Catabolic and Anabolic Pathways depend on ATP / ADP shuttle

Figure 10.0 Sunbeams

Question: Where does photosynthesis take place?Where does photosynthesis take place?

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Plants Autotrophs:Autotrophs: self-producers. Location: 1.Leaves a.stoma b.mesophyll cells Stoma Mesophyll Cell Chloroplast

Stomata (stoma) Poreswater gasesPores in a plant’s cuticle through which water and gases are exchanged between the plant and the atmosphere. Guard Cell Carbon Dioxide (CO 2 ) Oxygen (O 2 )

Mesophyll Cell Cell Wall Nucleus Chloroplast Central Vacuole

Chloroplast OrganellephotosynthesisOrganelle where photosynthesis takes place. Granum Thylakoid Stroma Outer Membrane Inner Membrane

Thylakoid Thylakoid Membrane Thylakoid Space Granum

Chloroplast Chlorophyll – green pigment located inside chloroplasts Found in mesophyll (interior of leaf) Double membrane Enclose stroma (dense liquid) containing grana made up of thylakoid membranes which contain chlorophyll

Photosynthesis H2OH2OH2OH2O CO 2 O2O2O2O2 C 6 H 12 O 6 Light Reaction Dark Reaction Light is Adsorbed ByChlorophyll Which splits water Chloroplast ATP and NADPH 2 ADPNADP Calvin Cycle Energy Used Energy and is recycled. + +

Photosynthesis anabolic, endergonic, carbon dioxide (CO 2 )light energy (photons)water (H 2 O)organic macromolecules (glucose).An anabolic, endergonic, carbon dioxide (CO 2 ) requiring process that uses light energy (photons) and water (H 2 O) to produce organic macromolecules (glucose). 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 glucose SUN photons

Question: Why are plants green?Why are plants green?

Chlorophyll Molecules thylakoid membranesLocated in the thylakoid membranes. Mg +Chlorophyll have Mg + in the center. Chlorophyll pigments absorbingwavelengthsblue-420 nmChlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 nm and red-660 nm are most important). Plantsgreen wavelengthreflectednot absorbedPlants are green because the green wavelength is reflected, not absorbed.

Light Absorption Spectrum

Absorption of Chlorophyll wavelength Absorption violet blue green yellow orange red

Question: During the fall, what causes the leaves to change colors?During the fall, what causes the leaves to change colors?

Fall Colors accessorypigmentsIn addition to the chlorophyll pigments, there are other accessory pigments present. green chlorophyll greatly reduced pigmentsDuring the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments. Carotenoidsred yellowCarotenoids are pigments that are either red or yellow.

Chromatography CHROMATOGRAPHYPigments can be separated out using the process of CHROMATOGRAPHY.

Redox Reaction transferonemore electrons one reactantanotherThe transfer of one or more electrons from one reactant to another. Two types:Two types: 1.Oxidation 2.Reduction

Oxidation Reaction losselectronsThe loss of electrons from a substance. gainoxygenOr the gain of oxygen. glucose 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Oxidation

Reduction Reaction gainThe gain of electrons to a substance. lossoxygenOr the loss of oxygen. glucose 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Reduction

Breakdown of Photosynthesis Two main parts (reactions).Two main parts (reactions). 1. Light Reaction or Light Dependent Reaction Light Dependent Reaction energysolar power(photons) ATPNADPH Produces energy from solar power (photons) in the form of ATP and NADPH.

Breakdown of Photosynthesis 2.Calvin Cycle or Light Independent Reaction or Carbon Fixation or C 3 Fixation energy(ATP and NADPH)light rxn sugar (glucose). Uses energy (ATP and NADPH) from light rxn to make sugar (glucose).

Chlorophyll Two different types : Chlorophyll a and b “a” – main pigment in photosynthesis “b” – accessory pigment –Both have similar structure but absorb different wavelengths of light

Chlorophyll absorbs light of a particular wavelength, electrons are excited and jump to higher energy level, drops back down and gives off heat This energy is passed along until it finds Chlorophyll a, which, when excited, passes electron to primary electron acceptor…powering light dependent reactions.

How a photosystem harvests light..

1. Light Dependent Reaction Thylakoid membranesOccurs in the Thylakoid membranes light reactiontwo possibleelectron flowDuring the light reaction, there are two possible routes for electron flow. A.Photosystem II B.Photosystem I *Pigments of the thylakoid space organize themselves into groups called photosystems

Chemiosmosis ATP synthesisPowers ATP synthesis. thylakoid membranesLocated in the thylakoid membranes. (enzyme)Uses ETC and ATP synthase (enzyme) to make ATP. Photophosphorylation:phosphate ADPATPPhotophosphorylation: addition of phosphate to ADP to make ATP.

Chemiosmosis…Making ATP

Things to Remember…. Light Reactions… Occur in the Thylakoid MembraneOccur in the Thylakoid Membrane Inputs are water and lightInputs are water and light Products : ATP, NADPH and O 2Products : ATP, NADPH and O 2 Oxygen produced comes from the water, not Carbon Dioxide!Oxygen produced comes from the water, not Carbon Dioxide! Two different pathways…..Two different pathways…..

Cyclic vs. Noncyclic Pathways… Noncyclic Light ReactionNoncyclic Light Reaction –Electrons taken from Chlorophyll a are not recycled back down to the ground state – therefore do not make it back to the chlorophyll molecule when the reaction is complete. Electrons end up on NADPH Cyclic Light ReactionCyclic Light Reaction –Uses ONLY Photosystem I, sunlight hits P700 –Energy given off down ETC, only produces ATP

…Because of the Calvin Cycle Calvin CycleCalvin Cycle uses more ATP than NADPH eventually Light ReactionThis is eventually a problem because the Light Reaction produces equal amounts of ATP and NADPH cyclic phase Light Independent ReactionPlants compensate for this disparity by dropping into the cyclic phase when ATP is needed to keep the Light Independent Reaction from coming to a grinding halt!!!

Calvin Cycle Granum Thylakoid Stroma Outer Membrane Inner Membrane Light-Independent Reaction takes place in Stroma Begins Synthesis Phase of Photosynthesis Chloroplast

Meet Mr. Melvin Calvin

Calvin Cycle ATP NADPHThe light reactions provide ATP and NADPH for the Calvin cycle CO 2Process of carbon fixation – CO 2 from air incorporated into organic molecules Fixed carbon reduced to form a carbohydrate (powered by NADPH electrons and energy from ATP) Enzyme “Rubisco” assists in reduction Product is actually glyceraldehyde-3- phosphate (G3P or GAP) – a 3-carbon molecule

Calvin Cycle 1 GAP 3For 1 molecule of GAP, the cycle must take place 3 times GAP can be used to make carbohydrates (like glucose), amino acids, lipids, nucleic acids, and other needed molecules. RuBPThe Calvin cycle begins and ends with ribulose-1,5-biphosphate (RuBP) 3 CO 2 6 GAPAt the end of the cycle, 3 CO 2 molecules have formed 6 GAP molecules. RuBPOne GAP molecule is used by the plant cell, the other 5 are used to regenerate RuBP

Calvin Cycle

Things to remember about Calvin Cycle (C 3 Fixation)… Occurs in Stroma of Chloroplast Inputs: NADPH, ATP and CO 2 Products: NADP+, ADP and a sugar. More ATP used than NADPH = need for Cyclic Photophosphorylation Carbon of sugar comes from CO 2 To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.

Some plants must make changes to the system in order to successfully use light to produce energy. Transpiration = water loss Stomata can be closed to prevent water loss, however they experience a shortage of CO 2 and the O 2 produced in photosynthesis is unable to leave plant. Guard Cell

Photorespiration hot, dry, bright daysOccurs on hot, dry, bright days. Stomates close. Fixation of O 2 instead of CO 2. 2-C molecules3-C sugar moleculesProduces 2-C molecules instead of 3-C sugar molecules. Produces no sugar molecules or no ATP. Result = plants have lowered capacity for growth

Photorespiration Because of photorespirationPlants special adaptations photorespirationBecause of photorespiration: Plants have special adaptations to limit the effect of photorespiration. 1.C4 plants 2.CAM plants

C 3 Plants Examples: rice, wheat, bluegrass, and soybeans The cyclic series of reactions whereby CO 2 is fixed into a 3-carbon carbohydrate during the Calvin cycle. During hot, dry days, these plants must keep their stomata closed to prevent water loss. O 2 build up and CO 2 cannot be replenished. Uses photorespiration to convert O 2 to CO 2. Produces no ATP nor food – actually decreases photosynthetic output.

C 4 Plants ExamplesExamples: tropical and desert plants, as well as sugar cane, and corn. (15% of plants) The series of reactions that efficiently fixes CO 2 into 4- carbon organic acids for later release and incorporation into the C 3 (Calvin) cycle. oxaloacetateThe 4-carbon molecule (oxaloacetate) can easily regenerate CO 2 that reenters the Calvin cycle. The reaction requires lots of ATP and is only advantageous when lots of light and little water are available.

C4 Plants vs. C3 Plants Has 2 different types of photosynthetic cells: Mesophyll Cells and Bundle Sheath Cells Divides photosynthesis spatially.Divides photosynthesis spatially. –Light rxn - mesophyll cells. –Calvin cycle - bundle sheath cells. PEP CarboxylaseC4 uses PEP Carboxylase to drive photosynthesis by fixing carbon.

C 4 Leaf Anatomy and the C 4 Pathway

CAM Plants Examples: succulents including many cacti and pineapples that live in very arid climates (5%) Open stomata at night and close them during the day. The mesophyll cells of CAM plants store the CO 2 (at night) in the form of acids until needed the next day. During the day when stomata are closed, CO 2 is released from the organic acids and enters the Calvin cycle. This must occur during the day instead of night because the light reactions must supply ATP and NADPH for the Calvin cycle.

C 4 vs. CAM Plants

A Review of Photosynthesis