Biomolecules (Everything)

The Structure and Function of Large Biological Molecules

Lecture Outline

Overview: The Molecules of Life

• Within all cells, small organic molecules are joined together to form larger molecules.

• All living things are made up of four main classes of macromolecules: carbohydrates, lipids, proteins, and nucleic acids.

• These large macromolecules may consist of thousands of covalently bonded atoms, some with mass greater than 100,000 daltons.

• Biochemists have determined the detailed structures of many macromolecules, which

exhibit unique emergent properties arising from the orderly arrangement of their atoms.

Most macromolecules are polymers, built from monomers

  • • Three of the four classes of macromolecules—carbohydrates, proteins, and nucleic acids—form chain-like molecules called polymers.

    • ○ A polymer is a long molecule consisting of many similar or identical building blocks linked by covalent bonds.

    • ○ The repeated units are small molecules called monomers.

    • ○ Some of the molecules that serve as monomers have other functions of their own.

  • • The chemical mechanisms which cells use to make and break polymers are similar for all classes of macromolecules.

    • ○ These processes are facilitated by enzymes, specialized macromolecules that speed up chemical reactions in cells.

  • • Monomers are connected by covalent bonds that form through the loss of a water molecule. This reaction is called a dehydration reaction.

    • ○ When a bond forms between two monomers, each monomer contributes part of the water molecule that is lost. One monomer provides a hydroxyl group (—OH), while the other provides a hydrogen atom (—H).

  • ○ Cells invest energy to carry out dehydration reactions.

  • • The covalent bonds that connect monomers in a polymer are disassembled by hydrolysis, a reaction that is effectively the reverse of dehydration.

  • ○ In hydrolysis, bonds are broken by the addition of water molecules. A hydrogen atom attaches to one monomer, and a hydroxyl group attaches to the adjacent monomer.

  • ○ The process of digestion is an example of hydrolysis within the human body.

  • ○ We take in food as organic polymers that are too large for our cells to absorb. In the digestive tract, enzymes direct the hydrolysis of specific polymers. The