01 Understanding Genetics and Your Body
Overview of DNA
To understand the structure and function of DNA, including how it replicates itself.
DNA, or deoxyribonucleic acid, is the hereditary material in humans and other organisms. Nearly every cell in a person’s body contains the same DNA. The genetic information in DNA is stored as a code made up of four coding elements (called bases): adenine (A), guanine (G), cytosine (C), and thymine (T). There are roughly 3 billion bases in human DNA, and more than 99% of these bases are the same in all people.1
Just as letters of the alphabet must be in a certain order to form words and sentences, so does the sequencing of the chemical bases in DNA determine the information available for building and maintaining an organism. The bases pair up with each other — A pairs with T, and C pairs with G — to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate form a nucleotide.
In DNA, nucleotides are arranged in two long strands that form a double helix, a spiral-like structure that resembles a ladder. The base pairs serve as the ladder’s rungs and the sugar and phosphate molecules form the side pieces that serve as the ladder’s backbone.1
One of the most important functions of DNA is its role in creating proteins. During a process called transcription, the information stored in a gene’s DNA is transferred to a similar molecule known as RNA (ribonucleic acid) in the cell’s nucleus. Both DNA and RNA are made up of a chain of nucleotide bases, although they have slightly different chemical properties. The type of RNA that contains the information for making a protein is known as messenger RNA (mRNA) because it carries that information, or message, from the DNA out of the nucleus into the cytoplasm.2
Translation, the second step in protein production, takes place in the cytoplasm, where the mRNA interacts with a ribosome, which “reads” the sequence of mRNA bases. Each sequence of three bases, known as a codon, usually codes for one particular amino acid (the so-called “building blocks” of proteins). A type of RNA called transfer RNA (tRNA) assembles the protein, one amino acid at a time. The protein assembly process continues until the ribosome encounters a “stop” codon, which is a sequence of three bases that does not code for an amino acid.2
The flow of genetic information from DNA to RNA to proteins is one of the fundamental principles of molecular biology – a principle so important that it is sometimes referred to as the “central dogma.”2
Flow of Genetic Information1,3
Another important property of DNA is its ability to replicate or make copies of itself. Each strand of DNA in the double helix can provide a pattern for duplicating the sequence of the base pairs. This property is critical for cell division because each new cell needs an exact copy of the DNA contained in the original cell.1
Additional Interesting Fact
DNA mostly resides in the cell nucleus, where it is known as nuclear DNA, but a small amount of DNA is housed in the mitochondria (mitochondrial DNA).1
DNA, the hereditary material in humans and most other organisms, stores genetic information as a code made up of four chemical bases that must be sequenced in a certain order to determine the information available for building and maintaining an organism.
DNA plays a key role in the so-called “central dogma”: the flow of genetic information from DNA to RNA to proteins.
The ability of DNA to self-replicate is critical for cell division because each new cell needs an exact copy of the DNA contained in the original cell.
Continue learning about genetics and your body in the next section
What is a Gene?
To understand the fundamental role genes play in heredity.
Help me understand genetics: cells and DNA. MedlinePlus. U.S. National Library of Medicine, National Institutes of Health, U.S. Department of Health and Human Services; 2021. https://medlineplus.gov/genetics/understanding/basics/dna/. Accessed December 21, 2021.
Help me understand genetics: how genes work. MedlinePlus. U.S. National Library of Medicine, National Institutes of Health, U.S. Department of Health and Human Services; 2021. https://medlineplus.gov/genetics/understanding/howgeneswork/makingprotein/. Accessed December 21, 2021.
- Help me understand how genes work: how do genes direct the production of proteins. Medline Plus. U.S. National Library of Medicine, National Institutes of Health, U.S. Department of Health and Human Services; 2021. https://medlineplus.gov/genetics/understanding/howgeneswork/makingprotein/. Accessed June 20, 2022.