Question

A typical slice of white bread contains 1.5 grams of sucrose and 10.2 grams of starch. on average there is an estimated 25 trillion red blood cells in the human body. assuming that the only source of energy is coming from the sucrose and starch in bread, how many slices of bread would you need to eat to provide the energy required to fill all 25 trillion red blood cells with hemoglobin? problem

Answer 1

Disclaimer: I have based the computation for this through normal values and various evidence-based estimates. 

First of all, we would like to know how many hemoglobin molecules per red blood cell. There are 250 million hemoglobin molecules per red blood cell [1]. Second, we need to know how many amino acids in a hemoglobin molecule. In 1 alpha chain, there are 141 amino acids; and in 1 beta chain, there are 146 amino acids. Since we have 2 alpha chains and 2 beta chains, there will be a total of 576 amino acids [2]. Next, we need to know how many ATP (energy) needed to synthesize 1 amino acid, and that is 5 ATP is needed per amino acid (2 for activation, 2 for elongation, 1 for error correction) [3]. Now we have to compute:

(5 ATP needed per amino acid) x (576 amino acids in 1 molecule of Hgb) = 2870 ATP needed to synthesize 1 molecule of hemoglobin. 

Since we have 250 million molecules of hemoglobin, then (2870 ATP per 1 molecule of hemoglobin) x (250 million molecules of hemoglobin per RBC) = 71.75 x 10¹⁰ ATP needed to produce 1 RBC. 

We are given a total of 25 trillion RBC, then (71.75 x 10¹⁰ ATP per 1 RBC) x (25 trillion RBC) = 1.79 x 10²⁵ ATP in total needed. Next we convert ATP to calories (kcal). 

According to Guyton et.al, 1 ATP = 12 kcal. Therefore, (1.79 x 10²⁵ ATP/12) = 1.49 x 10²⁴ kcal needed to produce 25 trillion RBC.

Now we compute for calories (kcal) in the bread. It is given that there are 10.2 grams of starch and 1.5 of sucrose in 1 slice of bread. Both starch and sucrose are carbohydrates so let's simplify that at 11.7 grams of carbohydrates per slice of bread. 1 gram of carbohydrate is equal to 4 kcal [2]. Now we have to compute:

(11.7 grams of carbohydrates per slice of bread) x (4 kcal per gram carbohydrate) = 46.8 kcal per bread. 

Lastly, we need to know how many breads to eat to produce 25 trillion RBC. The last computation is (1.49 x 10²⁴ kcal in total/46.8 kcal per bread) = 3.18 x 10²² breads needed

The individual has to eat 3180000000000000000000000 breads to make 25 trillion RBC.

References:
[1] https://faculty.etsu.edu/currie/hemoglobin.htm
[2] Harper's Illustrated Biochemistry textbook
[3] Ribosome and transcript copy numbers, polysome occupancy and enzyme dynamics in Arabidopsis by Piques et. al