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Definition
DNA is a substance primarily found within a cell's nucleus that determines heredity and cell function. This substance is a type of nucleic acid, which is a specialized compound of molecules. Ultimately, DNA is used to determine the characteristics of an organism.
Composition
DNA is made of nucleotides. Nucleotides are compounds of phosphates, nitrogen bases and a sugar. The sugar component within DNA is deoxyribose, of which part of the name "deoxyribonucleic acid" is derived. The nitrogen bases within DNA are combinations of adenine, cytosine, guanine and thymine. Adenine and guanine are classified as purine nitrogen bases, whereas cytosine and thymine are pyrimidine nitrogen bases. Phosphates are combinations of phosphorous and oxygen bonded together.
Structure
DNA can take on many shapes, but is primarily assembled in an intertwined spiral called a helix. The most common DNA structure is two strands of DNA linked to form a double helix; which under a microscope has the appearance of a spiraled ladder.
Roles
Some portions of a DNA strand determine cell functions, such as its cell growth and protein production, also called protein synthesis. However, other portions of the strand contain information specific to an organism's heredity. This information is called genetic coding, and the portion of DNA that contains genetic coding is called a gene. Subsequent portions of a DNA strand manage how that genetic coding is used.
Protein Synthesis
Proteins are comprised of amino acids. How a protein is used within an organism is determined by how the protein's amino acids are arranged. DNA genes contain the instructions how to arrange those amino acids. A function of ribonucleic acid or RNA is to transcribe the protein sequence instructions from the DNA gene, and transfer the information to cell structures called ribosomes. In turn, ribosomes produce proteins based on the translated DNA information it receives.
Chromosomes
When DNA, which includes its gene segments, binds with certain type of proteins called histones, a cell structure is formed called a chromosome. The number of chromosomes within organisms varies. Where an Adder's tongue fern has more than 1,000, an earthworm has 36. Humans generally have 46 chromosomes arranged in pairs, with 23 inherited from the mother and 23 inherited from the father. Chromosomes contain an array of genetic information that range from hair color to health conditions.