Proteins Defined, Hierarchy & Composition of Cells

Proteins are long chains of amino acids linked together by peptide bonds. Together with the other three biological macromolecules—carbohydrates, lipids, and nucleic acids—proteins are the building blocks of cells. Proteins are the most complex and abundant biological macromolecules in cells. Their complexity is illustrated here by the multiple ways in which proteins function, from enzyme catalysis, to hormonal signaling, to antibodies of the immune system. Protein enzymes in yeast help ferment grape juice into wine. Insulin helps the body utilize sugars. Antibodies are proteins that help fight infections. The word "protein" comes from the Greek word, "proteios," meaning "of first importance." As their name suggests, these versatile molecules are involved in almost every activity of the cell. Proteins themselves are made up of building block molecules called amino acids. There are 20 different amino acids that are either synthesized by the body, or must be obtained from our diet. When proteins are synthesized, the cell draws on this pool of 20 amino acids to construct a protein molecule, which then consists of long amino acid chains which fold into complex arrangements. It's interesting that a mixture of only 20 different kinds of amino acids contributes to the many functions of proteins and creates their diverse structures. How many different kinds of proteins are found in the common intestinal bacterium, E. co/i, versus a human cell? Bacterial cells contain 600 to 800 different types of proteins. Human and other eukaryotic cells contain tens of thousands of different proteins. Look at this diagram of a bacterial cell. if the bar graph depicts the relative composition of molecules and ions in this cell, which part of the bar graph do you predict represents the protein content of this cell given that proteins are "of first importance?" While most of the composition of cells is water, proteins make up most of the dry weight of cells. This makes proteins important to the structure and life of the cell.

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