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DNA -- Glossary



Adenine
One of the four bases in DNA that make up the letters ATGC, adenine is the "A." The other bases are guanine (G), cytosine (C), and thymine (T). Adenine always pairs with thymine.

Amino Acid
The smallest unit of a protein. There are 20 different amino acids that, when assembled into a long chain in a specified order, form a protein with its unique characteristics.

Amplification
The process of repeatedly making identical copies of a certain piece of DNA.

Base Pair
Two complementary DNA bases held together by weak hydrogen bonds. Each of the two bases attaches to one of the strands in the DNA duplex. Adenine always forms base pairs with thymine, and guanine always forms base pairs with cytosine.

Chromosome
A structure inside the cell nucleus that contains genes. Humans have 23 pairs of chromosomes (46 total) in every cell; each parent contributes one chromosome to each pair, so children get half of their chromosomes from their fathers and half from their mothers. Other animals have different numbers of chromosomes.

Cytosine
One of the four bases that make up DNA, often written as the letter "C." The other bases are adenine (A), guanine (G), and thymine (T). Cytosine always pairs with guanine.



DNA (deoxyribonucleic acid)
A chemical consisting of a sequence of hundreds of millions of nucleotides found in the nucleus of cells; DNA is shaped like a double-stranded helix. It is the genetic blueprint from which RNA and protein are made. All genetic information about an individual is contained within its DNA.

DNA replication
The process by which the DNA double helix unwinds and makes an exact copy of itself. The strands of DNA in the double helix are separated and each one is copied to produce a new strand. One of each parent strand is conserved and remains intact after replication has taken place.

Enzyme
A protein that carries out functions in the cell by facilitating a biochemical reaction. Organisms could not function if they had no enzymes.

Epigenetics
Patterns of inheritance, transferred from parent to offspring, which are not produced by changes in the nuclear DNA sequence.



Gel
A slab of jelly-like material used for separating DNA molecules of different sizes. When an electric field is applied to the gel, the DNA molecules move through the gel. Smaller pieces move faster than large ones, which get entangled in the structure of the gel. This method of separating molecules is called gel electrophoresis.

Gene
The fundamental unit of heredity: A piece of DNA in a particular position on a particular chromosome that contains the genetic code to make a particular protein, or part of a protein.

Gene Therapy
Replacing or supplementing genes that are not functioning correctly, with the goal of curing a disease.

Genome
All of the genetic material of a particular person or organism.

Genotype
The genetic makeup of an individual organism.

Guanine
One of the four bases that make up DNA, often written as the letter "G." The other bases are adenine (A), cytosine (C), and thymine (T). Guanine always pairs with cytosine.



Junk DNA
Stretches of DNA that do not code for genes, also called non-coding DNA. Most of the genome consists of non-coding DNA, and was therefore long thought to be ‘junk.’ More recently, at least parts of these non-coding stretches have bee found to have regulatory and other functions.

Knockout
Deleting, mutating or otherwise inactivating genes. A strategy used in research laboratories to study gene function of the deactivated gene in a patricular organism.

Ligase
Enzyme that can link two pieces of DNA together.

Leukemia
Cancer of the developing blood cells in the bone marrow. Leukemia leads to excessive production of white blood cells. Symptoms usually include anemia, fever, enlarged liver, spleen, and/or lymph nodes.




mRNA (messenger RNA)
Template for protein synthesis. Each set of three bases in mRNA specifies a certain amino acid in a long chain of amino acids that make up a protein. The sequence of a strand of mRNA is based on the sequence of a complementary strand of DNA.

Nucleotide
A piece of DNA or RNA that contains one base, one phosphate group, and one sugar unit. Thousands of nucleotides joined end-to-tail make a molecule of DNA or RNA.



PCR (polymerase chain reaction)
A fast, inexpensive technique for making an unlimited number of copies of any piece of DNA. With PCR, a single copy of a certain DNA sequence can be detected and mass-produced. PCR is an important technique in biological research as well as forensics.

Polymerase
The enzyme that adds DNA bases to a growing DNA strand. The polymerase uses one existing DNA chain as a template when building the matching strand. Polymerase copies the DNA in each chromosome during cell division.

Primer
A short DNA sequence used in a polymerase chain reaction (PCR). The primer is designed to match the starting point of the sequence that is copied in PCR.

Protease
An enzyme that breaks down other proteins into single amino acids. An example is the protease in HIV that is responsible for breaking the virus' protein strand into smaller pieces that are used to form a new virus.

Protein
A molecule consisting of many amino acids arranged in a specific order -- determined by the gene -- and folded into a unique, three-dimensional shape. Proteins are the key building blocks of cells, and therefore tissues and organs. Each protein has a specified function. Examples of proteins are enzymes, antibodies, and the muscle protein myosin.

Protein Complex
A group of different proteins assembled together to perform a complex task in the cells. Some protein complexes are considered to be protein "machines," performing important functions such as DNA repair, and cell-to-cell signaling.

Replication
See "DNA replication"

Ribosome
The structures in the cell where proteins are manufactured. Typical cells contain many ribosomes. Often called the cell's "protein factories," ribosomes are located outside the cell's nucleus, in the cellular cytoplasm. According to the messenger RNA of a specific gene, a ribosome assembles a chain of amino acids that folds into a protein.

RNA
A long chain of nucleotides involved in making proteins using the genetic information in the DNA. There are several types of RNA, the main ones being messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).

RNAi
RNA interference, or RNA silencing, is the mechanism by which double stranded RNA can prevent the expression of a gene with a DNA sequence that corresponds to its own sequence.



Somatic Cells
Any of the cells in the human body other than the reproductive cells -- the egg or the sperm cells.

Germ Cells
The reproductive cells in multicellular organisms; the female's egg cells and the male's sperm cells.

Thymine
One of the four bases that make up DNA, often written as the letter "T." The other bases are adenine (A), cytosine (C), and guanine (G). Thymine always pairs with adenine.

Transcription
The second step in the manufacture of proteins in cells, in which the information coded in mRNA (messenger RNA) is translated into sequences of amino acids.

Translation
The first step in the manufacture of proteins in cells, in which the genetic information coded in the DNA is transcribed or copied into mRNA (messenger RNA).



Virus
A biological entity that can reproduce only within a host cell. Viruses consist of nucleic acid covered by protein; some animal viruses are also surrounded by membrane. Inside the infected cell, the virus uses the machinery of the host to produce copies of itself.

Wild type
The form of an organism that has no mutations or genetic changes from the one that occurs most frequently in nature.

X chromosome
One of the two sex chromosomes, X and Y. An embryo inherits an X chromosome from its mother, and an X or Y chromosome from its father. An individual that has two X chromosomes develops into a female, and an individual that has one X and one Y chromosome develops into a male.

Y chromosome
One of the two sex chromosomes, X and Y. An embryo inherits an X chromosome from its mother, and an X or Y chromosome from its father. An individual that has one X and one Y chromosome develops into a male, and an individual that has two X chromosomes develops into a female.



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