17.4

5/27/2018 17.4

1/18

17.0 Photosynthesis

1) 17.1 Overview of photosynthesis2) 17.2 Absorption spectrum of

photosynthesis pigments3) 17.3 Light Dependent Reaction

4) 17.4 Light Independent Reaction/CalvinCycle

5) 17.5 Alternative mechanisms of CarbonFixation : Hatch Slack (C4) andCrassulacean Acid Metabolism (CAM)pathways

5/27/2018 17.4

2/18

Learning outcomes :

17.4 Light Independent Reaction/

Calvin Cycle

Describe Calvin Cycle involving

carbon fixation, reduction of

PGAL and regeneration of RUBP

5/27/2018 17.4

3/18

CALVIN CYCLE

Also known as the light independent

reaction

Occurs in stroma of the chloroplast

Results in the reduction of carbon

dioxide to synthesise carbohydrates

The power and energy for the varioussteps are provided by NADPHand ATP

from the light dependent reactions

Learning Outcomes :

17.4 : Describe Calvin cycle involving carbon fixation, reduction of PGAL and regeneration of RuBP

5/27/2018 17.4

4/18

Phases in Calvin Cycle

1) Carbon fixation

2) Reduction of PGAL3) Regeneration of Ribulose bisphosphate

(RuBP)

Learning Outcomes :


5/27/2018 17.4

5/18

Phase 1 : Carbon fixation

Learning Outcomes :


5/27/2018 17.4

6/18

Phase 1 : Carbon fixation

Each CO2molecule is

attachedto ribulose

bisphosphate (RuBP),

5C sugar to form 6C

compound which isunstable

Catalyzed by RuBP

carboxylaseor

RuBisCO

Learning Outcomes :


5/27/2018 17.4

7/18

The unstable 6C

compound breaks

down to form 2molecules of 3C

called 3-

phosphoglycerate(PGA), for each

CO2

Phase 1 : Carbon dioxide fixation

Learning Outcomes :


5/27/2018 17.4

8/18

Phase 2 : Reduction of PGAL

Learning Outcomes :


5/27/2018 17.4

9/18


Occurs in two steps:

Step 1 : Phosphorylation

Each molecule of 3-phosphoglycerate (PGA)

receives an additional

phosphate group from ATP

to form 1,3-bisphosphoglycerate

Learning Outcomes :


5/27/2018 17.4

10/18

Step 2 : Reduction

Electrons donated

fromNADPHreduces 1,3-

bisphosphoglycerate

to Glyceraldehyde-

3-phosphate (G3P)or PGAL


Learning Outcomes :


5/27/2018 17.4

11/18

The NADP+and ADP

formed in this process

return to thethylakoids to

regenerate NADPH

and ATPin the lightdependent reactions.


Learning Outcomes :


5/27/2018 17.4

12/18

After fixation and

reduction we would have

six molecules of G3P

One molecule exits thecycle to be used by the

plant

The otherfive molecules

must remainin the cycleto regenerate three

molecule of RuBP.


Learning Outcomes :


5/27/2018 17.4

13/18

Phase 3 : Regeneration of RuBP

Learning Outcomes :


5/27/2018 17.4

14/18

Regeneration of RuBP (the CO2acceptor)

Phase : Regeneration of RuBPLearning Outcomes :


5/27/2018 17.4

15/18

Involves a seriesof reactions :

5 molecules of

Glyceraldehyde-3-

phosphate (G3P)are converted to 3

molecules of

Ru5P (ribulose-5-

phosphate), the5C compound


Learning Outcomes :


5/27/2018 17.4

16/18

3 molecules of Ru5Pare phosphorylated to

regenerate RuBP

(ribulose

bisphosphate). Requires 3 ATP that

formed in the light

dependent reactions


Learning Outcomes :


5/27/2018 17.4

17/18

The remaining

G3P is used to

synthesizeorganic

molecules eg :

glucose


Learning Outcomes :


5/27/2018 17.4

18/18

Roles of ATP & NADPH

ATP: used in phosphorylation of PGAto form 1,3-bisphosphoglycerate

NADPH: used in reduction of 1,3-bisphosphoglycerate to form

G3P/PGAL

Learning Outcomes :


17.4

Documents