Question

Imagine that an extraterrestrial life-form has been recovered from a meteorite by a deep space probe that has a ravenous appetite for sand. Your job is to come up with a preliminary analysis of its bioenergetic pathway. On close examination you note that the biochemical pathway employed by this creature has some features in common with your own. You note that the alien has a basic cellular structure similar to that of Earth-based creatures. It has what you would consider to be a cytoplasm, nucleus, and other basic organelles. In addition, the creature appears to be capable of using oxygen in the course of its metabolism. Following a rigorous biochemical analysis, you note the following points:
a. A glycolysislike process begins with the alien's basic food stuff of sand particles. Specifically, the first molecule in the pathway contains 256 silicon atoms (Si256).
b. In the process of metabolizing the Si256, you note that the creature uses up 50 energy- carrying molecules that you have named ZTP (since it is an unknown triphosphate-bearing molecule that gives the creature 'zip') in converting the Si256 to 4 molecules of Si64. Also, in the process of breaking down one molecule of Si256, ten (10) molecules of an electron-carrying substance you have called EADH are formed.
c. Each Si64 molecule is broken into two molecule with the creation of 5 ZTP molecules and 4 EADH molecules. Each molecule of Si64 gives off four (4) SiO2 molecules in this step (Si30 left).
d. Each Si30 goes through a cyclic process in an organelle similar in structure to our own mitochondrion in which the Si30 is completely oxidized to SiO2. In the process, 8 ZTP, 4 EADH, and 7 EADH2 are released.
e. Each molecule of EADH is converted to 10 ZTP, and each molecule of EADH2 is converted to 5 ZTP. (NOTE: Each EADH formed in step (b) is converted to two molecules of EADH2 when it passes into the mitochondrion-like structure.) How many ZTP and SiO2 molecules will be formed in the complete metabolism of 1 molecule of Si256? Show your work in the space below.

Answer 1

Answer: 894 ZTP and 256 SiO2.

Work shown:

Start: 1 Si256.

Step b (Si256 -> 4 Si64):
- ZTP: used 50 (−50)
- EADH produced: +10

Step c (each Si64 -> 2 Si30 + 4 SiO2; per Si64: +5 ZTP, +4 EADH):
- Number of Si64 = 4
- ZTP produced: 4 × 5 = +20
- EADH produced: 4 × 4 = +16
- SiO2 produced (here): 4 × 4 = +16

Subtotal after c:
- EADH total so far = 10 (from b) + 16 (from c) = 26
- ZTP running total = −50 + 20 = −30
- SiO2 running total = 16

Step d (each Si30 -> completely oxidized to SiO2; per Si30: +8 ZTP, +4 EADH, +7 EADH2):
- Number of Si30 = from step c: 4 Si64 × 2 = 8 Si30
- ZTP produced: 8 × 8 = +64
- EADH produced: 8 × 4 = +32
- EADH2 produced: 8 × 7 = +56
- SiO2 produced: 8 × 30 = +240

Subtotal after d:
- EADH total = 26 + 32 = 58 (but see conversion note below)
- EADH2 total = 56
- ZTP running total = −30 + 64 = +34
- SiO2 running total = 16 + 240 = 256

Step e (conversion to ZTP):
- Note: the 10 EADH from step b are converted to 2 EADH2 each when entering the mitochondrion → 10 EADH → 20 EADH2.
- Therefore remaining EADH to convert directly to ZTP = total EADH (58) − 10 (the ones converted) = 48 EADH.
- EADH → 10 ZTP each: 48 × 10 = 480 ZTP
- EADH2 total = 56 (from d) + 20 (from conversion of the 10 EADH) = 76
- EADH2 → 5 ZTP each: 76 × 5 = 380 ZTP

Add carrier-conversion ZTP to running total:
- ZTP final = previous 34 + 480 + 380 = 894 ZTP

SiO2 final (from above) = 256 SiO2 (mass balance check: 256 Si atoms → 256 SiO2).

Final result: 894 ZTP molecules and 256 SiO2 molecules per 1 Si256 metabolized.