Photosynthesis Dark Reaction

PHOTOSYNTHESIS:

The process in which green plants prepare food by using carbon dioxide and water molecule in presence of sunlight and photosynthetic pigments.

Photosynthesis process is divided into two phases;

1-LIGHT DEPENDENT REACTION

2-LIGHT INDEPENDENT REACTION

Here in this blog we will study the LIGHT INDEPENDENT REACTION in detail:

LIGHT INDEPENDENT REACTIONs:

It is called as light independent reaction because the sunlight is not directly require for this reaction to occur.

These reactions are also called Dark reaction(because it not require sunlight directly).

These reactions are also termed as CALVIN CYCLE because these reactions are explored by MELVIN CALVIN and his co-workers in 1950.

These reactions occur in stroma of chloroplast and taking course of reactions called as CALVIN BENSON CYCLE.

REQUIREMENTS FOR THESE REACTIONS:

CO2,ENZYMES,ATP AND NADPH2(produced in light dependent reaction)

MAIN PURPOSE OF DARK CYCLE:

The main purpose of this cycle is to use ATP AND NADPH2 produce in light reaction to form organic food molecule GLUCOSE.

Dark cycle reactions completed in 3 steps we will discuss each step oin detail:

1-CARBON FIXATION:

The dark cycle starts when ribulose biphosphate (5 carbon sugar) already present in stroma of chloroplast reacts with CO2 from air to form 6 carbon compound which is unstable and instantly splits into two molecules of phosphoglycertae(PGA).This process is accelerated by enzyme RUBISCO(ribulose biphosphate carboxylase)(abundant protein in nature) .

The carbon that was part of CO2 molecule now part of organic molecule PGA anf this process is called CARBON FIXATION.

PGA is classified as first product of photosynthesis.

RUBP + CO2 = short lived 6 CARBON COMPOUND

6 CARBON COMPOUND = 2 PGA

2-REDUCTION :

In previous step 2 PGA molecules were formed now in this step PGA molecules will reduced into PGAL(phosphoglyceraldehyde) by suing ATP and NADPH2 produced in light reaction.

Each molecule of PGA receives energy from ATP and hydrogen from NADPH2 and convert to PGAL.

PGA + NADPH2 + ATP = PGAL + WATER + ADP + Pi + NADP

ADP and NADP returns back to light reaction where ADP convert to ATP and NADP reduced into NADPH.

In this reduction process fixed carbon reduced into PGAL.

3-REGENERATION OF RUBP:

In this step the RUBP molecules are regenerated so as to continue the cycle.

The PGAL molecules formed in reduction step has many alternatives.

Out of every six molecules of PGAL only one molecule leaves the cycle to produce one glucose molecule while other 5 molecules are recycled to form 3 RUBP molecueles of 5 carbon.

6G3P(REDUCED FORM OF PGAL) = 5G3P + 1G3P(Produce glucose molecule).

5G3P + 3ATP = 3RUBP + ADP

Now RUBP is formed again it will accept CO2 and start cycle again.

With the regeneration of RUBP the dark cycle completes.