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In order to unwind DNA, these interactions between base pairs must be broken. This is performed by an enzyme known as DNA helicase.
DNA helicase disrupts the hydrogen bonding between base pairs to separate the strands into a Y shape known as the replication fork. This area will be the template for replication to begin. DNA is directional in both strands, signified by a 5' and 3' end. This notation signifies which side group is attached the DNA backbone.
The 5' end has a phosphate P group attached, while the 3' end has a hydroxyl OH group attached. This directionality is important for replication as it only progresses in the 5' to 3' direction. However, the replication fork is bi-directional; one strand is oriented in the 3' to 5' direction leading strand while the other is oriented 5' to 3' lagging strand. The two sides are therefore replicated with two different processes to accommodate the directional difference.
The leading strand is the simplest to replicate. The primer always binds as the starting point for replication. Primers are generated by the enzyme DNA primase. Enzymes known as DNA polymerases are responsible creating the new strand by a process called elongation. There are five different known types of DNA polymerases in bacteria and human cells.
In bacteria such as E. DNA polymerase III binds to the strand at the site of the primer and begins adding new base pairs complementary to the strand during replication. In eukaryotic cells, polymerases alpha, delta, and epsilon are the primary polymerases involved in DNA replication.
Because replication proceeds in the 5' to 3' direction on the leading strand, the newly formed strand is continuous. The lagging strand begins replication by binding with multiple primers. Each primer is only several bases apart. This process of replication is discontinuous as the newly created fragments are disjointed. Once both the continuous and discontinuous strands are formed, an enzyme called exonuclease removes all RNA primers from the original strands. These primers are then replaced with appropriate bases.
Another enzyme called DNA ligase joins Okazaki fragments together forming a single unified strand. The ends of the parent strands consist of repeated DNA sequences called telomeres. Telomeres act as protective caps at the end of chromosomes to prevent nearby chromosomes from fusing. A special type of DNA polymerase enzyme called telomerase catalyzes the synthesis of telomere sequences at the ends of the DNA. Creating an account will give you access to additional content and tools.
Evolution: DNA and the Unity of Life is an eight-week, comprehensive curriculum unit that sharply illuminates the underlying role of genetics in evolution by maintaining a conceptual connection to DNA and heredity throughout. Through paper-based and interactive multimedia lessons, the unit aligns with the Next Generation Science Standards NGSS by engaging students in questioning, using models, identifying patterns, analyzing skill-level appropriate data from published scientific studies, and constructing evidence-based arguments.
Modules can be used individually or together in sequence. When used in their entirety and in the suggested sequence, the modules establish an understanding of DNA as a blueprint for all living things, and how it underlies variations in traits that are acted upon by natural selection leading to the diversity of life.
A scaffolded claims-evidence- reasoning framework is integrated into the unit to incrementally build skill in constructing arguments from evidence over the course of the module sequence.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author s and do not necessarily reflect the views of the National Science Foundation. Log in Register. View large Download slide. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Table 1. Questionnaire for high school students. Question 1 Do you think all living organisms have DNA? Question 2 Do you think all living organisms originated from the same ancestor?
Question 3 Do you think DNA is a chemical substance? Question 4 Do you think living organisms have become diverse while maintaining unity? Question 5 Living organisms are widely classified into the following five groups: Question 6 Did you realize that the extracted material was DNA? View Large. Table 2. Questionnaire for biology teachers. Question 1 Do you wish to teach the DNA extraction experiments that we performed today in a Basic Biology class at the school where you are teaching?
Question 2 Please present the reasons why you replied in that way. Question 3 With regard to the DNA extraction experiments that we performed today, please write positive points and points of potential improvement. Question 4 Please write any of your impressions of this activity. Table 3. Questionnaire for high school students in improved practice experiment. Question 1 Do you think DNA is a chemical substance?
Question 2 Do you think living organisms have become diverse while maintaining unity? Question 3 Living organisms are widely classified into the following five groups:. Figure 8.
Figure 9. Figure Table 4. Questionnaire for biology teachers: excerpts from replies to question 2. These contents seem to be well suited for teaching about the commonness of living organisms because they are simple and inexpensive. It is interesting that the DNA of all five kingdoms of living organisms can be examined simultaneously.
It can be performed simply and the unity of the five categories can be understood. If well prepared in advance, middle-ranking students of my school can understand and perform the contents. I wish to conduct these exercises if materials and instruments are made available and if the number of people is adjusted well.
It is effective for learning that DNA is found in all living organisms. We learned methods and materials that can be implemented in a high school setting. We wish to promote cooperation between businesses and schools. It is possible to see and confirm using our hands that DNA is included. Table 5. Questionnaire for biology teachers: excerpts from replies to question 3. Good Points Materials that are familiar to the students and which represent the five kingdoms are used. We can realize that the same material is obtainable from different living organisms.
Materials were carefully selected, yield is high, and DNA extraction from all five kingdoms was realized. All living organisms, some from each of the five kingdoms, are used for experiments. Experiments using SDS, a transparent disposable cup, and scissors might be accepted willingly by students at the school.
We were able to understand that extraction of DNA from all living organisms is possible. Experiments are related to the five kingdoms. They are risk-free and they are simple. Familiar cooking ingredients can be used. Points Demanding Improvement We wish to use an activator with economically good performance for living organisms with poor yield, unless SDS is used.
Please find a method by which students can notice that this is DNA. Functions of each chemical should be explained in the class. Students would not be impressed with white milk-like substances.
We suggest that helical geometry by X-ray diffraction photograph in the illustration or competition for elucidation of the DNA structure be introduced.
The issue here is whether the experiment can be promoted skillfully or not. Handling one or two types is no problem. The key is whether living organisms of five types can be handled successfully or not.
Steps to confirm that this substance is DNA should be sought. Why this experiment is necessary should be shown in the guidance sheet to convince the students to promote the experiment smoothly. It is doubtful whether it is really DNA or not. Students would understand more easily and teachers would be able to teach them more easily if criteria were available showing what materials should be crushed and to what degree.
Alozie, N. Promoting 21st-century skills in the science classroom by adapting cookbook lab activities: the case of DNA extraction of wheat germ.
Balgopal, M. Banba, N. A revision of the laboratory work on extraction of DNA at lower secondary school level [in Japanese with English abstract]. Hearn, R. Katayama, N. Kobayashi, K. Krebs, R. Nishino, H. Development of experiments for recognizing genuine extracted DNA: for identification of deoxyribonucleic acid as non-protein, non-polysaccharides helix structure and acidic compound [in Japanese with English abstract]. Rode, G.
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