It’s important for you and other animals to eat food with protein because we cannot syn-
thesize some of these amino acids ourselves. You can get proteins both from plant sources
such as beans and from animal sources, like milk or meat. When you eat food with protein,
your body breaks the proteins down into individual amino acids and uses them to build new
proteins. Therefore, you really are what you eat!
Lipids
The lipids - the fats, oils, and waxes - are a diverse group of organic compounds.Lipidsare
not soluble in water. (As you probably know, oil and water don’t mix.) The most common
lipids in your diet are probably fats and oils. Fats are solid at room temperature, whereas
oils are fluid. Animals use fats for long-term energy storage and insulation. Plants use oils
for long-term energy storage. When preparing food, we often use animal fats, such as lard
and butter, or plant oils, such as olive oil or canola oil.
There are many more type of lipids that are important to life. One of the most important are
thephospholipids(see the chapter titledCell Functions) that make up the membranes that
surround all cells. Steroidsare the basis for the hormones like testosterone and estrogen.
Waxesare useful lipids for plants and animals since they are waterproof. Plants coat their
leavesinawaxycoveringtopreventwaterloss, whilebeesusewaxtomaketheirhoneycombs.
Nucleic acids
Nucleicacidsarelongchainsofnucleotides,whichareunitscomposedofasugar,anitrogen-
containing base, and a phosphate group. Deoxyribonucleic acid (DNA) and ribonucleic
acid (RNA) are the two main nucleic acids. DNA is the molecule that stores our genetic
information and RNA is involved in making proteins. Nucleotides also make up the high-
energy molecule Adenosine Triphosphate (ATP). ATP is the energy currency of the cell.
Every time you think a thought or move a muscle, you are using the energy stored in ATP.
The following series ofFigures2.12,2.13,2.14and2.15show examples.
Figure 2.12: (A) A molecule of glucose (a carbohydrate). ( 4 )