NANOTECHNOLOGY—TECHNOLOGY ON A MOLECULAR SCALE - Chemistry: Notable Research and Discoveries - page 44

(continued)
bonds between the bases hold the strands together—these
bonds stabilize DNA, maintaining its structure for the life-
time of the cell (otherwise, the cell will die). Certain sequenc-
es encode genes, but before these sequences can be read,
the strands must be pulled apart to expose the bases. If the
strands were connected by strong bonds, pulling them apart
would be a major operation. With weak hydrogen bonds, the
strands can be repeatedly separated and then reconnected,
allowing the cell to read out the genes but maintaining the
stability and longevity of its DNA.
with water molecules, and some are hydrophobic, strongly avoiding
water molecules. One of the major factors governing the shape of most
proteins is that they usually function in aqueous solution and fold in
such a way that hides hydrophobic amino acids on the inside.
Other molecular forces are electrical. Large molecules often have
charged groups attached at certain points, and these charges exert
electrical forces on one another as well as on charged molecules in the
surroundings. One of the most important of the weaker bonds is elec-
trical in nature and arises because of unequal charge distribution. This
bond, usually called a hydrogen bond, is important in a lot of molecular
structures, including protein folding and the joining of two strands of a
double helix of deoxyribonucleic acid (DNA). As described in the side-
bar on pages 42-44, this bond is known as a hydrogen bond because
one of the participants is a hydrogen atom.
Creating novel molecules is a process of finding the right building
blocks and the conditions under which they form bonds. Chemists of-
ten synthesize substances by setting up a chemical reaction or a series of
reactions whose final product is the desired substance; supramolecular
chemistry is similar, but generally it involves large molecules and non-
covalent bonds.
Under ideal circumstances, the component molecules will self-
assemble—in which case chemists do not have to perform an elabo-