Lesson: Chapter - 5

The Molecules of Life

The elements involved in life processes can, and do, form millions of different compounds. Thankfully, these millions of compounds fall into four major groups: carbohydrates, proteins, lipids, and nucleic acids. Though all of these groups are organized around carbon, each group has its own special structure and function.

Carbohydrates

Carbohydrates are compounds that have carbon, hydrogen, and oxygen atoms in a ratio of about 1:2:1. If you’re stuck on an SAT II Biology question about whether a compound is a carbohydrate, just count up the atoms and see if they fit this ratio. Carbohydrates are often sugars, which provide energy for cellular processes.

Like all of the biologically important classes of compounds, carbohydrates can be monomers, dimers, or polymers. The names of most carbohydrates end in “-ose”: glucose, fructose, sucrose, and maltose are some common examples.

Monosaccharides

Carbohydrate monomers are known as monosaccharides. This group includes glucose, C₆H₁₂O₆, which is a key substance in biochemistry. Sugars that an animal eats are converted into glucose, which is then converted into energy to fuel the animal’s activities by respiration (see Cell Processes).

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