Name: ____________________________________________________

Reinforcement: The Molecule of Heredity (DNA)

1. A nucleotide is made of three parts: a ___________________ group, a five carbon __________________, and a nitrogen containing _____________________

2.The sides of the DNA ladder consist of alternating ______________ and phosphates.

3. The 5’ end of a single DNA strand contains a free __________________, while the 3’ end contains a free __________________________.

4. Chromosomes consist of DNA wrapped around _________________________.

5.  DNA was not thought to be the genetic blueprint originally; instead many scientists hypothesized that _______________________ contained the genetic code and blueprint of life.  (They were later proven wrong.)

6. Purines have _________ rings, and pyrimidines have  ____________ ring.

7. Check each of the following statements that are true with regard to Griffith’s experiments.

a. ______  Griffith discovered transformation in bacteria.
b. ______ Mice injected with smooth bacteria quickly became sick and died.
c. ______ Encapsulated bacteria can become “naked” bacteria.
d. ______ Bacteria that do not have capsules tend to be harmless.
e. ______ Smooth bacteria develop a capsule only after exposure to the DNA of encapsulated (rough) bacteria.
f. ______ Griffith’s transforming factor was the protein in the capsule.
g. ______ Transformation allows bacteria to acquire new genes.
h.  ______ Enzymes that destroyed DNA would prevent transformation.

8. Check each of the following statements that are true with regard to the Hershey-Chase experiment.


a. _______ DNA was labeled with radioactive phosphorus.
b. _______ Protein was not labeled.
c. _______ Radioactive sulfur was found in the offspring phages after they emerged from the cell.
d. _______ Phage proteins were not transmitted to host cell or to offspring
e. _______ New phages contained radioactive phosphorous in their DNA.

9. Chargaff’s rule states that the DNA of any species contains equal amounts of ______________ & ____________  and also equal amounts of  _________________ &  __________________

10.  In DNA, thymine is complementary to ________________ ; cytosine is complementary to _____________

11. In a strand of DNA, the percentage of thymine is 30 %.  What is the percentage of cytosine in the same DNA strand?  _________________

12. Number the steps of DNA replication in the correct order (1, 2, 3)

_______Polymerase travels down the DNA parent strand from the 3’ to 5’ direction.
______  DNA unwinds
______  Ligase binds okazaki fragments together


13. Why is DNA replication called “semi-conservative”? ________________________________

14.  What enzyme unwinds or unzips the parent strand?  ________________

15. The junction between separated strands is called the ________________________________

16. What enzyme synthesizes the new DNA strand by adding bases?  _______________________

17.  What enzyme binds fragments of DNA on the lagging strand?  ______________________

18.  DNA polymerase only travels in the  ________   to  _________  direction.

19.  On the diagram:

Label the 3’ and 5’ ends.
Circle a nucleotide.
Label the sugar and phosphate.
Label the bases that are not already labeled.

20. The two sides of the DNA helix are held together by ________________________

21. Write out the complete name for DNA: __________________________________________

22. Name the scientist(s) responsible for each of the following discoveries.

_____________________________________ Bacterial transformation
_____________________________________ The base-pair rule
_____________________________________ DNA was the hereditary material of viruses
_____________________________________ Determined the shaep of DNA from X-rays
_____________________________________ Established the entire structure of DNA