1. Chapter 6: Energy Pathways Wasilla High School 2015 - 2016

2. Energy Energy is capacity to do work; cells must continually use energy to do biological work.  Kinetic energy is energy of motion; all moving objects have kinetic energy.  Potential energy is stored energy.  Ex. Water behind a dam has potential energy that can be converted to kinetic energy.

3. 3 Flow of Energy

4. Laws of Thermodynamics  First Law:  Law of conservation of energy  Energy cannot be created or destroyed, but  Energy CAN be changed from one form to another  Second Law:  Law of ENTROPY  When energy is changed from one form to another, there is a loss of usable energy  Waste energy goes to increase disorder

5. Laws of Thermodynamics  Second law: (Law of ENTROPY)  Energy conversions result in heat and therefore the entropy of the universe is always increasing.  It takes a constant input of usable energy from the food you eat to keep you organized.

6. General Energy Principles  Most metabolic pathways are similar in all organisms, from bacteria to plants, to humans  In eukaryotes, metabolic pathways are compartmentalized by organelles  Metabolic pathways are controlled by enzymes  Chemical energy available to do work is called free energy

7. Gibbs Free Energy (  G)  “Available energy”  Energy that can do work under cellular conditions  Concept from Thermodynamics  “Available energy”  Energy that can do work under cellular conditions  Concept from Thermodynamics

9. Loss of order or free energy flow results in death.

10. An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics.

11. Increased disorder and entropy are offset by biological processes that maintain or increase order.

12. Reactions are Coupled Together  Reactions are exergonic or endergonic  Exergonic – releases energy  Cell Respiration  Catabolism  ATP is hydrolized => ATP into ADP  Fuels the endergonic synthesis of ATP from ADP and P i  Endergonic – require energy  Active Transport  Anabolism  ATP is formed from ADP and P i

13. Metabolic Reactions and Energy Transformations  Catabolic pathways  release energy by breaking down complex molecules to simpler compounds.  Ex: Cellular respiration - degrades glucose to carbon dioxide & water; provides energy for cellular work.  Anabolic pathways  consume energy to build complicated molecules from simpler ones.  Ex: Photosynthesis - synthesizes glucose from carbon dioxide & water

14. Catabolic & Anabolic Reactions  Cells need both types of reactions; both require enzymes Anna – builds things Cats – break things

15. ATP Hydrolysis  Adenosine triphosphate, ATP, is energy currency  Made of adenine (same as adenine in DNA) bonded to ribose  This is attached to a sequence of three phosphate groups  When ATP loses a phosphate a boost of energy is released

16. 16 The ATP Cycle *High energy compound used to drive metabolic reactions *Constantly being generated from adenosine diphosphate (ADP)

17. Redox Reactions (Another Chem Crash Course)  LEO the lion goes GER  Losing Electrons Oxidation  Gaining Electrons Reduction  Since we often don't follow oxygen, let's look at it in terms of Hydrogen  Losing Hydrogen is oxidation  Gaining Hydrogen is reduction  When NADH is oxidized it becomes NAD +  When NAD + is reduced it becomes NADH

18. Redox in Terms of Energy  When NADH is oxidized into NAD + it is highly exergonic  This means that a large burst of energy is released  When NAD + is reduced into NADH it is highly endergonic  This means that it TAKES energy to go from NAD + into NADH  So what does this mean about the molecule NADH?  It is an energy/electron carrier  ATP, NADH and FADH 2 are like rechargeable batteries

19. Oxidative Phosphorylation  Cells need a way to connect the two coenzymes ATP and NADH  We need to transfer the energy from NADH into ATP  Process is called oxidative phosphorylation  NADH is oxidized: NADH -> NAD + + H + + 2e + energy Phosphorylation is the process of adding a phosphate  The energy from the above reaction is harnessed and used to fuel:  ADP + Pi -> ATP

20. Chemiosmosis – Yet another scary science word  The hydrogen protons released from NADH create a concentration gradient that diffuses across the plasma membrane  Creates potential energy building up outside the membrane  The H + protons are needed to move a very important enzyme machine called ATP synthase  H + ions are pulled into ATP synthase causing the enzyme wheel to turn  The wheel literally smashes ADP into P i forming ATP

21. When and Where does chemiosmosis occur?  In eukaryotic organisms this can occur in two different places  Mitochondria – during aerobic cellular respiration  Allows a HUGE amount of ATP (32 per glucose) to form  H + gradient forms in the inner membrane  In plants: Chloroplasts – during photosynthesis light reaction  Occurs in the Thylakoid membrane using energy from light  Energy from ATP is used to create sugar

22. Cellular Respiration

23. Let's Talk Aerobic Cellular Respiration  What is it?  A cellular process that requires oxygen and gives off carbon dioxide  Usually involves breakdown of glucose to carbon dioxide and water  Energy extracted from glucose molecule:

24. Overview of Cellular Respiration  Glycolysis:  Occurs in cytoplasm  Glucose broken down to two molecules of pyruvate  ATP is formed  Link Reaction  Both pyruvates are oxidized  Electron energy is stored in NADH  Two carbons are released as CO 2  Citric Acid (Krebs) Cycle:  Electron energy is stored in NADH and FADH 2  ATP is formed  Four carbons are released as CO 2  Electron transport chain:  Extracts energy from NADH & FADH 2  Produces 32 or 34 molecules of ATP

25. 25 Glucose Breakdown: Overview of 4 Phases

26. Step 1: Glycolysis o Glycolysis – glucose (sugar) is broken down and split into pyruvate o Occurs in the cytoplasm o Requires energy input to get energy out – 2 ATP are used to start the reaction o Products are: 2 pyruvate molecules, 2 ATP and 2 NAD + gain e - and become NADH o Technically 4 ATP are produced but you only have a net gain of 2 because the reaction required 2 to begin o ATP is produced by substrate level phosphorylation

27. 27 Glycolysis: The Balance Sheet

28. Step 2 Part I: The Link Reaction  End product of glycolysis, pyruvate, enters the mitochondrial matrix  Pyruvate converted to 2-carbon acetyl group  Attached to Coenzyme A to form acetyl-CoA  Electron picked up (as hydrogen atom) by NAD +  CO 2 released, and transported out of mitochondria into the cytoplasm

29. 29 Mitochondrion:Structure & Function

30. Step 2: Kreb’s Cycle (aka Citric Acid Cycle)  Occurs in matrix of mitochondria  Both acetyl (C 2 ) groups received from the link reaction:  Join with an enzyme CoA molecule to make acetyl-CoA  NADH, FADH 2 capture energy rich electrons  ATP formed by substrate-level phosphorylation

31. Step 3: Electron Transport Chain  Occurs in the cristae of the mitochondria  Large amount of ATP is made using chemiosmosis and oxidative phosphorylation  NADH and FADH2 are oxidized and give up their H+  The H+ creates a concentration gradient in the inner membrane space  H+ is used to turn the ATP synthase crank  32 ATP is made IF oxygen is present

32. Why does Oxygen need to be present?  Once the H+ comes back through the ATP synthase it can build up  Oxygen binds with the excess H+ and forms water  Waste products of cellular respiration are:  CO2 (from Citric Acid Cycle)  Water

33. 33 Organization of Cristae

34. 34 Glucose Catabolism: Overall Energy Yield  Net yield per glucose:  From glycolysis – 2 ATP  From citric acid cycle – 2 ATP  From electron transport chain – 32 ATP  Energy content:  Reactant (glucose) 686 kcal  Energy yield (36 ATP) 263 kcal  Efficiency 39%; balance is waste heat

35. 35 Overall Energy Yielded per Glucose Molecule

36. What happens if there is no Oxygen?  Anaerobic Respiration  Glycolysis ONLY occurs  Products are Pyruvate and 2 ATP  Pyruvate is converted into a waste product – process is called Fermentation  Humans undergo lactic acid fermentation  Alcoholic fermentation – performed in yeasts and plants  Yeast: CO2 production in breads

37. Photosynthesis

38.  A process that captures solar energy  Transforms solar energy into chemical energy  Energy ends up stored in a carbohydrate  Photosynthesis takes place in the green portions of plants  Leaf of flowering plant contains mesophyll tissue  Cells containing chloroplasts  Specialized to carry on photosynthesis

39. Photosynthesis  CO 2 enters leaf through stomata  Diffuses into chloroplasts in mesophyll cells  In stroma, CO 2 combined with H 2 O to form C 6 H 12 O 6 (sugar)  Energy supplied by light

40. Leaves & Photosynthesis

41. Photosynthetic Pigments  Pigments:  Chemicals that absorb some colors in rainbow more than others  Colors least absorbed reflected/transmitted most  Chloroplasts contain two pigments: Chlorophyll a and Chlorophyll b  Absorption Spectra  Graph showing relative absorption of the various colors of the rainbow  Chlorophyll is green because it absorbs much of the reds and blues of white light  Red and Blue wavelengths are absorbed, green wavelengths are reflected

43. Photosynthetic Pigments Pigments: Chemicals that absorb some colors in rainbow more than others Colors least absorbed reflected/transmitted most Absorption Spectra Graph showing relative absorption of the various colors of the rainbow Chlorophyll is green because it absorbs much of the reds and blues of white light

44. 2 Part Process  Light reactions  Purpose is to harness the sun's energy into NADPH and ATP  Our good friends, Chemiosmosis and Oxidative Phosphorylation, reappear: Products are ATP and NADPH  Carbon-fixation reaction (Dark reactions or Light-Independent)  CO 2 is reduced to a carbohydrate  Reduction requires the ATP and NADPH produced above

45. Absorption and Action Spectrum  Absorption spectrum: light absorbed vs wavelength  Action spectrum: biological activity vs wavelength

46. 46 Photosynthesis Overview

47. 47 Organization of a Thylakoid

48. 48 Organization of a Thylakoid

49. 49

51. 51 Light Reactions: Noncyclic Electron Pathway

52. 52 Non-Cyclic Electron Pathway

54. 54 Light Reactions: Cyclic Electron Pathway

56. Light Reactions: Photosystems  Light harvesting reaction centers are located in the thylakoid membrane of the chloroplast  Absorbed light is converted into chemical energy  Thylakoid has an electron transport system similar to the mitochondria  ATP produced chemiosmotically via photophosphorylation  Two different systems: one cyclic, the other noncyclic

57. Source of O 2 and H + in Photosystems  H 2 O is split by light energy  Photolysis  H+ builds up into a concentration gradient and used by ATP synthase to create ATP

58. ATP Production  Thylakoid space acts as a reservoir for hydrogen ions (H + )  Each time water is oxidized, two H + remain in the thylakoid space  Electrons yield energy  Used to pump H + across thylakoid membrane  Move from stroma into the thylakoid space  Chemiosmosis!

59. Calvin Cycle: Carbon fixation reactions  The energy provided by ATP and NADPH will drive the conversion of carbon dioxide into stored sugar  Extremely inefficient process that uses a molecule called ribulose bisphosphate (RuBP) (Rubisco)  A cyclic series of oxidation/reduction reactions in a metabolic pathway "fixes" carbon into glucose  Oxygen is a "waste" product Known as C3 photosynthesis 3 stages: 1. CO 2 Fixation 2. CO 2 Reduction 3. RuBP Regeneration

60. 60 InLine Figure p125 The Calvin Cycle Reduction of CO 2

61. 61 Calvin Cycle Reactions: Regeneration of RuBP  RuBP used in CO 2 fixation must be replaced  Every three turns of Calvin Cycle,  Five G3P (a 3-carbon molecule) used  To remake three RuBP (a 5-carbon molecule)  5 X 3 = 3 X 5

62. 62 The hydrocarbon skeleton of G3P can be converted to many other molecules