Download Making A DNA Model

Name: ________________
Date: _________________
Block: ________________
Making A DNA Model
Objective: To build a three dimensional model of a simplified DNA molecule.
Background:
In the 1950’s James Watson and Francis Crick discovered the structure of the
DNA molecule. They developed a model shaped like a double helix. This model helped
introduce a whole new field of biology, often called molecular genetics, which in turn has
led to areas as significant as genetic engineering and gene therapy.
DNA (deoxyribonucleic acid) is a molecule that makes up our genes and controls
traits in living things. The molecule is made up of a series of nucleotides. A nucleotide
is composed of sugar (deoxyribose), a phosphate group, and a nitrogen base (adenine,
thymine, cytosine, or guanine). Nucleotides bond to other nucleotides forming an
extremely long chain or polymer. In DNA, 2 such chains are bonded together and
twisted, resulting in a double helix structure.
Materials: 2 transparent straws
Scissors
2 - 40 cm. lengths of wire
2 popsicle sticks
2 straws each (of 4 different colors)
15 toothpicks
a handful of small marshmallows
Procedure:
1. Phosphate molecules: cut transparent straws into 2 cm. segments
Sugar molecules: represented by individual marshmallows
Nitrogen bases: Adenine = pink – cut several 2 cm lengths
Thymine = green
Cytosine = yellow
Guanine = orange
2. Attach the ends of the two pieces of wire to one popsicle stick. Put the wires
approximately 5 cm. apart.
3. Onto each wire, slide a segment of transparent straw (phosphate), then a
marshmallow (sugar). Continue stringing these two molecules, 14 more times for a
total of 15 groups. (**Tip: It helps to wipe the wire with a wet paper towel after each
marshmallow.)
4. Wrap the lower end of the wire around another popsicle stick.
5. Put two different colored straw segments onto a toothpick. Consult your color code
for the bases and REMEMBER! Adenine (pink) always pairs with Thymine (green)
Cytosine (yellow) always pairs with Guanine (orange)
6. Stick the toothpick into 2 opposite marshmallows.
7. Continue adding “base pairs” until you have completed 15 pairs. Rotate your DNA
molecule now. “Twist” it. Tie a string to the top popsicle stick, and hang your model
from the ceiling.
Analysis Questions:
1. Draw a picture of your DNA model and label each part (phosphate, deoxyribose
sugar, adenine, thymine, cytosine, and guanine).
2. In your model, what substances represent ONE nucleotide?
3. How many nucleotides are in one strand of your model? Does the other strand
contain the same number? Explain.
4. How many of each TYPE of nucleotide (A, T, C or G) are in your DNA molecule?
What do you notice about these numbers (which nucleotides MUS be equal in
number)?
5. What kind of bonds hold the nitrogen bases from each strand together? Are these
strong or weak bonds?
6. What molecule does DNA “code” for?
7. What is a section of DNA that codes for a specific protein called?
8. Put the following terms in order from smallest to largest: chromosome, gene, DNA
strand. Explain the relationship among these 3 terms.
9. What can occur if the DNA nucleotides are in an altered order?