TP28_Metabolic_Yield_Calculations\TP28_Metabolic_Yield_Calculations

Metabolic yield calculations

Solve each of the problems below on your own. You can use the handwritten metabolic map in the file “Saccharomyces_cerevisiae_metabolic_map_LARGE.jpeg” or simply find a metabolic map online. When you are done, follow this link that points to a Google Spreadsheet, where you should add your answer next to your name for each question.

Question 1:

How many ATP molecules are consumed per molecule of glucose in the glycolytic pathway from glucose to pyruvate?

Question 2:

How many ATP molecules are produced per molecule of glucose in the glycolytic pathway from glucose to pyruvate?

Question 3:

What is the theoretical molar yield of ethanol from glucose i.e. how many molecules of ethanol are produced from each molecule of glucose consumed.

Question 4:

What is the yield in Question 3 expressed in mass ethanol by mass glucose (g/g)? Ethanol has molecular weight of 46 g/mol and the molecular weight of glucose is 180 g/mol.

Question 5:

The first ethanol from cellulose (2^nd generation bioethanol) factory built in Germany 1898 used dilute acid to hydrolyze the cellulose to glucose and was able to produce 7.6 liters of 100% ethanol per 100 kg of dry wood. We can assume an ethanol density of 0.789 kg/L. The cellulose content of the wood used was 50%. What is the ethanol yield expressed in mol ethanol/mol glucose? Ethanol has molecular weight of 46 g/mol and the molecular weight of glucose is 180 g/mol. #

Question 6:

Saccharomyces cerevisiae can be engineered to metabolize the pentose sugar D-xylose by expressing either a D-xylose isomerase or a combination of D-xylose reductase and xylitol dehydrogenase. In either case D-xylose (5C) is metabolized into Fructose 3-phosphate (6C) and Glyceraldehyde 3-phosphate (3C) These two molecules are subsequently metabolized into ethanol. What is the theoretical molar yield of ethanol from D-xylose? See the metabolic map upper left corner.

Question 7:

What is the yield in Question 6 expressed in mass ethanol by mass D-xylose (g/g)? Ethanol has molecular weight of 46 g/mol and the molecular weight of D-xylose is 150 g/mol.

Question 8:

During World War I, there was a glycerol shortage in Germany due to glycerol being needed for the manufacture of explosives. This led to the development of a process for production of glycerol from sugar by fermentation with the yeast Saccharomyces cerevisiae. Bisulfite (HSO₃⁻) was added to the fermentation medium. The bisulfite reacted with acetaldehyde, so no ethanol could be produced (Figure 1).

This means that the NADH molecule normally consumed in the step from acetaldehyde to ethanol (Figure 2) has to be consumed in some other way.

We assume that the NADH is instead consumed by the G3PDH (Glycerol-3-Phosphate Dehydrogenase) enzyme (Gpd, Figure 3). How many grams of glycerol can be produced from 1000 g of glucose using this strategy? Glycerol has molecular weight of 92 g/mol and the molecular weight of glucose is 180 g/mol.

Question 9:

Some bacteria have the Entner–Doudoroff (ED) pathway instead of glycolysis. The pathway in Figure 4 ends with pyruvate, but the pyruvate is metabolized to ethanol in the same way as for glycolysis. How many ATP molecules are consumed and produced per molecule of glucose metabolized through the ED pathway from glucose to ethanol? Is the ED pathway more or less efficient than glycolysis?

Question 10:

The metabolic pathway (Figure 5) depicts fatty acid synthesis by the bacterial FASII system. How many NADPH, NADH and ATP molecules does it take to make one molecule of Palmitic acid-ACP? The molecular formula for this molecule is:

O

‖

CH₃(CH₂)₁₄C-S-ACP

This is essentially assuming that R in the figure at the position for “Fatty acid-ACP” is a 15 carbon chain. Figure 6 contains a link to a YouTube video with a nice recapitulation of fatty acid synthesis.

Question 11:

Formate dehydrogenase (FDH) catalyze the oxidation of formic acid to CO2 with the formation of one NADH or NAPDH. The FDH1 gene in yeast Saccharomyces cerevisiae encodes an enzyme that specifically makes NADH. A fermentation process yields 82.8 g ethanol and 18.4 glycerol from 180 g glucose. A similar second fermentation was performed but with the addition of formic acid. The second fermentation produced 87.4 g ethanol and 9.2 g glycerol from 180 g glucose consumed. How many grams of formic acid was metabolized in the process? The molecular weights of glucose, ethanol, glycerol and formic acid are 180, 46, 92 and 46 g/mol, respectively.

© Björn Johansson 2021