Question

4. Compare the function ATP in the light dependent and light independent(Calvin Cycle) reaction of photosynthesis to the three main activities of respiration (glycolysis, Krebs Cycle, and electron transport).

Answer 1

Role of ATP in Photosynthesis (light reaction and Calvin Cycle)

In light-dependent reaction, ATP has no function but it is synthesized from ADP by ATP-synthase due to electrochemical gradient produced by the difference in the concentration gradient of accumulated H+ ions in the thylakoid space, that makes the hydrogen ions to move through the ATP-synthase into the stroma. This process is known as photophosphorylation.

During the light-independent reaction or Calvin cycle, the energy of ATP is utilized in two ways. Energy from ATP is utilized to convert phosphoglycerate (3-PGA) into glyceraldehyde-3-phosphate (G3P). Energy from ATP is also utilized to reconvert the G3P unutilized during glucose production back into ribulose bisphosphate. In total 18 ATP molecuse supply th energy for the production of 1 molecule of gluocse.

Role of ATP in respiration (glycolysis, Krebs Cycle, electron transport)

During glycolysis, two ATP is required, one during the conversion of a glucose molecule into glucose-6-phosphate, and another during conversion of fructose-6-phosphate into fructose -1,6-biphosphate. However, ATP is also generated during the later part of glycolysis, during the conversion of 1,3-bisphosphoglycerate into 3-phosphoglycerate and conversion of phosphoenolpyruvate into pyruvate. Since two pyruvate molecules are produced by utilizing one molecule of glucose hence the total production of 4ATP molecules in the second half of the glycolysis, and this makes the gain of (4-2) or 2 ATPs in total through glycolysis of a glucose molecule.

In the Citric Acid Cycle, ATP has no functional role but ATP or GTP is produced during the conversion of Succinyl CoA into Succinate.

The NADH and FADH2 produced during the Krebs cycle or Citric Acid Cycle deliver hydrogen ions in the intermembrane space of the mitochondria and creates proton gradient in the intermembrane space. It also releases an electron in the membrane that is transported through the plasma membrane from one embedded protein to another and releasing energy during each step of this transport process which is used for the pumping of hydrogen ions into the intermembrane space from the mitochondrial matrix. The hydrogen ion that can pass back from the intermembrane space into the mitochondrial matrix through ATP-synthase by the proton-motive force developed due to the gradient of hydrogen ions in intermembrane space, results in the conversion of ADP into ATP.

One glucose molecule can produce up to 30-32 ATPs during the three stages of the respiration process.