Biotechnology
DNA and RNA Structure
Name
Date
Period
Score_____
PART A: DNA Structure
Deoxyribonucleic Acid is the genetic information of the cell and is the way information is passed from one
cell to another cell during cell division. It is located in the nucleus of Eukaryotic cells and the cytoplasm of
prokaryotic cells. DNA contains all the information a cell needs to function. Deoxyribonucleic Acid is
also the way information is passed on to you from your parents.
It took many years for scientists to put together the model of the DNA molecule. In 1871 Friedrich
Miescher discovered DNA in the puss from hospital bandages. Fleming in 1879 discovered chromatin
which we now call chromosomes. In 1884 Hertwig showed that DNA in the chromosomes is the molecular
carrier of heredity information. Deoxyribose sugar was crystallized in 1929 by Levene and the nitrogen
bases structure was determined by Erwin Chargaff in 1950. The final picture became clear with the x-ray
crystallography of DNA done by Rosalind Franklin and Marice Wilkins. Each of these scientists added a
piece of information for puzzle until in 1953 when Watson and Crick published the Structure of DNA in
Nature. They along with Marice Wilkins received the Nobel Prize for this structure in 1962.
1) What do the pieces look like?
DNA’s pieces are called nucleotides. Each nucleotide contains a sugar called deoxyribose, a
phosphoric acid and a nitrogen base (adenine, thymine, guanine, and cytosine).
a. First the deoxyribose sugar has five carbons arranged in a ring structure. The carbons are
number from right to left as shown.
b. Second is the phosphoric acid which has the structure shown below.
c. Last are the nitrogen bases, adenine, thymine, guanine, and cytosine. Their structures are
shown below. Notice how the structure of the pyrimidines is different from that of the
purines.
d.
A complete nucleotide is shown in below.
2. How does it fit together?
a. The sugar molecule and the phosphoric acid molecules form covalent bonds to make up the
back bone of the DNA molecule. Look for the 3’ and 5’ ends of the chain. Also notice the
negative charge on the phosphate molecule. It is this charge that allows us to perform gel
electrophoresis of DNA.
b. The nitrogen bases bond with hydrogen bonds like the rungs of a ladder between the sugar
phosphate backbone. Adenine binds with thymine and cytosine binds with guanine. These
base pairs are considered complimentary because they only bond with each other. Adenine
and thymine have two hydrogen bonds whereas, guanine and cytosine have three.
c. The 2-dimentional model of DNA looks like a ladder.
d. The 3-dimentional model of DNA is a double helix.
PART B: RNA Structure
DNA and RNA have similar structures. They are both comprised of nucleotides and have a sugar
phosphate backbone. They differ in two distinct ways.
1.
First RNA has Ribose instead of Deoxyribose. These two sugars differ only by one oxygen
molecule on the 2’ carbon. Look at the structures below can you find the 2’ carbon?
2.
Second RNA has the nitrogen base Uracil instead of Thymine. Uracil has hydrogen where thymine
has a methyl group.
3.
So a RNA nucleotide has the structure below.
Answer the following questions.
1.
Where is the DNA located in Eukaryotic cells?
2.
Where is the DNA located in Prokaryotic cells?
3. What is the significance of DNA?
4.
What are the three parts to a nucleotide?
5.
Which nitrogen bases pair with each other?
6.
What kinds of bonds hold the base pairs together?
7.
How many bonds are between adenine and thymine?
8.
How many bonds are between cytosine and guanine?
9.
What kind of bond holds the sugar-phosphate backbone together?
10. What is the charge on DNA? Where is the charge located?
11. Which end is the 3’ end of DNA?
12. Which end is the 5’ end of DNA?
13. Where is the DNA replicated in Eukaryotic cells? Why is DNA replication important?
14. How are DNA and RNA similar?
15. How are DNA and RNA different?