The mediam molecular weight of eukaryotic proteins is about 40,000 daltons. A fe
ID: 22014 • Letter: T
Question
The mediam molecular weight of eukaryotic proteins is about 40,000 daltons. A few proteins are much larger, such as a muscle cell protein called titin, which has a molecular weight of 3,000,000 daltons.
A) Estimate how long it will take a muscle cell to translate an mRNA coding for a protein of median size and one coding for titin. The average molecular mass of an amino acid is 110 daltons. Assume that the translation rate is two amino acids per second.
B) If the nucleotides in the coding portion of the mRN constitute 10% of the total nucleotides that are transcribed, how long will it take a muscle cell o transcribe a gene for a ptotein of median size versus the titin gene. Assume that the transcription rate is 50 nucleotides per second.
Explanation / Answer
(A) We can use a rate equation of time * speed = length.
We know the speed is 2 amino acids / second.
We also know the length is 3,000,000 daltons, which we can convert to amino acids as follows: 3,000,000 daltons * (1 amino acid / 110 daltons) = 27,272.72 amino acids.
Solving for time we get: time = length / speed = 27,272.72 amino acids / (2 amino acids / second) = 13,636.36 seconds.
(B) We begin with a protein that is 40,000 daltons long. We know that proteins represent only the coding portion of the mRNA, thus we need to calculate the total nucleotides that are actually transcribed. So, we can first convert daltons to nucleotides: 40k (for a medium size protein) daltons * (1 amino acid / 110 daltons) * (3 nucleotides / 1 amino acid) = 1090.9 nucleotides in a medium size protein.
Now because this is only the coding portion of the mRNA, and thus only 10% of the total), we can calculate the total nucleotides to be 10,909.
Using the rate equation from before (time = length / speed) we can calculate the time: 10,909 nucleotides / (50 nucleotides / second) = 218.18 seconds.
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