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DNA & Replication Worksheet

1. Write out the complete name for DNA: deoxyribonucleic acid

2. A nucleotide is made of three parts: a phosphate group, a five carbon sugar and a nitrogen containing base Label these three parts on the diagram to the right:

3. In a single strand of DNA, the phosphate group binds to the sugar of the next group.

4. The 5' end of a single DNA strand contains a free phosphate, while the 3' end contains a free OH.

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

6. Purines have two rings, and pyrimidines have one ring.

7. Chargaff's rule states that the DNA of any species contains equal amounts of adenine & thymine and also equal amounts of guanine & cytosine.

8. Wilkinsand Franklin studied the structure of DNA using x-ray crystallography and determined that the shape of the molecule was a helix.

9. James Watson and Francis Crick amended Franklin and Wilkin's conclusions and determined that the shape of the molecule was instead a double helix.

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

Griffith Bacterial transformation

Chargraff The base-pair rule

Hershey & Chase DNA was the hereditary material of viruses

Franklin (& Wilkins) The shape of DNA was a helix

Watson & Crick The shape of DNA was a double helix

11. In DNA, thymine is complementary to adenine ; cytosine is complementary to guanine.

12. In a strand of DNA, the percentage of thymine is 30%. What is the percentage of cytosine in the same DNA strand? 20%

13. The figure below shows DNA replicating. In the space provided, describe what is occurring.

[pic]

|DNA unwinds |Daughter strands are formed using |The DNA of the daughter strands winds together |

|Helicase splits apart helix |complementary base pairing |with its parent strand |

| |DNA polymerase adds DNA nucleotides | |

14. 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.

15. Why is DNA replication called "semi-conservative"? ½ is old, ½ is new

16. What enzyme unwinds or unzips the parent strand? helicase

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

18. DNA polymerase builds the DNA daughter strand in the 5’ to 3’ 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 hydrogen bonds- between nitrogen bases

(covalent bonds – between the sugars and phosphates in the backbone)

21. In your own words, explain why the discovery that DNA was the molecule of heredity was an important discovery.

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5’

3’

A

C

G

T

G

C

A

T

phosphate

sugar

sugar

phosphate

N base

3’

5’

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