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The DNA molecule is often and aptly compared to a written language that uses only 4 letters; A, C, G and T. The linear sequence of these letters provides information that guides the synthesis of RNA and proteins and through these products defines the characteristics and abilities of individual organisms. To assist students to understand how a 4-letter alphabet can carry coded information and how that information gets translated, we have developed a tool that students can assemble, and activities they can use to decipher the genetic code in fun and familiar ways. The tool is the RNA Decoder Ring that allows students to align the 64 codons specified by the 4-letter genetic alphabet to determine which amino acid each codon encodes. When single letter amino acid abbreviations are used, DNA sequences can be constructed that translate into amino acid sequences that spell out familiar words and phrases in English. We present activities that challenge students to decode messages written in DNA that spell out English words and phrases in their corresponding amino acid sequence. Students are also instructed how to design their own coded messages using the Decoder Ring in reverse. We also provide activities that illustrate the impact that various mutations in the DNA sequence can have on their protein products. Finally we provide an activity that illustrates how the coded language of DNA is used in cells going from DNA to RNA to the amino acid sequence using the initial portion of the human growth hormone gene.
At completion of this activity, students will:
· Understand the meaning of a codon and a gene.
· Understand the 3 to 1 correspondence between nucleotides and amino acids.
· Appreciate that there are redundancies in the genetic code and that more than one codon can code for the same amino acid.
· Be able to transcribe a DNA sequence into RNA, and translate an RNA sequence into an amino acid sequence.
· Understand how changes in a DNA sequence (mutation) may or may not alter the corresponding amino acid sequence.
· Appreciate that changes in amino acid sequences alter the properties of proteins.
Necessary Student Background
The RNA Decoder Ring is designed to provide tactile practice working with the genetic code, and is best utilized after covering the basics of DNA structure and the processes of transcription and translation. The A – T, G – C base-pairing rule for the DNA molecule and the A – U, G – C base pairing rule for transcription of DNA into RNA should also be discussed as students will need to apply these concepts when completing the RNA Decoder Ring activities. Covering the definition of a gene either prior to or during the use of the RNA Decoder Ring will allow students to recognize the presence of start and stop codons, and understand that a gene consists of a discrete length of DNA that contains enough information to direct the correct assembly of a protein. The impact of changes in the DNA sequence (mutations) on the proteins they encode can be introduced in conjunction with the mutation activities in this paper.
DNA, nucleotide, transcription, translation, codon, amino acids, mutation, ribosome
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