Download Constructing DNA

Constructing DNA
DNA is called the blueprint of life. It gets this name because it contains the instructions for
making every protein in your body. Why are proteins important? Proteins are important
because they are what your muscles and tissues are made of; they synthesize the pigments that
color your skin, hair, and eyes; they digest your food; they make (and sometimes are) the
hormones that regulate your growth; they defend you from infection. In short, proteins
determine your body’s form and carry out its functions. DNA determines what all of these
proteins will be.
The DNA molecule is a double helix. Think of it as a ladder that has been twisted into a
spiral. The outside of the ladder is made up of alternating sugar and phosphate groups. The
sugar is called deoxyribose. The steps of the ladder are made up of nitrogen-containing bases.
There are four different bases in DNA: adenine, guanine, cytosine, and thymine. These four
bases are of two types: purines and pyrimidines. Purines are large double-ring structures.
Adenine and guanine are purines. Pyrimidines are smaller single ring structures. Cytosine and
thymine are pyrimidines.
Inside the DNA ladder, two bases pair up to make a “rung”. One base sticks out from
each sugar-phosphate chain towards the inside of the ladder. It forms a pair with a base
sticking out from the opposite sugar-phosphate chain. There is only room for three rings
between two sugar-phosphate chains, so a pyrimidine and a purine form a pair. Because of the
chemical structures of the bases, adenine always pairs with thymine and cytosine always pairs
with guanine.
Directions:
1. Color and then cut out the pattern of the following pieces:
a. 8 Deoxyribose sugars
b. 8 phosphates
c. 2 adenines
d. 2 guanines
e. 2 cytosines
f. 2 thymines
2. Tape all of the Deoxyribose sugars to the phosphates at the location labeled “1”, matching
up the asterisks (*).
3. Tape each of the nitrogen bases to the deoxyribose sugar at the location labeled “2”, or
where the large circle is. (Match up the circles).
4. Turning four of the deoxyribose-phosphate-nitrogenous bases upside down, match up
thymine to adenine and cytosine to guanine.
5. Tape your DNA together at the location labeled “3” or the squares matching together.
6. Tape it into your journal.
Questions:
1. What base does adenine pair with?
2. What base does guanine pair with?
3. What is the smallest unit of DNA called?
4. What is the shape of the DNA molecule?
5. What is the name of the sugar in the DNA backbone?
6. Suppose you know the sequence of bases on one DNA strand is AGCTCAG. What is the
sequence of bases on the opposite strand?
7. Assume that in a 100 base-pair DNA double helix, there are 45 cytosines. How many
guanines are there?