1. Proteins 1.Chemical Composition  Proteins contain carbon, hydrogen, oxygen, and nitrogen.  Amino acids are the structural units of proteins. An amino acid consists of a central carbon atom (C) covalently bonded to a carboxyl group (COOH), an amino group (NH 2 ), a single hydrogen atom (H), and a side chain. *The side chain is different for each amino acid. Central Carbon

2. 2.Essential Amino Acids  Twenty essential amino acids are needed by the cells of the human body to make the proteins that build, maintain, and repair tissue.  Examples: (1) Glycine is the simplest amino acid. The side chain for glycine is H. (2) Alanine is an amino acid with a CH 3 group for a side chain. Glycine Alanine

3. 3.Functions of Proteins  Structural parts of cells and tissues, such as membranes, organelles, hair, and nails  Pigments in the blood, skin, and eyes  Hormones (chemical messengers)  Contractile material of muscle tissues  Antibodies that protect the body against foreign substances  Enzymes that enable complex chemical reactions to take place in the body

4. Check Your Understanding 1. How do amino acids differ from one another? 2. How are proteins constructed from amino acids? 3. High temperatures can weaken bonds within a protein molecule. How might this explain the effects of using a hot curling iron or rollers in one’s hair? 4. Describe the functions of the two types of nucleic acids.