AP Biology 2.3 Essential Life Process Information
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AP Biology 2.3 Essential Life Process Information. What percentage of the DNA would one expect to have radioactive nitrogen?
|AP Biology||Essential Life Process Information|
|Test Prep||AP Biology|
The cells were then given non-radioactively labeled nitrogen and allowed to replicate
by binary fission.
A sample was taken at this point to quantify what percentage of DNA was radioactively labeled.
What percentage of the DNA would one expect to have radioactive nitrogen?
And here are our answers…
Have you heard of the phrase, “you are what you eat?” [Man eating an apple and a man made from apples appears beside him]
It's actually pretty true…
…At the atomic level, that is.
We don't see a lot of people walking around made of burritos, which is good…no one wants [Burrito's walking and bump into each other]
an uptick in the cannibal population.
In this question, cells were fed radioactive nitrogen, which if we're not mistaken, is [A cell eating radioactive nitrogen]
the start of almost every cell-based superhero movie.
The way it behaves in the cell is basically the same, but since it’s radioactive, scientists [A superhero cell wearing a red cape]
can keep track of where it goes among all the other nitrogen found in the cell.
In this question, the researchers feed the cells with 100% radioactive nitrogen, which [Scientist feeding a cell radioactive nitrogen]
means that all of the nitrogen in the cell will have this special nitrogen label.
That's also why these cells need to adopt an alter-ego in their crime fighting lifestyle.
And since DNA is made of nitrogen, all the nitrogen in the DNA will be radioactively [Nitrogen in a DNA helix radioactively labeled]
Now, when the cells are allowed to divide, they're fed nitrogen that doesn’t have the
special radioactive sauce, which we think might be the same stuff put in A1...
So basically, this unlabeled nitrogen won’t give off any signal when incorporated into
So the question is, what happens to the specially-labeled DNA when binary fission occurs? [A man fishing]
A better question is, what the heck is binary fission?
Binary fission is when a single cell divides into two daughter cells. [A cell divides into two cells]
Imagine if when you grew up, you decided to split yourself in half…and then those halves
grew into two full versions of yourself.
That’s basically what binary fission is, except less painful and less…creepy. [Man splits in half and two identical people appear]
But what happens to the DNA when binary fission occurs?
Of course, both daughter cells need a full set of DNA. [daughter cells hold hands and walk away]
This means that before binary fission can occur, the cell must perform…
…The role of the Phantom in The Phantom of the Opera.
But after that's done, the cell has to perform DNA replication. [Cell replicating it's DNA]
When DNA replicates, the original DNA double helix separates, and DNA polymerase comes
in to add new bases to each single strand, resulting in TWO new helices. [DNA polymerase adding bases to two single strands of DNA and creates two new strands]
So going back to our original question, let’s imagine the parent DNA, completely labeled
with the radioactive nitrogen.
Now, when the cell is being fed with normal nitrogen and it prepares to divide, what happens
when DNA replication occurs?
Each daughter cell will get one strand of the parent’s original DNA, and one strand
that was freshly made by DNA polymerase. [DNA polymerase adding bases to two strands of DNA]
In this case, that means that each daughter will inherit one strand with the special sauce…mm,
A1… …which means that after one round of cell
division, 50% of the DNA will be radioactively labeled.
Which means our answer is C, 50%!
Which is coincidentally, our steak to A1 ratio. [Man eating steak with A1 sauce]
…More or less.