1. Nuclear pores are about 30-100 nm in diameter and those of the plasma membrane are about 0.8 nm. The plasma membrane pores are small enough to retain proteins and most other organic molecules in the cell, but those of the nuclear envelope must be large enough to allow RNA molecules, ribosomal subunits, histones, and other proteins to pass freely between the nucleoplasm and cytoplasm.

2. Since all deoxyribose components would be identical, a long chain of deoxyriboses would lack the variety needed to code for anything.

3. Evolution is genetic change in a population of organisms. Mutations cause genetic change and are unpredictable and not entirely preventable. Even if the exposure to mutagens is minimized, changes still occur because of replication errors during DNA replication. This introduces new alleles to the population and inevitably changes its genetic makeup.

4. The mRNA would have to have at least 900 bases to code for 300 amino acids, plus a stop codon of three bases. If we assume the hydrophobic leader sequence is not included in the 300-residue protein, then we would have to allow another 90 bases or so to code for this. So a protein composed of 300 amino acids would probably be encoded by an mRNA at least 993 bases long.

5. There are many examples to choose from. Three suitable examples are: (1) The double helical structure of DNA and its complementary base pairing, as Watson and Crick immediately realized, are the keys to one of its functions–DNA replication. (2) A change in DNA structure (a mutation) may result in a structural change in a protein that can impair its function, as in sickle cell disease. (3) The beads-on-a-string arrangement of chromatin is designed to allow DNA to function genetically, while keeping it organized in a way that avoids breakage and tangling.

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