Name ____________________________________________________ Period ___________ Date ___________________
DNA: The Molecule of Heredity Worksheet
DNA Structure
1. On the diagram to the right:
x
Circle and label a
nucleotide.
x
Label the sugar and
phosphate molecules.
x
Label the bases that are
not already labeled.
sugar/
phosphate hydrogen
backbone bonds
sugar/
phosphate
backbone
phosphate
nucleotide
sugar
x
Label a base pair.
x
Label the sugar-­
phosphate backbones.
x
Label the hydrogen
bonds.
phosphate
2. A nucleotide is made of three parts: a _________________________
group, a five carbon
nitrogen
sugar
_________________________,
and a _________________________ base.
sugar (deoxyribose)
3. In a single strand of DNA, the phosphate group binds to the _________________________
of the
next group.
4. Chargaff's rule states that the DNA of any species contains equal amounts of
adenine
thymine
_________________________
& _________________________
and also equal amounts of
guanine
cytosine
_________________________
& _________________________.
adenine
5. In DNA, thymine is complementary to (or pairs with) _________________________
;; cytosine is
guanine
complementary to _________________________.
6. In a strand of DNA, if the percentage of thymine is 30%, what would the percentage of cytosine
20% (Thymine matches Adenine so there has to be 30% adenine which leaves
in the same DNA strand be? _________________________.
40%- Guanine and cytosine have to be equal since they pair. So, 1/2 of 40 is 20%.)
7. James Watson and Francis Crick with, the help of Rosalind Franklin and others, determined
double helix
that the shape of the DNA molecule was a __________________________.
position of hydrogen bonding sites
8. Why do purines pair with pyrimidines? __________________________________________________
9. What type of bonds connect the deoxyribose sugars to the phosphate groups?
covalent
_________________________
hydrogen bonds
10. What type of bonds connect the bases to each other? _________________________
DNA Replication
1. Number the steps of DNA replication in the correct order (1, 2, 3):
2
_____
Daughter strands are formed using complementary base pairing.
1
_____
DNA unwinds
3
_____ The DNA of the daughter strands winds with together with its parent strand.
half of original is in each new strand
2. Why is DNA replication called “semi-­conservative”? _________________________________________
DNA helicase
3. What enzyme unwinds or unzips the parent strand? ________________________________________
4. What enzyme connects the new bases to the old bases in the DNA template?
DNA polymerase
___________________________________________________________________
5. What enzyme connects the new nucleotides together and proofreads them?
DNA polymerase
___________________________________________________________________
6. Show the complimentary base pairing that would occur in the replication of the short DNA
molecule below. Use two different colored pencils (or different pens, markers, etc.) to show which
strands are the original and which are newly synthesized.
Original
DNA
Strand 1
Original
DNA
Strand 2
Original
ĺ DNA Strand
1 (copy from
New DNA
Strand
+
New DNA
Strand
Original
DNA Strand
2 (copy from
left)
A-T
ĺ
C-G
ĺ
T-A
ĺ
T-A
ĺ
A-T
ĺ
C-G
ĺ
G-C
ĺ
C-G
ĺ
C-G
ĺ
G-C
ĺ
A-T
ĺ
T-A
ĺ
A
left)
+
T
G
C
T
A
A
T
A
T
+
C
G
+
T
A
+
T
A
T
G
+
G
A
T
G
T
+
A
+
C
G
G
C
+
C
G
G
+ C
G
C
T
C
+
C
C
A
+
G
C
+
A
G
C
T
A
T
A