DNA stands for Deoxyribo-Nucleic-Acid.
You can consider the DNA as set of instructions, in which is laid
down for each cell , which role the cell has in the organism - to
which part of the organism the cell belongs and how to function.
For the cells of each part of the ear is laid down, whether they are
cells of the vestibular organ, to which of the 3 semicircular canals
they belong, whether they are part of the Corti organ, and so on.
For the cells in the muscles is laid down, to which muscle they
belong, whether they are part of the muscles in the extremities, or
part of the muscles on the back, and so on.
For each cell of the eyes is laid down, to which
part of the eye they belong, if they belong to the retina, if they
belong to the iris, etc., and which function they have, if they are
photoreceptors, if they a cell in the lens, etc.
The DNA is in the nucleus and thus is in each body cell.
See cell structure.
The image is provided by the
U.S. National Library of Medicine.
|Click on the text to get a more
Click on the DNA, to see the
|The DNA is like a ladder, which is
called double helix.
The DNA consists of two strands - a left strand and a right
strand, which wind clock-wise (to the right).
strands = backbone have the same chemical structure,
but the elements of the right strand run in the opposite
direction to the left strand.
A backbone consists of repeating units: a sugar group =
deoxyribose (the 1st part of the name DNA) joined
with a phosphate group.
The rungs of the ladder = connection between the left
strand and the right strand are base pairs.
There are involved only 4 organic bases (nucleo-bases) to
build the rungs:
thymine (T) 1)
But not each base joins with each base. A larger base always
pairs with a smaller base:
|adenine only joins with
cytosine only joins with guanine.
The 2 bases of a base pair are connected by hydrogen
A sugar-group + phosphate group + 1 base is called a
1) Thymine is replaced by uracil (U) in the RNA.
We are coming later to what the RNA is.
When you look on
the chemical structure by clicking on the words in the
picture to the left, please hold in mind:
The molecules are sometimes rotated and/or flipped, the only
reason is to display a structure more organized = i.e. that
an element fits better into a diagram.
Now, as we have seen the basic chemical structure of the DNA, the
Is the DNA freely swimming in the nucleus?
See our next lesson about the chromosomes.