Unit 2 Genetics

Ch 12.1 Identifying the Substances of Genes

Several scientists made contributions to identifying DNA.  Analyze the following experiments to discover how the substance of genes was identified.

Griffith’s Experiment

Examine the data table also found on page 339.

1. What happened when the S-strain was injected into the mouse?
2.  What happened when the heat-killed  S-strain was injected into the mouse?
3.  What do you predict will be the result of the mixture of Heat-killed S strain and live R strain?
4.  What were the actual results?  Page 339
5. How could this have happened if the S-strain was heat-killed?
6. What did Griffith conclude from his experiment?
7. Define transformation.

The Molecular cause of Transformation- Avery’s experiment

Avery’s team repeated Griffin’s transformation experiment.  They wanted to determine the molecule that was important for transformation.

They extracted molecules from heat-killed bacteria and treated them with chemicals that destroyed various types of molecules.  Then, they retested to see if transformation occurred.

Examine the table.  What did Avery conclude from the data?

The Hershey-Chase Experiment

Viruses were grown in radioactive isotopes sulfur 35 and phosphorus 32.  Proteins contain almost no phosphorus and DNA contains almost no sulfur.

The tagged viruses were grown with bacteria.

1. If protein entered the bacteria, the cells would be filled with __________.
2. If DNA entered the bacteria, the cells would be filled with __________.
3.  What filled the cells?
4. What can you conclude about how DNA is transferred to the bacterial cell?

History of the discovery of DNA  14:28

http://www.youtube.com/watch?v=59XnRgnkcB8

Ch 12.2 Structure of DNA  pp. 344-348

Objectives:

1. What are the chemical components of DNA?
2. What clues helped scientists solve the structure of DNA?
3. What does the double helix model tell us about DNA?

Objective 1:  What are the chemical components of DNA?

DNA is a nucleic acid composed of smaller units called nucleotides.  Each nucleotide is composed of

1. sugar – deoxyribose
2. phosphate group
3. base (A, T, G, or C)

One puzzling fact of DNA is the relationship between its nucleotides.

Objective 2:  What clues helped scientists solve the structure of DNA?

Erwin Chargoff examined the proportion of A, T, G, and C in various organisms.  Examine the data and draw a conclusion about the relative proportions.

1. What do you notice about the proportions of the bases?  Which bases seem to “match”?
2. What does that suggest about the relationship among these bases?
3. If a species has 35 % A, what are the percentages of

• T = ____ %
• C= ____ %
• G= ____ %

Rosalind Franklin (page 346) was an x-ray crystallographer.   Her work focused on using x-rays diffraction photographs of DNA.

Although her picture did not show the structure of DNA, it was a valuable clue and was used by  Watson and Crick to build a model that explained the structure and properties of DNA.

In his book The Double Helix, Watson wrote. “The instant I saw the picture, my mouth fell open and my pulse began to race.”

James Watson and Francis Crick

Clues in Franklin’s x-ray pattern enabled Watson and Crick to build a model that explained the specific structure and specific properties of DNA.

Helpful review videos:

Discovery of DNA’s structure- Rosalind Franklin

http://www.youtube.com/watch?v=VegLVn_1oCE

DNA Structure 10:22

http://www.youtube.com/watch?v=igZdLN7nw6k

The amoeba sisters– DNA Structures: 8:53

https://www.youtube.com/watch?v=_POdWsii7AI

Objective 3:  What does the double helix model tell us about DNA?

The double helix model explains Chargaff’s rule of base pairing and how the two strands of DNA are held together.

Antiparallel lines– the two strands of DNA run in opposite directions.  This allows the bases on both strands to come in contact at the center of the molecule.  It also allows each strand of the double helix to carry a sequence of nucleotides- like letters in an alphabet.

analogy- 26 letters compose the many words of the English language

4 bases code for the many materials that make up your body.

Hydrogen boding– the bases on the two strands are held togther by weak hydrogen bonds.

Recall hydrogen bonds are the weak bonds that hold two different water molecules together

Base pairing- Watson and Crick’s model shows that the nitrogen bases must pair specifically-

• A with T
• G with C

Their model explains Chargoff’s rule

DNA:  Adenine, Guanine, Cytosine, Thymine and complimentary base pairing:  You need a subscription

http://education-portal.com/academy/lesson/dna-adenine-guanine-cytosine-thymine-complementary-base-pairing.html#lesson

Crash Course Biology:  DNA Structure + Replication

https://www.youtube.com/watch?v=8kK2zwjRV0M&list=PL3EED4C1D684D3ADF&index=11

DNA Replication

Review videos:

DNA Replication 2:38

mhttps://www.youtube.com/watch?v=vNXFk_d6y80

DNA Replication Super Easy 3:11.  Very good animation of DNA structure

mhttps://www.youtube.com/watch?v=dKubyIRiN84

Crash Course Biology # 10 DNA Structure and Replication:

mhttps://www.youtube.com/watch?v=8kK2zwjRV0M

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Chapter 13