30. Calvin cycle

ATP and NADPH produced by the light

reactions

are used to power carbon fixation

The Calvin cycle

traps CO2 gas as 3-phosphoglycerate, a

precursor to hexose sugars.

3 stages of the Calvin Cycle

Fixation, Reduction, Regeneration

Calvin cycle stage 1

includes the fixation of carbon dioxide to ribulose bisphosphate (RuBP) by the enzyme RuBisCO.

Calvin cycle stage 2

reduction of the fixed carbon to begin the synthesis of hexose.

Calvin cycle stage 3

involves the regeneration of ribulose bisphosphate (RuBP) to enable the cycle to continue.

How many turns of calvin cycle are needed to make 1 glucose

6 turns

Where is the light rxn generated ATP and NADPH used in calvin cycle

during reduction stage (stage 2)

Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO)

combines CO2 and

ribulose 1,5-bisphosphate to make 2 molecules of 3-phosphogylcerate

RuBisCo Activase

activates Rubisco by forming a carbamate that binds Mg2+ at the active site

Role of Mg2+ with ribulose 1,5-BP

coordinating Ribulose 1,5-BP to react with CO2

After stage 2 is done and G3p is produced, what happens

Part of gluconeogenesis

(except NADPH used rather

than NADH)

Phosphoglycerate kinase

is an enzyme that catalyzes the conversion of 3-phosphoglycerate to 1,3-bisphosphoglycerate using ATP.

Glyceraldehyde dehydrogenase

is an enzyme that catalyzes the conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate, using NADPH, producing NADP+

aldolase

converts G3P to F1,6BP

F1, 6 biphosphatse

is an enzyme that catalyzes the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate

What is produced at the end of plant gluconeogenesis

hexose monophosphate pool

1 fixed CO2 makes

2 GAPs

GAP

(Glyceraldehyde-3-phosphate) is a three-carbon sugar involved in the Calvin cycle and gluconeogenesis, serving as a key intermediate in carbohydrate metabolism.

2 GAPs are made from 1 CO2 fixation, then 1 GAP is used to

regenerate Ribulose

1,5-bisphosphate

Sucrose

Fructose + Glucose

UDP-glucose

What activated glucose is used to make starch?

ADP‑glucose in the chloroplast.

What activated glucose is used to make sucrose?

UDP‑glucose in the cytosol

What is the function of sucrose in plants?

Transport form of carbon

What activated glucose is used to make cellulose?

UDP‑glucose.

What is the function of cellulose?

Structural component of the plant cell wall.

Main form of stored carbon in plants

starch

What are the three major photosynthetic strategies?

C₃ (soybean), C₄ (corn), CAM (cactus).

Example of a C₃ plant?

soybean

Example of a C₄ plant?

corn

Example of a Crassulacean Acid Metabolism (CAM) plant?

cactus

Benefit of C4 and CAM compared to C3`

more water efficient

C3 plant fixation

3 carbon P-glycerate is the

first detectable product of CO2 Fixation

C4 plant metabolsim

4 carbon oxaloacetate is

the first product of CO2 Fixation

CAM plant metabolism

also involves the fixation of CO2 into a 4-carbon compound at night, minimizing water loss during the day.but produced malate is stored in vacuole

CAM malate production

during nighttime, malate accumulates in vacuoles for use during the day.

C4 and CAM plants are more water efficient because

they can close their stomata during the day to prevent water loss while its hot, and open the stomata at night to capture CO2 t

Calvin cycle occurs in the

stroma of chloroplasts

What regulates calvin cycle

energy status, indicated by the ratio of NADPH to NADP ext{ } and ATP to ADP.

Ferredoxin_red

reduces Thioredoxin

Thioredoxin

master regulator that activates many enzymes by breaking disulfide bonds

Thioredoxin directly activates which important enzyme

(Rubisco) by reducing disulfide bonds

What does thioredoxin do in humans

provides redox regulation

When lights come on, chloroplast uses reducing power to make

reduced thioredoxin

reduced thioredoxin

is the rubisco activase

Curent CO2, O2 levels

21% O2, ~0.040% CO2 (> 400 ppm)

IN the dark, when calvin cycle is OFF

high NADP+ and Fdox and H+ in stroma leads to reduced carbon fixation.

IN the light, when calvin cycle is ON

High NADPH, FDred and Mg2+ in stroma