Nucleic Acids

Nucleic acids account for only 2 percent of the body's weight, yet these molecules are extremely important because they are responsible for the storage, expression, and transmission of genetic information. It is the expression of genetic information (in the form of specific proteins) that determines whether one is a human being or a mouse, or whether a cell is a muscle cell or a nerve cell.

There are two classes of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

DNA molecules store genetic information coded in the sequence of their subunits, whereas RNA molecules are involved in the decoding of this information into instructions for linking together a specific sequence of amino acids to form a specific polypeptide chain. The mechanisms of gene expression and protein synthesis will be described in Chapter 5.

Both types of nucleic acids are polymers and are therefore composed of linear sequences of repeating subunits. Each subunit, known as a nucleotide, has

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

Chemical Composition of the Body CHAPTER TWO

Chemical Composition of the Body CHAPTER TWO

Cysteine

Polypeptide chain

Cysteine

H CH2

h2c h

II I OH

+ X—2H
Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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