Using Pop-Beads to Model DNA and Simulate its Replication
DNA is at the heart of biological evolution. It is the information storage molecule of life. By compare DNA sequences, we can see how all living creatures are related.
Evolution is the result of DNA changes over time. In order to properly understand biological evolution, it is helpful to understand the basic structure of DNA.
Summary: Students will build a model of DNA using Pop-Beads. Once they have made a model, they will use it to “synthesize” a new strand of DNA.
Age level: 9-adult
Time: Best in two or three class periods, depending on the students
Student Learning Goals:
- Students will demonstrate how information is stored in base pairs of the DNA molecule
- Students will demonstrate how DNA is made of complementary base pairs of ATCG.
- Students will demonstrate how point mutations can alter DNA and subsequently proteins.
- Students will be able to tell how changes in DNA affect evolution.
- Students will be able to discuss the usefulness and limitations of this model.
DNA is the information storage molecule of life. By creating a molecule of DNA, students gain a great understanding of how DNA stores information.
This activity uses Pop-beads, which are available from Carolina Biological Supply.
Notes to Instructor: This is a simplified demonstration of DNA and its replication. In this activity, the focus is on an overview of DNA structure.
Even though the models presented are simplified, it would be helpful for the teacher to have a deeper understanding of the process to answer student’s inevitable questions. A clear and thorough explanation of DNA is in the text book, Biology, by Neil Campbell, Jane B. Reese, and Lawrence G. Mitchell. This outstanding college biology textbook is permeated with great information on DNA and evolution.
- Download page demonstrating base pairing (optional)
- Pop-beads in the following colors:
- Purple = phosphate
- B=blue = adenine
- G=green = thymine
- Y=yellow = guanine
- R=red = cytosine
Make nucleotides. Attach purple “phosphate” bead to white “deoxyribose” bead. To the white bead, add one of the four bases: ATC or G.
Each bead color corresponds to a different nucleotide as follows:
Make a strand of DNA. Put red, yellow, blue and green nulceotides together corresponding to the DNA sequence below:
DNA Sequence: T-C-T-T-G-G-A-T-T-C-A-A-A-A-T-T-C-T-C-C-C-C-T-C-C-A-A
Color Code: G-R-G-G-Y-Y-B-G-G-R-B-B-B-B-G-G-R-G-R-R-R-R-G-R-R-B-B
When new cells are made, DNA is replicated and a copy is given to each new cell. In this activity, imagine that you are DNA polymerase, the enzyme that makes DNA using a DNA template.
Now imagine that the double stranded DNA helix was already unwound, and you are working with only one strand of the DNA, Put beads on another pipe cleaner that complement, or create base pairs, with the sequence of beads on the first pipe cleaner. Wherever there is a cytocine (red bead), compliment it with a guanine (yellow bead.) And where there is am adenine (blue bead,) compliment it with a thymine (green bead.)
Once you have added nucleotides to complement the original strand of DNA, create a double helix by twisting the two strands together. In the cell, the complementary base pairs stick together with hydrogen bonds. In the case of the C and G bond, there are 3 hydrogen bonds. In the case of AT, two hydrogen bonds. The DNA is going in opposite directions.
Discussion and Questions:
- Did anyone accidentally attach the wrong bead? This is a point mutation. If the mutation remains, what will happen to the mRNA and protein?
- How do point mutations affect evolution?
- If the mutation happens in a somatic cell, it will not affect evolution. But if it happens in a sperm or an egg cell, this change will be passed on to the next generation.
- What are some analogies of nucleotides? Letters of the alphabet? Computer code?
DNA is shared by all organisms. Although details vary, all organisms replicate their DNA, transcribe it into RNA and translate mRNA into proteins.
Can you think of examples of point mutations affects people?
One classic example is sickle-cell anemia.
- Each human cell contains about 2.5 meters of DNA.
- Human body contains 10-100 trillion cells.
- If stretched end to end, DNA from our bodies would go to the sun and back almost 70 times!
- Looked at another way, if stretched end to end, DNA from our bodies would go out a distance past the solar system, out over 4 light days!
- Humans have 20,000-30,000 genes in their genome
- Less than 5% of human genome encodes genes.
- Another 5% of human genome is made up of regulatory sequences.
Biology by Neil Campbell, Jane B. Reese, and Lawrence G. Mitchell. This outstanding biology textbook for college students is permeated with great information on DNA and evolution.
DNA Learning Center – comprehensive web site with lots of information of DNA. The Romanov Mystery is http://www.dnalc.org/home.html
Genetic Origins:” The Study of human evolution begins with your DNA. http://www.geneticorigins.org/geneticorigins/. This site provides biochemical methods and computer tools to allow students to use their own DNA “fingerprints” as a starting point in the study of human evolution. Two experiments are currently available, which are supported by reagents and ready-to-use kits available from Carolina Biological Supply Company.
National Genographic – “we are all related—descended from a common African ancestor who lived only 60,000 years ago.” https://www3.nationalgeographic.com/genographic/
National Standards Addressed (NRC):
- K-12: Unifying Concepts & Processes Standard: Evidence, models, and explanation
- 5-8: STRUCTURE AND FUNCTION IN LIVING SYSTEMS: Evidence, models, and explanation
- 9-12: This activity directly addresses two of the major six content standards for life sciences education in grades 9-12: Molecular basis of heredity and Biological evolution.
Following is pertinent text from the National Science Education Standards of the National Research Council:
THE MOLECULAR BASIS OF HEREDITY
- In all organisms, the instructions for specifying the characteristics of the organism are carried in DNA, a large polymer formed from subunits of four kinds (A, G, C, and T). The chemical and structural properties of DNA explain how the genetic information that underlies heredity is both encoded in genes (as a string of molecular “letters”) and replicated (by a templating mechanism). Each DNA molecule in a cell forms a single chromosome. [See Content Standard B (grades 9-12)]
- Changes in DNA (mutations) occur spontaneously at low rates. Some of these changes make no difference to the organism, whereas others can change cells and organisms. Only mutations in germ cells can create the variation that changes an organism’s offspring.
- Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring.
- The great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms.
- Natural selection and its evolutionary consequences provide a scientific explanation for the fossil record of ancient life forms, as well as for the striking molecular similarities observed among the diverse species of living organisms.
- The millions of different species of plants, animals, and microorganisms that live on earth today are related by descent from common ancestors.
- Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification.