Chapter 8 Photosynthesis

8-1 NRG and Living Things n Where does the NRG we use come from. n Directly or indirectly from the sun n Plants get their NRG directly from the sun n How?

n Plants use photosynthesis to convert light NRG into chemical NRG n Plants are autotrophs n Autotrophs convert light NRG or inorganic compounds to make organic compounds n Photoautotrophs use the sun n Chemoautotrophs use inorganic compounds

n Heterotrophs must eat things to aquire NRG from organic compounds n Cellular Respiration is how most heterotrophs, and most autotrophs get their NRG from organic compounds n Similar to burning fuel (uses oxygen), to build ATP

n Organisms get NRG from compounds by breaking chemical bonds n Some NRG gets released as heat when breaking chemical bonds n Most of the remaining NRG gets temporarily stored as ATP

ATP n ATP yields ADP + P + NRG n Made of a nitrogen base, ribose sugar, and three phosphate groups n How is the NRG released? n By breaking the chemical bond between phophate groups

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Concepts Stomata + Solar Energy n Photosynthesis: CO 2 + Water --> Sugar + O 2 Photosynthesis is the production of sugar (stored energy) and oxygen using energy from the sun to combine carbon dioxide and water. CO 2 is brought into plants and O 2 is released from plants through pores (stomata) in their leaves and other tissues. RUBISCO is the enzyme plants use to undergo photosynthesis.

8-2, 8-3 Photosynthesis n Stage One (Light Dependent RXNS) n Stage Two (Light Independent RXNS) n Chloroplast contain pigments that absorb solar NRG n Primary pigment is called chlorophyll and absorbs blue, red light waves n Two types of chlorophyll a and b

n Carotenoids are yellow and orange pigments n They absorb different wavelengths of light

Light Dependent Reactions n Pigments are located in chloroplast n Embedded in the membranes of thylakoids (disk shaped) n When light hits them, NRG is transferred to electrons n Makes them excited

n Excited electrons jump from chlorophyll molecules to other molecules in the thylakoid n These electrons fuel the second stage of photosynthesis

n Plants must replace these lost electrons n Water molecules get spilt by an enzyme n Electrons are taken from hydrogen atoms, leaving H+ n The oxygen is combined to form oxygen gas

Electron Transport Chain n Electrons are used to produce new molecules that store chemcal NRG n Electrons are passed between molecules in the thylakoid membrane n Called the Electron Transport Chain

n One type of e- chain contains a protein that acts like a membrane pump n The e- lose their NRG as they pass through the protein n This NRG is used to pump H+ into the thylakoid n This creates a concentration gradient inside the thylakoid

n The H+ then diffuse out the thylakoid through special carrier proteins n These carrier proteins function as enzymes and ion channels n These proteins catalyze a reaction that adds a phosphate group to ADP to create ATP

n ATP used to fuel the Light Independent Reactions

n Another e- transport chain makes NADPH n NADPH is an electron carrier that provides NRG to make carbonhydrogen bonds in stage 3 n NADP+ + Hydrogen ions=nadph n NADPH used to fuel the Light Independent Reactions

Light Dependent RXNS Summary n Pigments in thylakoids capture solar NRG n Electrons become excited and move through the e- transport chain n Electrons are replaced by splitting water molecules n H+ accumulate in thylakoid, helping to create ATP and NADPH

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Light Independent Reactions (The Calvin Cycle) n The Calvin cycle regenerates its starting material after molecules enter and leave the cycle. n CO 2 enters the cycle and leaves as sugar. n The cycle spends the energy of ATP and the reducing power of electrons carried by NADPH to make the sugar. n The actual sugar product of the Calvin cycle is not glucose, but a three-carbon sugar, glyceraldehyde-3-phosphate (G3P). Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

n Each turn of the Calvin cycle fixes one carbon. n For the net synthesis of one G3P molecule, the cycle must take place three times, fixing three molecules of CO 2. n To make one glucose molecules would require six cycles and the fixation of six CO 2 molecules. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

n The Calvin cycle has three phases. n In the carbon fixation phase, each CO 2 molecule is attached to a five-carbon sugar, ribulose bisphosphate (RuBP). This is catalyzed by RuBP carboxylase or rubisco. The six-carbon intermediate splits in half to form two molecules of 3-phosphoglycerate per CO 2. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

n During reduction, each 3-phosphoglycerate receives another phosphate group from ATP to form 1,3 bisphosphoglycerate. n A pair of electrons from NADPH reduces each 1,3 bisphosphoglycerate to G3P. The electrons reduce a carboxyl group to a carbonyl group. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

n If our goal was to produce one G3P net, we would start with 3 CO 2 (3C) and three RuBP (15C). n After fixation and reduction we would have six molecules of G3P (18C). One of these six G3P (3C) is a net gain of carbohydrate. n This molecule can exit the cycle to be used by the plant cell. The other five (15C) must remain in the cycle to regenerate three RuBP. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

n In the last phase, regeneration of the CO 2 acceptor (RuBP), these five G3P molecules are rearranged to form 3 RuBP molecules. n To do this, the cycle must spend three more molecules of ATP (one per RuBP) to complete the cycle and prepare for the next. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

n For the net synthesis of one G3P molecule, the Calvin recycle consumes nine ATP and six NAPDH. It costs three ATP and two NADPH per CO 2. n The G3P from the Calvin cycle is the starting material for metabolic pathways that synthesize other organic compounds, including glucose and other carbohydrates. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings