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Do-It-Yourself DNA Demonstration Slides

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The following items can be used to clarify layouts and processes for doing the DIY DNA kit. They can be used to make overhead transparencies, or reduced in size (to about a 6" hi x 10" wide max dimensions) for presenting as PowerPoint slides. On an overhead, parts can be covered up to show initial stages, then be uncovered as the stages progress. Labels can be exposed when students respond to prompts for those labels. Similarly, in PowerPoint, show first stages first, followed by later stages (as appropriate).

1. DNA Replication: This slide shows the replication in progress: DNA (in white) has partially "unzipped", and DNA nucleotides (pink) are moving into position on both DNA strands, producing two DNA molecules, each of which is half old and half new. This is greatly simplified, showing the essential elements of DNA replication. In reality, the nucleotides in each strand are actually inverted as compared to its opposite strand (one strand goes from 5' at the top down to 3' at the bottom, while the partner strand goes from 3' at the top down to 5' at the bottom. Furthermore, while one strand readily replicates from the 3' to 5' (of the original DNA strand), the other (inverted strand) replicates in the opposite direction (still 3' to 5' of its original strand, but in short segments). These are details that could confuse the casual student, so they are omitted here for the sake of giving the essential idea of DNA replication: 2 DNAs are made from 1 DNA. After students demonstrate this basic understanding, you could present these two details, if you think they can handle it. You might at least say that "It's actually a bit more complicated, but you should recognize the essential result of the process: How two DNA molecules are made from one."

2. Protein Synthesis Layout: This shows roughly how students should arrange all the parts of the Protein Synthesis materials on their desks. Point out that it could be reversed left-to-right, and still be OK. The "Nuclear Membrane" strip has been extended in blue, showing openings (portals) in the membrane through which the mRNA can leave the nucleus and go into the cytoplasm to a ribosome there.

3. Protein Synthesis Process: Once layed out, students should "unzip" the (white) DNA strip, exposing the bases of each DNA strand. Using just the right hand strand, build the mRNA molecule (using the blue nucleotides) that matches the right hand DNA strand. And so on, following directions with the kit. At some point (before starting, or after students have struggled with the process), you could show the class the Protein Synthesis Process slide. I would keep the bottom half covered at first, and even the right hand figures of the top part, revealing them as you talk through the process.

4. Protein Synthesis Analogies (blank and key): Many teachers find it helpful to suggest some process that might be more familiar to them, like a construction analogy, or a magnetic tape production analogy (outdated, I know, so try a DVD production version). Some teachers have their students figure out some other process that could serve as an analogy to protein synthesis. Once you have discussed an analogy with the class, show them this slide, or prepare as handout for a formative assessment quiz.

Pairs of students should practice demonstrating the process repeatedly to each other, taking turns, until both can do it without flawlessly without looking at the instructions. If you want, (especially if their text uses the terms), you could ask them what the first stage of protein synthesis is technically called (and why): they should recognize that the making of mRNA strand is called Transcription (DNA is transcribed into mRNA) while the process where mRNA directs the construction of a protein from available amino acids, and using tRNA to do the "heavy hauling", is called Translation (the nucleic acid sequence is translated into an amino acid sequence - a protein).

As in the DNA Replication kit, this Protein Synthesis kit has been greatly simplified to convey the essentials of the process: How DNA makes Proteins. You can do only this much, saying there are deeper details, or you can point out a few of the deeper details if your class is receptive. For example, once a strand of DNA has been transcribed (copied into the mRNA strand), many segments are cut out and discarded, then the few remaining parts are reassembled into the final mRNA, all in the nucleus. Each DNA sequence that we could call a "gene" consists of a few functional exons with lots of intermittent introns that are not functional (i.e., do not code for any part of the ultimate protein). [Think of exons as being the "expressed" parts of DNA, and the introns as the "intruders" - non-functional parts.] Furthermore, the mRNA out in the cytoplasm does not just lay on the outer surface of a ribosome, with it's bases exposed (as implied in the kit instructions). Instead, the two-part ribosome apparently grasps the mRNA at its beginning, then begins to bring in the appropriate tRNA that matches the corresponding mRNA codon (3-part sequence) and carrying its particular amino acid. This is done repeatedly for each amino acid which is linked to the previous amino acid, to build a chain of amino acids - ultimately a functional protein. After it's formed, the protein usually folds automatically into a particular shape that contributes to its function (e.g., an enzyme).

6. DNA Review & Practice: In addition to the Protein Synthesis Analogy Check, we have also posted a DNA Review & Practice sheet. There are parts on Recombinant DNA, DNA Fingerprinting, and the Human Genome Project, which you may want to omit if not included in your DNA unit.


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