12.2 The Structure of DNA, Chapet 12
8. How did Hershey and Chase confirm Avery's results?
Avery said that DNA transmits genetic information from one generation to the next. Hershey and Chase concluded that the genetic material of the bacteriophage was DNA and not protein, confirming what Avery said.
3. What was the purpose of Oswald Avery's experiments?
Avery wanted to find out which molecule in the heat-killed bacteria was the most important for transformation.
5. The nucleotides in DNA are joined by bonds.
covalent
2. Nucleotides in DNA are made of three basic components: a sugar called: , a , and a nitrogenous .
deoxyribose; phosphate; base
1. The building blocks of DNA are
nucleotides
4. In DNA, can be joined in any order.
nucleotides
5. What did Avery conclude?
He concluded that DNA transmits genetic information.
4. What experiments did Avery do?
He used enzymes that destroyed various molecules from the heat-killed bacteria, including lipids, proteins, carbohydrates, and RNA. Transformation still occurred, but when he used enzymes that broke down DNA, transformation did not occur.
A 9. nucleotide 10.nitrogenous base (adenine) hydrogen bonds deoxyribose sugar 8. 11. G C A G G C 13. A T T C phosphate group 12. base pair (guanine and cytosine)
LOOK AT 12.2 CHART IN NOTES
9. Complete this graphic organizer to summarize the assumptions that guided research on DNA in the middle of the twentieth century. Use an oak tree to give an example of each function. Function: Storing information Why this function is important: The DNA that makes up genes controls development and characteristics of different kinds of organisms. Example: The instructions that cause a single cell to develop into an oak tree must be written into the DNA of the organism. DNA must perform three functions: Function: Copying information Why this function is important: Genetic information must be copied accurately with every cell division. Example: After mitosis, each daughter oak-tree cell has the same genes and chromosomes as the parent cell. Function: Transmitting information Why this function is important: Genetic information must pass from one generation to the next. Example: The gametes of the oak tree carry information from parents to offspring, so the offspring develops as an oak tree.
LOOK AT 12.1 NOTES
14. The drawing below shows half of a DNA molecule. Fill in the appropriate letters for the other half. Explain why you drew your sketch the way you did. CG AT GC GC CG CG TA AT CG The bases link with hydrogen bonds in pairs across the "rungs" of the ladder: A with T and G with C.
LOOK AT 12.2 CHART IN NOTES
15. Complete this table to show how the structure of the DNA molecule allows it to perform each essential function. Key A = Adenine C = Cytosine G = Guanine T = Thymine Function Structure of the Molecule Store information Each strand of the double helix carries a sequence of bases, arranged something like letters in a four-letter alphabet. Copy information The base pairs can be copied when hydrogen bonds break and the strands pull apart. Transmit information When DNA is copied, the sequence of base pairs is copied, so genetic information can pass unchanged from one generation to the next.
LOOK AT 12.2 CHART IN NOTES
6. Complete the table to describe each scientist's contribution to solving the structure of DNA. Scientist Contribution Rosalind Franklin Took X-ray diffraction pictures that revealed the double-helix structure of DNA. Built a model of the DNA molecule that explained both the Crick structure and the properties of DNA. 7. Complete the table by estimating the percentages of each based on Chargaff's rules. 3 33 33 17 17 The Double-Helix Model For Questions 8-13, on the lines provided, label the parts of the DNA molecule that correspond to the numbers in the diagram. James Watson and Francis
LOOK AT 12.2 CHART IN NOTES
6. Fill in the blanks to summarize the experiments of Hershey and Chase. (Note: The circles represent radioactive labels.) Bacteriophage infects bacterium Radioactivity inside bacterium Phage infects bacterium No radioactivity inside bacterium DNA with radioactive label Protein with radioactive label
SEE 12.1 NOTES
2. What happened when Griffith injected mice with a mixture of heat-killed, pneumonia- causing bacteria and live bacteria of the harmless type?
The mice got pneumonia and many died.
1. What happened when Griffith injected mice with the pneumonia-causing strain of bacteria that had been heat-killed?
The mice stayed healthy.
11. By 1952, many scientists were convinced that genes are made of DNA, but they did not yet know how DNA worked. Why was it important to determine the structure of DNA to understand how DNA stored, copied, and transmitted information?
The structure of the molecule had to provide a way for instructions on "how to be a cell" to be coded and stored. DNA had to have something in its molecular structure that allowed it to copy itself with each cell division and pass from one cell to another during mitosis and meiosis.
7. What did Hershey and Chase conclude? Why?
They concluded that the genetic material must be DNA because the phage injected only DNA, not protein, into the bacterium.
12. Why was the fact of transformation so important to the study of DNA's role? What did transformation demonstrate?
Transformation showed that what a cell becomes is determined by DNA. If DNA in a cell was changed, then the cell itself changed. It demonstrated that DNA controlled the fate of a cell.
10. DNA is like a book titled How to Be a Cell. Explain why that title is appropriate for each of DNA's three functions.
a. Storing information: How to Be a Cell contains all the information needed to direct the cell's activities, from growth to energy use. b. Copying information: Multiple copies of How to Be a Cell can be "printed" every time a cell divides, so each daughter cell "knows" what to do. c. Transmitting information: Copies of How to Be a Cell can be passed from parents to offspring, so the offspring have the instructions needed to function.
3. DNA contains four kinds of nitrogenous bases:
adenine , thymine , guanine , and cytosine .
