DNA All life on earth uses a chemical called DNA to carry its genetic code or blueprint. In this lesson we be examining the structure of this unique molecule. {Point out the alligator’s eyes in the first picture.} By the way, can you make out what this is? *************************************************************** [The goal of this presentation is to introduce high school biology students to the chemical structure of DNA. It is meant to be presented in the classroom while accompanying the teacher’s lecture, under the control of the teacher.] Mr. Coleman Biology

Why do we study DNA? -its central importance to all life on Earth, We study DNA for many reasons, e.g., -its central importance to all life on Earth, -medical benefits such as cures for diseases, -better food crops. About better food crops, this area is controversial. There is a Dr. Charles Arntzen who is working on bioengineering foods with vaccines in them. People in poor countries could be immunized against diseases just by eating a banana, for instance.

DNA DNA is often called the blueprint of life. In simple terms, DNA contains the instructions for making proteins within the cell. Why is DNA called the blueprint of life?

Chromosomes and DNA Proteins are made from the blueprint that genes provide. Genes are on chromosomes in the cell’s nucleus. {Ask students where the chromosomes are in this picture. Or ask them where the DNA is. Remind them that the mitochondria also have DNA.} Chromosomes are made up of a chemical called DNA.

The Shape of the Molecule DNA is a very long polymer. The basic shape is like a twisted ladder or zipper. This is called a double helix. {Show students a model of the double helix. Explain what a spiral is and a helix is.}

Section 11.1 Summary – pages 281 - 287 A Little History of the Quest to Find the Carrier of Our Genetic Heritage In 1952 Alfred Hershey and Martha Chase performed an experiment using radioactively labeled viruses that infect bacteria. These viruses were made of only protein and DNA. Section 11.1 Summary – pages 281 - 287

Section 11.1 Summary – pages 281 - 287 Hershey and Chase labeled the virus DNA with a radioactive isotope and the virus protein with a different isotope. By following the infection of bacterial cells by the labeled viruses, they demonstrated that DNA, rather than protein, entered the cells and caused the bacteria to produce new viruses. Section 11.1 Summary – pages 281 - 287

Section 11.1 Summary – pages 281 - 287 In 1953, Rosalind Franklin first put forth the possibility of DNA having a double helixical shape. She based this on X-ray diffraction images of DNA crystals she had produced in the laboratory. Section 11.1 Summary – pages 281 - 287

Section 11.1 Summary – pages 281 - 287 Also in 1953, Watson and Crick proposed that DNA is made of two chains of nucleotides held together by nitrogenous bases. Section 11.1 Summary – pages 281 - 287

Watson and Crick proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring. Because DNA is composed of two strands twisted together, its shape is called double helix.

The Double Helix Molecule The DNA double helix has two strands twisted together. We will take apart the DNA molecule to see how it is put together. First, we will look at one strand.

One Strand of DNA The backbone of the molecule is alternating phosphate and deoxyribose, a sugar, parts. The teeth are nitrogenous bases. phosphate deoxyribose {Point to the 3-D mode, if you have one, to show the parts as you discuss them.} bases

Nucleotides O -P O O One deoxyribose (or ribose) together with its phosphate and base make a nucleotide. ATP O -P O O C O Phosphate {Ask students where they have seen a similar molecule before in this class. Answer: ATP . Emphasize that nucleotides are the basic building blocks or units of a DNA molecule and that a single molecule has many millions of nucleotides.} C Nitrogenous base C C Ribose O

One Strand of DNA One strand of DNA is a polymer of nucleotides. one nucleotide One strand of DNA is a polymer of nucleotides. One strand of DNA has many millions of nucleotides. {Point to the 3-D mode, if you have one, to show the parts as you discuss them.}

Four nitrogenous bases DNA has four different bases: Cytosine C Thymine T Adenine A Guanine G These four bases are abbreviated by using their respective first letters.

Two Kinds of Bases in DNA Pyrimidines are single ring bases. Purines are double ring bases.

Thymine and Cytosine are pyrimidines Thymine and cytosine each have one ring of carbon and nitrogen atoms.

Adenine and Guanine are purines Adenine and guanine each have two rings of carbon and nitrogen atoms.

Two Stranded DNA Remember, DNA has two strands that fit together something like a zipper. The teeth are the nitrogenous bases but why do they stick together? {Point to the 3-D model to show the parts as you discuss them.}

Hydrogen Bonds The bases attract each other because of hydrogen bonds. Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.

Hydrogen Bonds When making hydrogen bonds, cytosine always pairs up with guanine and adenine always pairs up with thymine.

Important: Adenine and Thymine always join together A T Cytosine and Guanine always join together C G

DNA by the numbers Each cell has about 2 m of DNA. The average human has 75 trillion cells. The average human has enough DNA to go from the earth to the sun more than 400 times. DNA has a diameter of only 0.000000002 m. The earth is 150 billion m or 93 million miles from the sun. If you unravel all the DNA in the chromosomes of one of your cells, it would stretch out 2 meters. If you did this to the DNA in all your cells, it would stretch from here to sun more than 400 hundred times!

1) In the Hershey Chase Experiment, DNA was labeled with __________, and bacteriophage (virus) protein was labeled with ____________. A. radioactive phosphorous, radioactive sulfur B. radioactive sulfur, radioactive phosphorous C. codons, anticodons D. DNA Polymerase, RNA polymerase

2) In the ladder analogy of the DNA molecule, the "rungs" of the ladder are: A. sugars B. phosphates C. paired nitrogenous bases D. joined sugar and phosphate

3) Which of the following best describes the arrangement of the sides of the DNA molecule? A. twisted B. antiparallel C. bonded D. alternating

4) If a DNA molecule is found to be composed of 40% thymine, what percentage of guanine would be expected. A. 10% B. 20% C. 40% D. 80%

5) A nucleotide consists of: A. a phosphate and a base B 5) A nucleotide consists of: A. a phosphate and a base B. a phosphate, and a sugar C. a base and an amino acid D. a phosphate, a sugar, and a base

6) The sugar in RNA is _____, the sugar in DNA is _______ A 6) The sugar in RNA is _____, the sugar in DNA is _______ A. deoxyribose, ribose B. ribose, deoxyribose C. ribose, phosphate D. ribose, uracil

7) Which of the following is found in RNA but not DNA. A. uracil B 7) Which of the following is found in RNA but not DNA? A. uracil B. deoxyribose C. phosphate D. adenine

8) DNA is a polymer of: A. nucleosides B. fatty acids C. deoxyribose sugars connected by phosphodiester bonds D. nucleotides

9) Which of the following are pyrimidines? A. adenine and cytosine B. adenine and guanine C. cytosine and guanine D. cytosine and thymine

10) Which of the following are purines? A. adenine and cytosine B. adenine and guanine C. cytosine and guanine D. cytosine and thymine

11) A nucleic acid was analyzed and found to contain 32 percent A, 18 percent G, 17 percent C, and 33 percent T. The nucleic acid must be A. single-stranded RNA B. single-stranded DNA C. double-stranded RNA D. double-stranded DNA

12) What does DNA stand for? A. Design of Natural Animals B. Deoxyribonucleic acid C. Doneoribonucleic acid D. None of the above

13) Where in a cell is DNA located at? A. Cytoplasm B. Food vacuole C. Nucleus D. Cell membrane

14) DNA’s function in the cell is … A. The instructions to the make-up to a living organism. B. To control what goes in and out of an organism. C. To take over the mind as a back-up. D. To give dreams and ideas in the mind.

15) The building blocks of DNA are called …… A. Legos B. Electrons C. Neoculiotis D. Nucleotides

16) The four DNA building blocks are … A. Guanine, Adenine, Riginine, Jynine B. Guanine, Adenine, Cynine, Thymine C. Guanine, Adenine, Cytosine, Uracil D. Guanine, Adenine, Cytosine, Thymine

17) A nucleic acid was analyzed and found to contain 37 percent A, 16 percent G, 22 percent C, and 25 percent U. The nucleic acid must be: A. single-stranded RNA B. single-stranded DNA C. double-stranded RNA D. double-stranded DNA

18) A nucleotide consists of A. a sugar, a protein, and adenine B. a sugar, an amino acid, and a starch C. a sugar, a phosphate group, and a nitrogen- containing base D. a starch, a phosphate group, and a nitrogen-

19) The part of the molecule for which deoxyribonucleic acid is named is the A. phosphate group B. sugar C. nitrogen base D. none of the above

20) Who are the three people connected with the discovery of the shape of DNA? A. Franklin, Watson, and Creap B. Franklin, Watson, and Crick C. Francis, Watson and Crick D. Francis, Watson, and Creap