The homework question says, “A sequenced DNA segment consists of the following nucleotides:
TAC — TGG — GTC — AGC — ACG
This sequence codes for the polypeptide fragment:
methionine — threonine — glutamine — serine — cysteine
Question: What would happen to the synthesis of the polypeptide if the fifth (5th) nucleotide in the sequence was replaced by a thymine nucleotide?”
Let’s say you are keeping up in biology and that you know several things that will help you answer the question: first, that a thymine nucleotide is represented by the letter “T”; next, that each letter in a sequence designates a nucleotide; also, that a unit of three nucleotides is known as a codon; and finally, that codons code for either specific amino acids or for stops in production.
However, what if the two things you cannot remember are which amino acids are produced by more than one codon and whether threonine might be one of them? In order to answer the homework question correctly, you must verify whether another amino acid results from the change of TGG to TTG or if it, too, results in threonine.
It’s common for a science text to have almost 600 pages. How do you find small facts in large chapters? You could use the book’s index to search for pages associated with threonine, and if that isn’t helpful, thymine, nucleotides, codons, amino acids, and/or polypeptides. Unfortunately, the index may not have some of your key word choices, or worse, have too many pages listed for each. Indices usually work best for very general key word searches (looking for a group of page numbers so you can pinpoint a chapter to read) or very specific terms (looking for the few places in the book the key word occurs).
A second route to the information requires consulting the book’s table of contents to locate the chapters on DNA. A quick scan down the list of chapters’ sub-headings might identify one on polypeptide synthesis. That should yield a page range narrow enough for fact-checking a homework question. But what if the question was on an open-book exam? The narrowed page-range for reading would now be too broad (and probably too time consuming) to be really useful.
Perhaps you vaguely recall seeing a chart of amino acids and their associated codons. A third approach, then, looks for a page listing all the “Tables and Figures.” These lists often follow the table of contents at the front of the book but sometimes they are placed at the back as a second kind of index. A chart is the quickest way to read that TTG codes for asparagine. You do, however, have to know that a list of visuals exists in your book and where it is located.
How much time might you save week after week during the semester if you start the term with a systematic skimming of the entire book?
Right now, while the semester is young and you are still fresh, do this with your textbooks:
Review the table of contents, including the chapter sub-headings, so you will know the full range of the book. If two or more chapters seem to cover seemingly similar material, read the chapter summary in each. (Note: some authors use a summary as part of the introduction; others place it at the end of the chapter.) Don’t worry if the material seems above your head right now. You aren’t reading for understanding yet. You are only familiarizing yourself with the scope of the book. (Reading summaries has the added advantage of previewing the author’s writing style. Is it filled with clear examples and good comparisons? Will you need to keep a dictionary close at hand?)
Review all other content list pages, such as those for tables, figures, or illustrations by chapter. You don’t need to remember what is in the lists, you just need to remember which lists are included and where to find them later.
Review the index. It is a cruel fact that index quality varies widely. Now is the time to see that every word in the index is highly specific and refers to only two or three pages. Conversely, the index may be short and stocked with only the general terms of the subject. Either way, you’ll have some sense of what key words might be listed (and how exact a match they must be) once you need to consult it.
Approach a textbook with a goal to viewing its structure first. Knowing how the book is organized will help you in your use of it later.