Download Genetics Assessment

Name
Date
Period
DNA Model Lab
Background Information
Deoxyribonucleic acid (DNA) is the molecule responsible for hereditary traits. Francis Crick
and James D. Watson worked in the early 1950’s to unravel the molecular structure of the DNA
molecule.
DNA can be compared to a “twisted” ladder. The uprights or sides of the ladder are composed
of phosphate groups and sugar molecules. There is an almost endless repetition of these
substances. Each rung of the ladder is composed of a pair of nitrogen compounds called bases.
DNA molecules are composed of combinations of four bases. They are guanine, cytosine,
adenine, and thymine. A deoxyribose molecule, phosphate group, and base form a nucleotide.
In the “rungs” of the DNA ladder, cytosine always pairs with guanine, and thymine always pairs
with adenine. Base pairing of these four bases results in specific sequences of nucleotides on a
chromosome which account for differences in genes. A gene may be thousands of these base
pairs.
In this investigation, you are to construct a two-dimensional model of a DNA molecule. You are
to determine the sequence of bases, deoxyribose, and phosphate groups from the sketch given
(figure 1).
Procedure
1. Using a different color for each shape, trace each shape the correct number of
times (the number is written on the shape on the TEMPLATE page).
2. Cut out all of the shapes.
3. Obtain a piece of white poster paper.
4. Using your knowledge of DNA and Figure 1, construct a two-dimensional DNA
model.
5. Glue the shapes onto the poster paper.
6. The first part of your DNA molecule should look EXACTLY like Figure 1.
7. Use the rest of the shapes to complete the molecule of DNA.
8. When you finish you should have 12 nucleotide pairs (24 individual nucleotides)
glued to your poster paper.
9. On your poster label one of each of the following (check the boxes as you label):
 Nucleotide
 Phosphate Group
 Deoxyribose Sugar
 Adenine
 Thymine
 Guanine
 Cytosine
 Rungs
 Backbone
Figure 1
DNA Model TEMPLATES
(NOTE: Number on each shape indicates the number of cutouts you need to make.)
24
24
(deoxyribose)
(phosphate group)
24 (carbon-nitrogen bond)
8
8
(guanine)
(cytosine)
48
8
8
(thymine)
(adenine)
(carbon-oxygen bond)
Name
Date
Period
DNA Model Lab
Questions
1. What is the structure (as discovered by Watson and Crick) of the DNA molecule?
2. What two (2) parts make up a DNA molecule?
3. What makes up the “backbone” of the DNA molecule?
4. What makes up the “rungs” (or steps) of the DNA molecule?
5. What three (3) parts make up a nucleotide?
6. What four (4) bases are found in a DNA molecule?
7. What base pairs with adenine?
8. What base pairs with cytosine?
9. Count your nitrogen bases and record the numbers below.
____ Adenine
____ Thymine
____ Cytosine
____ Guanine
10. What can you conclude about the number of adenine compared to the number of
thymine and the number of guanine compared to the number of cytosine?
11. Compare you DNA molecule to your classmates. Is yours exactly the same as
anyone else’s in the class?
How does your answer to question 11 compare to real DNA inside of living
organisms?