You are excited because your lab is studying the first microorganisms retrieved from Mars! Interestingly, their genetic material consists of a single-stranded nucleic acid with six different nitrogenous bases. Like organisms from Earth, segments of the nucleic acid contain the code for making proteins. If the genetic code in these organisms was read in groups of 2 bases instead of 3, what is the maximum number of amino acids that could be coded for assuming that only one codon functioned as a stop codon? (Enter your answer as a numeral, not a word; e.g., enter 17, not seventeen.)
Fill in the blank(s) with the appropriate word(s).
35
Clarify Question
• What is the key concept addressed by the question?
o This question addresses the genetic code.
• What type of thinking is required?
o This question is asking you to analyze the information given, using logic, to dissect the problem and determine the answer.
• What key words does the question contain and what do they mean?
o The genetic code is the set of codons that encode amino acids, by which mRNAs are read into proteins.
o Nitrogenous bases are the unique portions of nucleotides . On Earth, there are four: A, T, C, and G.
o The codons are the (normally) three-base codes, such as ATG or CCG.
Gather Content
• What do you already know about the genetic code?
o The genetic code is a set of 64 codons that encode amino acids using sets of three bases.
o Since there are only twenty amino acids, the code is degenerate-there are multiple ways to encode each of the amino acids.
Consider Possibilities
• What other information is related to the question? Which information is most useful?
o Consider the genetic code for Earthlings. There are 64 codons.
o There are four possible bases for spot 1, four possible bases for spot 2, and four possible bases for spot 3.
o In total, that makes 4 × 4 × 4 possible combinations of bases, or 64.
Choose Answer
• Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
o So for a Martian 2-base genetic code of 6 bases, there would be six possible bases for spot 1, and six possible bases for spot 2.
o In total, that makes 6 × 6 possible combinations of bases, or 36.
o One codon is reserved as a stop codon, so at most they could encode 35 possible amino acids.
Reflect on Process
• Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray?
How can you revise your approach to produce a more desirable result?
o This question asked how many amino acids could be encoded by a genetic code with 6 possible bases and 2 codon spots.
o The question required you to analyze the information given, using logic, to dissect the problem and determine the answer.
o Did you recognize that there would be six possibilities for each of the two bases?
o Did you recognize that this problem requires the product rule, since each base is independent?
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