Download The Synthesis of a Protein

Name: ______________________________ Per: ______ The Synthesis of a Protein Purpose: The chain of letters shown in Figure #1 contains a message that is very important to a living cell. This message is the information the cell must have in order to make a particular protein. The message may be difficult for you to understand because it is in code. In this investigation, you will learn how to “decode” the message in this piece of DNA (the gene) and to “translate” this message into the correct protein. Background Information: The chain of letters represents a portion of a DNA molecule contained in the nucleus of the cell. The four different types of letters (A,C,T,G) represent the four different nitrogenous bases that make up the DNA molecule. However, this is only one half of the DNA molecule called the instructing strand. The other half (not shown) is called the complementary strand. The sequence or order of these bases is very important. In our language, the order of letters determines the formation of a particular word. In a similar way, the order of bases determines the formation of a particular protein in the language of the cell. Today, a gene is defined as a sequence of DNA that codes for a protein. Explain the difference between DNA replication, transcription and translation (be sure to include where each event occurs in the cell) _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ Procedure: PART A: DNA Replication 1. Using the instructing strand in figure 1 above, and the rules of base pairing, draw the complementary strand of DNA below the instructing strand. FIGURE 1 “The DNA (Gene)” Instructing Strand A G T A C A C G A T G A A G G T T T T A A C G G G A G C T C C T A T T 1
PART B: TRANSCRIBING THE MESSAGE The DNA of a cell is found in the nucleus. However, the proteins themselves are assembled on ribosomes in the cytoplasm. The DNA molecules are too large to pass through the nuclear membrane so the DNA is used to produce a smaller molecule that can leave the nucleus. This smaller molecule is messenger RNA (m-­‐RNA). which acts as a go-­‐between. It is the messenger RNA (m-­‐RNA) that carries the message from the DNA to the cytoplasm. Messenger RNA, like DNA, is composed of nitrogenous bases. It contains the bases adenine, cytosine, guanine. However, in place of thymine, m-­‐RNA contains the base uracil. The message coded in the DNA molecule is copied by a messenger RNA molecule. This is possible because only certain bases can bond to each other. The DNA molecule “unzips” and specific RNA bases bond to the appropriate DNA bases to code for a specific protein. 2. Using the instructing strand of DNA below, draw the messenger RNA for this gene. Use a pencil and don’t forget one of the big differences between DNA and RNA!! A G T A C A C G A T G A A G G T T T T A A C G G G A G C T C C T A T T m-­‐RNA t-­‐RNA Amino Acid PART C: TRANSLATING THE MESSAGE Once the m-­‐RNA molecule is formed on the DNA strand it “peels off” and moves to the ribosome.The m-­‐
RNA molecule now carries the coded message for the protein. Each code word (codon) consists of three bases. For every three bases present on the m-­‐RNA molecule, an amino acid is added to the chain of amino acids that will form the protein. 3. Look at your strand of m-­‐RNA from # 2. Search along your m-­‐RNA strand for the initiation codon (look in your notes if you can’t remember). Once you find the initiation codon, divide the strand of m-­‐RNA three bases at a time. 4. Below the m-­‐RNA molecule list the transfer-­‐RNA (t-­‐RNA) anticodons that match with the m-­‐
RNA codons. 5. Using the transfer-­‐RNA (t-­‐RNA) molecules in figure 2, write out the sequence of amino acids transported to the m-­‐RNA by the t-­‐RNAs. Check your notes to see when you stop. FIGURE 2 2
As the amino acids are assembled and joined they fold into a special three dimensional shape. The shape of the protein is almost as important as the sequence of nitrogen bases. The proteins shape determines how the protein will perform its function. The protein you have deciphered (hopefully) is vasopressin. It is a hormone secreted by the pituitary gland. It has several important functions in the body. It allows the tubules in the kidneys to reabsorb water to prevent dehydration. Another important function is to decrease the diameter of the blood vessels, thereby increasing blood pressure. Data Analysis: 1. List the full names of the four nitrogenous bases of DNA ______________________________________ 2. List the full names of the four nitrogenous bases of RNA ______________________________________ 3. Why does the cell make an mRNA molecule rather than sending the DNA to the ribosome? (2pts) ____________________________________________________________________________________ ____________________________________________________________________________________
____________________________________________________________________________________ 4. What is a codon? ______________ 5. For what does a codon code? _____________________________ 6. How many bases make up one anticodon? __________ 7. What molecule carries an anticodon? ___________ 8. Where do the amino acids available in the cytoplasm of the cell originally come from? ___________________________________________________________________________________ 9. What are two functions of the hormone vasopressin? (2 pts) ____________________________________________________________________________________
____________________________________________________________________________________ 10. How many amino acids exist on Planet Earth? __________________ 11. What would the amino acid sequence be if the third A in DNA was eliminated? ________________________________________________ 12. What type of mutation occurred in question #11? ________________ 13. Would this still produce vasopressin? _____________ 3