Chapter 20

Question 1

Calvin Cycle definition

Answer 1

Reduce CO2 to carbohydrates using NADPH and ATP produced during the light reactions of photosynthesis

Question 2

3 Stages of Calvin Cycle

Answer 2

1) Fix
attach CO2 to ribulose 1,5-bisphosphate forming two molecules of 3-phosphoglycerate
2) Reduce
-3-phosphoglycerate to form hexose carbohydrates
3) Regenerate
-ribulose 1,5-bisphosphate

Question 3

Rubisco

Answer 3

OR Ribulose 1,5-bisphosphate carboxylase/oxygenase

Structure:
8 Large (L) subunits
-1 catalytic and regulatory site per L subunit

Most abundant enzyme on earth

Reaction rate is slow

Question 4

Rubisco activase

Answer 4

Catalyzes the formation of the carbamate
-carbamate will form spontaneously but at a lot slower rate

E amino group of R group lysine reacts with CO2 forming carbamate

Carbamate binds Mg2+ as part of the METAL CENTER

Question 5

Rubisco

-Metal Center

Answer 5

Metal Center
-Mg2+ is required for catalysis

Mg2+ Binds to:

• Glu
• Asp
• Lys carbamate-requires CO2 other than substrate CO2’s
• water

Ribulose 1,5-Bisphosphate binds and activates it

Question 6

Rubsico Carboxylase Activity

Answer 6

Fix CO2 (1C) to Ribulose 1,5-Bisphosphate (5C) producing an unstable intermediate (6C) which reacts to form 2 molecules of 3-Phosphoglycerate

In stroma: favored over oxygenase activity

Question 7

Rubisco oxygenase activity

Answer 7

adds O2

Reactants:

• Ribulose 1,5-bisphosphate
• oxygen

Products:

• Phosphoglycolate (2C) metabolic dead end
• 3-phosphoglycerate (3C)

Question 8

Photorespiratory reactions

Answer 8

• Recovers carbon skeleton from phosphoglycolate
• chloroplasts
• peroxisome (AKA microsome)
• Mitochondria

Question 9

Reduction of 3-phosphoglycerate to a hexose requires:

Answer 9

Reactants:
-3-phosphoglycerate (2 molecules)

Product:
-Fructose 6-Phosphate (1 molecule) interconverts into other hexoses

Energy provided by light reactions:

• ATP
• NADPH