Animation 3.1: Proteins, Carbohydrates, and Lipids

INTRODUCTION

Although living cells are primarily made up of water, a number of other molecules are also abundant. Gigantic molecules, called macromolecules, populate a cell and provide it with important functions for life. For example, macromolecules provide structural support, a source of stored fuel, the ability to store and retrieve genetic information, and the ability to speed biochemical reactions. Four major types of macromolecules—proteins, carbohydrates, nucleic acids, and lipids—play these important roles in the life of a cell. Here we will look at three of these macromolecules: proteins, carbohydrates, and lipids.

In terms of overall structure, all macromolecules except the lipids are considered polymers. A polymer is a chain of similar subunits, or monomers, that are linked together by covalent bonds. In proteins, the monomers are amino acids; in carbohydrates, the monomers are sugars. Lipids are a diverse group of molecules, which come in a variety of nonpolymeric forms.

Video titled: Animation 3.1: Proteins, Carbohydrates, and Lipids

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CONCLUSION

A macromolecule's structure is intimately connected with its function. Consider, for example, a protein. This type of polymer is made up of a chain of amino acids that are strung together in a precise sequence. The amino acid sequence determines the protein's 3-dimensional shape and chemical reactivity, which, in turn, endow a protein with its specific function. Some proteins, for example, have shapes that allow them to grab molecules and speed chemical reactions. Others, such as strong cables of collagen, provide structural support to cells and tissues.

Carbohydrates include the relatively small glucose molecule and the enormous glycogen molecule, which may consist of hundreds of thousands of glucose monomers. Carbohydrates are energy-rich. Many, such as glycogen, provide energy-storage functions. Other carbohydrates, such as cellulose—a component of plant cell walls—serve primarily structural roles in a cell.

Lipids are the only macromolecules that are not polymers. Lipids are diverse in structure and function, but all have in common that they are hydrophobic—that is, they are nonpolar and do not dissolve in water.

Textbook Reference: Key Concept 3.1 Macromolecules Characterize Living Things

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