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Living Organisms, DNA, and the Genetic Code
Asa Packer Elementary
School, Academic Year 2011-2012
Grade 3 |
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Dr. DeLeo brought a powerful microscope into our classroom that was connected to a television camera. He placed different things under the microscope and projected the picture on a screen. |
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Dr. DeLeo placed a dead spider under the microscope so it would look real big. It was really scary looking. We are sure glad that real bugs are not that big! Notice the spiky insect hairs on the photo below on the left. The middle photo shows a spider. The right photo shows a close-up of a joint. |
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| We knew it was a joint because we have been studying that in science! Dr. DeLeo gave one of the students a chance to make believe that she was a teacher. Click the play button on the photo on the far right to see a VIDEO. |
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| Even though the insects were really scary looking when they appeared so big, we were too excited and too interested to be frightened! Some of us even laughed! |
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Dr. DeLeo proceeded to place smaller and smaller things under the microscope. |
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| The photo just to the right shows pollen grains. They are not really that color; they are dyed to make them easier to see. The photo on the far right shows human blood cells. We guessed that one! |
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A single cell organism that can be found in pond water is called a paramecium. They are so small that you need a microscope to see them. Dr. DeLeo placed live paramecia under the microscope for us to see. They swim around in a drop of water by moving little hairs along the outside of their bodies. Just think of it - A human being has over 10,000,000,000,000 (ten trillion) cells, but a paramecium has just one! |
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| Check out the VIDEO just to the left by clicking on the play button! The video shows us trying to follow several paramecia. |
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We learned that each cell can make other cells. A cell does that by dividing into two cells, each the same as the original. That's how we get bigger, and how our body heals itself when we get hurt. Every cell in any plant or animal contains instructions for making that plant or animal. A cell on the tip of your nose contains the instructions for making your big toes. So, every time a cell divides into two cells, the dividing cell has to make two copies of these instructions, one for each of the new cells. The instructions are contained in what are called chromosomes. We call these instructions the "genetic code." |
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The picture on the left shows the cells in a plant. Plant cells are kind of boxy looking. The circles in the center of the cells are the cell nuclei, and they contain the chromosomes. Some of the cells in the picture are in the process of dividing into two cells. The red arrow points to a cell which is dividing into two cells, and the stringy things are the chromosomes going into both of the new cells! |
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We helped Dr. DeLeo find a really great cell! This one, shown on the right, has just about finished dividing, giving us two cells where before we had only one!
I'll bet Professor Kuchka from Lehigh's Biology Department could even tell us the name of this phase of cell division. Incidentally, Professor Kuchka gave Dr. DeLeo the idea for the next activity! |
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| But wait a minute! We seem to have a problem! Suppose we split a recipe for chocolate chip cookies in half. Would either of the two halves be a recipe for chocolate chip cookies? Of course not! In the same way, if our genetic code divides in half each time a cell divides, then this would be a big problem! |
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Dr. DeLeo spoke to us about DNA and the genetic code. The genetic code uses four different chemicals. One ordering makes someone who has blue eyes, another brown eyes. One order makes a human being, another makes an artichoke.
DNA is called a "double helix," a "helix" because it twists like a spiral staircase, and "double" because it is a pair of helixes. The four chemicals have names, but they can be abbreviated by the first letters, A, T, C, and G. The two strands making up the double helix are side-by-side. If there is an "A" on the left, then there will always be a "T" on the right. So, "A" goes with "T" (A-T). Similarly, "C" goes with "G" (C-G). This pairing makes it possible for our cells to divide and make exact duplicates. When a cell is about to divide, the strands come apart, and each one picks up just the right partners to make two new, identical double helixes, one in each of the two cells. |
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When a cell divides, the genetic code - the recipe for us - has to be duplicated so there is one for each cell. As we saw, a recipe is no good if you just tear it into halves. Dr. DeLeo used something like hinged Legos to show us how one double helix in one cell becomes two identical ones in two cells. Here is an animated VIDEO of what Dr. DeLeo showed us. Just click the play button. |
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| Dr. DeLeo helped us to understand all of this by giving us beads in fours colors, representing A, T, C, and G. We used a pipe cleaner to put together our make believe DNA. Dr. DeLeo and our teachers helped us get started. |
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Here are pictures of us putting together our DNA models. We can place any of the four colors in any order along one of the strands. However, where ever there is a blue bead on one side, we must have a yellow bead on the other. And, where ever there is a red bead on one side, we must have a green bead on the other. When we were done, we twisted the strands gently to give it the shape of a helix. We placed an extra twist at the top to hold in the beads, and then bent the sharp end of the pipe cleaner so we wouldn't get poked. |
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Some of us made patterns like red-blue-red-blue... (of course with green-yellow-green-yellow... next to it). Since some of us made models with the same pattern, Dr. DeLeo asked us what we call people with the same genetic code. Many of us knew that the answer was identical twins! |
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In addition to the DNA models, we each got a cool placemat on human anatomy. We love science! |
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I hope you have enjoyed this web presentation as much as we enjoyed sharing the actual learning experience with your son or daughter. Although we have endeavored to exclude photographs where permission has been denied, it is possible for errors to occur. If you would like us to remove a photograph of your son or daughter for any reason, please send me an e-mail message at lgd0@lehigh.edu or call me at 610-758-3413, and we will remove it promptly. Please note that we will never associate a child's full or last name with a photograph except in circumstances where special permission was explicitly provided. Thank you. Gary DeLeo. |
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