Introduction: (Initial Observation)
Making a model is the best way of learning about the elements of a DNA molecule. You can use your model as a separate school project or as an addition to any DNA related science project.
A well made model enhances your display and results a higher level of attention to your presentation.
This is a display or model making project related to biology and genetics.
Find out about DNA. Read books, magazines or ask professionals who might know in order to learn about the double Helix structure of DNA molecules. Keep track of where you got your information from.
Following are samples of information you may find:
With over 100,000 different proteins to manufacture, how the heck does our body get it right? When one thinks of the amount of information the body needs to keep track of, – eye, hair and skin color, protein sequence, toenail size, etc. – it would seem a task for a supercomputer to record all of the necessary information. In essence it is. But not a supercomputer made of silicon wafers and TV screens, rather one made of an intricate biomolecule called DNA.
DNA (deoxyribonucleic acid) is in the family of molecules referred to as nucleic acids. One strand of DNA has a backbone consisting of a polymer of the simple sugar deoxyribose bonded to something called a phosphate unit. Very unimpressively then, the backbone of a strand of DNA resembles this:
In our model we use a white ball to represent sugar and a red ball to represent phosphate.
What is impressive about DNA is that each sugar molecule in the strand also binds to one of four different nucleotide bases. These bases: Adenine (A), Guanine (G), Cytosine (C) and Thymine (T), are the beginnings of what we will soon see is a molecular alphabet. Each sugar molecule in the DNA strand will bind to one nucleotide base. Thus, as our description of DNA unfolds, we see that a single strand of the molecule looks more like this:
In our model we use light blue balls for Cytosine, light green balls for Guanine, yellow balls for Adenine and Orange balls for Thymine.
Each strand of DNA contains millions or even billions (in the case of human DNA) of nucleotide bases. These bases are arranged in a specific order according to our genetic ancestry. The order of these base units makes up the code for specific characteristics in the body, such as eye color or nose-hair length. Just as we use 26 letters in various sequences to code for the words you are now reading, our body’s DNA uses 4 letters (the 4 nucleotide bases) to code for millions of different characteristics.
Each molecule of DNA is actually made up of 2 strands of DNA cross-linked together. Each nucleotide base in the DNA strand will cross-link (via hydrogen bonds) with a nucleotide base in a second strand of DNA forming a structure that resembles a ladder. These bases cross-link in a very specific order: A will only link with T (and vice-versa), and C will only link with G (and vice-versa). Thus our picture of DNA now looks like this:
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to make a model of Double Helix DNA molecule. This model may be used for demonstration or teaching about DNA.
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
This is not an experimental project, so you will not define variables.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
This is not an experimental project, so you will not suggest a hypothesis.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
How to make the model?
Paint all the balls with water based or latex color. Following are the colors that we used in our model.
- Yellow is for Adenine (A)
- Green is for Guanine (G)
- Blue is for Cytosine (C)
- Orange is for Thymine (T)
- White is for Sugar
- Red is for Phosphate
Use toothpicks to make pairs of Adenine Thymine with sugars on the ends.
Also make pairs of Cytosine Guanine with sugars on the ends.
These pairs form the steps of the ladder in a DNA molecule.
The number of different color balls in our model is as follows:
|Molecule||Color of ball||Quantity|
Connect the wood dowels together using wood glue to make a longer wood dowel. It may take a few hours for glue to dry.
Insert the long wood dowel into the base.
Place the first pair on the base and use a wire or string to tie it to the wood dowel.
Insert toothpicks in red balls (phosphates) so that the ball will be centered on the tooth pick. Insert one red ball over each white ball (sugar) and adjust the angles so your DNA model will become double helix
Mount the second pair over the previous one. Toothpicks from phosphates will enter the sugars of the new pair.
Continue with another set of phosphates and new pairs on top of each other. After a few rows, use another wire or string to tie the last pair to the column (wood dowel).
Continue that until your DNA model is ready.
If you want to separate your DNA model from the base, you will need to use a small amount of wood glue on the ends of toothpicks. If you do this, you can later remove the strings that you used to tie some of the pairs to the column and your DNA model will be removable. For more strength, you may use a very thin wire or string to connect the center of pairs together. If you do this, tie the string to the center of ladder every few steps and make sure that the string is well stretched.
Materials and Equipment:
To construct a DNA model you will need the following material:
- Styrofoam balls (about 100)
- Double end toothpicks (75)
- Wooden or metal laboratory stand
- Brushes for painting the balls
- Additional material such as paint or water color, glue, string.
You may purchase all the required material separately from different local stores or you may prefer to order a kit; however, you should know that kits do not come with paint and glue.
You may already have white glue and water color at home. If not, you may purchase paints and glues from any local hardware store or paint store.
DNA model kit comes with 100 white balls that you must paint them with any water based or latex paint. (paint is not included)
A kit also contains a base and a column that together form a stand for your DNA model.
A stand makes it easier for your model to be transported from home to school or your science fair.
Kit also includes brush and matching toothpicks for the balls.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
You will construct the model. No experiments and results are needed.
No calculations are required.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.