Name: Period: Date: Living Environment Lab DNA & Protein Synthesis #21 Introduction Of all the molecules that is in the body, DNA is perhaps the most important. DNA or dioxiribosenucleic acid is important because is contains all the information needed to make an organism. DNA instructs the cell to make the nessessary molecules needed by the body to function properly. These protein molecules are then used to repair, maintain and/or create new cells. The DNA molecule is found tightly wound on the chromosomes. The secret to DNA s success lies in its shape. The DNA molecule is a double stranded, double helix shaped molecule, made up of a combination of four nucleic bases: Adenine, Thymine, Guanine and Cytosine (abbreviated A, T, G and C). These bases pair together to form the double strand; Adenine bonds with Thymine (A-T) and Guanine bonds with Cytosine (G-C). The DNA molecule is very long. There is over 220 million base pair on a single chromosome (there are 46 chromosomes in each human cell). These DNA molecules are tightly packed so that they can fit in the nucleus of the cell. When it is time to make more DNA (replication), the DNA molecule unzips itself. The bond that held the bases to each other breaks and the two strands begin to move away from each other. As they move away, free-floating bases begin to attach themselves to the vacant spot and a new chain begins to form. When the process is finished, two new DNA molecules will have formed (each molecule will have s stand from the old DNA molecule and a new strand formed from the floating bases).
1) Complete the DNA molecule that just unzipped. When it is time for the DNA molecule to instruct the cell to make a protein, a section of the DNA unzips. This section of DNA is called a gene. A gene is a section of DNA that codes for a specific protein molecule. Because you body makes thousands of different proteins, the DNA molecule must contain thousands of genes to make them. As the section of DNA unzips, RNA begins to assemble onto the exposed DNA strand. This process is called Transcription. Unlike DNA replication, the RNA molecule does not use thymine bases; instead it uses a base called uracil. Uracil binds to the adenine base just like the thymine base. 2) Complete the RNA transcription. Once the unzipped portion on the DNA has been copied, the single strand of RNA detaches and exits the nucleus. This type of RNA is called massager RNA or mrna. The mrna now attaches to a ribosome. Once attached, a transfer RNA of trna brings amino acids to the ribosome. Each trna has a unique binding site that correlates with a particular amino acid. When the trna brings the amino acid to the ribosome, it must match the code on the mrna before it attaches. These codes are grouped in sets of three nucleic bases along the mrna strand.
When the trna reads the code on the mrna, it reads the nucleic bases as a set of three. Each set of tree nucleic bases is called a codon. If the code on the trna doesn t match the codon on the mrna, the trna will leave and another will try to match. If the binding site of the trna matches the codon on the mrna, the trna will leave the amino acid in the ribosome. As more trna binds to the mrna, they leave their amino acid, creating a chain. When all of the mrna s sequenced has been bound, the amino acid chain is complete producing a protein. 3) Circle each codon on the mrna molecule and match the appropriate trna to each codon. MET PHE VAL THR SER Sometimes during replication the DNA is not copied correctly. This accidently mistake in the DNA sequence is called a mutation. There are three ways that this can occur: Substitution when the wrong base is added to the DNA, Addition when an additional base is added to the sequence, and Deletion when a base is deleted from the sequence. Because the sequence is changed, that section of the DNA now is coded for a different protein. Sometimes these mutations affect an important protein that can cause death to an organism. While sometimes the mutation doesn t cause any harmful effect to the organism. 4) What is the difference between DNA replication and DNA transcription?
5) What are two differences between DNA and RNA? 6) Why is a mutation in DNA replication dangerous to an organism? Explain. 7) Identify whether the new strand of DNA s mutation is Addition, Substitution or Deletion. Original Strand of DNA A. A. B. B. C. C.
Purpose Students will learn how a protein is synthesized using DNA and RNA. Procedure 1. Use the Universal Genetic Code Chart to fill in the blanks on the next page. 2. Some blanks will be for the three base sequence of the DNA molecule, some blanks will be for the three base sequence of the mrna, and some of the blanks will be for the amino acid attached to the trna (you must use the binding sites of the trna)
Fill in the blanks below 8) Determine the sequence of amino acids from this gene. AUG TTA GCG TCG AAT GGT ACC TCT AAA TTC GTC CTC ATC UAA --------------, ---------------, --------------, ---------------, --------------, ---------------, --------------, ---------------, --------------, ---------------, --------------, ---------------, --------------, ---------------,