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

PhotosynthesisLight-independent reaction

(Dark Reaction)Does not require light

Calvin CycleOccurs in stroma of chloroplastRequires CO2

Uses ATP and NADPH as fuel to runMakes glucose sugar from CO2 and

Hydrogen

The Calvin cycle uses products from the light reactions + CO2 to make sugars and other compounds

What are the products of the light reactions?

Where does the CO2 come from?

Calvin Cycle

Calvin Cycle

CO2 is changed to sugar in a series of chemical reactions:

CO2 + RuBP 6-Carbon molecule RuBP = 5 Carbon sugar

The Enzyme that catalyzes this reaction is rubisco = the most abundant protein in nature(25%)

Step 1CO2 is diffused into the stroma of the

chloroplast

A 5-Carbon molecule named RuBP combines to the CO2

This becomes a 6-Carbon molecule that is

very unstableSplit to become two 3-Carbon molecules

called 3-phosphoglycerate (3-PGA)

6-Carbon Sugar 3-PGA + 3-PGA

Step 2

3-PGA is still unstable3-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 3One G3P molecule leaves the Calvin

cycle 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 G3P + P RuBP

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

Photosynthesis Formula

Light energy

6CO2 + 6H2O C6H12O6 + 6O2

Redox Reactions

Reduction

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?

StomaThis opening how plants exchange

gases!

Why are they stomata located on the bottom of leaves?

StomaStoma Open

CO2 can increase

O2 will decrease and leave cells

Stoma ClosedCO2

decreaseO2

increases

C4 Pathway

Plants that use this are called C4 plants and have stomata closed during hot part of day

Enzyme fixes CO2 to a 4-carbon compound when CO2 is low and O2 is high

Corn, sugar cane, & crab grass

Usually tropical climates

CAM Pathway

Water conserving pathway

Hot dry climates

Stoma closed during day & open at nightOpposite of ordinary plants

Pineapples & cactuses

CAM Pathway

During the dayStoma are closedCO2 is released from compounds and

enters Calvin cycle

During the nightStoma are openTake in CO2 and fix into carbon

compounds

PHOTOSYNTHESIS

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

photosynthesis increases

PHOTOSYNTHESIS

What affects photosynthesis? Carbon Dioxide: As CO2 increases, rate of

photosynthesis increases

PHOTOSYNTHESIS

What affects photosynthesis?Temperature:

Temperature Low = Rate of photosynthesis low

Temperature Increases = Rate of photosynthesis increases

If temperature too hot, rate drops