Post Lab Questions l2k4v

POST-LAB QUESTIONS

1. Draw the structure of the major purine and pyrimidine bases that are part of the DNA molecule.

Thymine

Cytosine

Adenine

Guanine

2. Draw the structures of ribose and deoxyribose.

Deoxyribose

Ribose

3. What is the purpose of adding Solution 3 to the pellet? The propose of adding Solution 3 to the pellet is to further purify the pellet.

4. How are peas cells lysed? Peas cells are lysed by grinding and smashing the peas.

5. It is important that you understand the steps in the extraction procedure and why each step was necessary. Each step in the procedure aided in isolation the DNA form other cellular materials. Match the procedure with its function: PROCEDURE A. Filter pea slurry through cheesecloth B. Mush pea with Solution 1 and 2 C. Initial smashing and grinding of pea D. Addition of ethanol to filtered extract

D A C B

FUNCTION To precipitate DNA from solution To separate components of the cell To break open the cells To break up proteins and dissolve cell membranes

6. Why is it important for scientist to be able to remove DNA from an organism? List two reasons. - To analyze the DNA. Some diseases are linked to differences in people’s DNA, so studying DNA can help scientists find cures and create vaccines. - To change the DNA. Creating genetically modified foods, for example, could create crops that are resistant to certain pests/insects or that grow larger or faster.

7. What is the DNA look like? Relate what you know about the chemical structure of DNA to what you observed in the lab? The DNA looked like spider webs. The DNA precipitates look like long and thin fibres. The molecular structure is so long and narrow. 8. A person cannot see single cotton thread 100 feet away, but if you wound thousands of threads together into a rope, it would be visible much further away. Is this statement analogous to your DNA extraction? Explain. DNA is only a few angstroms in diameter, which is somewhat analogous to the thread, in that a thread would appear to be that ridiculously small from 100 feet away. On the other hand, many cells contain many threads of DNA, and the process of extraction puts them into a large tangled mess. This is a bit like many threads woven into a rope. Even though each individual strand is too small to see (in the visible spectrum of light), they form a large visible mass if you collect enough of them.

9. Why must you have handled the diphenylamine reagent with the great care? Diphenylamine reagent must be handled with care because it contains glacial acetic acid and concentrated sulfuric acid, which are caustic.