Lesson Plan : DNA Replicaion
Teacher Name: | Kevin Beckner |
Grade: | Grade 9-10 |
Subject: | Science |
Topic: | DNA Replication |
Content: | |
Goals: | Standard II (Life Science): Understand the properties, structures, and processes of living things and the interdependence of living Things and their environments. 9-12 Benchmark II: Understand the genetic basis for inheritance and the basic concepts of biological evolution |
Objectives: | • Students will understand the importance of DNA replication in the creation of new cells in an organism. • Students will understand the actions of enzymes in DNA replication such as primase, polymerase, helicase, and ligase. • Students will recognize replication as being able to add bases in the 5' to 3' direction and how this leads to the formation of Okazaki fragments. |
Materials: | • Overhead projector for teacher demo • Large pony beads and floral or electrical wire • Petri dish to hold demo beads |
Introduction: | • Diagnostic Assessment o Each student will write three things in that they know about DNA replication. o Each student will also write three questions they now have about DNA and how a cell makes more DNA. • Hook (Engage) o A model of DNA made out of candy will be shown to the class and a brief introduction as to how DNA can replicate itself will be presented. • Introduction to Goals o We will explain the importance of understanding DNA replication in biotechnology. o We will also discuss the importance of making simple models of complex processes in order to explain what is happening, something each student will have a chance to do. |
Development: | • What should they know? o DNA synthesis can only occur in the 5' to 3' direction. o Ligase must piece together Okazaki fragments on the lagging strand due to the direction of replication. o DNA must be replicated accurately so that new cells can form with complete, identical DNA. o Each enzyme has a specific function that is critical to accurate DNA replication. • How will it link to other ideas in Biology? o Replication is an important element of cell mitosis and meiosis. o Replication is one of the processes that can result in genetic mutations, leading to a variety of conditions. o Replication demonstrates the importance and function of enzymes in biological processes. • Are you bringing in any other skills from other disciplines? o Students will have to create models in order to explain the process of replication. o Students will be responsible for written explanations of how their models represent replication. • How will it link to the real world? o DNA replication is important to the utilization of many different biotechnological methods. o Some common diseases can be caused by mutations in DNA replication. |
Practice: | When scientist Rosalind Franklin first saw the model of DNA created by Watson and Crick based on her research, Ms. Franklin exclaimed, "All that matters is the beauty." By creating jewelry models of DNA, you too can experience Ms. Franklin's delight in the beauty of the master molecule of life. Part 1 - Creating a DNA Jewelry Model While creating your DNA model jewelry, keep the following hints in mind: • Your teacher's demonstration model is there to serve as a guide - refer to it if you need to! • Remember that the "uprights" (helixes) in the model will be double threaded. Be sure to pick beads with large enough holes to accommodate both wires. (Can test by using second wire as a blind, as you thread, and pull the extra through after both sugar-phosphate strands are complete.) • Using needle-nose pliers to "tie-off" the or twist the ends of each wire will save your fingertips. Also, remember that it is easier to thread the wire directly through the beads while they are in the dish rather than trying to pick up the beads with your fingers. NOTE: Except where noted otherwise, the procedure of making key chains, earrings, bracelets, etc.. is exactly the same. To make earrings, you might prefer the small (1.5 mm dia.) seed beads; to make key chains, use the larger (3 mm dia.) E-beads. Procedure: • Step 1: Decide which colors you want to use for your model (you will need to choose beads of six different colors - two different colors for the sugars and phosphates, and four different colors for the base pairs. • Step 2: To make a keychain, earrings, pendant, or central molecule for a silk cord necklace, bracelet, or ankle bracelet, cut two 15 cm (6") strands of wire. Twist two wires together at one end to prevent beads from slipping off as you string them. These strands of wire will be the helixes, or "uprights" of your DNA model. • Step 3: String an equal and even number of beads of alternating colors onto each of the wires, to represent alternating sugars and phosphates. Make sure to start with the same color bead on each wire. When you have strung the beads on each of the wires, twist a loop at the tops of the "uprights" separately to prevent the beads from falling off. Use a minimum of 26 beads for the basic 2 inch molecule. (when twisted) (Leave one inch of "slack" at the top. If you bead right to the top, it'll be very difficult to wire the bases.) • Step 4: Cut 30 cm (12") of wire and fold it in half to make an elongated "U". Next, string and center two different colored beads on the wire (or each wire, for earrings), to form the first "rung" or pair of nitrogenous bases. • Step 5: Thread each end of the wire with the "bases" beads through the third and fourth beads from the bottom of each of the sugar and phosphate "uprights" and pull tight. You've made the first rung. Be sure that the "u-wire's" ends are even. • Step 6: Pull the ends of the bases wire into the center of the ladder and thread two more bases onto one side of the bases wire and take the other bases wire and thread through the two just-threaded bases to make rung at a right angle to the uprights. *** Important!! The bases wires go through each other in opposite directions.*** (These additional complementary bases can be either the same or different colors from the first two sets of bases you used, depending on your personal preference.) • Step 7: Continue threading the bases wire up through the next sugar and phosphate on each "upright". Now add two additional complementary bases to the bases wire as you did in Step 6. (At the end of this activity, you will use whatever combination of bases you decided on to determine the amino acids coded for in your model.) Thread the bases wire through the next sugar and phosphate set, and add another base pair. • Steps 5-7 repeat!! Basic pattern is: Up two on both sides Add two in the middle Cross through the two in the middle Up the next two on both sides. And again, and again, and again... • Step 8: Repeat steps 6 and 7 until you have attached alternating base pairs to each sugar and phosphate set of the "uprights". You should do at least thirteen base pairs to have a large enough molecule to twist. • Step 9: Twist all of the wires at the top of the ladder together. You can twist and cut closely or finish with one last pony-bead or E-bead around the point where the wires form the model and the keychain or earring holder connect. If the molecule is loose, untwist the bottom two wires and gently pull on each . This will tighten the sides and make the bases perpendicular to the sides. Retwist together and trim after tightening. (Not too tight because you still need to twist into a double helix!) • Step 10: Twist your model into the Double Helix, and tape it onto the accompanying worksheet. Make sure you tape the model so that the top of it corresponds to the order of the colors listed in your color key. • Step 11: Then complete Part 2 of your model and decode your model. The jewelry you created will be yours to keep and wear/use after you have handed in this completed worksheet and your teacher has corrected it. NOTE: Provided you have the optional materials needed, you can also use this pattern to make necklaces, bracelets, tie clips, or other pieces of DNA jewelry. To make larger models, start with two lengths of wire for the sugars-phosphates strands approximately double the desired length of the finished piece of jewelry. String the beads as directed, (Steps 1-9). Hint: Thread the bases in sections--18" of wire in the u-shape for base threading is manageable. Finish off the necklace or bracelet with a barrel clasp, a keychain, or earring wires, as directed in Step 9. Some students might want to make the standard two inch DNA model and use cording to finish into a necklace or bracelet. |
Accommodations: | The student with ED will participate on a choice of individually or with a group. I will encourage the group choice to develop social skills. All other achievement levels will remain intact.If any problems during the lesson occur the protocol in the IEP will be followed. |
Checking For Understanding: | The model and the decoding sheet can be quickly checked for accuracy. Since the activity usually takes two hours to complete. I would assess and grade this based on the completion of the model and its accuracy. SEE Pass/Fail check list |
Closure: | o While using their models, the students will have a worksheet which will guide them through the process of replication. o The worksheet will include a diagram of replication on which the students will label where each enzyme in replication acts in the process. o The worksheet will also ask questions about potential problems in DNA replication and why it is so important for DNA to be copied accurately. The worksheet will allow for a better assessment of the verbal learning group while creating the models will allow for a better assessment of the visual learning group. • Summarize o The students will write in their journals three things that they learned about DNA replication in the day's lesson and three new questions they have about DNA. |
Evaluation: | Check List Yes No Model resembles DNA Model has correct colors Model shows accuracy to distance Model can be used for study |
Teacher Reflections: | To be completed at the end of the lesson. |
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