Question

Bacteriorhodopsin is a protein found in Halobacterium halobium that converts light energy into a transmembrane proton gradient that is used for ATP synthesis. After light is absorbed by the protein, the following initial reaction sequence occurss:

Br   ----->   J   ----->   K          where:  k1 = 2.0 x 10^12 s^-1    and    k2 = 3.3 x 10^11 s^-1

Construct plots of the concentration of each species versus time in excel. Please show all steps and data plugged into excel.

Answer 1

According to the reaction, Br is converted into J in step 1 which is further converted into K in step 2, as a final product. It can be seen from the image that the reaction constant for step 1 is much higher than reaction constant of step 2. This suggests that the reaction of step 1 is highly spontaneous in nature and the substrate Br is immediately converted into a mid-product J as soon as light energy is available. However, the reaction constant for step 2 is also large enough to decipher that the step 2 reaction is also spontaneous. However, the order of k1 is higher than k2 by 2*10^12/3.3*10^11 or nearly 6 times. This suggests that the reaction velocity of step 1 is much higher than step 2 thus implying that :

1. The substrate Br will be converted into J as soon as light energy is available. This reaction is very spontaneous in nature.
2. As soon as J appears, it will be conveted into K.
3. The total time taken for converting Br to J will be less than the time taken for converting J to K, and similarly, the area under the curve for the concentration gradient for Br to J will be less than that for J to k.

The graphical representation showing concentrations of Br, J and K with time in the presence of light is as shown below: