Bedienungsanleitung Knex 78780 - Education DNA Replication Teachers Guide (Seite 37 von 46) (Alle Sprachen)

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• Afterthedoublehelicalsegmentcodingforglucagonisdeterminedbydefiningboththetemplate

and coding strand, divide the sequence into 24-base pair segments and have different student

groups make as many of the pieces of the full DNA structure as possible. Glucagon has 29 amino

acids; therefore, 87 base pairs are required to code the entire protein. If start and stop codons are

added, the entire sequence will have 93 base pairs; therefore, four student groups should be able to

create the “gene” sequence. The entire glucagon “gene” may then be mounted as a twisted double

helix on the single piece of flexible tubing found in the K’NEX DNA, Replication and Transcription

Class Pack.

intrOductiOn

The amino acid sequences of many different proteins can be found on the Internet. The addresses

for several of these web sites are provided at the end of this lesson. Several well-known web sites

serve as repositories for sequences and structures of proteins that have been published by scientists

following strict “peer review” procedures that are designed to check the work for accuracy. Despite

the care taken to ensure the validity of published sequences, students may find several different

proposed DNA sequences and different amino acid sequences for a given protein such as glucagon.

This is because the same protein may have slightly different amino acid sequence in different animals.

Thus, the source of a protein or DNA sequence usually is listed with any sequence information that

is provided.

Although the “same” protein may vary somewhat in amino acid composition between species, the

composition never varies enough to totally interfere with the protein’s major function in the cell. For

example, hemoglobin, the protein that carries oxygen in your blood, will likely have slightly different

DNA sequences in the genomes of humans and pigs. Proteins with such homology between species

can sometimes, but not always, be switched between species and still remain functional.

Most proteins are very large. They may contain hundreds of amino acids formed from several

separate chains. The DNA coding sequences for these proteins may easily be over ten thousand

base-pairs long. For this reason, students should target small proteins, often called peptides, for

exercises suggested in this lesson. Glucagon is a good example of such a small protein or peptide.

creAte/Assess

• AftercreatingtheglucagonDNA,transcribetheDNAbacktomRNA,takingcaretorememberwhich

of the DNA strands is the coding and which is the template strand.

 • WhatvariationsarepossibleinboththeDNAandmRNAsequenceandwhy?

 • Whatotherpossibilitiesexist?

[Assessment Note: Teachers may use this as a lab practicum activity.]

LESSON 5

MODULE III: CODING, TRANSLATION, AND MUTATIONS

Figure 3: Possible student journal entry showing mRNA, template DNA and coding DNA sequences for glucagon.

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