Chemical Component of The Cell

Element Percentage of Body Mass (Campbell, 2011)

Natural elements in living things

Of the naturally occurring elements on Earth, only about 25 are essential to living organisms. Notice that four of the elements—carbon, hydrogen, oxygen, and nitrogen—together make up more than 96 percent of the mass of a human body.

Trace elements

Some of the elements listed in table, such as iron and copper, are present in living things in very small amounts. Such elements are known as trace elements. They play a vital role in maintaining healthy cells in all organisms.

           

Compounds

Table salt is a substance that is familiar to everyone; however, table salt is not an element. Rather, salt is a type of substance called a compound. A compound is a substance that is composed of atoms of two or more different elements that are chemically combined. Table salt (NaCl) is a compound composed of the elements sodium and chlorine.

Water and Its Importance

Water is perhaps the most important compound in living organisms. Most life processes can occur only when molecules and ions are free to move and collide with one another. This condition exists when they are dissolved in water. Water also serves to transport materials in organisms. For example, blood and plant sap, which are mostly water, transport materials in animals and plants. In fact, water makes up 70 to 95 percent of most organisms.

Large Biological Molecules (Biomolecules)

Given the rich complexity of life on Earth, we might expect organisms to have an enormous diversity of molecules. Remarkably, however, the critically important large molecules of all living things—from bacteria to elephants—fall into just four main classes: carbohydrates, lipids, proteins, and nucleic acids.

On the molecular scale, members of three of these classes—carbohydrates, proteins, and nucleic acids—are huge and are therefore called macromolecules.

Large Biomolecules	Function	Example	% of The Total Cellular Mass
Carbohydrate	serve as energy source and building material	glucose, fructose, cellulose, starch, glycogen, chitin	3
Proteins	wide range of function	storage molecule: albumin, enzyme, hormone, cell motor: actin and myosin, structure: horn, finger nails,	10 – 15
Nucleic Acids	store, transmit, and express heredity information	DNA RNA	5 – 7
Lipids	energy source and membrane component	fats/oils, phospholipids bilayer, steroids	2

Compound Percentage of Cellular Mass 

Chemical Reactions

Chemical reactions occur when bonds are formed or broken, causing substances to recombine into different substances. In organisms, chemical reactions occur inside cells. All of the chemical reactions that occur within an organism are referred to as that organism’s metabolism. These reactions break down and build molecules that are important for the functioning of organisms.