This is a question for a biologist (or someone with a good understanding of biology) who is also a creationist. But, so that everyone can get the jist of the argument, I will do my best to explain everything.
Starting with some background:
Photosynthesis is the process by which plants, and some animals, make food in the form of glucose typically from sunlight, CO2, and water. Photosynthesis has two main parts:
1) Light reactions: light energy is used to split H2O into H+ (protons) and O2, and to use those protons to make energy (in the form of ATP and NADPH).
This energy is then used to power the second part of photosynthesis,
2) The Calvin Cycle: Basically constructs sugar from CO2 in a number of steps, which I will not cover.
The first part of the Calvin Cycle is Carbon Fixation, where the CO2 is attached to RuBP, a five-carbon sugar, by an enzyme called Ribulose-Biphosphate Carboxylase, or Rubisco.
CO2 attaches to the active site (a part of an enzyme) and is then attached to RuBP. However, O2 is also a good fit for the active site of Rubisco. In fact, O2 is a better fit than CO2, and therefore is a competitive inhibitor; that is, Rubisco will accept O2 before CO2.
When O2 gets to rubisco first, bad things happen for the plant. Instead of making a 6-carbon sugar as it should, the mistaken rubisco will actually cause the 5-carbon sugar to split into a 3- and 2-carbon sugar. The 2-carbon sugar is useless, and is exported from the chloroplast. This process of mistaken substrate is called photorespiration, and is bad for plants because it depletes its stores of starch.
But why does rubisco accept the oxygen, when that leads to disaster for the plant? Well, according to modern theory, it is evolutionary baggage. When rubisco first came around about 1.5 Billion years ago, there wasn't much oxygen in the atmosphere. Therefore, it didn't really matter whether or not rubisco accepted O2 at all, much less over CO2.
This all leads to my question:
What is the creationist reason for rubisco's flaw?
-Joe
*EDIT*
For clarification, rubisco's flaw is that it has a higher affinity for oxygen than carbon dioxide, thus causing the problem of photorespiraton.
Edited by joeferrari15, : Clarification
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