The karyotype of a male human being
- It can make copies of itself. If you pull the two strands apart, each can be used to make the other one (and a new DNA molecule).
- It can carry information. The order of the bases along a strand is a code – a code for making proteins.
A gene is a length of DNA that codes for a specific protein. So, for example, one gene will code for the protein insulin, which is important role in helping your body to control the amount of sugar in your blood.
The DNA double helix showing base pairs
There are four types of base: adenine (A), thymine (T), guanine (G) and cytosine (C). These bases link in a very specific way: A always pairs with T, and C always pairs with G.
The sex chromosomes determine whether you are a boy (XY) or a girl (XX). The other chromosomes are called autosomes.
The largest chromosome, chromosome 1, contains about 8000 genes. The smallest chromosome, chromosome 21, contains about 300 genes. (Chromosome 22 should be the smallest, but the scientists made a mistake when they first numbered them!).
The packaging of DNA into chromosomes
Your genes are part of what makes you the person you are. You are different from everyone alive now and everyone who has ever lived.
DNA, genes and chromosomes Your genes are part of what makes you the person you are. You are different from everyone alive now and everyone who has ever lived. But your genes also mean
DNA bases pair up with each other, A with T and C 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 are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.
The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.
A basic explanation and illustration of DNA can be found on Arizona State University’s “Ask a Biologist” website.
The New Genetics, a publication of the National Institute of General Medical Sciences, discusses the structure of DNA and how it was discovered .
DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone.
The Virtual Genetics Education Centre, created by the University of Leicester, offers additional information on DNA, genes, and chromosomes .
DNA, or deoxyribonucleic acid, 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 are structures within cells that convert the energy from food into a form that cells can use.
The National Human Genome Research Institute fact sheet Deoxyribonucleic Acid (DNA) provides an introduction to this molecule.
An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.
What is DNA? DNA, or deoxyribonucleic acid, 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