Download DNA stucture - worldofbiology09

Unravelling
DNA
DNA
Deoxyribonucleic acid-the chemical of life.
Click on an area below to
find out more about DNA
structure
function
packaging
replication
structure
In the form of a double helix structure.
Made up of a sugar-phosphate back bone
and four types of nitrogen bases.
The four nitrogen bases are adenine (A),
guanine (G), cytosine (C) and thymine (T).
The sugar-phosphatenitrogen base unit is referred
to as a nucleotide.
packaging
Human DNA is up to 1m in length (ie. 3
million base pairs in length). Yet we have
46 molecules within the nucleus of our
body cells.
DNA is tightly wound up into structures
we call chromosomes.
DNA molecule
Histone proteins
Chromosomes are a
package of DNA and
protein called chromatin.
DNA coils around histone proteins.
8 ball-shaped histone proteins and
DNA forms a nucleosome.
Pair of sister
chromatids,
the DNA
molecule has
replicated in
preparation
for cell
division.
For more on
how DNA copies
itself see the
replication
section.
DNA is ubiquitous to life.
Sections of DNA are known to code for the
manufacture of proteins.
These sections are called genes.
function
Proteins are a diverse group of organic
substances that essentially make up living
organisms.
Hence DNA contains instructions for
making a living organism, whether it be a
bacteria, flea, elephant or human.
Gene for skin
pigment, eg
melanin
production
Gene for lactose
production
chromosome
The characteristics of an
organism, as determined
by the genes, can also be
passed on from one
generation to the next.
Hence DNA is also the
vehicle for inheritance of
characteristics.
For cells to divide into new cells and still
contain all the necessary instructions (genes),
DNA must have the ability to replicate itself.
DNA replication is said to be semi-conservative
as each new DNA molecule contains one strand
from the original and one newly synthesised
strand.
DNA replicates with the help of enzymes (DNA
helicase, DNA polymerase and DNA ligase).
After DNA unwinds and unzips, DNA polymerase
adds free nucleotides to each strand (base pair rule).
One strand is created continuously while the other
needs to be created in segments due to the 5΄ and 3΄
polarity of DNA
replication