DNA, chromosomes and genes
short for DeoxyriboNucleic Acid and is a molecule that contains the entire set
of hereditary material of humans and almost all other organisms.
DNA lives in the cells and nearly every cell in a person's body has the
information in DNA is stored as a code made up of four
bases: adenine (A), cytosine (C), guanine
(G) and thymine (T). The order of these bases determines the
information available for building an maintaining an organism. This is
similar to the way in which letters of an alphabet appear in a certain
order to form words and sentences.
DNA bases pair
up with each other, A with T and C with G, to form units called base
each base is attached a sugar molecule and a phosphate molecule and
together this forms a nucleic acid or nucleotide. Nucleotides are
arranged in long strings that form a spiral called a double helix and
this is our DNA. DNA looks
a bit like a
twisted ladder, in which the base pairs form the ladder's rungs and the
sugar and phosphate molecules form the vertical sidepieces of the
each cell the DNA molecule is packaged into thread-like structures
called chromosomes. Each chromosome is made up of DNA tightly coiled
many times around proteins called histones that support its structure.
humans, each cell normally contains 23 pairs of chromosomes, for a
total of 46. Twenty-two of these pairs look the same in both males and
females. The 23rd pair, the sex chromosomes, differ between males and
females. Females have two copies of the X chromosome, while males have
one X and one Y chromosome.
A gene is basically a piece
of the DNA string
and is located on one of the chromosomes. It can be defined as a region
of DNA that controls one hereditary characteristic.
act as instructions to make molecules called proteins. These proteins are large, complex molecules
that play many critical roles in the body. They are required for the
structure, function and regulation of the body's tissue and organs.
human body has between 20.000 and 25.000 genes and their size varies
from a few hundred DNA bases to more than 2 million bases.
in the DNA sequence that make up a gene are called mutations. These
mutations are often the cause for inherited disorders.
Read further about the MCAD mutation >