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Instructions - You can type your answers directly onto this website.  This will NOT save your work.  Once you are completed please print out this webpage.  If in class computer lab, click File, Print, then choose Find Printer, in Location Box type 220, choose printer listed then click OK.

 

Exploring The Basic Structure DNA

Content Goals:  
To understand the basic structure of DNA.

History of DNA Structure

In the 1950's, Rosalind Franklin used X-ray diffraction to examine the structure of DNA.  All previous work from other scientists had not shown the structure accurately. Sadly, she died in 1958 of cancer, before she was able to receive the Nobel Prize for her work.  Click on the link to learn about x-ray diffraction then answer the questions below.

   

How big is DNA compared to proteins?

 

What was Rosalind's x-ray diffraction photo of DNA called that was later used by Watson and Crick? (after answering look at this famous photo above on the right)

 


In 1953,James Watson and Francis Crick published an article discussing the discovery of the double helix structure of DNA.  What is a double helix?  It's like a ladder that has been twisted around.  Watson and Crick used Rosalind Franklin's x-ray diffraction photo of DNA (Photo 51) to make this huge discovery.

                  

What was the structure of DNA that was discovered by Watson and Crick?

 

Describe what that answer means - give me a description...

 

What did they learn?  Specific pairing was the key feature of the model of DNA.  The pairing of nucleotide subunits.  Don't worry you will learn what a nucleotide is later in this lesson.  After realizing the structural similarities of these paired nucleotides they were soon able to produce their double helix model of DNA.  Their cool discovery then led on to the ability to understand how DNA could replicate itself so easily based on this double helix structure. 

What helped Watson and Crick discover that the model of DNA was a double helix?

 

Watson and Crick received the Nobel Prize for this discovery in determining the structure of DNA in 1962.

 

 


So What is DNA?

Tell me something in or on your body that has DNA?  (if you don't know take a guess!)

DNA carries the genetic information of the cell. So what does DNA stand for?  Deoxyribonucleic acid.  Huh?   De - oxy - ribo - nu - cleic acid.  DNA is special because it can do things other chemicals and molecules can not do like:

What does DNA stand for?

What does DNA carry for the cell?

 

In Eukaryotic cells, DNA is found in the nucleus.

Like plants and animal cells - like cells found in us. 

In Prokaryotic cells, DNA is found in the cytoplasm because there is no nucleus present.

Like bacteria.

What is the job of DNA?  The job of DNA in our cells is to code for making proteins.  What is a code?  Did you ever use codes to communicate to your friends?  Codes are system of words, letters, figures or other symbols used to represent something for the purposes of keeping it secret.  WHAT?  So DNA is keeping things secret? No!  Codes are also used to represent the content of a message in "short" form. Click here to try a code activity

What is the job of DNA?

       

 

DNA carries the instructions to make those proteins from 20 different amino acids. Proteins are created and used by your body every day.  You also eat proteins daily which break down in your body to amino acids, which then are used by DNA to make new proteins.

Tell me a protein that you like to eat?  (hint: protein is best known for making muscles)

                    

 


Back to DNA Structure - Nucleotides

Ok we have learned that DNA is a double helix. Now let's break that structure down. 

DNA is made up of smaller chemicals called nucleotides

DNA is composed to 2 strands held together by hydrogen bonds that are then twisted together with nitrogen bases acting as the "steps" or "rungs" of the ladder.

 

The Nucleotide in DNA is made of 3 basic parts:  Watch short video clip

 

What is a nucleotide?

How many strands are in DNA that make up the "ladder"?

   

What are the 3 parts of a nucleotide?

 

The backbone or strands that form the DNA molecule are made of sugar (deoxyribose) and phosphate.

 

What two things is the DNA backbone (strands) made of?

 


In DNA, there are 4 possible nitrogen bases that can make up the "rungs" or "steps" of the DNA ladder.  The nitrogen bases on one strand of DNA pair up with its complementary base on the other strand.  What does complementary mean?  These nitrogen bases are held together by weak hydrogen bonds. 

For scientific purposes, we often shorten the names of the nitrogen bases down to a single letter.

Adenine = A

Thymine = T

Guanine = G

Cytosine = C

 

 

In DNA, there are 4 possible nitrogen bases that can make up the "rungs" or "steps" of the DNA ladder.  The nitrogen bases on one strand of DNA pair up with its complementary base on the other strand.

  

In DNA, there are 4 possible nitrogen bases that can make up the "rungs" or "steps" of the DNA ladder.  The nitrogen bases on one strand of DNA pair up with its complementary base on the other strand.

Click on This Video Clip

Adenine and Thymine bond together.

Guanine and Cytosine bond together.

 

This rule is called BASE PAIRING.  In DNA, for every adenine there must be a thymine bonded to it and for every guanine there must be a cytosine bonded to it.  This base pairing is what allowed Watson and Crick to determine that DNA was a double helix. 

   

          

How many nitrogen bases are in DNA?

 

What are the nitrogen bases found in DNA?

 

What nitrogen base pairs with ADENINE?

 

What nitrogen base pairs with GUANINE?

 

What is that rule that says these nitrogen bases must pair together?

 


What was the most interesting thing you learned about from this activity? I want a good answer please.


 

How could this activity / lesson be improved? Again I want honest good answers.

 

Please print out this webpage once you have typed in all your responses....Don't forget to type in your name at the top!