CK12 Life Science

Table 2.1: The Four Main Classes of Organic Molecules

Proteins Carbohydrates Lipids Nucleic Acids

Elements C,H,O,N,S C,H,O C,H,O,P C,H,O,P,N

Examples Enzymes, mus-

cle fibers, anti-

bodies

Sugar, Starch,

Glycogen, Cel-

lulose

Phospholipids

in membranes,

fats, oils, waxes,

steroids

DNA, RNA,

ATP

Monomer

(small building

block molecule)

Amino acids Sugars Often include

fatty acids

Nucleotides

Organic compounds all contain the elements carbon (C) and hydrogen (H). The chain of
carbon and hydrogen in organic compounds is sometimes called the “backbone” of organic
compounds since they make up the core center structure. What makes organic compounds
different from one another is thefunctional groups, groups of atoms that have unique
chemical properties. The addition of a functional group vastly changes the properties of
the carbon-hydrogen backbone of organic compounds. Each organic compound is therefore
suited to its unique role in living things.

Carbohydrates

Essentially, carbohydrates are sugars or long chains of sugars. An important role ofcarbo-
hydratesis to store energy. Glucose is a simple sugar molecule with the chemical formula
C 6 H 12 O 6. Sugar is one type of carbohydrate, but carbohydrates also include long chains of
connected sugar molecules. These chains of sugar molecules can be used to store sugar for
later use, such as in the form of starches or glycogen. Plants store sugar in long chains called
starch, whereas animals store sugar in long chains calledglycogen. Both storage molecules
contain hundreds or thousands of linked glucose molecules. Chains of sugar molecules also
can be used as structural molecules. For example, the hard skeletons of insects and lob-
sters are made of chitin, a type of carbohydrate. These long chains of sugar molecules are
know aspolysaccharides. You get the carbohydrates you need for energy from eating
carbohydrate-rich foods, including fruits and vegetables, as well as grains such as bread,
rice, or corn.

The chemical formula C 6 H 12 O 6 of glucose means that this molecule has 24 atoms: 6 carbon
atoms, 12 hydrogen atoms, and 6 oxygen atoms. Carbohydrates have a general chemical
formula consisting of twice as many hydrogen atoms as carbon and oxygen atoms. Glucose
is amonomer, a single unit that when linked together with other monomers forms a long
chain known as a polymer. Starch is an example of a polymer.