Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.
Understanding DNA Replication
One of the hardest parts of biology is comprehending topics like DNA replication, or when one DNA molecule becomes two. This series of activities will give students a solid foundation that can be used to build upon more complex topics like protein synthesis, either as standalone lessons and/or alongside textbook lessons.
This activity introduces students to DNA. By being able to 'see' the DNA, students will be better prepared to learn about replication.
- Isopropyl alcohol (store in the freezer)
- Test tube
- Beakers (250 and 100 milliliters)
- Dish soap
- Ziploc bags
- Strainer (or a coffee filter and funnel)
- Stirring spoon or rod
- Measuring spoons
- Graduated cylinder
1.) Ask students what they know about DNA; record their answers on the board, and work with them to come up with a good definition. Then tell students they will get to see DNA!
2.) Begin the lab by placing 90 milliliters (mL) of water into a beaker.
3.) Add 10 mL of dish soap to the water and mix.
4.) Add 1/4 teaspoon of salt to the dish soap/water mixture.
5.) Remove the stem from a strawberry, and place it in a Ziploc bag.
6.) Add the dish soap/salt water mixture to the Ziploc, seal the bag and smash the contents.
7.) Place a coffee filter in a funnel over a beaker. Pour the mixture through the funnel.
8.) Move the mixture to a smaller beaker, and add one teaspoon of chilled isopropyl alcohol.
9.) Use a stirring rod or spoon to scoop out the top white layer. This is the DNA.
- What is the function of DNA?
- Where in the cell is DNA found?
- Why do cells need to divide?
- How do new cells get DNA?
- Explain to students that strawberries have more DNA than other fruits.
- Humans are diploid, meaning they have two copies of each chromosome.
- Strawberries are octoploid (8 copies!).
DNA Replication Bingo
This game allows students to learn/practice all of the vocabulary words associated with DNA replication.
Suggested Vocabulary Words
- 3' to 5'
- 5'to 3'
- DNA ligase
- DNA polymerase
- Hydrogen bond
- Lagging strand
- Leading strand
- Replication fork
- Bingo boards with vocabulary words (download or make your own)
- Bingo chips
- Definitions for each word
1.) Use this lesson as a follow-up to a lesson on the vocabulary words associated with DNA replication.
2.) Read the clue, and ask students to place a chip on the board for the corresponding vocabulary word.
Student Replication Game
This game allows students to demonstrate DNA replication by being DNA. Prior to the start of the activity, students should be familiar with DNA's function, location and why cells need to divide. They should also know that cytosine and guanine pair together and adenine and thymine pair together.
- Five signs of each base: adenine (A), cytosine (C), guanine (G) and thymine (T)
- One sign of each:
- DNA helicase
- 5' to 3'
- 3' to 5'
- DNA polymerase
- DNA ligase
- Image of DNA replication to show on an overhead
- Science journals, markers and pencils
1.) Begin by telling students they are going to demonstrate DNA replication as a class and that each student will have a role and a sign.
2.) Using the image of replication as reference, have students build a model of DNA using their signs. For example, each letter denotes a student base:
- Original strand: AGCTA
- Corresponding: TCGAT
1.) Have students illustrate the process of replication based on your cues.
2.) Provide them with some suggestions:
- Ask students to line up in pairs and hold hands to represent the hydrogen bonds.
- Have 'DNA helicase' walk through the two lines of students and break apart the 'hydrogen bonds' holding the complementary bases together.
- Place the 5' to 3' sign in front of one strand of students (leading strand).
- Have DNA polymerase bring bases to the leading strand.
- Place the 3' to 5' sign in front of the second strand (lagging strand).
- Have DNA polymerase bring bases in chunks, creating Okazaki fragments.
- Have DNA ligase piece the Okazaki fragments together.
3.) Repeat the activity again, but this time, have your students cue the steps.
4.) Now have students list and illustrate each step in their science journals.
This activity allows students to explore DNA replication with candy. This can be used as a follow-up or in lieu of the previous game.
Materials (per student pair)
- Four pieces of licorice (two red, two black)
- Package of gummy bears (assign each base a color, i.e. adenine is a red gummy bear)
1.) Begin the activity by building the parent molecule, where the gummy bears are the bases and the two pieces of red licorice are the backbones. Use toothpicks to connect the gummy bears to the licorice and the gummy bears to their corresponding bases.
2.) Have students twist their models to show the double helix.
3.) Begin the replication processes with students playing the parts of DNA helicase and DNA ligase:
- DNA helicase removes the toothpicks that connect the gummy bears to their corresponding bases.
- DNA polymerase adds gummy bears to the 5' to 3' strand. Add a black licorice backbone to complete the first strand.
- DNA polymerase adds the gummy bears in fragments (Okazaki fragments) to the 3' to 5' end.
- DNA ligase pieces the fragments together. Add a black licorice backbone to complete the second strand.
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