Cell: The basic structural and functional unit in people and all living things. Each cell is a small container of chemicals and water wrapped in a membrane.

Each cell in the human body -- there are 100 trillion cells in each of us -- contains the entire human genome, all the genetic information necessary to build a human being. This information is encoded within the cell nucleus in 6 billion base pairs, subunits of DNA, packaged in 23 pairs of chromosomes, one chromosome in each pair coming from each parent. Each of the 46 human chromosomes contains the DNA for thousands of individual genes, the units of heredity.

There are notable exceptions including the egg and sperm cells (each of which have only 23 chromosomes containing half the usual amount of DNA) and mature red blood cells (which no longer have a nucleus and so lack chromosomes and DNA).

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All life requires protein since it is the chief tissue builder and part of every cell in the body. Among other functions, proteins help to: make hemoglobin in the blood that carries oxygen to the cells; form anti-bodies that fight infection; supply nitrogen for DNA and RNA genetic material; and supply energy.

Proteins are necessary for nutrition because they contain amino acids. Among the 20 or more amino acids, the human body is unable to synthesize 8, therefore, these amino acids are called essential amino acids. A food containing protein may be of poor biological value if it is deficient in one or more of the 8 essential amino acids: lysine, tryptophan, methionine, leucine, isoleucine, phenylalanine, valine, and threonine. Proteins of animal origin have the highest biological value because they contain a greater amount of the essential amino acids. Foods with the best quality protein are listed in diminishing quality order: whole eggs, milk, soybeans, meats, vegetables, and grains.

source=http://www.elmhurst.edu/~chm/vchembook/5900verviewmet.html