Protein+Synthesis

Back: Assignments Various Topics


 * Protein Synthesis Activity**

The processes of transcription and translation will be modeled in this activity.

There are two steps to protein synthesis. Messenger RNA is made in the nucleus during the first step. During this step, the base pairs in a section of DNA separate and the bases of many RNA nucleotides pair up with these exposed bases. Then m-RNA is formed by the joining of these RNA nucleotides into a single strand. In essence, the genetic codes for proteins in DNA molecules are used as patterns to make molecules of m-RNA Protein is made at a ribosome during the second step. During this step, the sequence of bases in the m-RNA are translate into a sequence of amino acids by transfer RNA. In this process, every three bases of the m-RNA pair with the three bases on specific t-RNA. These t-RNA bring specific amino acids with them when they pair with the m-RNA. Once the amino acids are transferred to the ribosome, they are connected into a strand forming a protein. The first step in protein synthesis is called transcription and the second step is called translation.

Materials: Paper Model Sheets Print outs of the paper models representing a ribosome, t-RNA molecules, and amino acids. A strip of paper about an inch wide and 8 feet 4 inches long. Cut sheets of paper into ten strips measuring 1 x 11 inches and connect them. Tape or glue stick / Scissors / Various Tables included in this activity.


 * __Transcription__**: M-RNA is made using the bases in a DNA molecule.

To make a model of messenger RNA, pairing rules will be used to determine the RNA bases that correspond to the DNA bases given in a table. The table presents the DNA bases three at a time which is called a codon. Remember that each sequence of three bases in a codon specifies for a specific amino acid. Next, the sequence of RNA bases will be written on a long strip of paper in order, providing a model of m-RNA. (In the actual formation of m-RNA, the nucleotides are matched up with DNA bases and added to the RNA strand one at a time.) Base Pairing Between RNA and DNA: For RNA, the base U pairs with A, the base A pairs with T, and C pairs with G, and G pairs with C. In other words, if you see an A, write a U, if you see a T, write an A, if you see a G, write a C and if you see a C, write a G.

__Procedure__: 1. Write the corresponding RNA codons to the right of the DNA codons given in the table above. Read and use the base-pairing directions presented above the table to do this. 2. Cut out the ribosome model, if you haven't already done so. It is labeled with the word “Ribosome.” 3. Cut ten, 1 x 11 inch strips of paper and connect them. This long strip of paper will be the m-RNA model. Draw a line across it every 4 inches for its entire length. All the other paper models in this activity are 4 inches wide and can be used as a guide. 4. Write each codon, that your wrote in the table above, evenly spaced between the lines on the long piece of paper. Read left to right across the table starting at the top. Write the codons from left to right on the strip. This long strip of paper with codons of RNA bases written on it is a model of messenger RNA
 * __Translation__:** Matching t-RNA to m-RNA for determining the sequence of amino acids.

To model the making of a protein, the codons on the m-RNA model will be matched with the codons on the various t-RNA models over the ribosome model. The end of each t-RNA model opposite these codons will indicate the amino acid it carries to the ribosome. The amino acid models will be connected in the order indicated by the matching of the various t-RNA codons to the m-RNA codons. Proteins are made of connected amino acids.

http://www.geneticengineering.org/chemis/Chemis-NucleicAcid/Graphics/ProteinSynt.gif

__Procedure__:

Setup procedure: 1. Cut out 13 of the paper models shaped like a“T”. 2. Evenly spaced cross the top of each “T” shaped piece of paper, write the letters for one codon found in the table on the left. 3. At the base of each “T” of the t-RNA models, write the three letter abbreviation for the corresponding protein. 4. Cut out the various amino acid models with the three letter abbreviations. 5. Set the t-RNA models out in an organize manner and then place the matching amino acid model at the base each t-RNA model.

Translation procedure: 1. Take the end of the m-RNA model with the codon ACC and place it at the top of the Ribosome model. 2. Place the t-RNA model with the codon UGG under the ACC of the M-RNA model and transfer its amino acid model (TRP) with it. Remember, A pairs with U and C pairs with G. The reverse is also true. 3. Slide the m-RNA model with the t-RNA and TRP amino acid left, so the next codon is over the ribosome. 4. Then place the t-RNA model that corresponds to this next codon under it and transfer its amino acid with it. 5. Connect the second amino acid to the first. (Only two t-RNAs are used by the ribosome at a time.) 6. Slide the m-RNA, t-RNA, and amino acid models left again, so the next codon is over the ribosome. Match a t-RNA to this codon and connect its amino acid. Once the transferred amino acid is connected, the t-RNA leaves to find another amino acid to transfer. 7. Repeat this sliding left, matching codons and connecting amino acid process until the end of the m-RNA is reached. The amino acids making up the protein can be connected at any angle to take up less space. This chain of amino acids is a model of a protein. 8. Finally, get the single letter abbreviation for each amino acid in your chain from the following table. Write these letters in order like a sentence using the (stops) as space. You should be reading a message that was transcribed and translated from the original DNA code.