1. Explain why researchers originally thought protein was the

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1. Explain why researchers originally thought protein was the Powered By Docstoc
					1. Explain why researchers originally thought protein was the genetic material.

• Proteins are macromolecules with great heterogeneity and functional specificity • Little was known about nucleic acids • The physical and chemical properties of DNA seemed too uniform to account for the multitude of inherited traits 

2. Describe the experiment that led to the discovery that DNA was the genetic material in cells. • Frederick Griffith in 1928 • Trying to find a vaccine to fight pneumonia • Experimented with the two strains of pneumococcus; smooth & rough • Smooth caused the disease, rough did not • When dead S strain was mixed with live R, the mice DID die, indicating an acquired ability 

3. Define „transformation‟ and briefly discuss viruses and their effects on bacteria.

• Change in phenotype due to the assimilation of external genetic material by a cell • Viruses can inject their information into cells and cause drastic changes in behavior 

4. List the three components of a nucleotide.

1. Pentose (5-C sugar) 2. Phosphate 3. Nitrogenous base 

5. List the nitrogenous bases found in DNA, and distinguish between pyrimidine and purine.

• • •

Pyrimidines Purines 6 membered ring of • 5 membered ring carbon and with 6 membered nitrogen ring C – cytosine • A – adenine T – thymine (DNA) • G – guanine  U – uracil (RNA)

6. Explain how Watson and Crick deduced the structure of DNA, and describe what evidence they used. • Built models to conform to x-ray data - sugar phosphate backbone - nitrogenous base interior 

7. Explain the “base-pairing rule” and describe it‟s significance.
• A – T : 2 hydrogen bonds • G – C : 3 hydrogen bonds • Suggests the mechanisms for DNA replication • Dictates combination of complementary pairs 

8. Describe the structure of DNA, and explain what kind of chemical bond connects the nucleotides of each strand and what type of bond holds the two strands together.

• Hydrogen bonds hold the nucleotides together • Van der Waals forces help keep helix spiral shape 

9. Explain semiconservative replication and the Meselson-Stahl experiment.

10. Describe the process of DNA replication, and explain the role of helicase, single strand binding protein, DNA polymerase, ligase, and primase.
1. 2. 3.     The helical molecule untwists while it copies its 2 antiparallel strands simultaneously Very rapid – only a few hours to copy 6 billion bases of a human cell Very accurate – one in a billion nucleotides are incorrect Helicase  catalyzes the unwinding of the parental double helix to expose the template Single strand binding protein  keeps the separated strands apart and stabilizes the unwound DNA Polymerase and ligase  catalyze the filling-in process Primase  the enzymes that polymerize the short segments of RNA (primers) 

11. Explain what energy source drives endergonic synthesis of DNA.

• It is the hydrolysis of nucleoside triphosphates, which are nucleotides with a triphosphate covalently linked to the 5‟ carbon of the pentose • Exergonic hydrolysis of this phosphate bond drives the endergonic synthesis of DNA  it provides the required energy to form the new covalent linkages between nucleotides 

12. Define antiparallel, and explain why continuous synthesis of both DNA strands is not possible.
• Antiparallel  the sugar-phosphate backbones of the 2 complementary DNA strands run in opposite directions • DNA can only elongate in the 5‟ to 3‟ direction due to polarity issues - 3‟ end has a hydroxyl group - 5‟ end has a phosphate 

13. Distinguish between the leading strand and the lagging strand.
• Leading  continuous DNA synthesis, it is synthesized as a single polymer in the 5‟ to 3‟ direction towards the replication fork • Lagging  the DNA strand that is discontinuously synthesized against the overall direction of replication 

14. Explain how the lagging strand is synthesized when DNA polymerase can add nucleotides only to the 3‟ end.
• The lagging strand is produced as a series of Okazaki fragments in the 5‟  3‟ direction • Fragments are ligated by DNA ligase which catalyzes the formation of a covalent bond between the 3‟ end of each fragment to the 5‟ end of the chain 

15. Explain the role of DNA polymerase, ligase, and repair enzymes in DNA proofreading and repair.

• DNA polymerase and ligase catalyze the filling-in process of the new DNA strands • Repair enzymes excise ( remove) the damaged segments and the gap is filled in by the correct nucleotides  The End!!

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