Learn about the chemical bonds and different levels of structure that take amino acid monomers to a whole other level, a more complex protein polymer.

Inorganic and Organic Molecules

Inorganic molecules are substances that don’t have carbon-hydrogen (C-H) bonds. They are generally simple and are not normally found in living things.

Organic molecules, substances that contain carbon-hydrogen bonds, are found in living things. The major classes of organic molecule include carbohydrates, proteins, lipids and nucleic acids.

Amino Acids

Proteins are polymers composed of monomers called amino acids.

Each amino acid contains contain a…

• base amino group ( -NH2)
• acidic carboxyl group ( -COOH)
• hydrogen atom

…all attached to same carbon atom (the α–carbon or alpha carbon). A fourth bond attaches α-carbon to a side group that varies among different amino acids. These side groups are important, as they affect the way a protein’s amino acids interact with one another, and how a protein interacts with other molecules.

Although there are hundreds of different amino acids, most organisms use only 21 to build proteins.

Peptide Bonds

Peptide bonds are the covalent bonds which link amino acids together into chains, like the beads on a necklace. A dipeptide is composed of 2 amino acids linked together, a polypeptide is more than two.

Levels of Protein Structure

Every protein has at least three levels of structure: primary, secondary and tertiary. Quaternary structure is a grouping of more than one theriary structure protein.

Primary Structure

Amino acids linked together by peptide bonds into a peptide chains.

Secondary Structure

Ionic bonds, hydrogen bonds, and hydrophilic/hydrophobic characteristics cause many polypeptide chains to fold into coils (α–helices), or accordion-like structures (β-pleated sheets).

Proteins are typically composed of both α–helices and β-pleated sheets linked by short sequences of amino acids.

Tertiary Structure

This is the three-dimensional structure of single protein molecule; a spatial arrangement of secondary structures.

Quaternary Structure

This level of structure represents a complex of several protein molecules or polypeptide chains, which function as part of the protein complex.

Protein Structure and Function

Structure of a protein is directly related to its function, so that anything that severely disrupts the shape will also disrupt the function.

Denaturation is alteration of a protein shape through some form of external stress (for example, by applying heat, acid or alkali), in such a way that it can’t carry out its cellular function

Additional Organic Chemistry Resources

To learn more about organic molecules and cell biology, see Science Prof Online and the Organic Chemistry Help page or look to additional Suite101 articles including, What Is a Carbohydrate, Nucleotides and Nucleic Acids, What Is a Lipid and What are Organic Molecules.

Sources

Bauman, R. (2005) Microbiology.

Park Talaro, K. (2008) Foundations in Microbiology.