4.2 Practice problems

These practice problems are designed to get you thinking about biological scale. To answer some of these you may need to use the hints to look through a biology textbook. To do the calculations you may need to look at the section on SI units in Chapter 5.

1. Do you think that the protein myoglobin is bigger or smaller than the messenger RNA molecule which codes for it? Explain why or why not.
   Hint: Which is bigger, a nucleotide or an amino acid? How many nucleotides are in a codon? What is a codon?
2. How many orders of magnitude is the atomic radius bigger than the atomic nucleus?
3. The average bacillus ranges between 1 and 10 microns (µm) in length, and the mitochondria of both plant and animal cells measure in the same range. Do you think this is just a coincidence? Explain your reasoning.
   Hint: What is the proposed evolutionary origin of mitochondria? What is endosymbiosis?
4. If the distance between bases is approximately 0.3 nm, the number of base pairs (bp) in the human genome is approximately 3 Gbp and most of our cells are diploid (have 2 copies of the genome), then how long is the DNA in a human cell?
   Hint: The prefix n means nano and modifies the base unit by 10^–9. The prefix G means giga and modifies the base unit by 10⁹.
5. How does your answer to question 4 compare to the size of a cell’s nucleus? What are the implications of this? What is chromatin? What are chromosomes?

Solution to Practice Problem 4.4.