Question

A membrane consists of 36.0 % protein by weight and 64.0 % phosphoglycerides by weight. The average molecular weight of the lipids is 890. Da, and the average molecular weight of the proteins is 55200 Da.

Calculate the molar ratio of lipid to protein.

(Enter your answer in number form. Fractional ratios will not be accepted.)

Answer 1

Given that

A membrane consists of 36.0 % protein by weight and 64.0 % phosphoglycerides by weight

Average molecular weight of the lipids = 890. Da,

Average molecular weight of the proteins = 55200 Da.

Assume that the total amount of membrane is 100 g, then calculate the amount of lipid and proteins as follows:

Lipid: 64.0%* 100

= 64/100 *100

= 64 g

Protein: : 36%* 100

= 36/100 *100

= 36 g

We know that, 1 Da = 1g/mole

Now calculate the number of moles of both as follows:

Number of moles = amount in g / molar mass

Lipid moles = 64 g/ 890 g/ mole

= 0.072 mole

Protein mole = 36 g/ 55200 g/ mole

= 0.000652 mole

To find the whole-number ratio of moles, the mathematically simplest thing to do is to divide through by the smaller number of moles, which in this is 0.000652 mole, protein.

Lipid = 0.072 /0.000652 mole =110.43 mole

Protein = 0.000652 mole/0.000652 mole = 1 mole

Hence; lipid: protein :: 110.43 : 1 mole