MRC 1953 User manual

1953

What is DNA?
DNA stands for Deoxy-ribo Nucleic* Acid, a molecule made of carbon, phosphorous, oxygen, nitrogen
and hydrogen atoms. Nucleic acids, along with lipids (fat), proteins and carbohydrates (sugars), are the
fundamental building blocks of life. If one were to look at it very closely, DNA looks like a spiral staircase or
double helix made of two banisters (the backbone) with steps (the bases) linking the two. There are four
bases (guanine, cytosine, adenine and thymine) - using different combinations they are used to store and
transmit genetic information.
Why is DNA important?
DNA is present in all forms of life: from plants and fungi to large mammals, through to bacteria and viruses.
DNA contains all the information required to make up a living organism**. For example, DNA has instructions
to determine your number of ngers, eye and hair colour. That is why DNA is often referred to as the “carrier”
of the genetic information or life’s 'instruction manual'.
What is Genetics?
Genetics is a branch of biology that studies heredity. Geneticists measure differences in the visible characteristics (traits) of live
organisms and try to understand how they are transmitted to the next generation. This way, they learn about the function of different
genes (the units of information in DNA), and how the traits relate to the genetic make-up of individuals.
What can we learn by studying DNA?
Chemists rst identied DNA in the late 19th century. In the early 20th century, scientists showed
that it is essential for the transmission of hereditary traits from one generation to the next. LMB
scientists in Cambridge built a model of DNA based on X-ray data collected by Rosalind Franklin and
Raymond Gosling in London. This model showed that DNA forms a double-helix. The exciting part
was that the model explained how the genetic information could be duplicated and transmitted to the
next generation. The discovery of the structure of DNA marked the beginning of the era of molecular
biology.
In 1962, James Watson, Francis Crick and Maurice Wilkins were awarded the Nobel Prize for
physiology and medicine for their elucidation of the structure of DNA. This Lego model simplies the
key features of Watson and Crick's Model. It was designed by John Schollar at the National Centre
for Biotechnology Education, whose support we gratefully acknowledge.
* the term nucleic refers to the fact that DNA is found in the nucleus of cells.
** in some viruses the genetic information is contained in a slightly different nucleic acid called RNA. James Watson and Francis Crick
Francis Crick sketch 1953.

1
2
Blue blocks represent
adenine base.
1x 1x
2x

3 4
Clear Blocks represent Hydrogen
Bonds between the bases. These
"weak" bonds hold our DNA
strands together.
Green (thymine) pairs with blue
(adenine). When DNA is copied,
these base pairs are 'melted'.
Note that adenine is a larger
base than thymine.
2x 1x

5 6
7
Grey Blocks represent the sugar
(deoxyribose): one unit of sugar
and the nucleobase combined is
called a nucleoside.
2x 2x
1x

8 9 1x
2x1x

10 11 2x2x

The black blocks represent
the phosphate groups of the
backbone.
You've completed a full
nucleotide base pair -
now start building the
next tier.
12 13 2x2x

14
15
Red blocks represent
the base guanine.
1x 1x
2x

16 17
Yellow bricks show cytosine,
which pairs with guanine -
notice the difference between
the sizes.
2x 1x

18 19
20
2x 2x
1x

21
23
22
24
2x
2x 2x
1x 2x

25
Add this base pair
(red/yellow) to the
base (blue/green) to
make the rst turn of
your double helix.

26 27
Repeat steps 14-24.Repeat steps 1-8, 10-13.

28 1x 26 1x 27
Add nucleotide 'base
pairs' to start forming
the helix.

4x 26 3x 27
29

Compare your lego model to the Watson-
Crick model - what are the similarities and
the differences? Where is the information
stored and how could you access it?
1:1 100,000,000:1
Sugar
Phosphate
backbone
Adenine
Guanine
Thymine
Cytosine
2 nm ~20 cm
3.4 nm
(34Å)
~34 cm
One strand of DNA measures about 2
nanometers in diameter. It would take
about 12,500 strands of DNA to equal
the diameter of a human hair!
G:C
A:T

LEGO SCALE MODEL
The scale of this Lego model is 1:100,000,000.
At this scale just one
gene that determines
eye colour (called
OLA2, 340,457 base pairs) would reach over
10 km.
The model contains 11 base pairs, in a human
cell there are 6 billion base pairs. If you
unravelled all the DNA from one human cell it
would measure 2 metres. At the scale of the
Lego model that would reach more than half
way to the moon!

DNA SCALE MODEL
If the DNA from all the cells in your body were stretched
end-to-end it would reach from the Earth to the Sun
and back more than 250 times!
How can all this DNA t?
DNA has to be packaged.
A chromosome is a single piece of coiled DNA
which is packaged up with proteins. Humans have
46 chromosomes, receiving 23 from each parent.
Humans are 99.8% genetically identical, so just
a 0.2% difference provides all the diversity and
variation seen in the human population.

Lego kits were designed by John
Schollar at the National Centre for
Biotechnology Education.
Images were supplied by:
The Wellcome Library
LMB Visual Aids