Problem 216 The average human chromosome contains about 1 x

Problem 21.6 The average human chromosome contains about 1 x 105 bp of DNA. Part A If each base pair has a mass of about 660 daltons and there are about 2 g of protein (histones plus nonhistones) per gram of DNA, how much does such a chromosome weigh (in grams)? Express your answers using two significant figures. Submit My Answers Give Up

Solution

Problem A:

It is given that, 1 bp = 660 daltons

and the total bp present in average human chromosome is, 1X10⁸

So, the weight (mass) of total bp in human chromosome in daltons = 660 daltons X 1X10⁸ = 6.6 X 10¹⁰ daltons

Now we know that, 1 dalton = 1.66054X10^-24 g

So, the weight (mass) of total bp in human chromosome in grams =(6.6 X 10¹⁰) X (1.66054X10^-24)  = 1.0956 X 10^-13 g

Now each gram of DNA is associated with 2 g of protein (1 g DNA = 2 g protein)

So the total protein content = 2 X 1.0956 X 10^-13 g = 2.1912 X 10^-13 g

Now the total weight of chromosome should be (weight of DNA + weight of protein) = 1.0956 X 10^-13 g + 2.1912 X 10^-13 g = 3.2668 X 10^-13 g

If we express this result in 2 significant digits it would be = 3.27 X 10^-13 g

Problem B:

We know that distance between two consecutive bases is 3.4 X 10^-10 meters

So, the total length of extended DNA = (1X10⁸)X (3.4 X 10^-10) = 3.4 X 10^-2 m

Problem C:

Calculated extended length = 3.4 X 10^-2 m

Actual length = 5X10^-6 m

So, Compaction ratio = Extended/Actual = 3.4 X 10^-2 / 5X10^-6 = 6.8X10³ m

So, compaction ratio is 6800:1

Problem D:

Length of total DNA = extended length of average DNA X total chromosomes per cell X total number of cells

= 3.4 X 10^-2 m X 46 X 4X10¹² = 6.256 X 10¹² meters = 6.256 X 10⁹ kilometers

If we divide this length by sun-earth distance we would get the ratio of these two lengths

So ratio of length = 6.256 X 10⁹ / 1.5 X 10⁸ = 41.7

So the approximate extended length of all of your DNA is 42 times the distance between earth & sun !!

Hope this helps