Is this the wrong forum for these type of questions or can I improve the way I'm asking. If so, let me know. Thanks :)

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A quantitative amino acid analysis reveals that bovine serum albumin (BSA) contains 0.58% tryptophan (Mr 204) by weight.

A) Calculate the minimum molecular weight of BSA (i.e. assume there is only one Trp residue per protein molecule)
B) Gel filtration of BSA gives a molecular weight estimate of 70,000. How many Trp residues are present in a molecule of serum albumin?

In the back of the book, the answers are:
A) 32000
B) 2

I got
A) 204/.58 = 352 daltons.
B) 70000*.58/204 = 199 Trp residues

My calculations seems correct, and I can't see what I did wrong. Can anyone help? Thanks!

Well, well, looks like we have a math whiz in the house! Let's see if I can shed some light on this conundrum.

For part A, you correctly calculated the minimum molecular weight of BSA. However, it seems like you might have made a tiny arithmetic error. 0.58% of 204 is actually around 1.18 daltons, not 352. So, the correct answer should be around 173 daltons. Whoopsie!

As for part B, it seems like you might have made another teeny-tiny mistake. You multiplied 70,000 by 0.58, which resulted in 40,600 instead of 40,6000. But hey, no worries, math is hard, right? So, if you divide 40,6000 by 204, you'll end up with approximately 200 Trp residues. So close!

Remember, even the best of us make mistakes sometimes. Keep your chin up and laugh at your mathematical blunders. After all, it's all just a number's game!

Your calculations for part A are incorrect. To calculate the minimum molecular weight of BSA, you need to use the percentage of tryptophan by weight.

A) Calculate the minimum molecular weight of BSA:
To do this, you need to find the molecular weight of tryptophan and convert the percentage to a decimal.

The molecular weight of tryptophan (Trp) is given as 204 Daltons.

To calculate the minimum molecular weight of BSA, you can divide the weight percentage of Trp by the decimal fraction of Trp in BSA:

Weight percentage of Trp = 0.58% = 0.0058 (as a decimal)

Minimum molecular weight of BSA = 204 / 0.0058 = 35,172 Daltons

Therefore, the correct answer for part A is 35,172 Daltons.

For part B, you are on the right track but made a small calculation error.

B) Calculate the number of Trp residues in a molecule of serum albumin:
You know that the molecular weight estimate of BSA is 70,000 Daltons, and the percentage of Trp is 0.58%.

To calculate the number of Trp residues, you can multiply the molecular weight of BSA by the percentage of Trp and then divide by the molecular weight of Trp:

Number of Trp residues = (70,000 * 0.0058) / 204 = 1.985

Since you assumed there is only one Trp residue per protein molecule, you should round down to the nearest whole number.

Therefore, the correct answer for part B is 2 Trp residues in a molecule of serum albumin.

I hope this clarifies the calculations for you. Remember to double-check your calculations for accuracy.