This is Just one question not multipple, please help. I always rate. States to r

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This is Just one question not multipple, please help. I always rate. States to remember to write out your calculations and explanations for ALL problems.

17. In onc mammalian ccll it is cstimated that 10,000 to 20,000 different types of mRNA can be found. Abundant mRNAs exist in many copies per ccll (up to 12,000 copies/ccll); but scarcc mRNAs (5 to 15 copies cell) can also be detected. At any instant, a snapshot of mRNA content would reveal a total of 360,000 mRNAs. The cell usually has about 10 times as many ribosomes as mRNAs. Assume 75% of the ribosomes are involved in protein synthesis at any instant in time a. What is the maximum number of proteins that could be in the process of synthesis at any instant? b. How many scarce proteins (use 5 copies/cell) could be in the process of being made? (hint: usc that 7.5 ribosomes are reading cach of the 5 mRNAs, but explain or show calculations for why you should use this). c. How many abundant proteins could be in the process of being made? (hint: use that 7.5 ribosomes are reading each of the 12,000 mRNAs, but explain or show calculations for why you should use this). d. What is the ratio of developing abundant proteins to developing scarce proteins?

Explanation / Answer

c)At any instant there are about 360,000 mRNAs per cell.

There are about 10 times as many ribosomes, i.e For each mRNA, there are 10 ribosomes available.

But if only 75% of the ribosomes are translating at any instant, then 75% of 10= 7.5 ribosomes/mRNA are translating at any instant.

a) The maximum number of proteins that could be in the process of synthesis at any instant:

That means all 360,000 mRNAs would be translated by 7.5 ribosomes each, ie 360, 000 x 7.5= 2,700, 000.

b) The ratio of scarce to abundant mRNA is 5:12000= 1:2400

That is for every 1 type of scarce mRNA there are 2400 abundant types of mRNAs

So the number of scarce mRNAs in 360000 mRNAs is 1/(1+2400)= 1/2401 x 360,000=149.9 =~150 types of scarce mRNAs

So total number of scarce proteins= 150 types of scarce mRNA x 5 copies each x 7.5 ribosomes/mRNA= 5625 proteins are scarce proteins

c) The total number of abundant proteins is 2,700,000-5625= 26,94,375 proteins are abundant proteins.

d) The ratio of abundant to scarce proteins = 2694375: 5625= 479: 1

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