[2024]Digital Global Overview Report 2024 Meltwater.pdf
Light independent reactions of photosynthesis
1. Light Independent Reactions of
Photosynthesis
Dr. Mark A. McGinley
Honors College and Department of
Biological Sciences
Texas Tech University
2. Results of the Light Dependent
Reactions
• The potential energy in the ATP and NADPH
produced during the light dependent
reactions of photosynthesis can only be stored
for a fraction of a second
– Thus this energy must be used immediately or the
energy will be lost
3. Calvin Cycle
• The Calvin Cycle is the chemical process that
helps to convert potential energy from ATP
and NADPH into potential energy stored in
glucose
• The Calvin Cycle occurs in the stroma
4. Calvin Cycle
First Reaction
C02 reacts with RUBP to form unstable 6 C
intermediate
5. Where Does the CO2 Come From?
• The CO2 comes from the environment
– Terrestrial plants pick up CO2 from the air
– Marine and aquatic plants pick up CO2 from the
water
6. RuBP Carboxylase
• The reaction of CO2 +
RUBP is calatlyzed by
the enzyme RuBP
carboxylase
– rubisco
7. RuBP Carboxylase
• The most abundant protein on the planet
– More than50% of protein in some plant cells
– 40 million Kg of RuBP carboxlyase created each
year
• 1000 Kg per second!!
8. RuBP Carboxylase
• Protein with quaternary structure
– 8 large subunits
– 8 small subunits
• Large subunits coded for by chloroplast DNA
• Small subunits coded for by nuclear DNA
9. Calvin Cycle
CO2 + RuBP => unstable 6 carbon intermediate
2 molecules of PGA
(3 phosphoglycerate)
11. Calvin Cycle
Important Points
• Converting PGA to Glyceraldehyde phosphate
(G3P) requires the addition of energy released
by ATP and NADPH
– (this is the same ATP and NADPH that were just
produced in the Light Dependent Reactions)
12. Calvin Cycle
Important Points
• Glyceraldehyde 3 Phospate (G3P)
– Can be used to produced glucose
• Potential energy stored in chemical bonds of glucose
– Can be used to make RUBP
• Converting G3P to RUBP requires the input of energy
from ATP (also created by the light dependent
reactions)
13. Light Independent Reactions
• Please don’t call these the “Dark Reactions”
(you will sometimes see this term, but try to
avoid it)
– Light independent reactions must take place in the
light because light is required to put potential
energy in the bonds of ATP and NADPH
14. Light Independent Reactions
• Potential energy in ATP and NADPH is
converted to potential energy held in glucose
• CO2 => => glucose