This lesson is an activity where function of DNA and the genetic code are explored. This lesson relates the structure of DNA to its integral function of protein synthesis.
Objectives:
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-Students will be able to design a gene which codes for a polypeptide chain.
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-Students will be able to manipulate and set-up a polypeptide.
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-Students will be able to apply learning and employ the genetic code.
Introduction:
This lesson can be initiated with a question: “Can anyone give me an example of a protein?” The brainstormed ideas should be written on the board. Each student could be required to give some sort of response. The teacher would distinguish proteins from other macromolecules.
Content:
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1. Review of proteins, amino acids, and dehydration synthesis.
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2. Review of transcription, translation and the genetic code.
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3. Make a small protein using labeled cutouts of amino acids, color coded for chemical property.
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4. Design the gene that coded for your small protein.
Methods and Procedure:
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1. Initiate lesson with above question, validating all brainstormed responses.
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2. Review all content.
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3. Provide students will pre cutout amino acids. Each amino acid would be a part of a large lock and key model, that will fit together only after you cleave (cut) off one hydrogen from one amino group and and oxygen and hydrogen from the carboxyl group of another amino acid. For instance:
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H - [ISOLEUCINE ] - OH
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H - [GLUTAMIC ACID] - OH
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To form a peptide bond between the two will remove the OH from isoleucine and the H from glutamic acid. One water molecule has been removed and one bond has been formed.
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4. Each student will form a small protein that is 15 amino acids long.
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5. Once the protein is made, students will work backwards to determine the segment of DNA that coded for this protein, and then will be required to design the piece of complementary messenger RNA.
Closure:
This lesson can be closed with a statement about how essential proteins are to the cell. There are tens of thousands of proteins, each coded for by an individual’s DNA. Point out how mutations in DNA can affect the proteins made. Point out how the redundancy in the genetic code allows a little room for this. Lastly point out how good nutrition is also key since the proteins you eat provide you with the amino acids your body needs. Our bodies can make only 12 amino acids, the other 8 we must ingest.
Resources and Materials:
You (or student) will need to make the different amino acid cutouts, enough for 15 per student. Ideally these will be color coded to represent chemical property. In addition, tape and surface paper will be needed.
In Appendix D you will find the genetic code and in Appendix E you will find a list of the 20 common amino acids and their chemical property.
Assignment:
In addition to having to design the gene and the mRNA complement, students should report how many water molecules they produced and how many peptide bonds were formed and attempt to predict any chemical property of their protein.
