Genetics is a young and dynamic field; it is an ever changing field. And while what is written in this chapter is really quite firm, keep in mind that some dramatic new discovery capable of changing everything could be lurking just over the horizon. For this very reason, too, your students may have learned some genetic truism that was assumed just a few years ago to be completely orthodox but is now looked upon with a great deal more skepticism.
Chapter 16 needs careful discernment. It is of utmost importance that you review this chapter carefully before assigning it to your class. Be certain you yourself understand some of the intricacies of gene function so that you can help the students who are having difficulty with the different concepts.
Make decisions about your coverage of this material based on your own course objectives.
Even though Lewis has done a very fine job of explaining the molecular components of gene function, some of this material may be beyond the needs of your class. Examine your course objectives carefully. The first three sections of this chapter will probably be more difficult for your students than the last section.
Go back through your coverage of Chapter 15 so that you can correlate what you did there with the material you will be covering in this chapter.
The Tables in Chapter 16 should be especially helpful to you in planning your coverage of this material.
You might wish to copy and distribute to your students the Overview of Chapter Objectives flowchart found at the beginning of this Instructor's Manual Chapter.
The students will need a diagram to see the totality of this process. Figure 16.1 is good for this purpose. Or, you might try drawing a larger figure that looks something like this:
With this type of diagram (drawn either vertically or horizontally), you can traverse the lines as often as you wish with the names of enzymes and processes that are a part of protein synthesis. You can also bring in ribosomes and tRNA and any other structures or functions that may fit the needs of your class.
A major problem in this chapter is understanding the code. Students always think they have the base pairings down a little bit better than they actually do have. Therefore, they often have problems with which base goes where; they have trouble labeling the various strands of DNA and RNA. And they have trouble shifting back and forth between the strands and then relating these shifts to the final amino acid sequence.
The genetic code was "written" for mRNA. Of course, corresponding codes could be "written" for DNA, tRNA, or almost any other nucleic acid strand. Students often wonder why the code is written for the mRNA when it is the anti-codon of the tRNA that dictates which amino acid is picked up. One plausible explanation is that the messenger (mRNA) is dictating what gets brought in.
When you write some of the DNA/RNA sequences on the board or overhead, separate the triplets. You can tell the students these triplets are not separated in "real life" but that you are separating them to make viewing them easier. Students do not have a problem with that type of editorial license and those who have any kind of convergent/divergent vision problems will be very appreciative!
- I. Be certain the students have a clear view of the sequence of the major events in this process before you get into the particulars. If they don't see the broad picture, they will almost invariably be lost as the protein synthesis story unfolds.
Write out a simplified version, such as the one on the previous page, or as Figure 16.2, and then augment it.
Note the sentence: "RNA is essentially a mobile copy of a gene's information." That sentence will make sense to the students.
Genes code for proteins; they don't code for hair color or tree bark. Students need to see that bridge.
As an aside, some scientists believe that in many ways it is RNA, not DNA, that is the real key to genetic understanding.
- I.A. Recall that lactose is really a disaccharide, a carbohydrate.
On page 327 you will find the lactose trigger feedback loop. If you do not understand this yourself, you may have difficulty explaining it to your students.
- I.C. I suggest putting up on the board this simple little diagram:
Sometimes students need to be able to visualize the base pairings. As straight forward as base pairings seem to most of us, for some of our students this concept is a major stumbling block.
Some books call the antisense strand the non-sense strand.
- II.A. The messenger takes the message.
- II.B. The transfer RNA literally transfers the amino acid.
- III.A. Some of this section seems very "common sense." Nevertheless, going through this may help some of your students who are confused by such ideas as triplets and codons.
- III.D. Make a point of the importance of computer analysis in discovering the intricacies of molecular genetics.
- IV. Relate this entire section to material found in the previous chapters.
Most of this material will be quite interesting to your students.
