Transcript The Light-Independent reaction

The Light-Independent
reaction
often called….
The Calvin Cycle
Location of the reaction
The light-independent reaction takes place in the stroma of
the chloroplasts.
The light-independent reaction can also be called the “dark
reactions”, or the Calvin Cycle.
The reaction consists of a cycle of enzyme-controlled
processes making complex molecules such as carbohydrates.
stroma
Rubisco
• Ribulose 1,5-bisphosphate (RuBP) carboxylase-oxygenase
• catalyses CO2 fixation into C3 compounds
• is the most abundant protein on the planet
Active site
Rubisco is made from 8 small and 8 large subunits
The light-independent reaction
Products of the Calvin cycle
Products of the light-independent reaction that pass back
into the light-dependent reaction:

NADP

ADP

inorganic phosphate
Products of the light-independent reaction that are used in
other processes:

triose phosphate – used to build complex
carbohydrates, amino acids and lipids.
Making complex molecules
Triose phosphate is a three-carbon sugar that can be used
to make a variety of complex biological molecules.
Pairs of TP molecules combine to form
hexose sugars, such as glucose, some
of which may isomerize to form fructose.
These monosaccharides can combine to form disaccharides
such as sucrose, and polysaccharides such as cellulose and
starch.
TP can be converted to glycerol and this may be combined
with fatty acids to make lipids.
The dark reactions: capturing CO2
The numbers are HUGE
• Atmospheric CO2 is 0.038% (and rising!)
• Total CO2 in atmosphere 700 x 109 tonnes
• Photosynthesis fixes ~100 x 109 tonnes per year
• ~15% of total atmospheric CO2 moves into
photosynthetic organisms each year!
How much can you remember?
Summary of photosynthesis
light
lightdependent
reactions
lightindependent
reactions
carbohydrates, other
complex molecules
Assembly of photosynthesis complexes
chloroplast
nuclear
gene product
gene product
• All complexes contain at least one nuclear-encoded subunit
• Requires coordination of plastid and nuclear gene expression
Photosynthesis: true or false?
Glossary
What’s the keyword?
Inputs and outputs to the reactions
Multiple-choice quiz