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UNCW BIO 105 - DNA

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BIO 105 1st Edition Lecture 5Outline of Last Lecture I. How do people become male or female?II. Why are certain genetic traits more common in men/boys than in woman/girls?III. How can you tell how human traits are inherited?IV. What happens if a person inherits the wrong number of chromosomes?Outline of Current Lecture I. How do people get their genetic traits?II. How does DNA work?III. How is DNA passed on?IV. How can we use DNA to identify the source of a biological sample?Current LectureBiology 105 DNA Essential Questions 1. How do people get their genetic traits? 2. How does DNA work? 3. How is DNA passed on?4. How can we use DNA to identify the source of a biological sample? Interactive Class NotesThe discovery of the structure and function of DNA was the single most important breakthrough in biology in the 20th century, leading to advances in genetic engineering, reproductive technologies, genetically modified food, and genetic medicine. How do people get their genetic traits?I. DNA as the genetic material A. What is the physical basis of inheritance? 1. Mendel studied genetics in the late 1800's, but the significance of what he had learned wasn't understood until 1900, after his death. 2. In the first few decades of the 20th century many researchers were attracted to the field, andthe rules of inheritance became well known and understood a. The fruit fly became the genetic research organism of choice; it was small, easy to care for,and best of all, it provided a new generation every two weeks. Progress in understanding how These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.genes were transmitted was rapid and satisfying. b. Mysteries remained, though ...what were genes really made of? What substance brought information from the parents to the offspring? And how did it work? B.The search for the carrier of genetic information 1. Fred Griffith studied virulence (ability to cause disease) of pneumococcus bacteria, which cause pneumonia. He had two strains of bacteria, S and R (for smooth and rough). He did the following experiments on them: S bacteria + mice ® dead mice R bacteria + mice ® healthy mice heat killed S bacteria + mice ® healthy mice. Conclusion: (What is needed to kill the mice?) Living S Bacteria heat killed S bacteria + live R bacteria + mice ® dead mice, containing live S bacteria. Conclusion: (The live S bacteria killed the mice, but where did they come from?) Came from the R string of bacteria (Note: bacteria are like people...once they die, they stay dead) 2. Avery, McLeod, and McCarty followed up on this observation and extended it. They hypothesized that something in the S cells caused this genetic transformation. They did the following experiment: S cell extract + R cells ® dead mice, containing live S bacteria a. This supported the hypothesis that something in the S cells caused the transformation. Next they wanted to know what part of the S cell extract caused the transformation. They hypothesized that it might be protein, RNA, or DNA, the best known cellular chemicals, and did the following set of experiments: S cell extract + R cells + protease (destroys proteins) ® dead mice S cell extract + R cells + RNAse (destroys RNA) ® dead mice S cell extract + R cells + DNAse (destroys DNA) ® live miceConclusion: (What chemical causes the transformation?)DNA C. At the time, not all scientists were convinced. Arguments against DNA being the genetic material included: 1. DNA has a relatively simple chemical makeup.2. DNA from all organisms seemed to be the same. 3. In addition, many people did not think higher animals would have the same sort of genetic material as bacteria.How does DNA work? I. DNA structure A. Once DNA was thought to be genetic material, the race was on to understand its structure and function. 1. Chemically, DNA was known to be a long, unbranched chain of small molecules called nucleotides, each of which consisted of 3 parts: a sugar called deoxyribose, a phosphate, and a base. 2. The sugars and phosphates of all of the DNA nucleotides are the same, but there are 4 different bases. Therefore, there are 4 different types of nucleotides. The bases (and nucleotides) are abbreviated A, G, T, and C. a. an early idea called the tetranucleotide hypothesis stated that a molecule of DNA consisted of millions of repetitions of the same 4 letter sequence, for example ACGTACGTACGT….. Thisobviously would not have much information content and would not make DNA a good choice forthe carrier of genetic ____________________________. Proponents of the tetranucleotide hypothesis believed that DNA had a structural role in cells. B. Erwin Chargaff was a chemist who studied DNA: 1. He found that each member of a species has the _____________ proportions of the 4 bases. a. So all humans have the same % A, T, G, and C – but not all 25%. 2. He also found that different species have different proportions of the 4 bases, so the %G in humans is different than the %G in moths 3. His most interesting discovery was called Chargaff’s rule: the %A in a sample = the % T, and the % C = % G. This was most intriguing; no one could explain it but everyone thought it significant. 4. Chargaff’s data did NOT support the tetranucleotide hypothesis and did support an informational function for DNA C. X-ray diffraction images taken by Rosalind Franklin (and used without her permission) showed that DNA was a long, thin molecule, with a constant diameter, and repetitious structure. D. Using Chargaff's and Franklin's data the structure of DNA was worked out by Watson & Crick. They made models of the nucleotides and put them together in different patterns until they found one that was consistent with all of the data: the double helix. E. Features of the double helix 1. The double helix consists of two separate strands of nucleotides held together by complementary bonds. This means that certain nucleotides "complement" or attract one another chemically. A always binds to T, and C to G. a. This explains Chargaff’s


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