Page 9 - Curriculum Visions Dynamic Book

Hydrogen bonds and the genetic code
Life depends on two fundamental blueprint acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). These acids carry the genetic code from one generation to another.
Each DNA molecule is made of a number
of short segments or units that are connected together forming two long, twisting coils known as a double helix.
bond: chemical bonding is either a transfer or sharing of electrons by two or more atoms. There are a number of types of chemical bond, some very strong (such
as covalent bonds), others weak (such
as hydrogen bonds). Chemical bonds
form because the linked molecule is more stable than the unlinked atoms from which it formed. For example, the hydrogen molecule (H2) is more stable than single atoms of hydrogen, which is why hydrogen gas is always found as molecules of two hydrogen atoms.
hydrogen bond: a type of attractive force that holds one molecule to another. It is one of the weaker forms of intermolecular attractive force.
Also...
Hydrogen bonds occur because of the way that hydrogen is attracted to some other atoms, such as oxygen. The oxygen pulls
at the hydrogen in such a way that the side of the hydrogen atom facing away from the oxygen is left with a slight positive charge. This allows the hydrogen to attract other molecules that are negatively charged and to form a link, or bond. In this sense, hydrogen bonding is rather like the way a balloon sticks to a sweater after it has been rubbed vigorously. It can be pulled off and stuck back at will, a very flexible, if not very strong, electrical attraction.
Hydrogen bonds are very weak compared to other bonds that hold atoms together as molecules. They are nowhere as strong as the (ionic) bonds in salt or the bonds in the metal iron or a mineral like silica. But these other very strong types of bond seldom allow materials to be flexible, or to break up and re-form easily.
Hydrogen bonding also has a special effect on H2O – water. Water should actually be
a gas since its molecules are relatively simple. (The more complex the molecule, the more attracted one molecule is to another and
the less likely it is to be a gas.) But hydrogen bonding between the molecules keeps
water as a liquid, unless a lot of heat energy
is applied.
 This spider’s web is held together by hydrogen bonding. The silk in the web is made of proteins
stuck together by hydrogen bonds so that the silk has flexibility yet has as much strength as a strand of steel the same size.
The coils have to be held together firmly and yet
be able to split up easily and re-form as part of the process of reproduction. The key to this is that the two coils are held together by hydrogen bonds.
During reproduction, the two coils have to unzip and each has to copy itself. The unzipping is easy because hydrogen bonds are relatively weak. Each separated strand then attracts new molecules,
in a very specific order, which bond to the coils
by hydrogen bonds until a new pair of coils has been produced.
Hydrogen bond
 The double helix structure of DNA.
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