Chapter 12-1 Scientists & DNA Structure Notes. DNA: The Molecule of Heredity

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1 Chapter 12-1 Scientists & DNA Structure Notes DNA: The Molecule of Heredity

2 I. DNA s Experiment History A. Griffith In 1928 an army medical officer named Frederick Griffith was trying to find a vaccine against streptococcus pneumoniae (the bacteria that causes pneumonia, a lung disease), but instead made a breakthrough in the world of heredity. He did four experiments in which he injected strands of bacteria into mice, one strand that was harmless (R) and one that was harmful (S).

3 Griffith worked with two strains of streptococcus pneumoniae (the bacteria that causes pneumonia, a lung disease) one encircled by a carbohydrate capsule that was deadly, and another that lacked a capsule and was not deadly (harmless).

4 Nonencapsulated 1. How do certain types of bacteria cause pneumonia? 2. The experiment that tested this question led to new knowledge. 3. Genetic information could be transformed from one bacterium to another. Encapsulated

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6 No protein coat Protein coat Genetic Info. Transferred

7 Griffith found from this experiment that even though he had killed the S cells, he hadn t destroyed their hereditary material, which was the one part that caused the disease! When more experiments had been done, it was discovered that the harmless R cells had used the information from the hereditary material of the dead S cells and became harmful; he called this hereditary transformation. (Oh and by the way he never did find the vaccine.)

8 B. Avery & DNA 1. Avery and a group of scientists decided to repeat Griffith s experiment (1932) 2. To determine which molecule in the heat killed bacteria was needed for transformation

9 3. Made an extract (juice) from heat killed bacteria and added enzymes that destroy proteins, carbohydrates, & lipids a. Transformation still occurred! = DNA is transforming agent! 4. Repeated the experiment but added enzymes that destroy DNA a. Transformation DID NOT occur!!

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11 In 1944, he and his colleagues reported that the transforming substances the genetic material of the cell was DNA. This result was met initially with skepticism, as many scientists believed that proteins would prove to be the genetic information.

12 C. Hershey-Chase Experiment 1. Studied viruses; specifically bacteriophages a. Bacterio = bacteria Phage = eater Bacteria eater 2. Viruses are made up of DNA and a protein coat

13 3. Research Question: Which part of the virus enters the infected bacteria cell? a. Grew viruses in the presence of radioactive markers 32 P and 35 S.

14 **Label missing parts b. Sulfur is found in protein coat c. Phosphorus is found in DNA

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16 D. What DNA Looks Like 1. Rosalind Franklin a. Used X-Ray diffraction (x-ray crystallography) patterns to discover that DNA twisted around each other like a helix

17 2. Watson & Crick a. While trying to build a 3-D model of DNA, Watson was shown Franklin s photograph (without her permission, leaked by Wilkins, her partner) and within weeks, figured out the structure of DNA

18 3. Chargaff a. Base-pairing rules b. A pairs with T, C pairs with G c. Found equal ratios of Adenine and Thymine and Cytosine and Guanine in DNA of multiple species

19 II. What we ve learned so far A. Cells make proteins

20 B. Genetic information is passed on through chromosomes 1. Mitosis = Cell Division 2. Meiosis = Sexual reproduction (new offspring)

21 C. Genes are located on chromosomes (specifically on the DNA) DNA (contain genes) Chromatin Chromosome (cell division) Protein (amino acid sequence) Trait (like eye color)

22 D. Let s Review: 1. Chromatin (interphase) = granular material within the nucleus (loose DNA) 2. Chromosome = visible during mitosis and can be clearly seen under the microscope as an X (two sister chromatids) consisting of DNA tightly coiled around histone proteins.

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24 III. DNA = deoxyribonucleic acid A. Genetic material of organisms 1. Molecule of heredity (passes genes from 1 generation to the next) 2. Stores information in cells in the form of a genetic code a. This info is used to form all enzymes and structural proteins Prokaroyotes single chromosome

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26 Avery and other scientists discovered that 1. DNA is found in a protein coat. 2. DNA stores and transmits genetic information from one generation to the next. 3. transformation does not affect bacteria. 4. proteins transmit genetic information from one generation to the next. Answer Now DNA is found in a protein... 0% 0% 0% 0% DNA stores and transmit... transformation does not... proteins transmit genetic... 20

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29 3. The more closely related two organisms, the more alike their DNA will be Three phylogenetic trees were reconstructed based on the DNA sequences of: (a) 4700 bp of mitochondrial DNA, (b) the testis specific protein on the Y chromosome, (c) noncoding regions of the - globin gene.

30 4.Can be copied 5.Condenses into chromosomes 6.Exists inside the nucleus

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33 DNA is a long molecule made of monomers called 1. nucleotides. 2. purines. 3. pyrimidines. 4. sugars. 0% 0% 0% 0% Answer Now nucleotides. purines. pyrimidines. sugars. 20

34 IV. DNA Structure A. DNA is a polymer made up of smaller units called nucleotides (monomer)

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36 B. Each nucleotide consists of: 1. Simple 5-carbon sugar (deoxyribose) 2. Phosphate group 3. Nitrogen base

37 a. Four nitrogen bases exist: i. Adenine A ii. Thymine T iii. Cytosine C iv. Guanine G

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39 Drag-and-Drop DNA Model el1a.htm

40 Which of the following is a nucleotide found in DNA? 1. ribose + phosphate group + thymine 2. ribose + phosphate group + uracil 3. deoxyribose + phosphate group + uracil 4. deoxyribose + phosphate group + cytosine 0% 0% 0% 0% ribose + phosphate grou... Answer Now ribose + phosphate group.. deoxyribose + phosphat... deoxyribose + phosphat... 20

41 C. These nucleotides combine to form two long chains called strands (joined by hydrogen bonds) that are twisted = double helix

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43 1. The Sugar and phosphate make up the back bone. (sides of the ladder held by covalent bonds)

44 2. The Nitrogen bases make up the center (steps of the ladder hydrogen bonds; any base sequence is possible)

45 3. The 2 strands are antiparallel, one right side up and one upside down.

46 D. Chargaff s RulesIn DNA, Adenine (A) pairs with Thymine (T); and Cytosine (C) pairs with Guanine (G).

47 In DNA, the following base pairs occur: 1. A with C, and G with T. 2. A with T, and C with G. 3. A with G, and C with T. 4. A with T, and C with U. 0% 0% 0% 0% Answer Now A with C, and G with T. A with T, and C with G. A with G, and C with T. A with T, and C with U. 20

48 Chargaff's rules state that the number of guanine nucleotides must equal the number of 1. cytosine nucleotides. 2. adenine nucleotides. 3. thymine nucleotides. 4. thymine plus adenine nucleotides. Answer Now cytosine nucleotides. 0% 0% 0% 0% adenine nucleotides. thymine nucleotides. thymine plus adenine n... 20

49 A DNA molecule separates, and the sequence GCGAATTCG occurs in one strand. What is the base sequence on the other strand? 1. GCGAATTCG 2. CGCTTAAGC 3. TATCCGGAT 4. GATGGCCAG 0% 0% 0% 0% Answer Now GCGAATTCG CGCTTAAGC TATCCGGAT GATGGCCAG 25

50 1. Purines: Adenine & Guanine (2 rings) 2. Pyrimidines: Thymine & Cytosine (1 ring)

51 3. A & T are said to be complimentary to each other, so are C and G 4. A purine must always bind with a pyrimidine because only 3 rings can fit in the center of DNA

52 E. Eukaryotic chromosomes contain DNA (double helix) wrapped around proteins called histones.

53 1. Strands of nucleosomes are tightly coiled and supercoiled to form chromosomes

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56 In prokaryotic cells, DNA is found in the 1. cytoplasm. 2. nucleus. 3. ribosome. 4. cell membrane. 0% 0% 0% 0% Answer Now cytoplasm. nucleus. ribosome. cell membrane. 20

57 Which of the following include all the others? 1. DNA molecules 2. histones 3. chromosomes 4. nucleosomes 0% 0% 0% 0% Answer Now DNA molecules histones chromosomes nucleosomes 20

58 a. What phase of the cell cycle do chromosomes appear? End of Interphase beginning of Mitosis Mitosis

59 Bellwork a) Describe the relationship between chromatin and a chromosome. b) In what phase of the cell cycle is the DNA in it s chromatin form? c) In what phase of the cell cycle is DNA in its chromosome form? d) Draw a duplicated chromosome. Label the chromosome and the sister chromatids. COMPLETE SENTENCES!

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