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Urgent homework help needed - DNA extraction practical

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Urgent homework help needed - DNA extraction practical

Postby SparklyOne » Thu Feb 12, 2009 4:09 pm

We did a practical in class in which we had to extract DNA from a banana by mashing the banana to a pulp, adding a mixture of water, salt, dishwashing liquid and boiling it at a temp. of 60 degrees celsius for 15 min, then placing it in ice-water for 5min. After that we had to filter the solution and add alcohol to it and - voila! DNA is extracted. I have to answer questions on the practical though and my text book that we use for school isn't very helpful. I was wondering if you guys could help! :-)

Here are the questions I'm stuck on:

1) What is the function of salt in this experiment?
- my teacher said it had something to do with enzymes being Ph sensitive, but I'm not sure how that relates to this practical

2) What is the correct term of "breaking down" of the cells?

3) Name another 2 ways in which the scientists could remove/destroy the proteins to ensure a pure DNA extract.

4) What is the purpose of pulping the fruit?
- I think it might be to break down the cell membrane - but the dishwashing liquid does that???

5) Give one reason why:
a) the pulp should be heated
b) should not be overheated

6) DNA is soluble in water. What effect does the alcohol have on the DNA?
Give a reason for your answer.

7) Predict how results would differ if, instead of a banana, you used the same quantity of:
gametes from a banana plant.
- Wouldn't there just be less DNA extracted??

8) Describe how you would use this practical to determine whether paw-paw or melon has more DNA per gram.
- I don't even know how you would weigh the DNA??

9) List 3 ways in which you can ensure the accuracy of the experiment in question 9.

10) List 3 reasons why DNA would be extracted from living material in a laboratory.

That's it. I'm not dumping all my homework on you to do - I have answered some of the other questions, it's just these that confuse me. I need the answers by tonight because it's due tomorrow. Any help would be much appreciated.

Thank you! :-)
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Re: Urgent homework help needed - DNA extraction practical

Postby GeGnome » Thu Feb 12, 2009 4:45 pm

SparklyOne wrote:
1) What is the function of salt in this experiment?
- my teacher said it had something to do with enzymes being Ph sensitive, but I'm not sure how that relates to this practical


The enzyme performs best in a particular pH, so you make a buffer to utilize the enzyme's maximum potential.

2) What is the correct term of "breaking down" of the cells?


Lysing the cells, cell lysis

3) Name another 2 ways in which the scientists could remove/destroy the proteins to ensure a pure DNA extract.


I feel like I'm doing your homework for you. Anyway, you can google this. I'll give you one other method: Phenol-Chloroform, you might want to learn how it's done before putting it down.

4) What is the purpose of pulping the fruit?
- I think it might be to break down the cell membrane - but the dishwashing liquid does that???


Breaks up the bonds and makes it less dense, therefore decreasing the amount of time it takes to do the DNA extraction.

5) Give one reason why:
a) the pulp should be heated
b) should not be overheated


You should be able to answer this one on your own. I'll give you some obvious hints: what happens to chocolate when you melt it, why? What happens to proteins in high temperatures, why?

6) DNA is soluble in water. What effect does the alcohol have on the DNA?
Give a reason for your answer.


The question kind of gives away part of the answer. This is a gimme question.

7) Predict how results would differ if, instead of a banana, you used the same quantity of:
gametes from a banana plant.
- Wouldn't there just be less DNA extracted??


I imagine you would want whole DNA.

8) Describe how you would use this practical to determine whether paw-paw or melon has more DNA per gram.
- I don't even know how you would weigh the DNA??


Google it. Luckily for you, I found a good site that explains it pretty well: http://www.accessexcellence.org/AE/SH/N ... dnalab.php Search for: Data analysis and interpretation

9) List 3 ways in which you can ensure the accuracy of the experiment in question 9.


Just look back at your DNA extraction protocol and think about ways you could prevent it from going wrong

10) List 3 reasons why DNA would be extracted from living material in a laboratory.


I see no reason why you shouldn't be able to answer this. This is another gimme question.
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Postby SparklyOne » Thu Feb 12, 2009 5:26 pm

Thank you very much! :-) I appreciate your help.
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Postby Jones » Fri Feb 13, 2009 3:39 pm

Although I think there's a rule about doing a persons homework for them...
Especially considering most of the answers to those questions you could have found on your own, and easily...
J o n e s i e
A question that sometimes drives me hazy: am I or are the others crazy? -Albert Einstein
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Postby SparklyOne » Sun Feb 15, 2009 1:10 pm

I did try and get the answers from my textbook and I searched for some of the others on the internet. I don't normally ask for help like this - I don't think people should have their homework done for them, but in this case, I needed help because I didn't actually understand how the things in the practical related to the questions. I am definitely not lazy - just needed some explanation.
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