Photosynthesis:Light-Independent Stage

Building Sugars• What products came from the

light-dependent reactions?– ATP and NADPH

• Light-independent reactions use ATP and NADPH to build sugars from CO2

– ATP energy source– NADPH high energy electrons

and H+

• Where do these reactions happen?– Stroma of the chloroplasts

• Who mapped it out?– Melvin Calvin (called Calvin

Cycle)

The Calvin Cycle: Part 1• Where do we also find GP?

– Half-way point in glycolysis– Can start glycolysis from here

Phase 1: Carbon Fixation1) CO2 is fixed to 1,5-

bisphosphate (RuBP) by the enzyme RuBP carboxylase/oxygenase (rubisco) creating a 6-C sugar

2) 6-C is broken into two 3-phosphateglycerates (PGA)

CO2+ATP+NADPHADP+Pi+NADP++glyceraldehyde-3-phosphate(GP)

The Calvin Cycle: Part 2Phase 2: Reduction3) NADPH and ATP supply the energy, electrons, and H+ needed to change PGA into GP• How many GP do we have?

– 2• How many do we need to make

glucose?– 2

• Why do plants NOT just make sugar with the 2 GP?– Need to regenerate RuBP or cycle

shuts down• Where have we seen this before?

– Oxaloacetate in the Krebs cycle

The Calvin Cycle: Part 3Phase 3: Regeneration4) GP molecules will be used to build RuBP molecules • 3 turns of the cycle will produce 6

GP but 5 will be used to place the RuBP used; the left over G3P is used to build sugars

3 Turns:- 3 CO2 and 3 RuBP (5-C) 18 C

- 6 GPs produced- 5 GPs 15 C 3 RuBP- Last GP builds a sugar• How many turns are needed to

make glucose?– 6! That is really complex

• How many ATP are used to make glucose?– 18 ATP (3 ATP/Turn; 6 Turns)

Calvin Cycle: Regulation• What is used to regulate the

cycle?– ATP and NADPH levels

• What enzyme do they effect?– Rubisco

• Rubisco is found in all photosynthetic organisms and up to 50% of all proteins in a leaf; most abundant protein on Earth (6kg/person)

• What does the name RuBP carboxylase/oxygenase tell you about the enzyme?– Reacts with both CO2 and O2

– Competitively inhibit each other

The Problem with Gas Exchange• How does CO2 and O2 get

in and out of a plant?– Stromata under the

leaves• What else can escape

through a stromata that the plant needs?– H2O

• What problems must plants in dry, hot climates deal with?– The plant needs to take

in CO2 and release O2, but the open stromata will also release H2O

H2O out

Homework• Read Ch 10 and do Ch

10 vocabulary• Do Ch 9 vocabulary• “Test Your knowledge”

for Ch 9 and “Apply Evolutionary Thinking”

• Lab reports due next Thursday

• Ch 10 and 11 are left and then a test on Ch 9, 10 and 11