Use a simple explanation that DNA is in all cells of living organisms and that it has a special alphabet made up of 4 letters, A, C, T and G that determine everything that the cell can do. The alphabet spells “words” that are amino acids and these amino acids then make “sentences” that tell the cell what to do next. Every cell has special functions depending on where it is in the body. So a heart muscle cell will use different information from the DNA strand than will eye cells, for example.
Explain that they will extract DNA from a plant and that they need to try to work out what plant the DNA is from, using the clues that you will give them.
Activity 1: Prepare the fruit extract following steps 1-6. Keep the solutions on ice until ready to use in class. Young students are given a tube of extract each and the ethanol is added by the teacher. They are then able to spool the DNA onto the wooden applicator stick.
Before you add the ethanol, ask the students to smell the extract and look at its color and try to guess what fruit it might have come from (This works well if you use strawberries for the extraction).
Show students how to use the Genetic Code Table. The first letter is read from the left side of the table. The second letter is read from the top list and the third letter is found inside the boxes. Each group of three letters specifies an amino acid whose name appears in abbreviated form next to the triplet code. The full name for each abbreviation is in the section “What is DNA?” The short hand used by scientists to designate each amino acid is in brackets and it is this letter that the students will use to fill in the puzzle clue below. You may have to do this as a class activity for those students who are not yet reading well.
Table of Standard Genetic Code
Here is the name of the plant that the DNA is from. Can you work it out using your copy of “TABLE OF STANDARD GENETIC CODE”?
TCT ACT CGT GCT TGG B GAA CGT CGT TAT
___ ___ ___ ___ ___ B ___ ___ ___ ___
Did you guess the answer correctly?
Activity - DNA Extraction
Students in this age group can easily accomplish all steps in the extraction procedure. (However, if time is a problem the instructor can complete the first part of the activity by following steps 1-6 and provide students with the extracted fruit or vegetable solution, ready for the ethanol to be added.)
Discuss the reason for each step before beginning the procedure and then reinforce the information while the children are waiting at steps 3 and 4. Remember to emphasize that plants have cell walls that need to be broken in order to access the cell whereas animals do not.
You may need to provide some help for the youngest children when working on the worksheet provided in the activity but I have used this with several groups of this age and have found that most of them can understand more than enough to answer the questions.
Grades 4, 5 and 6
This activity provides a brief introduction into chemistry, physics and biology.
Explain that many molecules have positive or negative charges that make them attractive to other molecules that have the opposite charge. In this experiment the molecules of dye will move through a buffer solution (which doesn’t have a charge) to the electrode that has the charge opposite to the dye.
The dyes are first loaded into a gel that has been made from the buffer solution and a compound called agarose, which comes from seaweed. This gel is made in a similar way to which they make Jello at home. The agarose is added to the buffer solution and then heated, so that it melts into the solution. As the mixture cools, the agarose molecules will bind together to form a soft gel. These molecules stick together but they leave spaces between themselves that we call “pores”. These pores can be small or large depending on how much of the agarose we first put into the solution.
The comb that is placed into the gel solution before it cools will form spaces called “wells” when the comb is removed from the solidified gel. It is into these wells that the dye solutions are loaded. You can load the gel yourself or have some of the children do it. (It helps if you make a practice gel first using light colored finger Jello and the combs and let the children practice loading the dyes or food coloring.)
When the electric current is applied the dyes move through the gel, at different rates and in different directions. This is related to the size and charge of the dye molecule. Explain to the children that all the pores within the gel can form different tunnels through the gel. Imagine that these tunnels are like a winding rabbit burrow. If a rabbit goes into the burrow it can move quickly through all the twists and turns and get to the bottom. If a fox tries to go into the burrow though it will take him a much longer time to move through the burrow and get to the end. So, the smaller molecules can move quickly through the pores of the gel but the larger molecules will take a longer time to find their way through.
You can use fewer dyes if you wish but make sure that some of them are negatively charged and some are positive. Children love to watch the dyes actually moving and I have found it works well to place the whole apparatus on an overhead projector so that they can all see what is happening while they begin to answer the questions on the activity sheet. All the 4 th-6 th grades that I have worked with are able to answer the questions, with a little prompting as necessary.
To modify this activity it is not necessary to actually carry out the restriction digestion. Talk to the students about how the process actually works and that it is the basis for the DNA fingerprinting that they hear about on shows such as CSI. Remind them that unlike some of the dyes in Activity 2, DNA is a negatively charged molecule. Therefore the DNA is loaded at one end of the gel instead of in the middle and it runs towards the positive electrode.
To study DNA in more detail it can be cut into pieces by restriction enzymes. Each enzyme cuts the DNA in different places and so the pieces that result from one enzyme will be different from the pieces that result from a different enzyme. Once the DNA molecule has been cut into smaller pieces by the enzymes it is loaded into a gel and the pieces are separated by electrophoresis. The smaller pieces move quickest through the gel and the larger pieces move slowest. This results in separate bands of DNA that each has a specific size.
Many genes have “alleles”, in which the sequence of bases in the DNA are a little different from one another, but the genes still have a similar function in the cell. For example, you may have an allele that results in your eyes being blue whereas your brother may have an allele that results in his eyes being brown. Both the alleles tell the cell to make eye color but each one results in a different color.
It is because of the little differences in the alleles of each persons DNA that we can make a “fingerprint” of their DNA. Because of different alleles along the DNA, the restriction enzymes cannot always find their matching DNA sequence at exactly the same place in every person. When the DNA is cut the bands that result are then of different lengths and migrate at different rates in the gel.
Activity - Restriction Enzyme Digestion
Students will investigate the DNA from a sick plant and try to find out which plant is sick.
They will need to use the Table of Standard Genetic Code to work out the correct answer to which sick plant we took the DNA from.
Use the Table of Genetic code to find out which letter goes in each space. The letter you are looking for is in brackets on the table and has a three letter code. The first letter of the code is found in the left side of the Table, the second letter is on the top of the Table. Within the box where the first two letters intersect you have four choices for the last letter of your code. Find the correct one and look at the letter that is in brackets, next to the abbreviated word. It is this letter that you will use to fill in the blanks on the sheet.
Here is the name of the plant that the DNA is from. Can you decipher it using your copy of “TABLE OF STANDARD GENETIC CODE”?
Did you work out the answer correctly using the Restriction enzyme clue?
See if you can work out what these two questions are and then answer them.
TGG CAT GCT ACT ATT TCT GAT AAT GCG?
TGG CAT GCT ACT ATT TCT GAT AAT GCG?
__ __ __ __ __ __ __ __ __?
TGC GCA AAT TGG GAG ATG GCT AAA GAG GAT AAC GCT
ACA AGG GCA GTA GAG TTG TGG ATT ACA CAC ATA AAT GCG GGC GAG CTG?
__ __ __ __ __ __ __ __ __ __ __ __
__ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ ?
Grades 4, 5 and 6
This activity works well as a demonstration with this age group .
Talk with the students before beginning to explain the process of transformation i.e. introducing foreign DNA into a cell in order to alter the way in which the cell or organism will function.
In this instance we are introducing a small, circular piece of DNA, called a plasmid, into an E. coli bacteria cell. This plasmid has been altered to contain two genes – one that enables it to process ampicillin in its environment and a second that, when translated, results in the production of a protein that glows green under UV light. Once the plasmid has been incorporated into the cell, the bacterium is able to do two new things.
Normally the bacterium E. coli will die if it is exposed to ampicillin, which is why antibiotics are used to treat bacterial infections.
Students should be able to answer questions 1-9 of the activity sheet. There may be some advanced mathematics students who will want to attempt question 10.
I have had teachers of 5th grades work on this activity in their classroom The students enjoy trying to clone the plant material, however, the most important aspect of the procedure is the emphasis on sterility. Since most students this age do not always understand the difference between 'clean' and 'sterile' they can still learn a lot even if the end result for many of them is infected explants rather than a new plantlet.
Alternatively, the activity can also be undertaken as a demonstration by the teacher. The students make observations on the development of the plantlets from callus, to shoot formation, to root formation.
At this point they can each bring in a small container with soil mix (margarine containers with holes in the bottom work well) and the teacher can divide the rooted plantlets between the class. The students are responsible for maintaining moisture levels and gradually exposing the plants to more light until they are hardy enough to be taken home and planted outside.
The students should be able to answer the questions on the activity sheet if the teacher has explained the steps during the activity.
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