The Calvin The Calvin CycleCycle Part II of PhotosynthesisPart II of Photosynthesis

CalvinCalvinNamed after American Named after American

biochemist Melvin Calvinbiochemist Melvin CalvinMost commonly used pathway by most Most commonly used pathway by most

plantsplantsCalvin cycle is used by plants that are Calvin cycle is used by plants that are

called C3 because of the 3-Carbon called C3 because of the 3-Carbon molecules that are mademolecules that are made

PhotosynthesisPhotosynthesisLight-independent reaction (Dark Light-independent reaction (Dark

Reaction)Reaction)Does not require lightDoes not require light

Calvin CycleCalvin CycleOccurs in stroma of chloroplastOccurs in stroma of chloroplastRequires CORequires CO22Uses ATP and NADPH as fuel to runUses ATP and NADPH as fuel to runMakes glucose sugar from COMakes glucose sugar from CO22 and and

HydrogenHydrogen

The Calvin cycle uses products from The Calvin cycle uses products from the light reactions + COthe light reactions + CO22 to make to make sugars and other compoundssugars and other compounds

What are the products of the light What are the products of the light reactions?reactions?

Where does the COWhere does the CO22 come from? come from?

Calvin CycleCalvin Cycle

Calvin CycleCalvin CycleCOCO2 2 is changed to sugar in a series of is changed to sugar in a series of

chemical reactions:chemical reactions:COCO22 + RuBP + RuBP 6-Carbon molecule 6-Carbon molecule

RuBP = 5 Carbon sugarRuBP = 5 Carbon sugarThe Enzyme that catalyzes this reaction is The Enzyme that catalyzes this reaction is

rubisco = the most abundant protein in rubisco = the most abundant protein in nature(25%)nature(25%)

Step 1Step 1COCO22 is diffused into the stroma of the is diffused into the stroma of the

chloroplast chloroplast A 5-Carbon molecule named RuBP combines A 5-Carbon molecule named RuBP combines

to the COto the CO22This becomes a 6-Carbon molecule that is very This becomes a 6-Carbon molecule that is very

unstableunstableSplit to become two 3-Carbon molecules called 3-Split to become two 3-Carbon molecules called 3-

phosphoglycerate (3-PGA)phosphoglycerate (3-PGA)6-Carbon Sugar 6-Carbon Sugar 3-PGA + 3-PGA 3-PGA + 3-PGA

Step 2Step 23-PGA is still 3-PGA is still unstableunstable3-PGA 3-PGA glyceraldehyde 3-phosphate (G3P) glyceraldehyde 3-phosphate (G3P)For this to occur, each3-PGA molecule For this to occur, each3-PGA molecule

gets a phosphate from ATP and a gets a phosphate from ATP and a proton from NADPHproton from NADPH

Once the molecule receives the P and Once the molecule receives the P and proton it converts into G3Pproton it converts into G3P

3-PGA + P + H 3-PGA + P + H G3PG3P

Where did the P and H come Where did the P and H come from?from?

*ATP*ATP ADP + P ADP + P *NADPH *NADPH NADP NADP++ + H + H

Step 3Step 3One G3P molecule leaves the Calvin One G3P molecule leaves the Calvin

cycle cycle This will be used to make a carbohydrate This will be used to make a carbohydrate

laterlater

Step 4Step 4Other G3P molecule gets converted BACK to Other G3P molecule gets converted BACK to

RuBP due to an addition of another phosphate RuBP due to an addition of another phosphate from ATPfrom ATP G3P + P G3P + P RuBP RuBP

This RuBP goes back to the Calvin cycle to be This RuBP goes back to the Calvin cycle to be fixed againfixed again

Photosynthesis Photosynthesis FormulaFormula

Light energyLight energy

6CO6CO2 2 + 6H+ 6H22O O C C66HH1212OO6 6 + 6O+ 6O22

Redox ReactionsRedox ReactionsReduction Reduction Gain electronsGain electrons

OxidationOxidationLoses Loses

electronselectrons

Oxidation ReactionOxidation ReactionLoss of electrons from a Loss of electrons from a

substance in a chemical substance in a chemical reactionreaction

What molecules were What molecules were oxidized during oxidized during photosynthesis?photosynthesis?

Reduction Reduction ReactionReaction

The gain of electrons by The gain of electrons by a substance in a a substance in a chemical reactionchemical reaction

Which substances were Which substances were reduced during reduced during photosynthesis?photosynthesis?

StomaStomaThis opening how plants exchange This opening how plants exchange

gases!gases!

Why are the Why are the stomata located stomata located on the bottom of on the bottom of leaves?leaves?

StomaStomaStoma OpenStoma Open

COCO22 can can increaseincrease

OO22 will will decrease and decrease and leave cellsleave cells

Stoma Stoma ClosedClosedCOCO22

decreasedecreaseOO22

increasesincreases

CC44 Pathway PathwayPlants that use this are called CPlants that use this are called C44 plants plants

and have stomata closed during hot part and have stomata closed during hot part of dayof day

Enzyme fixes COEnzyme fixes CO22 to a 4-carbon to a 4-carbon compound when COcompound when CO2 2 is low and Ois low and O22 is high is high

Corn, sugar cane, & crab grassCorn, sugar cane, & crab grassUsually tropical climatesUsually tropical climates

CAM PathwayCAM Pathway

Water conserving pathwayWater conserving pathwayHot dry climatesHot dry climatesStoma closed during day & open at nightStoma closed during day & open at night

Opposite of ordinary plantsOpposite of ordinary plantsPineapples & cactusesPineapples & cactuses

CAM PathwayCAM PathwayDuring the dayDuring the day

Stoma are closedStoma are closedCOCO22 is released from compounds and is released from compounds and

enters Calvin cycleenters Calvin cycleDuring the nightDuring the night

Stoma are openStoma are openTake in COTake in CO2 2 and fix into carbon and fix into carbon

compoundscompounds

PHOTOSYNTHESISPHOTOSYNTHESISWhat affects photosynthesis?What affects photosynthesis?

Light intensity: as light increases, rate of Light intensity: as light increases, rate of photosynthesis increases photosynthesis increases

PHOTOSYNTHESISPHOTOSYNTHESISWhat affects photosynthesis?What affects photosynthesis?

Carbon Dioxide: As COCarbon Dioxide: As CO22 increases, rate of increases, rate of photosynthesis increasesphotosynthesis increases

PHOTOSYNTHESISPHOTOSYNTHESISWhat affects photosynthesis?What affects photosynthesis?

Temperature: Temperature: Temperature Low = Rate of photosynthesis lowTemperature Low = Rate of photosynthesis low Temperature Increases = Rate of photosynthesis Temperature Increases = Rate of photosynthesis

increasesincreases If temperature too hot, rate dropsIf temperature too hot, rate drops