PhotosynthesisPhotosynthesisThe Calvin CycleThe Calvin Cycle

Melvin CalvinMelvin Calvin

It’s a cycleIt’s a cycle

• Like a sugar factory in the cell• Starting molecule regenerated

• Like a sugar factory in the cell• Starting molecule regenerated

“Roo Bee Pee”

Comparison of Citric Acid Cycle and Calvin Cycle

Comparison of Citric Acid Cycle and Calvin Cycle

Cell Respiration

Citric acid cycle is catabolic -

oxidizes glucose and releases

energy

Cell Respiration

Citric acid cycle is catabolic -

oxidizes glucose and releases

energy

Photosynthesis

Calvin cycle is anabolic - building

sugar and consuming energy

Photosynthesis

Calvin cycle is anabolic - building

sugar and consuming energy

General OverviewGeneral Overview• In Calvin cycle - CO2 enters, 3-C sugar

exits

• Cycle uses ATP for energy and uses NADPH as a reducing agent to add electrons to make the sugar– The ATP and NADPH come from the Light

Reactions

• In Calvin cycle - CO2 enters, 3-C sugar exits

• Cycle uses ATP for energy and uses NADPH as a reducing agent to add electrons to make the sugar– The ATP and NADPH come from the Light

Reactions

Quick ThinkQuick Think

• With someone near you, discuss how the light reactions support the dark reactions (aka the Calvin Cycle)

• Be prepared to share your discussion

• With someone near you, discuss how the light reactions support the dark reactions (aka the Calvin Cycle)

• Be prepared to share your discussion

• Calvin cycle makes a 3-carbon sugar called G3P (glyceraldehyde-3-phosphate)

• Calvin cycle makes a 3-carbon sugar called G3P (glyceraldehyde-3-phosphate)

Input

Three CO2

Six 3-PGA

Six

Six ADP + Six

Six

Six NADP

Six G3P

Glucose andother compounds

Output

Five G3P

Three

Three ADP

Three RuBP

CalvinCalvincyclecycle

1

2

3

4

One G3P

Calvin Cycle - 3 phases + regeneration of starting molecule

Phase 1- Carbon FixationPhase 1- Carbon Fixation• 3 CO2 molecules enter Calvin Cycle 1 at a

time • Each one is attached to a 5-C sugar -

ribulose biphosphate (RuBP)• Enzyme rubisco (RuBP carboxylase)

catalyzes this reaction– Rubisco is likely the most abundant protein on

earth

• Product of this phase is a 6-C highly unstable molecule that immediately splits in 1/2 to make 2 molecules of 3-phosphoglycerate for each CO2 that entered (so 6 total)

• 3 CO2 molecules enter Calvin Cycle 1 at a time

• Each one is attached to a 5-C sugar - ribulose biphosphate (RuBP)

• Enzyme rubisco (RuBP carboxylase) catalyzes this reaction– Rubisco is likely the most abundant protein on

earth

• Product of this phase is a 6-C highly unstable molecule that immediately splits in 1/2 to make 2 molecules of 3-phosphoglycerate for each CO2 that entered (so 6 total)

The product of Phase 1, 6 made

Go to your diagrams

Quick ThinkQuick Think

• With someone near you, summarize what happens in the first phase of the Calvin Cycle

• Be prepared to share

• With someone near you, summarize what happens in the first phase of the Calvin Cycle

• Be prepared to share

Phase 2 - ReductionPhase 2 - Reduction

1. Each 3-phosphogylcerate gets an extra phosphate group from ATP to become 1,3-biphosphoglycerate

1. Each 3-phosphogylcerate gets an extra phosphate group from ATP to become 1,3-biphosphoglycerate

6 made, takes 6 ATP to do this

Phase 2 - ReductionPhase 2 - Reduction

2. A pair of electrons donated by NADPH reduces 1,3-biphosphoglycerate to G3P- the electrons from NADPH reduce the carboxyl group of 3-phosphoglycerate to the aldehyde group of G3P, which stores more potential energy

2. A pair of electrons donated by NADPH reduces 1,3-biphosphoglycerate to G3P- the electrons from NADPH reduce the carboxyl group of 3-phosphoglycerate to the aldehyde group of G3P, which stores more potential energy

Phase 2 - ReductionPhase 2 - Reduction

• For every 3 molecules of CO2

that enter the cycle, 6 molecules of G3P are formed

• Only 1 counts as a net gain because the other 5 must recycled back to RuBP to allow the cycle to continue

• For every 3 molecules of CO2

that enter the cycle, 6 molecules of G3P are formed

• Only 1 counts as a net gain because the other 5 must recycled back to RuBP to allow the cycle to continue

Go to your diagrams

Quick ThinkQuick Think

• With someone near you, summarize what happens in the 1st AND 2nd phases of the Calvin Cycle

• Be prepared to share

• With someone near you, summarize what happens in the 1st AND 2nd phases of the Calvin Cycle

• Be prepared to share

Phase 3 - Regeneration of the CO2 acceptor (RuBP)

Phase 3 - Regeneration of the CO2 acceptor (RuBP)

• The 5 G3Ps are rearranged into 3 molecules of RuBP

• Requires 3 ATP to do this

• RuBP can now continue cycle and accept new CO2s that enter

• The 5 G3Ps are rearranged into 3 molecules of RuBP

• Requires 3 ATP to do this

• RuBP can now continue cycle and accept new CO2s that enter

Go to your diagrams

Quick ThinkQuick Think

• With someone near you, summarize all 3 phases of the Calvin cycle

• Be prepared to share

• With someone near you, summarize all 3 phases of the Calvin cycle

• Be prepared to share

Calvin Cycle SummaryCalvin Cycle Summary

• Net - 1 G3P sugar• Consumed - 9 ATP, 6

NADPH

• G3P that exits the cycle becomes the starting molecule in various metabolic pathways that make different organic compounds including glucose

• Net - 1 G3P sugar• Consumed - 9 ATP, 6

NADPH

• G3P that exits the cycle becomes the starting molecule in various metabolic pathways that make different organic compounds including glucose

Calvin Cycle SummaryCalvin Cycle Summary

• To make 1 molecule of glucose, the Calvin cycle uses 6 molecules of CO2, 18 molecules of ATP, 12 molecules of NADPH

• To make 1 molecule of glucose, the Calvin cycle uses 6 molecules of CO2, 18 molecules of ATP, 12 molecules of NADPH

Quick ThinkQuick Think

• With someone near you, discuss why it is called the Calvin CYCLE

• Be prepared to share

• With someone near you, discuss why it is called the Calvin CYCLE

• Be prepared to share

That’s a lot of ATP…That’s a lot of ATP…

• It take a lot of ATP to make glucose, but it is worth it because glucose stores so much potential energy for the cell

• It take a lot of ATP to make glucose, but it is worth it because glucose stores so much potential energy for the cell

Connections between the Light Reactions and the Calvin CycleConnections between the Light Reactions and the Calvin Cycle

• Light reactions produce ATP and NADPH, which are used during the Calvin Cycle

• Calvin cycle returns ADP and NADP+ to the chloroplast, so they can be used again in the Light Reactions

• Light reactions produce ATP and NADPH, which are used during the Calvin Cycle

• Calvin cycle returns ADP and NADP+ to the chloroplast, so they can be used again in the Light Reactions

Quick ThinkQuick Think

• With someone near you, discuss how the light reactions and the Calvin cycle support each other

• Be prepared to share

• With someone near you, discuss how the light reactions and the Calvin cycle support each other

• Be prepared to share

1.•What is the overall chemical equation for photosynthesis?

2.•What molecule goes in to the Calvin Cycle?

3.•What molecule comes out of the Calvin cycle?

4. Bonus•What is the name of the enzyme that fixes carbon dioxide?

5. Bonus•How many sugar molecules leave the Calvin Cycle?