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I need to know why DNA has a negative charge.
What about it makes it have a negative charge?  When placed between two opposing magnetic fields, why is it drawn to the positive pole?
This is for a basic molecular biology class.  I would really like some input on this as soon as possible.  I have a test this weekend.
In advance Thank you, Thank You, THANK YOU!!!!
Struggling Student!

Well, Hi!
Hope to help a little bit with your struggle.

First, do not over complicate this. The simple answer is that the phosphate groups all along the DNA ladder make the very large negative charge.  I do not know about magnetic attractions, but when DNA is put in an electric field, it moves to the positive pole because DNA is negative and opposites attract.  It is quite common to put DNA in a gel material and apply an electric current to the gel.  The DNA then moves toward the positive pole.  The smaller pieces can move faster through the pores in the gel. This way one can separate DNA by its size.
Dr. Pat

Dr. Pat,
Thanks, Your answer helped a lot.

The actual question I have to answer is: Why is the net charge of DNA negative? And How are "they" utilizing the charge in the dye box?
So, placing the DNA in a gel with the electric current moves the DNA to the positive pole -- we've done that --- it moves toward the positive pole because it has a negative charge and the phosphate along the ladder makes it negative.?? How? Why?
You may not be able to answer this in time for my quiz but having the info will help anyway.
I will leave my computer at 4:00pm west coast time, today. If you get this before then, Help!
If not thanks for what you've done already!!!!!!!!!

Dear Carolyn,
I will try to answer your questions, but I do not understand the one about the 'dye box'.

When you ask why phosphate groups are charged, you get to a basic attribute of atoms.  They can lose or gain electrons.  Electrons are negative and protons are positive and they are present in equal numbers in the atom. When you put matter into water, all sorts of things can happen.  One is that the atoms can lose an electron or gain an electron.  This makes the atom either negatively charged or positively charged, because the atom always retains all of its protons.  Phosphate groups are made of phosphate bonded to oxygen.  The oxygen atoms are among those atoms that can gain an electron and become negatively charged in water.  This is why phosphate groups and therefore DNA is negatively charged.

Dr. Pat,
I really want to thank you for your help.!!  This course is a for teachers k-12, but the material is for 2nd year Biology majors. I read the material but it doesn't always make sense. You have helped to confirm what I thought to be true.
I only have two class meetings left so I think things will be O.K. from here.
Thanks again! God Bless You!!!

Hi there!!
Love your site so much!  My grade 7 class has also enjoyed it a great deal--we go to school until the end of June here in Canada.  We've all found the site to be extremely accessible, making it easy to understand a difficult topic.

We do have some questions, if you have the time!!
1. What were the first cells that evolved on the earth called? (Not primordial soup cells, I hope!)
2. What cells came next? And were they simpler than modern cells, or pretty much the same?
What's the best theory about how cells came to be? (This may be a big question, but a short answer would be fine!)

Anyways, love your site. Don't worry if you don't have time to respond. And have a very nice day!!

Dear Henry,
Thank you so much for your kind comments about our site.

I am afraid that the primordial soup cells are the beginnings of cells.  Of course, it cannot be known with absolute certainty, since we are at a loss as to exactly what primordial soup was.

As the theory goes, the primordial soup was gurgling along, minding its own business (as primordial soup is wont to do). As lots and lots of time passed, simple small molecules were created by random chemical reactions between primordial soup ingredients. Another version of the theory has the simple small molecules riding to earth on meteorites and such. In any case, after even more time, the small molecules include amino acids, fats, and eventually short chains of RNA.

The RNA is unique among the small primordial molecules because it can contain information. It can act as a template to make its exact opposite sequence (C for G and A for U). Then, the exact-opposite-sequence RNA can serve as a template to make the original sequence of RNA. So, by this time, a pre-cell would have amino acids and maybe some short proteins that had random orders of amino acids and some short RNA molecules that could "reproduce" themselves. These would all be surrounded by a layer of fat (fat will 'bead' up in a water environment). Even later in time, the RNA begins to act as the information source for creating exact sequences of amino acids to faithfully produce specific protein. Eventually, DNA evolves as the molecule that stores the information and RNA is the working version.

So, somewhere in this vast period of time, a cell has resulted that can reproduce itself.  Like bacteria, it would have no organelles (they come much later in evolution).  They would feed on the energy most abundant at that time, like methane (this was well before plants and the oxygen atmosphere we have today).  I believe that the oldest bacteria now present on earth are the methanobacteria or archibacteria.  Your class might try to find a web site that talks about the deep ocean vents and the types of life that exist at those places.  These vents could be considered as sort of primordial (as well as of extreme pressure).  All sorts of life exists there, in conditions we certainly could not endure.  And these forms of life can not endure where we live.

Thank you again for your interest in our site. Hope this helps. Oh, and by the way, I do not know of a name for the first cells; perhaps your class can give them an appropriate title.
Dr. Pat



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