Biology190 Unit 1
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Date Created: 01/30/16
BIOL190 Study Guide for Unit 1 Exam 1. Seminal Research on DNA : Our understanding of DNA comes from the works of many researchers. Describe the contributions of each of these three research teams to our current understanding of DNA. Include full description of their work. Be sure to explain what aspects of their results led them to their conclusion. (400-500 words) Hershey and Chase: Hershey and Chase experimented to discover which component, DNA or protein, was responsible for genetic material being produced in new cells. They started with 2 batches of either radioactive proteins ( S) or radioactive DNA ( p) and labeled that DNA was green and protein was yellow. Then they infected each radioactive labeled phage batch with bacteria. Then they used a blender to shake off the loose phages that stayed outside of the bacterial cell (virus-leftovers). Then they used a process of centrifugation which formed a pellet at the bottom of the test tube. Finally they measured the radioactivity in the pellet and the liquid. The result was the pellet showed radioactivity of 32p. What they concluded was 32 that since the p was in the pellet, it suggested that DNA was inside of the bacterial cells and their contribution to our understanding of DNA was that they figured out that DNA contained genetic material from their experiment results. The results also suggested that the radioactive 3S was in the liquid hence the protein did not enter the cell. Watson and Crick: From the Franklin’s data which was an X-ray crystallography, Watson studied the image and was able to see the basic shape of DNA which had a diameter of 2nm. From this they contributed to our understanding of the DNA was the DNA strands was a double helix. From this knowledge, Watson and Crick started to make a wire model of the double helix. They learned from Chargaff was that the amount of adenine was equal to the amount of thymine and the amount of guanine was equal to cytosol. From this information they contributed more to our understanding of DNA which was that a Purine (A, G) and a Pyrimidine (T, C) was base pair together. With their model of DNA, the contributed an understanding of genes and chromosomes which was that in a chromosome there must be an encoded nucleotide sequence. By knowing the information of which base pair went with each other, they also contributed an idea for how DNA is copied by predicting that a parental strand and a daughter strand connect to each other to make new double helixes. Jacob and Monod: They studied E. coli and the enzymes that they created. They used lactose to determined when enzymes were on and off, which they saw that when lactose was present all enzymes were absent. This suggested the idea of an operon. Then they figured out that there were sections of DNA that helped control the enzymes in genes which were promoters and operator. They also learned from the presence of lactose was that repressors can turn transcription off. They contributed to our understanding of gene control. Word Count: 453 2. DNA Function VERSION 1: DNA has two important roles in the cell: transmission of genetic information and control of cellular structure and function. The main function that involves replication in transmission of genetic information because it accurately creates new cells with the same exact DNA replicated in each that can be passed on through generations. The main function that involves transcription and translation is the control of cellular structure and function because gene expression requires the processes of DNA transcription and mRNA translation. Transcription is used to make mRNA, tRNA, and rRNA and it takes place in the nucleus. Translation is used to synthesize proteins and it takes place in the cytoplasm. In DNA replication, it starts out with a parental molecule of DNA. The parental strand separates with the enzyme called helicase and it serves as a template during the DNA replication process. When the two strands of the double helix separate, free nucleotides can base pair along each strand and the nucleotides are bonded with hydrogen bonds, which leads to the synthesis of new complementary strands. DNA polymerase then helps join the nucleotides during complementary base pairing. One of the main ways DNA's antiparallel structure affects replication is due to the fact that DNA polymerases connects nucleotides to make the new DNA, so that on one of the DNA strands which goes from 5’ to 3’ direction. But on the other strand (the lagging strand) the enzyme, DNA polymerase, works in the opposite direction which means that it can only build discontinuous fragments as the double helix unwinds. The semi-conservative model is useful during this process because it shows how during DNA replication, half of the parental molecule is maintained in each daughter molecule. After base paring the daughter and parental strands, the DNA ligase enzyme links the fragments together covalently. And it finishes with 2 identical daughter molecules of DNA are formed. Proofreading is so important because it removes any incorrect base paring during the complementary base paring process. If the pairs are not fixed then there are mistakes in RNA and in encoding of proteins which then can cause a mutation in the DNA sequence. Mutations are permanent changes in the base sequences of DNA in one gene region. These mutation can be passed down through generations and can affect the next generation’s abilities either physically or mentally. An example of a mutation that gets passed down through generations is sickle-cell disease which is the result of one protein that is changed. Word Count: 403 DNA FUNCTION VERSION 2: The main function that involves replication in transmission of genetic information because it accurately creates new cells with the same exact DNA replicated in each that can be passed on through generations. The main function that involves transcription and translation is the control of cellular structure and function because gene expression requires the processes of DNA transcription and mRNA translation. Transcription is used to make mRNA, tRNA, and rRNA and it takes place in the nucleus. Translation is used to synthesize proteins and it takes place in the cytoplasm. The steps of transcription start with the RNA polymerase binding at a promoter region of the Template strand of a gene. The RNA polymerase unwinds the DNA locally as it moves along the template since helicase is not need in this process. The free nucleotides covalently bond in the 5’ to 3’ direction. The process stops when it hits at a terminator region. The DNA comes back together and rewinds into a helix shape once again. The RNA then goes to the cytoplasm through the nuclear pores. During DNA coding there are 3 types of RNA that are used. The mRNA holds that genetic information from the DNA that is processed in the nucleus to the translation machinery of the cell. In an mRNA molecule there is a 5’ cap and a 3’ tail sequences that is added for stability, the introns are cut out, and the exons are spliced together. The tRNA acts as an interpreter which converts codons to the amino acids of proteins. Amino acids themselves cannot recognize the codons on mRNA so tRNA is desperately needed. During the tRNA process, it picks up the appropriate amino acid and recognizes the appropriate codon in the mRNA. Each amino acid is joined to the correct tRNA by a specific enzyme in which there are 20 different enzymes for amino acids. The resulting amino acids are then added to a growing polypeptide chain. A ribosome consists of 2 subunits which are proteins and rRNA. Specific rRNA molecules assemble with either a small/large ribosomal subunit. The steps of translation are initiation, elongation, and termination. During the initiation phase, the start codon (AUG) binds to a small ribosomal subunit which moves along the mRNA strand. It stops once it hits a STOP codon (UAA, UGA, or UAG). Then a Large ribosomal subunit joins. The site is then open ready for tRNA called for by codon in the A site. During Elongation. The amino acids are added to the polypeptide chain until there is a STOP codon. It starts with the anticodon pairs with mRNA codon at the A site. Then the polypeptide separates at the P site and bonds to the amino acid in the A site, which adds more amino acids to the growing polypeptide chain. Finally the P site tRNA now leaves the ribosome and the ribosome moves to the P site. The codon and anticodon are hydrogen bonded. It finishes with a STOP codon which then the completed polypeptide is freed from the last tRNA and the ribosome splits back into its separate subunit. If there is an error in the DNA, the RNA copies and the protein that is produced is all incorrect resulting in maximal effect on a mutation for the next generation. If there is an error in the mRNA, there would be no error in the DNA, 1 error in 1000 RNA copies and 1000 incorrect proteins products from a million proteins. The effect is least for mutation then previous in the next generation. If there is an error in the protein, there I no error in the DNA or RNA copies, but there would be one error in the protein produced from a million. This has the minimal effect for mutation in the next generation. Word Count: 631 3. Complementary Bair Pairing: Explain and discuss the central role of complementary base paring in DNA structure and expression. Rosalind Franklin made an x-ray diffraction of DNA to come up with the idea that a purine and a pyrimidine has to be paired with each other to create a diameter of 2 nm helix width. Chargaff discovered that there is equal amounts of adenine and thymine and there were equal amounts of guanine and cytosine. His rule, Chargaff rule, explains that A always pairs with T and C always pairs with G. Watson and Crick started to make a wire model of the double helix from the information they learned from Franklin and Chargaff. They paired a purine and a pyrimidine on opposite strands and either had A with T or C with G hydrogen bonded. They thought of the double helix as a rope ladder that was twisted into a spiral. The side of the rope would resemble the sugar-phosphate backbone and the bars resemble the pairs of nitrogen bases that are joined by hydrogen bonds. Complementary base pairing plays a central role in the DNA structure because it allows the separated sugar phosphate backbone strands to bond together to make the double helix structure of DNA. CBP plays a central role in DNA replication because it makes it possible to precisely replicate the DNA which ensures that the genetic info is transmitted every time the cell divides. When 2 strands separate, free nucleotides base pair along the parental strand to replicate a new complementary strand. In transcription, CBP is central role after the DNA separate, it serves as a template so that the RNA can hydrogen bond to it with base pairing. CBP is used in translation by bonding the codons with the anticodons so that polypeptides are formed. Word Count: 308 Scientific Inquiry and Experimental Design: Summarize: This experiment was designed to determine if high or low resistance strength training was more beneficiary for elderly subjects with knee osteoarthritis. Subjects were chosen from the Department of Orthopedics, National Taiwan University Hospital during the time frame of January 2004 to June 2005, there were 102 subjects. Before the experiment began, the subjects were required to do different exercises to test their walking speed, pain, and physical sub scores. The subjects were divided into groups, the subjects did the assigned training for a total of 8 weeks. When the 8 weeksin were over, they were then tested for their walking speed, pain, and physical sub scores. The data was then compared to data before the experiment and to the control group. The data showed that high resistance strength training was more beneficiary for elderly subjects with knee osteoarthritis by slightly compared to the low resistance strength training group. Specific Question: Which exercises, high- and low-resistance strength training, is more beneficiary for elderly subjects with knee osteoarthritis? Hypothesis: (state or implied): Knowing that high-resistance exercise has been proven to be more beneficial than low resistance exercise for young subjects, its hypothesized that high resistance strength training will have a better effect in elderly subjects with knee osteoarthritis. Subjects: One hundred two subjects were randomly assigned to groups that received 8 weeks of high-resistance exercise, 8 weeks of low-resistance exercise, or no exercise Control group: No exercise Experiment Group: high resistance exercise for 8 weeks and low resistance exercise for 8 weeks. Experimental/ Independent Variables: High and Low resistance exercises Dependent Variables: Walking time, WOMAC pain subscale, and WOMAC physical function subscale Key Control Variables: All subjects were given health education on knee osteoarthritis, All subjects did a starting baseline assessment of WOMAC pain and physical function subscale scores, walking time on 4 different surfaces, and muscle torque of the knee joint in sequence, All participants were subjected to the same follow- up assessment 3 days after completing the intervention, the Age of the subjects, the Weight/Height of the subject, and Each subject did a total of 17 different tasks. Key Results: There was an improvement for both the low and high resistance exercises for the 8 week time period. However there wasn’t a huge difference between the high resistance and low resistance groups. Based on the comparison to the control group’s results, the high resistance exercise group improved more than the low resistance group. Explain whether and how the results support or refute the hypothesis as you have stated above: The results support the hypothesis since the data given showed that the high resistance training exercise had a greater improvement in walking time and in pain/physical function subscale was greater for the high resistance training than the low resistance exercise training compared to the control group of no exercise Both the high-resistance and low resistance exercise training showed a reduction in the pain and improved functions in patients with knee Osteoarthritis. Even though high resistance strength training showed a greater effect than the low resistance strength training, the difference between them was not very large to be significant.
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