Download Calvin Cycle - WordPress.com

CALVIN CYCLE
LIGHT-INDEPENDENT REACTIONS
PHOTOSYNTHESIS
• So far we have
looked at how
photoautotrophs
use light energy to
excite electrons,
and in conjunction
with H2O they
produce O2, ATP,
and NADPH
• Now we look at
how NADPH and
ATP are utilized
THE CALVIN CYCLE
• Who are the players?
•
•
•
•
CO2
NADPH
ATP
C6H12O6
• The Calvin Cycle has 3
phases that takes CO2
and uses ATP and NADPH
to form glucose
PHASE 1 – CARBON FIXATION
Ribulose-1,5-biphosphate
3-Phosphoglyceric Acid
• Carbon fixation = conversion from inorganic to organic
• CO2 (inorganic) enters the stroma through stoma
openings and begins the cycle by reacting with RuBP
(rubisco catalyst) to form 2 3-PGA (organic)
• Called “C3 Metabolism” – taking a 5 carbon molecule
and forming two 3 carbon molecules
PHASE 2 - REDUCTION
• This phase requires a lot of energy
which is provided by the ATP and
NADPH we produced during lightdependent reactions
• 3-Phosphoglyceric Acid has an
additional phosphate added by
hydrolysis of ATP
• After Phosphate is added it is reduced
using the electrons from NADPH to
form Glyceraldehyde 3-phosphate
• 1 of the G3P exits the cycle and is used to
form Glucose
PHASE 3 - REGENERATION
• The other 5 G3P are rearranged
using ATP to reform RuBP
• NOTE: don’t let the values in these
pictures mislead you… in reality it
takes 3 cycles of the calvin cycle to
produce one extra G3P to be used
to form glucose
THE COMPLETE CALVIN CYCLE
REMEMBER: each turn of the cycle
produces an extra carbon when G3P is
converted to RuBP; this is why it takes 3
turns to form 1 usable G3P for Glucose
OTHER THINGS YOU NEED TO KNOW
1. This process goes from a fully oxidized carbon
molecule to a highly reduced glucose molecule –
endergonic
2. Rubisco (ribulose 1,5-biphosphate carboxylase
oxygenase) – most important protein/enzyme in
the biosphere: provides majority of the worlds
organic carbon
3. Plants use G3P and reverse-process glycolysis to
produce glucose and other simple sugars