DNA or deoxyribonucleic acid contains all of the hereditary or genetic material in humans and most other organisms, so the DNA is what lets people know what genetic material is in a person or is in a certain creature or other organism.

Now each cell and organism have the same DNA, so if someone were to get a piece of your hair, and fingernail, and a piece of skin, and look at it very closely and look at the DNA, the DNA in all three would be the same.

Mini-test: DNA 

Question 1: Which of the following correctly pairs the chemical bases of DNA?
Question 2: A strand of nucleic acid was analyzed and found to contain 40 percent A, 10 percent G, 40 percent T, and 10 percent C. The nucleic acid is most likely to be:


The next lesson: Gene Mutation, both lessons are included in Practice Tests.

The transcript is provided for your convenience.

It would let whoever was looking at this know that all three of those articles came from the same person.This is the same for other organisms. Each cell in the organism’s body is going to have the same DNA pattern so that you’ll be able to tell that it came from the same creature.

Most NDA is found in the nucleus of a cell. There is some DNA in the mitochondria, and then it is known as mitochondrial DNA or it would look like this, mtDNA, if you saw an abbreviation for it. If you see the little “mt” before DNA in the abbreviation, mtDNA, that’s because it’s mitochondrial DNA and it’s found in the mitochondria instead of the nucleus. But most DNA is going to be in the nucleus.

Now that important hereditary information found in DNA is stored as a code made up of four chemical bases. We’ve got adenine, guanine, cytosine, and thymine. Each one of those bases is only going to pair with one other base. They can’t all pair up with any of the other three, so adenine pairs with thymine and guanine pairs with cytosine to form base pairs.

A way that I remember that is that the ones with the straight lines in their abbreviation letter, the A and T that can be made with straight lines go together and the ones that require a curved line go together. I hope that you remember that adenine pairs with thymine, these straight lines that form A and straight lines to form T and guanine goes with cytosine because of the curved shape that it takes to make each of those abbreviation letters.

The sequence of the adenine, thymine, guanine, cytosine pairs determines how the organism builds and maintains itself. It’s important to think about this: not every organism or every person is going to have the exact same sequence of base pairs and you might think of the alphabet. We use 26 letters to form all of our words and sentences. But the way that they’re arranged, the sequence of those letters is what lets us know what word is being communicated, what sentence is trying to be communicated, and each word has a different meaning, even though it’s made up of the same 26 letters or some subset of those letters. It works the same way.

You’re going to have some sequence of adenine, thymine, guanine, cytosine, and those base pair sequence is going to let you know or let a scientist know what that organism does to maintain itself, what kind it is. Is it functioning properly? Is everything in the right order? What does that order tell us the same way that seeing CAT tells us tha is the word cat and it’s talking about a mammal with pointy ears and whiskers and a tail that’s kept as a pet.

Let’s look at the next part. Each base pair, so our adenine-thymine pair or guanine-cytosine pair is going to attach to a sugar molecule and to a phosphate molecule. Once those attach, once a base pair attaches to the sugar molecule and phosphate molecule, it forms a nucleotide. These nucleotides form two long strands that spiral into a double helix. That is the shape the DNA takes on.

I did my best to give you an example of a double helix that kind of spirals around. If you were to curl a ribbon around my pen, it would form that kind of double-helix shape we’re talking about. You should think of a twisted ladder with the base pairs as rungs. So if we were looking at this picture here, this will be our double-helix shape that’s spiraling around.

Each one of these little rungs on the ladder would be a base pair, so we would have adenine and thymine together, and they will be paired up. Then here, you would have guanine and cytosine paired up. Then you would have adenine and thymine, guanine and cytosine, all the way down the ladder where you’ve got your sugar molecules and phosphate molecules that bound to your base pairs, making up the sides of the ladder here and you just have this long DNA chain.

Then the sequence that you see is going to let you know how that organism builds and maintains itself because not every creature’s DNA is going to be the same. Everyone has a very unique DNA pattern.

DNA can replicate or make copies of itself by splitting the ladder in half. So if we’re looking at this, and we just decided to go through and cut this ladder in half, we would be separating those base pairs all the way down, so then you have A-G, A-G and any other base pairs you’ve got. So we know we’ve got adenine-guanine, adenine-guanine. Because we know what’s on one side of the ladder, each strand or half of that ladder serves as a pattern for duplicating bases.

Since we know we’ve got adenine here, we know the thing that has to pair with it is thymine. If we’ve got guanine, cytosine has to pair with it. Since in DNA, adenine and thymine always pair together and guanine and cytosine pair together, you will know or the cell will know, “Okay, I’ve got this DNA. I’ve only got half of it, but it’s a pattern. If I have adenine, I need to add thymine to the other side. If I’ve got cytosine, I add to add guanine to the other side.”

The cell will know based on that half, that strand that it gets from DNA how to make a complete DNA molecule and be able to form that double helix and complete the DNA strand.

Each new cell needs an exact copy of DNA from the old cell because remember each cell and organism has the exact same DNA. If the DNA is replicating itself, it needs to be giving an exact copy to a new cell, so that this can continue and the organism is going to continue to have the same DNA in it.

You will see a lot about DNA in biology and it’s important to remember that DNA is the hereditary or genetic material. It’s usually found in the nucleus. Remember which bases pair with which. Your straight line in adenine, A, pair with your straight line in thymine, T, and your curved G for guanine goes with your curved C for cytosine.

DNA is the hereditary or genetic material. It is usually found in the nucleus, sometimes in the mitochondria. The most important thing to remember is that it’s where all the genetic material is going to be found. It’s a big identifier for a cell or for an organism.

The next lesson: Gene Mutation, both lessons are included in Practice Tests.