The Calvin Cycle

1. Photosynthesis
The Calvin Cycle
Melvin CalvinMelvin Calvin

2. It’s a cycle
• Like a sugar factory in the cell
• Starting molecule regenerated
“Roo
Bee
Pee”

3. Comparison of Citric AcidComparison of Citric Acid
Cycle and Calvin CycleCycle and Calvin Cycle
Cell RespirationCell Respiration
Citric acid cycle isCitric acid cycle is
catabolic -catabolic -
oxidizes glucoseoxidizes glucose
and releasesand releases
energyenergy
PhotosynthesisPhotosynthesis
Calvin cycle isCalvin cycle is
anabolic - buildinganabolic - building
sugar andsugar and
consuming energyconsuming energy

4. General 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

5. Quick Think
• With someone near you,
discuss how the light reactions
support the dark reactions
(aka the Calvin Cycle)
• Be prepared to share your
discussion

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

8. Input
Three CO2
Six 3-PGA
Six
Six ADP + Six
Six
Six NADP+
Six G3P
Glucose and
other compounds
Output
Five G3P
Three
Three ADP
Three RuBP
CalvinCalvin
cyclecycle
1
2
3
4
One G3P
Calvin Cycle - 3
phases
+ regeneration of
starting molecule

9. Phase 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)
The product
of Phase 1,
6 made

10. Go to your diagrams

11. Quick Think
• With someone near you,
summarize what happens in
the first phase of the Calvin
Cycle
• Be prepared to share

12. Phase 2 - Reduction
Each 3-phosphogylcerate
gets an extra phosphate
group from ATP to
become 1,3-
biphosphoglycerate
Each 3-phosphogylcerate
gets an extra phosphate
group from ATP to
become 1,3-
biphosphoglycerate
6
intermediate
molecules
made, takes
6 ATP to do
this

13. Phase 2 - Reduction
A pair of electrons donated by
NADPH to make G3P
- the electrons from NADPH
reduce the carboxyl group of
3-phosphoglycerate to the
aldehyde group of G3P, which
stores more potential energy

15. Phase 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
Go to your diagrams

16. Quick Think
• With someone near you,
summarize what happens in
the 1st AND 2nd phases of the
Calvin Cycle
• Be prepared to share

17. 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

18. Go to your diagrams

19. Quick Think
• With someone near you,
summarize all 3 phases of the
Calvin cycle
• Be prepared to share

20. Calvin 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

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

24. Quick Think
• With someone near you,
discuss why it is called the
Calvin CYCLE
• Be prepared to share

25. 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

26. Connections 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

27. Quick Think
• With someone near you,
discuss how the light reactions
and the Calvin cycle support
each other
• Be prepared to share