Light Independent Reactions

Question 1

3 major steps of Calvin cycle

Answer 1

Carboxylation => PGA
Reduction => GAP
Regeneration => RubBp

Question 2

Output of calvin cycle

Answer 2

Triose phosphate

Question 3

PGA

Answer 3

3-Phosphoglycerate

Question 4

GAP

Answer 4

Glayceraldehyde phosphate = triose phosphate

Question 5

RubBp

Answer 5

Ribulose-1,5-bisphosphat

Question 6

RubisCo

Answer 6

Carboxylase and oxygenase activity

Question 7

carboxylation step

Answer 7

RubBp => PGA (phosphoglycerate)
Mediated by carboxylase activity of RubBp

Question 8

Calvin Cycle
Reduction phase

Answer 8

GAP production in 2 steps

1) PGA kinase phosphorylates PGA using 2ATP
2) GADPH reduces 1,3 bis PGA using 2 NADPH

=> 6 GPA created from 3 CO2
=> one used for sugar biosynthesis, other 4 used for regeneration of RubBp

Question 9

What derives from Calvin Benson cycle?

Answer 9

Sugars => Sucrose
Isoprenoids
Starch
Shikimate
Thiamine (immune, vitamins)
Nucleotides

Question 10

Fructose-1,6-bisphosphate

Answer 10

derives from GAP
=> goes to hexose monophosphate pool (glucose and fructose precursors for energy storage)
=> activation with UTP/ATP

Question 11

Biosynthesis of sucrose

Answer 11

Fructose-6-phosphate + UDP-glucose
=> sucrose-6-phosphat (dimer) + UDP

Question 12

Starch Biosynthesis

Answer 12

ADP glucose assembles to chain of glucose polymer
= amylose

Question 13

Amylose

Answer 13

Crystalline structure that forms starch granules
=> layers

Question 14

How are enzymes of the calvin cycle activated?

Answer 14

Ferredoxin transfers electron => reduces enzyme
In reduced state, no disulfide bond = active

Inactive complex/supercomplex of proteins in low light condition (oxidized) => due to disulfide bonds

Question 15

Oxygenase activity of RubisCo leads to

Answer 15

1 Phosphoglycerate (PGA) and one 1 2-phosphoglycolate (2 carbon compound)

Question 16

How can RubisCo activity be increased?

Answer 16

Increase conc. (50% of proteins in a leaf are RubisCo)
Concentrate CO2 around RubisCo

Question 17

Structure of RubisCo

Answer 17

L8S8

(Large => catalytic/small => regulatorysubunits)

Large encoded by plastid genome

Question 18

RubisCo activation

Answer 18

Requires:
binding of Substrate (CO2)
= Carbamylation at Lys (E)
Mg2+

Question 19

Inhibition of RubisCo

Answer 19

RubBp
Xylose phosphate

Question 20

Photorespiration

Answer 20

Phosphoglycolate conversion into phosphoglycerate

Involves chloroplast, peroxysome and mitochondria => very energy consuming process

Question 21

Why did RubisCo evolve oxygenase activity?

Answer 21

Evolved in low oxygen atmosphere => but similar molecules (CO2 & O2) => by chance?