ECU. Biology Department

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Corey Dalton
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1 ECU Biology Department

2 hotosynthesis O 2 CO 2 H2 O C 6 H 12 O 6 An Energy Absorbing athway

3 CO is the 2 source sunlight is the source hotosynthesis is the main biosynthetic pathway by which carbon and energy enters the web of life as food (C 6 H 12 O 6 )

4 hotosynthesis is O 2 vital to life as we O 2 O 2 know it for two O 2 reasons: O 2 O 2 O 2 O 2 in the atmosphere comes from photosynthesis O 2

5 hotosynthesis is vital to life as we know it for two reasons: O 2 in the atmosphere comes from photosynthesis All our food and the food of almost every other organism comes, directly or indirectly from photosynthesis

6 The basic equation for photosynthesis carbon dioxide + water sugar + (a carbohydrate) oxygen + water 6CO + 12 H O C H O + 6O + 6H O

7 Topics Related to hotosynthesis Anatomy of a leaf AT and NADH 2 Distinct hases of hotosynthesis Light Reactions Dark Reactions Click on the topic that you want to review

8 hotosynthesis takes place in plant cells that have chlorophyll to absorb appropriate energy from a light source

9 vein chloroplast Cross-section of a leaf upper epidermis guard cell stomata palisade layer spongy mesophyll lower epidermis

10 vein chloroplast Cross-section of a leaf upper epidermis guard cell palisade layer spongy mesophyll stomata lower epidermis

11 Chloroplast inner membrane outer membrane granum stroma thylakoid membrane To understand how chloroplasts function, one must understand their structure

12 Chloroplast The thylakoid membranes form interconnecting sacs which lie parallel to each other. Each sac encloses a distinct compartment separate from the stroma To understand how chloroplasts function, one must understand their structure

13 Chloroplast pigments enzymes carrier molecules Within the thylakoid membrane itself are various pigments, enzymes, and carrier molecules which carry on the light dependent phase of photosynthesis

14 Chloroplast These membranebound molecules produce AT and NADH in the stroma Within the thylakoid membrane itself are various pigments, enzymes, and carrier molecules which carry on the light dependent phase of photosynthesis Click here to return to main menu

15 An AD-AT system converts light energy to chemical energy for use in metabolic processes AD=Adenosine diphosphate (a nucleotide) phosphate phosphate Adenine Ribose sugar high energy bond

16 An AD-AT system converts light energy to chemical energy for use in metabolic processes AT=Adenosine triphosphate light energy phosphate phosphate phosphate Adenine Ribose sugar higher energy bond The absorbed energy is used to make AT from AD

17 Later the energy in AT fuels other metabolic reactions AT Adenine phosphate phosphate phosphate Ribose sugar phosphate phosphate phosphate Adenine AD + phosphate Ribose sugar energy

18 ...and vice versa AT Adenine phosphate phosphate phosphate Ribose sugar energy phosphate phosphate phosphate Adenine AD + phosphate Ribose sugar adding a phosphate group is called HOSHORYLATION

19 HOSHORYLATION is a means by which energy is stored in cells AD + phosphate + light energy AT + H 2 O When light energy powers the addition of phosphate, it is called... hotophosphorylation

20 hotophosphorylation AD + phosphate + light energy AT + H 2 O

21 An additional storage compound, NADH, is also a place in which energy can be stored N A D H icotinimide denine inucleotide hosphate

22 NADH is the reduced form of NAD + oxidized form Oxidation is the loss of electrons A molecule losing an electron is called a donor A molecule gaining an electron is called an acceptor donor oxidized e- acceptor molecule molecule reduced

23 When NAD + gains a hydrogen ion and 2e, it forms NADH e - H + e - Since NADH has gained electrons, it is said to be reduced NADH + Temporary energy storage is achieved by this reaction Click here to return to main menu

24 hotosynthesis occurs in two stages a. light dependent or energy trapping phase This phase produces two products, AT and NADH which are needed in the light independent phase b. light independent or carbon fixation phase This phase uses energy from AT to combine H + (from NADH) with CO 2 to produce sugar (C 6 H 12 O 6 )

25 hotosynthesis occurs in two stages a) light dependent or energy trapping phase This phase produces two products, AT and NADH which are needed in the light independent phase The green pigment, chlorophyll, is the central molecule in the light trapping phase

26 Mg O=C CH CCH 3 CHCH 3 CHCH CH 3 2 CHCH 3 Its light trapping site is a porphyrin ring which surrounds a magnesium atom Attached to this site is a long C-H tail which is associated with the thylakoid membrane The green pigment, chlorophyll, is the central molecule in the light trapping phase CH 3

27 The ultimate source of energy for photosynthesis is light from the sun Red Orange prism White light from the sun is composed of several wavelengths of energy which we see as different colors Yellow Green Blue Indigo Violet only some wavelengths are absorbed by chlorophyll and other pigments

28 Chlorophyll extract taken from a green plant Red end of the spectrum has been aborbed prism Yellow Green Blue only some wavelengths are absorbed by chlorophyll and other pigments Most of the blue end of the spectrum has been absorbed

29 There are several kinds of chlorophyll CH 3 H C O Mg O=C CH CCH 3 CHCH 3 CHCH CH 3 2 CHCH 3 CH 3 Their slight differences in structure enable them to absorb different wavelengths of light chlorophyll a Mg O=C CH CCH 3 CHCH 3 CHCH 3 CHCH 3 CH 3 chlorophyll b

30 Remember: Within the thylakoid membranes are distinct packets of pigments. pigments enzymes carrier molecules Within the thylakoid membrane itself are various pigments, enzymes, and carrier molecules which carry on the light dependent phase of photosynthesis

31 Thylakoid membrane hotosystem hotosystem A photosystem consists of a group of various chlorophylls and other pigments (carotenoids); electron carriers; and the proteins that bind them.

32 Thylakoid membrane hotosystem hotosystem A photosystem consists of a group of various chlorophylls and other pigments (carotenoids); electron carriers; and the proteins that bind them.

33 Thylakoid membrane hotosystem igments within the photosystem hotosystem

34 Thylakoid membrane hotosystem igments within the photosystem hotosystem There are several hundred pigment molecules in each hotosystem

35 Thylakoid membrane hotosystem Chlorophyll A hotosystem A The other pigments act as antennae to trap There are several photons of hundred light and pigment pass that energy molecules to in a each REACTION hotosystem CENTER

36 Two different reaction centers exist, differing only in the molecules bound to Chlorophyll A 700 hotosystem I = pigment 700 or 680 = absorption wavelength 680 hotosystem II

37 The Z Scheme -1.2 S II S I 700* 680* -0.6 NAD + E o 0 Cyt. b/f 700 NADH 0.6 H 2 0 OEC

38 There are two processes in the light dependent reaction 1. Noncyclic photophosphorylation Energy is absorbed by both photosystems producing AT and NADH and O 2 NADH O 2 AT hotosystem I hotosystem II

39 There are two processes in the light dependent reaction 1. Noncyclic photophosphorylation Energy is absorbed by both photosystems producing AT and NADH and O 2 producing AT and NADH and O 2 2. Cyclic photophosphorylation Energy is absorbed by hotosystem I producing only AT AT 700 hotosystem I

40 Non-Cyclic hotophosphorylation Light entering hotosystem II is picked up by antennal molecules and passed to 680 1e oxidized Electrons are raised to a higher energy level 680 hotosystem II

41 heophytin 1e oxidized An electron is raised to a higher energy level hotosystem II...and transferred to the electron acceptor pheophytin which is also located in the thylakoid membrane

42 heophytin oxidized 1e reduced Qa ELECTRON TRANSORT CHAIN 1e reduced Qb 2 H + The pheophytin passes electrons along the ETC 2e Qb - QbH hotosystem II As electrons are passed, the acceptors in the ETC are alternately reduced and oxidized

43 heophytin 2e Qa energy AT 680 oxidized QbH 2 ELECTRON TRANSORT CHAIN Cytochrome b/f lastocyanin hotosystem II

44 Electron acceptor At the end of the chain, the electrons are accepted by 700 filling the electron gap produced earlier AT 2e oxidized energy oxidized oxidized ELECTRON TRANSORT CHAIN Cytochrome b/f b/f 1e lastocyanin 1e hotosystem II hotosystem I

45 heophytin Now the 680 chlorophyll needs to replace its lost electrons AT 2e energy oxidized 680 ELECTRON TRANSORT CHAIN 700 hotosystem II hotosystem I

46 heophytin AT energy ELECTRON TRANSORT CHAIN 680 2e 4e O hotosystem II 4H + 2 H 2 O hotosystem I The electron replacement for 680 comes from H 2 O

47 The splitting of water 1. fills the electron gap 680 4e 2. produces H + (stored) 4H + 3. produces O 2 (waste) O 2 2 H 2 O

48 hotosynthetic Q Cycle Occurs in two steps that are similar to the steps in the mitochondrial Q Cycle Qb 1 e - Qb - QbH 2 2H e - - e -- lastocyanin 1 e - - Cytochrome f 1 e - STE ONE

49 hotosynthetic Q Cycle Occurs in two steps that are similar to the steps in the mitochondrial Q Cycle Qb - 2 H + QbH 2 1 e - another QbH 2 2H + 1 e - Cytochrome f 1 e - 1 e e - - lastocyanin STE TWO

50 Meanwhile hotosystem I

51 A o 1e 700 The absorption of light energy by 700 raises electrons to a higher energy level hotosystem I Excited electrons leave 700 and are passed to a strong electron acceptor known as A o A o

52 A o 1e 700 oxidized A 1 1e oxidized reduced Fe-S 1e 1e oxidized reduced 1e 1e oxidized reduced Fd This is one of the major products of the light dependent phase 2e hotosystem I NADH + reduced A o passes electrons via other carrier molecules to NAD +

53 A o 700 oxidized reduced oxidized A 1 reduced oxidized Fe-S oxidized reduced Fd This is one of the major products of the light dependent phase hotosystem I NADH ox reduced is now missing electrons which 700 will be regained from hotosystem II

54 heophytin AT 2x1e hotosystem II 2H + Qa ELECTRON TRANSORT CHAIN 4e - Qb H 2 O O 2 Qb- energy QbH 2 2x1e A o A 1 hotosystem I Fe-S Fd NADH hotosystem I and II work in tandem

55 heophytin AT 2x1e hotosystem II 2H + Qa ELECTRON Cyt. b/f TRANSORT CHAIN 4e QbH 2 H 2 O O 2 energy A o 2x1e hotosystem I This summarizes NON-CYCLIC HOTOHOSHORYLATION C A 1 Fe-S Fd NADH

56 Cyclic photophosphorylation AT Ao 1e 700 1e ELECTRON TRANSORT CHAIN 2e A 1 1e Fe-S Fd energy 1e hotosystem I Cytochrome b/f NAD + This summarizes CYCLIC HOTOHOSHORYLATION

57 The end products of the light dependent reaction are AT and NADH

58 The Chemiosmotic Model explains how AT is produced This involves: 1. the generation of a proton (H + ) gradient 2. the use of the gradient to produce AT

59 thylakoid membrane thylakoid lumen stroma A proton (H + ) gradient can be built up in a cell by a membrane

60 thylakoid membrane thylakoid lumen H+ H+ H+ H+ H+ H+ H+ stroma The membrane serves as a barrier storing protons (H+) inside

61 rotons (H + ) can only move back into the stroma through a membrane protein known as AT synthase AD + thylakoid lumen energy H+ H+ H+ H+ H+ H+ H+ stroma AT H+ AT synthase Since light is the original power source, this form of AT synthesis is called hotophosphorylation

62 2H 2 O---> 4H + + O 2 + 4e Thylakoid Lumen electron flow Electron Transport Chain H + H H + + H + H + H + H + H + Membrane Stroma hotosystem II with its ETC H + Electron Transport & Chemiosmosis NAD + Cytochrome H + hotosystem I with its ETC H + H + e NADH + e AD + AT Synthase H + AT NAD + H +

63 In Summary... The hotosystems pass electrons down their ETC. H 2 O is also broken down in the thylakoid lumen increasing the H + content. As some molecules in the ETC undergo oxidation/reduction, protons (H + ) in the stroma are translocated to the lumen (Q cycle). rotons are also removed from the stroma for use in the formation of NADH. These events result in the production of NADH and AT. The net result of this activity is the establishment of a proton gradient. Click here to return to main menu

AP Bio Photosynthesis & Respiration

AP Bio Photosynthesis & Respiration Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. 1. What is the term used for the metabolic pathway in which