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UNIT 3

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  1. UNIT 3 Chapter 9: Cellular Respiration Chapter 10: Photosynthesis Chapter 11: Cell Communication

  2. The Basics • The sun is the ultimate source of energy for all living things • Light energy trapped in organic molecules • Trapped energy available to autotrophs and heterotrophs

  3. Cellular Respiration & Fermentation • Catabolic pathways can proceed with or without oxygen present • Fermentation occurs when oxygen is NOT present • Cellular respiration occurs with oxygen and is much more efficient than fermentation • Most of cellular respiration occurs in the mitochondria Organic molecules + O2 CO2 + H20 + energy

  4. ATP Hydrolysis & Redox Reactions • The removal of a phosphate group from ATP releases energy • Phosphorylation is a common tool used to power reactions

  5. Redox (reduction-oxidation) reactions release energy when electrons are moved • Loss of electrons = oxidation • Gain of electrons = reduction • Redox reactions are used to synthesize ATP • Creating NaCl (table salt) is a redox reaction: Na + Cl  Na+ + Cl-

  6. The electron donor is called the reducing agent and the electron recipient is called the oxidizing agent Na + Cl  Na+ + Cl-

  7. The Function of Coenzymes • Glucose is not simply broken down in a single step to yield energy • Steps to break down components of glucose using specific enzymes • Hydrogen atoms and electrons ripped off of glucose and given to coenzymes like NAD+ • Nicotinamide Adenine Dinucleotide H-C-OH + NAD+ CO2 + NADH + H+

  8. Steps of Cellular Respiration • Cellular respiration involves three steps: • Glycolysis • The Krebs cycle • The Electron transport chain and oxidative phosphorylation

  9. Glycolysis – An Overview • Glycolysis occurs in the cytoplasm • Glucose is split into two three-carbon sugars • Sugars are oxidized and rearranged to form pyruvate • 10 steps of glycolysis are catalyzed by specific enzymes • Energy investment phase and energy payoff phase

  10. Energy investment • ATP provides energy to phosphorylate glucose • 2 ATP per glucose • Energy payoff • 4 ATP and 2 NADH are produced per glucose

  11. Glycolysis produces a net of 2 ATP and 2 NADH • Happens with or without oxygen and no CO2 is produced • However, if oxygen is present, pyruvate molecules can move in to the Krebs cycle • NADH will play a role later in the process (the electron transport chain)

  12. The Krebs Cycle • Pyruvate still holds a lot of the original glucose molecule’s chemical energy • Pyruvate enters the mitochondria and is modified • CO2 removed to produce acetyl CoA

  13. Each pyruvate used to produce: • 1 acetyl CoA, which is used to produce: • 1 ATP • 3 NADH • 1 FADH2 (an electron transport carrier similar to NADH)

  14. The Electron Transport Chain (E.T.C.) • Respiration ultimately produces 38 ATP (max), but so far, only 4 have been produced • 8 NADH and 2 FADH2 molecules enter the electron transport chain • The electrons are used to power ATP synthesis • Each mitochondrion has thousands of sets of the E.T.C. in the cristae

  15. The electron transport chain shuttles electrons from NADH towards increasingly more electronegative atoms, ultimately to oxygen • Process occurs in inner membrane of mitochondria • Oxygen “captures” e- and H+ to make water

  16. Electrons from NADH and FADH2 are ultimately passed off to oxygen • For every two electron carriers (4 electrons), one O2 molecule is reduced  2 H2O • The electrons moving down the E.T.C. are used to pump H+ ions into the inter membrane space of the mitochondrion • An H+ ion gradient is created and is referred to as proton-motive force • H+ ions diffuse back into the mitochondrial matrix through ATP Synthase

  17. As H+ ions move through ATP Synthase, that protein shifts its conformation • Shift joins a phosphate group to ADP • That entire process is called chemiosmosis • Chemiosmosis occurs in plants also, but it is driven by light energy

  18. Intermembrane Space O NADH + + + + + + + + + + + + + + + + + + NAD+ H H P P P P P P Adenine Adenine Matrix

  19. Summary of Cellular Respiration

  20. Fermentation • Some cells can produce ATP whether oxygen is present (aerobic) or not (anaerobic) • Two types of fermentation exist: • Alcoholic fermentation • Lactic acid fermentation

  21. In alcoholic fermentation, pyruvate is ultimately converted to ethanol • In lactic acid fermentation, pyruvate is converted into lactic acid

  22. Some organisms, like bacteria and yeast can produce enough ATP to survive • These organisms are called facultative anaerobes • Human muscle cells can behave as facultative anaerobes, for a very short time • Cori Cycle • The presence of oxygen allows for the production of up to 38 ATP molecules, but without oxygen, only 2 ATP are created END

  23. Chloroplasts Make Photosynthesis Possible • Any green part of a plant possesses chloroplasts which contain a green photopigment: chlorophyll • Chloroplasts are found mainly in the mesophyll cells in the interior of the plant’s leaves • O2 exits and CO2 enters through pores called stomata on the leaf’s surface

  24. Chloroplasts are double-membrane organelles around a central space: stroma • In the stroma are membranous sacs called thylakoids • Internal space called thylakoid space • Stacked into grana

  25. The Basics of Photosynthesis • The general reaction of photosynthesis: • Basically, carbon is extracted from carbon dioxide to make sugar, while oxygen is released into the atmosphere SUN 6CO2 + 12H2O  C6H12O6 + 6H2O + 6O2

  26. The Light Reactions & The Calvin Cycle • Photosynthesis is a two step process • Light reactions • Converts solar energy into chemical energy • Calvin cycle • Incorporates CO2 into organic molecules and uses chemical energy from light reactions to create sugar

  27. The light reactions – an overview • Water is split, hydrogen and electrons used to reduce NADP+ to NADPH (an electron carrier) • ATP is generated by photophosphorylation • The Calvin cycle – an overview • CO2 is incorporated into what will become sugar during carbon fixation • NADPH and ATP are used to create the new organic molecule

  28. The light reactions & Calvin cycle:

  29. The Photopigments of Photosynthesis • A number of pigments exist in plants, but only one, chlorophyll a, is directly involved in the photosynthetic reactions • Accessory pigments can funnel light energy to chlorophyll a • Chlorophyll b • Carotenoids • Xanthophylls

  30. Photons of light are absorbed by pigments in thylakoid membranes

  31. In the thylakoid membrane, a “light antenna” called a photosystem channels light energy • Energy transferred from molecule to molecule until it reaches the reaction center chlorophyll a

  32. Photosystems • Two types of photosystems work in the light reactions of photosynthesis • Photosystem I & Photosystem II • Photosystem I (P700) absorbs light best at 700nm (far red) • Photosystem II (P680) absorbs light best at 680nm

  33. 2. Water is split creating ½ O2, which is joined with another ½ O2 to form O2 3. Excited electrons are passed down an E.T.C. (which creates ATP) to P700 4. An electron acceptor in P700 captures the electrons and uses them to reduce NADP+ 1. P680 is hit by light and excites 2 electrons, sending it to the primary electron acceptor

  34. Electron flow takes electrons from water, and uses them to reduce NADP+ • ATP created on the way through E.T.C. • O2 is a byproduct of splitting water

  35. ATP Synthesis • Chloroplasts and mitochondria both create ATP using chemiosmosis • Chloroplasts transform light energy into chemical energy

  36. The Calvin Cycle • The Calvin cycle uses ATP and NADPH to create sugar • Not actually “glucose,” but glyceraldehyde-3-phosphate (G3P), a 3-Carbon sugar • Each turn through the Calvin cycle fixes one carbon • There are three phases to the Calvin cycle • Carbon fixation, Reduction, Regeneration of the CO2 acceptor

  37. ATP is used to add another phosphate group to EACH of the 3-Carbon sugars Some G3P sugars are modified by 3 more ATP molecules to regenerate RuBP NADPH is used to remove one of the phosphates from each sugar, creating a G3P sugar Net cost per G3P = 9 ATP + 6 NADPH + 3 CO2 3CO2 are attached to 3 5-Carbon sugars (RuBP) by rubisco The new 6-Carbon sugars split into 6, 3-carbon sugars

  38. The Calvin Cycle: CARBON FIXATION C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C P P P P P P P P P P P P P P P P P P O O O O O O rubisco rubisco rubisco ATP ATP ATP ATP ATP ATP ADP ADP ADP ADP ADP ADP RuBP RuBP RuBP

  39. The Calvin Cycle: REDUCTION C C C C C C C C C C C C C C C C C C P P P P P P P P P P P P EXITS CYCLE NADPH NADP+ NADPH NADP+ NADP+ NADP+ NADPH NADPH NADPH NADP+ NADP+ NADPH G3P G3P G3P G3P G3P G3P

  40. The Calvin Cycle: REGENERATION OF THE CO2 ACCEPTOR (RuBP) C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C P P P P P P P P P P P P P P COMPLEX REACTIONS! ATP ATP ATP ADP ADP ADP G3P 15 Carbons 5 Phosphates Two G3P molecules will be combined to form one glucose molecule. 15 Carbons 6 Phosphates 3 RuBP molecules

  41. The Need for Alternative Methods of Carbon Fixation • The Calvin cycle is not the only way plants fix carbon • Dehydration is a huge problem for plants since water can evaporate through the stomata • Hot dry days  plants close stomata • Most plants, called C3 plants, fix CO2 to RuBP using rubisco

  42. On hot, dry days, C3 plants close their stomata • CO2 levels drop as it’s used in the Calvin cycle • O2 levels rise as it cannot escape the leaf • Rubisco will then fix O2 to RuBP, which then degrades and produces no G3P • This process is called photorespiration and can severely affect the productivity of photosynthesis in a plant

  43. Avoiding Photorespiration • A number of plants, called C4 plants, will first fix CO2 to a 4-carbon compound (organic acid) • PEP carboxylase has a high affinity for CO2 and is much more efficient than rubisco • 4-carbon compound moved to bundle sheath cells where the Calvin cycle can take place • C4 plants are usually found in very hot regions with intense sunlight

  44. A second strategy for avoiding photorespiration can be found in CAM plants • Cacti, pineapples, succulents • CAM plants close their stomata during the day, and open them at night • Night: plants fix CO2 into organic acids in the mesophyll cells • Day: CO2 released from organic acids and light reactions create ATP and NADPH

  45. In C4 plants, carbon fixation and the Calvin cycle are spatially separated • In CAM plants, carbon fixation and the Calvin cycle are temporally separated END

  46. Stages of Signal Transduction • The three stages of signal transduction are: • Reception, transduction, response • Cells can communicate with other cells they are physically connected to • Across great distances using hormones • Target cell is intended recipient for signal

  47. Reception • A Chemical signal called a ligand binds to protein in the target cell’s membrane • Protein changes conformation • Change in conformation sets in motion a series of other changes inside the cell

  48. Transduction • Transduction relays signals from reception to cellular responses • At each step, the signal is transduced in a different form • Usually a protein changing its comformation • Kinases are a common group of intracellular proteins