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In this science project we will make a 3-D cut out model of DNA. We will  learn about the structure of
DNA. It will take about and 1 1/2 hours to complete. Our model will have 16 nucleotide units.

Materials for 3-D DNA Model

  • Printer and computer (color printer works best)
  • Clear transparency over head sheets (optional but looks the best)
  • Paper if not using transparency sheets
  • scissors
  • Heavy duty needle or object to punch holes.
  • Glue
  • Straws
  • Thin String
  • Razor Craft Knife and Crayons (optional)

Process for Making 3-D DNA Model

1)  Make several copies of the nucleotide templates on card. Ten nucleotide pairs are required for a
complete turn of the double helix. To see the major and minor grooves in the double helix clearly, the
model needs to have at least 16 nucleotide pairs.

Click Here For 3-D DNA Model Template

2) If desired, colour in the pieces appropriately. The colours that are often used in sequencing
markers for DNA bases are: Cytosine=Blue; Guanine=Yellow; Adenine=Green; Thymine=Red.

3) Cut out the nucleotide pairs around the thicker, outer lines. Make two small cuts into the card by the
phosphate groups where indicated. OPTIONAL: Use a sharp craft knife to make cuts above the
deoxyribose molecules where shown.

4) Carefully punch a small hole in each cut-out where shown. This will be the axis of the DNA model
through which the string will be threaded. Do not make these holes too big!

5) Fold the sugar-phosphate 'backbones' where indicated by dotted lines. These folds must be made
in the directions shown on the diagram in the PDF file. Take care not to make left-handed DNA!

6) Cut 25 mm lengths of drinking straw. You will need one less piece of straw than you have
nucleotide pairs.

7) Glue the phosphate group on one cut-out onto the deoxyribose on the next. Do the same with the
opposite sugar-phosphate strand. Remember that the sugar-phosphate chains run in opposite (anti-
parallel) directions. The orientation of the letters on the card should help you to assemble the model

8) Hold a piece of drinking straw between the holes in the cut-outs, and thread the string through

9) Repeat steps 5-8 for as many nucleotide pairs as desired.

10) Cut out the genetic code, and glue the two sides together onto the string at the bottom of the
model. This will help the model to hand vertically.

The Science of DNA

Deoxyribonucleic acid ( /diˈɒksɪˈraɪboʊnuˈkliɪk ˈæsɪd/ (help·info)) (DNA) is a nucleic acid that
contains the genetic instructions used in the development and functioning of all known living
organisms and some viruses. The main role of DNA molecules is the long-term storage of
information. DNA is often compared to a set of blueprints or a recipe, or a code, since it contains the
instructions needed to construct other components of cells, such as proteins and RNA molecules.
The DNA segments that carry this genetic information are called genes, but other DNA sequences
have structural purposes, or are involved in regulating the use of this genetic information.

Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones
made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite
directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of
molecules called bases. It is the sequence of these four bases along the backbone that encodes
information. This information is read using the genetic code, which specifies the sequence of the
amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic
acid RNA, in a process called transcription.

Within cells, DNA is organized into long structures called chromosomes. These chromosomes are
duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms (animals,
plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in
organelles, such as mitochondria or chloroplasts. In contrast, prokaryotes (bacteria and archaea)
store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones
compact and organize DNA. These compact structures guide the interactions between DNA and other
proteins, helping control which parts of the DNA are transcribed.

Chemical structure of DNA. Hydrogen bonds shown as dotted lines.

DNA is a long polymer made from repeating units called nucleotides. The DNA chain is 22 to 26
Ångströms wide (2.2 to 2.6 nanometres), and one nucleotide unit is 3.3 Å (0.33 nm) long.[5] Although
each individual repeating unit is very small, DNA polymers can be very large molecules containing
millions of nucleotides. For instance, the largest human chromosome, chromosome number 1, is
approximately 220 million base pairs long.

In living organisms, DNA does not usually exist as a single molecule, but instead as a pair of
molecules that are held tightly together. These two long strands entwine like vines, in the shape of a
double helix. The nucleotide repeats contain both the segment of the backbone of the molecule,
which holds the chain together, and a base, which interacts with the other DNA strand in the helix. A
base linked to a sugar is called a nucleoside and a base linked to a sugar and one or more
phosphate groups is called a nucleotide. If multiple nucleotides are linked together, as in DNA, this
polymer is called a polynucleotide.

The backbone of the DNA strand is made from alternating phosphate and sugar residues. The sugar
in DNA is 2-deoxyribose, which is a pentose (five-carbon) sugar. The sugars are joined together by
phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of
adjacent sugar rings. These asymmetric bonds mean a strand of DNA has a direction. In a double
helix the direction of the nucleotides in one strand is opposite to their direction in the other strand: the
strands are antiparallel. The asymmetric ends of DNA strands are called the 5′ (five prime) and 3′
(three prime) ends, with the 5' end having a terminal phosphate group and the 3' end a terminal
hydroxyl group. One major difference between DNA and RNA is the sugar, with the 2-deoxyribose in
DNA being replaced by the alternative pentose sugar ribose in RNA.

A section of DNA. The bases lie horizontally between the two spiraling strands. Animated version at
File:DNA orbit animated.gif.The DNA double helix is stabilized by hydrogen bonds between the bases
attached to the two strands. The four bases found in DNA are adenine (abbreviated A), cytosine (C),
guanine (G) and thymine (T). These four bases are attached to the sugar/phosphate to form the
complete nucleotide, as shown for adenosine monophosphate.

These bases are classified into two types; adenine and guanine are fused five- and six-membered
heterocyclic compounds called purines, while cytosine and thymine are six-membered rings called
pyrimidines. A fifth pyrimidine base, called uracil (U), usually takes the place of thymine in RNA and
differs from thymine by lacking a methyl group on its ring. Uracil is not usually found in DNA, occurring
only as a breakdown product of cytosine. In addition to RNA and DNA, a large number of artificial
nucleic acid analogues have also been created to study the proprieties of nucleic acids, or for use in

Credits:  It was devised by Van Rensselaer Potter in 1958 and
appeared the following year in his book Nucleic Acid Outlines. Sadly, Dr Potter, a bioethicist and
oncologist at the University of Wisconsin-Madison, died in 2001 before we learnt that he had devised
the original model. DNA information from Wikipedia.
Double Helix
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