Download DNA – The Double Helix In 1952, Rosalind Franklin discovered that

DNA – The Double Helix
In 1952, Rosalind Franklin discovered that DNA (deoxyribonucleic acid) is two chains of
molecules in a spiral form. In 1953, using the work of Franklin and other scientists, James
Watson and Francis Crick established the structure of DNA. They determined that the shape of
DNA is a double helix, which is like a “twisted ladder”. (IN 1962, Watson and Crick (along with
Maurice Wilkins) won the Nobel Peace Prize (in medicine/physiology) for their discovery of the
structure of DNA.
The sides of the ladder are made of alternating sugar and phosphate molecules. The sugar
is deoxyribose.
The rungs of the ladder are pairs of 4 types of nitrogen bases. These bases are known by
their coded letters: A, T, C, and G. These bases always bond in a certain way. Adenine will only
bond with Thymine. Guanine will only bond with Cytosine. This means the amount of cytosine in a
cell will always equal the amount of guanine and the amount of adenine will always equal the
amount of thymine. These bases can occur in any order along a strand of DNA.
***Note that the bases attach to the sides of the ladder at the sugars and not the phosphates**
The DNA helix is actually made of repeating units called nucleotides. Each nucleotide
consists of three molecules: a sugar (deoxyribose), a phosphate (which links the sugars together)
and then one of the four bases (A, T, C, and G).
The two sides of the DNA ladder are held together loosely by hydrogen bonds. The DNA
can actually “unzip” when it needs to replicate (copy).
Every cell in your body has the same “blueprint” or the same DNA. Like the blueprints of a
house tell the builders how to construct a house, the DNA “blueprint” tells the cell how to build
the organism.
Answer the following:
1. Write out the full name of DNA. ______________________________________________
2. Where in the cell are the chromosomes located? __________________________________
3. What two scientists established the structure of DNA? _____________ & _____________
4. What is the shape of DNA? __________________________________________________
5. What are the sides of the DNA ladder made of? __________________________________
6. What are the rungs of the DNA ladder made of? __________________________________
7. What sugar is found in DNA? _________________________________________________
8. The DNA helix is made of repeating units called ______________________________ .
9. The units in #8 are made of three molecules: a _________________, a _____________ and
one of the _______ __________.
Color the DNA below. Create a color key for the DNA which indicates each part listed
below:
Sugar (S) = ________________
Adenine (A) = __________ shape:
Phosphate (P) = _____________
Thymine (T) = __________ shape:
Hydrogen Bonds = ___________
Cytosine (C) = __________ shape
Guanine (G) = __________ shape
Remember the bonding:
A bonds with _____.
C bonds with _____.