Deoxyribonucleic Acid (DNA)

We say that DNA is what makes you "you"

DNA is what makes you different than a frog

Class Discussion:

-What is it?

-What does it look like?

-How does it work?

Group Discussion:

Get into groups of 4 and talk about what DNA is to you. You have 8 minutes and then you are going to share with the class

-DNA is the most important thing in Biology and Life.

-Is it weird that most people do not know how it works?

-Are you interested in learning how it works?

-Why do you want to learn about it or why not?

Lecture:

Deoxyribonucleic Acid is a nucleic acid which is a polymer made of nucleotides. The nucleotides are made of a nitrogen base (either Adenine, Guanine, Thymine, or Cytosine) a phosphate, and a 5 carbon sugar. In this case the 5 carbon sugar, ribose, is missing an oxygen.

When you connect millions of these together you have DNA

We did not always know that DNA was the molecule of heredity.

-At first we thought it was proteins.

-There are only 4 types of nitrogen bases in DNA molecules but there are 21 different amino acids in eukaryote proteins

-For how complex living organisms are it would make sense that the molecule that determines how we are made would be more complex than only four bases

Hershey and Chase to test whether or not DNA is the genetic material of living things turned to viruses

A viruses is only made of protein and DNA

-We knew that when a viruses attacked a living thing it injected a genetic code that became part of that organisms genetic code

-All we had to do was see if it was protein or DNA that the virus was injecting

After experimenting with bacteriaphages (virus) we found that it was DNA that was injected into the bacteria.

-This must mean that DNA was the molecule that held genetic code

Group Discussion:

Get into groups and I want you to come up with a way to test which nucleotides pair up. Remember when scientists were testing which nucleotides paired up with each other they could not see DNA. DNA and nucleotides are too small to see under a microscope. So how would you test it?

Lecture:

In the 1940's a biochemist named Chargaff discovered that no matter what the organism was (fish, frog, or human) the organisms DNA had an equal amount of Adenine and Thymine, also the DNA would have an equal amount of Guanine and Cytosine. This was called Chargaff's Rule. If there was always the same amount of Adenine and Thymine it must mean that these two come in pairs and the same would be true for Guanine and Cytosine.

-These are now called complementary base pairs

In 1953 Watson and Crick discovered the double helix structure of DNA

-This might not seem like a big deal but imagine trying to describe the structure of something so small we cannot see it.

-The double helix structure along with the complementary base pairing successfully explains all of DNA replication, transcription, and translation (things we will be learning about this month).

When describing the structure of DNA we say that it has a sugar-phosphate backbone simply because the sugar and phosphate of the nucleotide make up the spines of DNA and the base pairs are what connect it all in the middle

When your book talks about the structure of DNA it compares it to a ladder. The uprights of the ladder are the sugar-phosphate groups and the rungs of the ladder are the nitrogen bases

Draw DNA