DNA: The Genetic Material Chapter 9 DNA: The Genetic Material

Just a thought… Make a stack of books totaling about 10,000 pages. That the stack of books represents only about one-fiftieth of the information contained in the DNA of every human cell. Correlate this with the amount of information required to code for a human being.

Answers 1. A chromosome consists of two replicated strands of DNA tightly coiled around proteins. The two strands, called chromatids, are attached at a point called a centromere. 2. A gene is a segment of DNA that codes for a protein or RNA molecule. 3. A cell’s DNA is copied during the synthesis (S) phase. 4. When chromosomes break, the broken pieces can detach completely or can reattach in various ways. Therefore, the chromosome is changed, or mutated.

5. (a) For each inherited trait, an individual has two copies of the gene, one from each parent. (b) There may be alternative versions of genes. (c) When two different alleles occur together, one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance. (d) When gametes are formed, the alleles for each gene in an individual separate independently of one another, and when gametes unite during fertilization, each gamete contributes one allele.

Vocabulary chapter 9 Section 1 vaccine (190) virulent (190) transformation (191) bacteriophage (192) Section 2 double helix (194) nucleotide (194) deoxyribose (194) base-pairing rules (197) complementary base pair (197) Section 3 DNA replication (198) DNA helicase (198) replication fork (199) DNA polymerase (199)

Chapter: DNA: The Genetic Material 1. Identifying the Genetic Material A. Transformation B. Viral Genes and DNA

Identifying the Genetic Material The experiments of Griffith and of Avery yielded results that suggested DNA was the genetic material.

Griffith’s Discovery of Transformation

Transformation Something in the heat-killed bacteria that once were able to produce a capsule that caused them to kill the mice was able to “transform” the once non-virulent bacteria into capsule producing, virulent ones! But what was that something????

Avery’s experiment DNA destroying enzymes helped prove it was the DNA not proteins that were the transforming factors!

Hershey and Chase used the bacteriophage T2 and radioactive labels to show that viral genes are made of DNA, not protein.

The Hershey-Chase Experiment

The radioactive sulfur remained outside with the protein coat of the virus. The radioactive Phosphorus went inside the bacteria and showed that the DNA was the component that went inside and produced more viral proteins.

DNA stores the information that tells cells which proteins to make and when to make them.

1. In 1928, the experiments of Griffith demonstrated transformation of a. R bacteria into S bacteria. b. S bacteria into R bacteria. c. heat-killed S bacteria into R bacteria. d. S bacteria into heat-killed R bacteria. 2. In 1952, Hershey and Chase used the bacteriophage T2 to determine that genetic material is made of which of the following? a. protein c. DNA b. RNA d. 35S 3. A microorganism that is virulent is a. able to cause disease. c. a bacteriophage. b. transformed. d. harmless.

4. Avery’s experiments showed that a. DNA is responsible for transformation. b. proteins are responsible for transformation. c. bacteriophages are responsible for transformation. d. virulent bacteria are responsible for transformation. 5. Hershey and Chase injected phages with a. S bacteria. c. radioactive isotopes. b. R bacteria. d. vaccines. 6. Hershey and Chase found that T2 bacteriophages a. inject their DNA into host cells. b. cause host cells to produce viral DNA and proteins. c. keep most of their viral proteins outside the host cell. d. All of the above

______ 7. radioactive sulfur and phosphorous ______ 8. transformation ______ 9. bacteriophage ______10. vaccine a. discovered by Griffith b. infects bacteria c. used in the Hershey and Chase experiments d. helps protect the body against future infections by specific disease-causing agents

GENETIC MATERIAL answers 1. a 6. d 2. c 7. c 3. a 8. a 4. a 9. b 5. c 10. d

2. The Structure of DNA A. A Winding Staircase B. Discovering DNA’s Structure

The Structure of DNA DNA is made of two strands of nucleotides twisted into the form of a double helix.

Each nucleotide in DNA is made of the sugar deoxyribose, a phosphate group, and one of four nitrogen bases. The four nitrogen bases found in DNA nucleotides are adenine (A), thymine (T), guanine (G), and cytosine (C).

The two strands of DNA are complementary—each A on one strand pairs with a T on the opposite strand, and each G on one strand pairs with a C on the opposite strand.

Watson and Crick announced their discovery of the structure of DNA in 1953 with the help of data gathered by Wilkins, Franklin, and Chargaff.

3. The Replication of DNA A. The Roles of Enzymes in DNA Replication Summarize the steps of DNA replication

B. The Rate of Replication p 200 To go fast, there are multiple replication forks!

The Replication of DNA Before a cell divides, it copies its DNA by a process called DNA replication. In DNA replication, enzymes work to unwind and separate the double helix and add complementary nucleotides to the exposed strands.

The result of DNA replication is two exact copies of the cell’s original DNA. Each new double helix is composed of one original DNA strand and one new DNA strand. .

DNA polymerase proofreads DNA during its replication so that very few errors occur

Replication forks