The Basics Genes and How They Work

This section gives you information on the basics of cells, DNA, genes, chromosomes, and proteins. 

Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. Cells also contain the body s hereditary material and can make copies of themselves. 

Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell. Human cells contain the following major parts, listed in alphabetical order  

6 This appendix is an excerpt from the National Library of Medicine s handbook, Help Me Understand Genetics. For the full text of the Help Me Understand Genetics handbook, see httpi ghr.nlm.nih.gov/handbook. 

or deoxyribonucleic add, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA). 

Mitochondria Mitochondria are complex organelles that convert energy from food into a form that the ceU can use. They have their own genetic material, separate from the DNA in the nucleus, and can make copies of themselves. 

Nucleus The nucleus serves as the cell s command center, sending directions to the cell to grow, mature, divide, or die. It also houses DNA (deoxyribonucleic acid), the cell s hereditary material. The nucleus is surrounded hy a membrane called the nuclear envelope, which protects the DNA and separates the nucleus from the rest of the cell. 

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To figure out how genes work and how they direct the production of specific proteins that allow organisms to inherit traits, scientists started with the fact that chromosomes were known to be made up of protein and DNA. A series of experiments using bacteria and viruses that infect bacteria established that DNA, not protein, was the basic genetic material. Scientists figured out how DNA worked as the genetic material, how it was copied when a cell divided into two identical cells, and how DNA determined traits—that is, determined the sequence of amino acids in each protein that allow different traits to be expressed. 

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