The Calvin Cycle Part II of Photosynthesis

Calvin Named after American biochemist Melvin Calvin Most commonly used pathway by most plants Calvin cycle is used by plants that are called C3 because of the 3-Carbon molecules that are made

Photosynthesis Light-independent reaction (Dark Reaction) Light-independent reaction (Dark Reaction) Does not require light Does not require light Calvin Cycle Calvin Cycle Occurs in stroma of chloroplast Occurs in stroma of chloroplast Requires CO 2 Requires CO 2 Uses ATP and NADPH as fuel to run Uses ATP and NADPH as fuel to run Makes glucose sugar from CO 2 and Hydrogen Makes glucose sugar from CO 2 and Hydrogen

The Calvin cycle uses products from the light reactions + CO 2 to make sugars and other compounds What are the products of the light reactions? Where does the CO 2 come from? Calvin Cycle

CO 2 is changed to sugar in a series of chemical reactions: CO 2 + RuBP  6-Carbon molecule RuBP = 5 Carbon sugar The Enzyme that catalyzes this reaction is rubisco = the most abundant protein in nature(25%)

Step 1 CO 2 is diffused into the stroma of the chloroplast A 5-Carbon molecule named RuBP combines to the CO 2 This becomes a 6-Carbon molecule that is very unstable Split to become two 3-Carbon molecules called 3- phosphoglycerate (3-PGA) 6-Carbon Sugar  3-PGA + 3-PGA

Step 2 3-PGA is still unstable 3-PGA  glyceraldehyde 3-phosphate (G3P) For this to occur, each3-PGA molecule gets a phosphate from ATP and a proton from NADPH Once the molecule receives the P and proton it converts into G3P

3-PGA + P + H  G3P Where did the P and H come from? *ATP  ADP + P *NADPH  NADP + + H

Step 3 One G3P molecule leaves the Calvin cycle One G3P molecule leaves the Calvin cycle This will be used to make a carbohydrate later This will be used to make a carbohydrate later

Step 4 Other G3P molecule gets converted BACK to RuBP due to an addition of another phosphate from ATP Other G3P molecule gets converted BACK to RuBP due to an addition of another phosphate from ATP G3P + P  RuBP G3P + P  RuBP This RuBP goes back to the Calvin cycle to be fixed again This RuBP goes back to the Calvin cycle to be fixed again

Photosynthesis Formula Light energy 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2

Redox Reactions Reduction Gain electrons Gain electrons Oxidation Loses electrons

Oxidation Reaction Loss of electrons from a substance in a chemical reaction What molecules were oxidized during photosynthesis?

Reduction Reaction The gain of electrons by a substance in a chemical reaction Which substances were reduced during photosynthesis?

Stoma This opening how plants exchange gases! Why are they stomata located on the bottom of leaves?

Stoma Stoma Open CO 2 can increase O 2 will decrease and leave cells Stoma Closed CO 2 decrease O 2 increases

C 4 Pathway Plants that use this are called C 4 plants and have stomata closed during hot part of day Enzyme fixes CO 2 to a 4-carbon compound when CO 2 is low and O 2 is high Corn, sugar cane, & crab grass Usually tropical climates

CAM Pathway Water conserving pathway Hot dry climates Stoma closed during day & open at night Opposite of ordinary plants Pineapples & cactuses

CAM Pathway During the day Stoma are closed CO 2 is released from compounds and enters Calvin cycle During the night Stoma are open Take in CO 2 and fix into carbon compounds

PHOTOSYNTHESIS What affects photosynthesis? What affects photosynthesis? Light intensity: as light increases, rate of photosynthesis increases Light intensity: as light increases, rate of photosynthesis increases

PHOTOSYNTHESIS What affects photosynthesis? Carbon Dioxide: As CO 2 increases, rate of photosynthesis increases

PHOTOSYNTHESIS What affects photosynthesis? What affects photosynthesis? Temperature: Temperature: Temperature Low = Rate of photosynthesis low Temperature Low = Rate of photosynthesis low Temperature Increases = Rate of photosynthesis increases Temperature Increases = Rate of photosynthesis increases If temperature too hot, rate drops If temperature too hot, rate drops