemically modified to enter glycolysis • Lipids/proteins also oxidised to yield energy Substrate Energy (kJ/g) Carbohydrate 17 Lipid 39 Protein 23

  47. Respiration of Lipids • When energy demands are great or carbohydrates in short supply triglycerides stored in fatty tissue are respired • Hydrolysed to glycerol and fatty acids • Glycerol (3C) converted to triose sugar dihydroxyacetone phosphate which is converted to glyceraldehdye 3- phosphate an intermediate in glycolysis • Produces 19 ATP per molecule

  48. Respiration of Lipids Cont’d • Fatty acids are oxidised and fed into Kreb’s cycle as Acetyl Co A • Energy yield depends on length of hydrocarbon chains • Up to 150 ATP per molecule

  49. Respiration of Proteins • Only respired in cases of severe starvation • Hydrolysedto amino acids • Amino acids deaminated • Amino group converted to urea and excreted • Carbon backbone fed into glycolysis or Kreb’s cycle directly or after modification

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