Name: Block: Date: Purpose: To better understand the roles played by DNA, m-rna, and t-rna and amino acids in enzyme formation and gene expression.

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1 Name: Block: Date: Adapted from: Blueprint Gene to Working (Protein) Enzyme: Breaking the Genetic Code Purpose: To better understand the roles played by DNA, m-rna, and t-rna and amino acids in enzyme formation and gene expression. Getting Ready: Throughout the instructions for this activity you will notice a box after each major step. Sometimes the instructions simply want you to take a careful look at something while others will have you DO something. DON T skip any steps. PLACE a checkmark in each box as you complete each step. Now, check this box right now! Cut out all 8 of the molecules from the photocopy of page 84. Be sure to cut each molecule CAREFULLY! When you have finished cutting out the 8 molecules, begin with step One. Step One: Setting Up the Molecules in the Cell You will need to clear a flat surface. Place your photocopy of page 83 on a flat surface and notice that it shows a DNA molecule within the nucleus of a cell. The cytoplasm is labeled on the right side of the page. Consider that the cytoplasm of this cell would extend to the right of page 83 onto your workspace. This is the area where your enzyme (protein) molecule will be put together. Place the 3 Transfer RNA (t-rna) and the 4 amino acid molecules in a mixed-up arrangement in the cytoplasm of your cell. The long remaining molecule is marked m-rna. This stands for Messenger RNA. Place the m-rna molecule in the nucleus of the cell, an inch or so to the right of the DNA molecule. Notice that the rungs of the DNA are made up of the typical base pairs, A, T, C, and G. This type of model of DNA does not show the sugar and phosphate segments of the twisted ladder. This model only shows the sequence of the base pairs in order to keep things simple. Note that the DNA is composed of two strands whereas the m-rna is composed of only one strand. Note also that there is a different nitrogen base in the m-rna. 1. What nucleotide base is found in m-rna and not found in DNA? 2. What DNA base does this m-rna base replace? (Carefully examine the DNA and m-rna molecules) 3. Can this m-rna base also be found in the t-rna? Let s assume that the genetic code in your DNA model gene is for brown eyes. The sequence of nitrogen bases can be read down one of the strands of the DNA. This CODED MESSGE can tell the cytoplasm how to put together the enzyme (protein) B that is required for brown eyes.

2 REMEMBER that the nucleus is like the information and control center of a factory that makes LIFE. Also remember that the messages coded in the DNA are like priceless, irreplaceable blueprints for the items that the factory makes. If you were in charge of the control center, would you send the ORIGINAL blueprints down to the factory floor every time they were needed, or would you make PHOTOCOPIES of the irreplaceable blueprints and send them instead? Answer: This is the situation in the cell when the construction of enzyme (protein) B begins. Copies of the coded messages must somehow get from the DNA, inside the nucleus, to the cytoplasm outside the nucleus where the amino acids are to be found. A photocopy molecule, the messenger RNA (m-rna), accomplishes the carrying of this coded message from the DNA to the cytoplasm. At this point slide and fit your m-rna molecule model along both sides of the DNA molecule until you get a fit. 4. What nitrogen base in DNA does each m-rna nitrogen base pair with? (Carefully examine your paper models!) 5. Which side of the DNA does the m-rna fit with? (Right or Left) Once assembled, the m-rna copy of the DNA moves through special pores in the nuclear membrane out into the cytoplasm. Move your paper m-rna out into the cytoplasm of your paper cell. The m-rna carries the coded message that was on the DNA molecule since the sequence of the m-rna bases corresponds to the sequence of bases in the DNA. 6. What is the coded nitrogen base sequence on the DNA molecule for this enzyme (protein). Step Two: Using the Coded Blueprint! Construction begins on the Brown Eye Enzyme. Now, try to fit each transfer RNA (t-rna) molecule to each of the 4 amino acid molecules found in the cytoplasm. This fit actually represents a chemical bond formed between the t-rna and each amino acid. You should have one amino acid molecule left that none of the 3 t-rna s will fit (bond) to. Next, each t-rna carries (or transfers) its bonded amino acid over to the m-rna molecule, which has positioned itself on ribosome s that are in the cytoplasm. Move your t-rna s, along with their bonded amino acids, over to the m-rna and slide the t-rna part along the m-rna until you get a fit for each t-rna onto some spot on the m-rna. If you examine the situation that exists for your paper cell, you should have 3 amino acids arranged, one above the other, in a sequence. 7. What is the sequence from top to bottom of these 3 amino acids? (Use the numbers on each amino acid to show the sequence)

3 For the next step you will need a small amount of scotch tape. Note that the amino acids molecules are actual molecules made of C, H, O and N atoms. Where one amino acid touches another, a bond results. To create this bond, tape the 3 amino acids together at the two tabs that show a bond between the C and N atoms. Next, move the chain of 3 bonded amino acids away from the t-rna s. This chain of amino acids now represents a simplified version of enzyme (protein) B. Next, move the 3 t-rna molecules away from the m-rna. These t-rna molecules are now free to move through the cytoplasm and pick up other amino acids and bring them back to the m-rna and produce another chain of amino acids or enzymes. Remember that the enzyme you have created is a PROTEIN! (All enzymes are proteins). This is the way a cell builds all enzymes and other proteins needed to make life work. It is important to note that the sequence of this enzyme, enzyme B for brown eyes, could have had no other sequence of amino acids. 8. Explain why this enzyme (protein), which you just made, could have had no other sequence as long as the DNA blueprint remains what it is in the nucleus. Now that enzyme B has been constructed according to the DNA blueprint, it is ready to convert colorless substance X to brown pigment for the eye. To check your understanding, return to the models and try to repeat the steps as before, but this time without looking at the written directions. Analysis 1. Based on this activity, what do you think is the role of RNA in a cell? 2. You worked with both DNA and RNA in this lab. What are 3 things that are different between these two molecules? 3. RNA is considered disposable. Explain! 4. There were 2 types of RNA being used in this activity. But, there are 3. Identify the type of RNA NOT being represented. Next, explain the function of each type of RNA, including the one not represented.

4 5. In Part 1, transcription occurred. Explain how this process occurs below. 6. Why doesn t the DNA go out into the cytoplasm to begin construction of the enzyme B (protein B)? 7. In Part 2, translation is being used to read the genetic code. Explain the steps necessary to do this. 8. In this lab you are trying to create enzyme B which codes for brown eyes. What do you think would happen if this code was incorrectly read? (Basically, what would happen if a mistake occurred?)

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