Page 86 - Demo 1

Organic molecules, also known as biological molecules, make up porons of
cells, ssues, and organs. There are four major classes of biological molecules:
lipids, carbohydrates, proteins, and nucleic acids; each is an important
component of the cell and performs a wide array of funcons.

LIPIDS

Fats and all other biological molecules which are insoluble in water but
soluble in oil are called lipids. Lipids do not dissolve in water because they are
hydrophobic, containing hydrocarbons that include only non-polar
carbon–carbon or carbon–hydrogen bonds. In water, fat molecules cluster
together and are unable to form hydrogen bonds with water molecules. This
is the reason why oil forms into a layer on top of water when the two
substances are combined.

Fats and Oils: Long-Term Energy Storage
Fats (e.g., bacon fat, lard, and buer) and oils (e.g., coconut oil, corn oil,
and olive oil) are very common examples of lipids. Fats differ from oils in their
state at room temperature (i.e., fats are solid while oils are liquid). In animals,
cells store energy for long-term use in the form of fats. Fats keep marine
mammals insulated from the harsh condions of the arcc, and protect their
internal organs from damage. On the other hand, oils help keep aquac birds
and mammals dry because of their water-repelling nature. In plants, oils are
used for long-term energy storage.

Fats and oils consist of two types of subunit molecules: glycerol and fay
acid. Glycerol is an organic compound with three carbon atoms, five hydrogen
atoms, and three hydroxyl (–OH) groups. A fay acid has a long chain of
hydrocarbons to which an acidic carboxyl group is aached. The number of
carbons in the fay acid may range from 4 to 36; most common are those
containing 12-18 carbons. In a fat molecule, a fay acid is aached to each of the
three oxygen atoms in the –OH groups of the glycerol molecule with a covalent
bond. Because three long fay acids are aached to the glycerol molecule, fats
and oils are also referred to as triglycerides. This structure is capable of packing
a lot of energy into one molecule, that is why fats and oils are the body’s main
molecule for long-term energy storage.

78