How have humans genetically manipulated other organisms in the past?

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Janel Mitchell
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1 Genetic Engineering Have you eaten genetically modified food? Frito-Lay Corn Chips Cap n Crunch Cereal Kellogg s Corn Flakes General Mills Total Corn Flakes Cereal Quaker Chewy Granola Bars Nabisco Snackwell s Granola Bars Duncan Hines Cake Mix Ritz crackers Jiffy Corn Muffin Mix Old El Paso Taco Shells Ball Park Franks Aunt Jemima Pancake Mix All of the listed foods contain genetically modified ingredients. The United States does not require manufacturers to label genetically modified foods. Recent polls show that most Americans think the government should require the labeling of all food products that come from genetically modified crops. Are genetically modified foods harmful? Are there any benefits? For one point of view about genetically modified foods, check the True Food Network website: To explore these questions and examine why genetic engineering has become an environmental concern, we need to learn about genes and genetic engineering. How have humans genetically manipulated other organisms in the past? For thousands of years people have artificially selected certain characteristics in plants, animals, and even fungi by breeding parents with desirable traits. Artificial selection differs from natural selection because the characteristics selected may not increase an organism s survival and reproduction. In fact, people may breed organisms that are less like to survive or reproduce successfully. For example, turkeys have been bred to have very large breasts to provide more white meat. Now, male turkeys have such large chests they can no longer breed with females. Farmers must use artificial insemination to breed turkeys. What is a gene? In the past no one understood how an organism s characteristics were determined or passed from parents to offspring. Mendel s work in the nineteenth

2 century established the fact that there were discrete units of inheritance that we call genes. It wasn t until the twentieth century that scientists showed that the genetic material is deoxyribonucleic acid (DNA). In 1953, Watson and Crick elucidated the structure of the DNA molecule. A gene is a section of DNA that gives a cell instructions for making a specific protein or part of a protein. What is the structure of DNA? DNA is a large molecule that seems very complicated. Actually, it is made of small building blocks called nucleotides. A nucleotide has three basic parts: a phosphate group, a 5-carbon sugar called deoxyribose, and one of four nitrogenous bases. deoxyribose phosphate group One of the nitrogenous bases looks like this: There are four different nitrogenous bases in DNA: adenine, thymine, guanine, and cytosine. Remember that each nucleotide has 1 phosphate group, 1 deoxyribose sugar, and 1 of the 4 nitrogenous bases. When we put these three parts together, a nucleotide looks like this:

What is the double helix? Watson and Crick discovered that the DNA molecule is not just a single strand, but in fact forms a double strand like a ladder.

3 What is the double helix? Watson and Crick discovered that the DNA molecule is not just a single strand, but in fact forms a double strand like a ladder. The phosphate groups and sugars form the sides of the ladder and the nitrogenous bases join together to make rungs. They also found that there is a rule about the pairing of nitrogenous bases. Adenine (A) always binds with thymine (T) and cytosine (C) always binds with guanine (G). The DNA molecule twists so that it resembles a spiral staircase. How is DNA copied? When new cells are produced, they must have copies of all of the DNA in the original cell. To make a copy of the DNA (replication), the cell uses an enzyme to unzip the molecule between the nitrogenous bases. The cell then uses the A- T, C-G rule to add the correct new nucleotides to each original strand. One nucleotide is brought in to base pair with the original nucleotide at a time. Two identical DNA molecules are formed. If a mistake is made (perhaps a guanine is added where a thymine should be) a mutation has occurred. Unzip the original DNA molecule and use each strand as a pattern to add new nucleotides. You should create two identical DNA molecules. This process is called replication. How is DNA used as a blueprint or genetic code? In most cells, the DNA is stored in the nucleus. The assembly line for making proteins is outside the nucleus. The cell uses DNA as a pattern for making RNA (ribonucleic acid) molecules that leave the nucleus and help in the assembly of proteins. There are 3 types of RNA: m-rna (messenger RNA) is a complementary copy of a section of DNA r-rna (ribosomal RNA) forms little structures that act as the workbench for making proteins t-rna (transfer RNA) picks up and carries one specific type of amino acid RNA molecules are similar to DNA in some ways. Both are made of nucleotides, but instead of thymine, RNA has a different nitrogenous base called uracil (U). Uracil binds with adenine (A). RNA does have adenine (A), guanine (G), and cytosine. Instead of deoxyribose sugar, RNA has ribose. RNA molecules are a single strand.

How do genes determine an organism s characteristics? A gene is a section of a DNA molecule that gives a cell instructions for making a specific protein or part of a protein.

4 How do genes determine an organism s characteristics? A gene is a section of a DNA molecule that gives a cell instructions for making a specific protein or part of a protein. Proteins are used as building blocks in cells. The protein keratin forms most of your hair. Some proteins have special functions like hemoglobin which carries oxygen around the body. Other proteins are enzymes that make chemical reactions occur. For example, lactase is a protein that helps digest milk sugar. If a person body doesn t make lactase he can t digest milk very well. If a person didn t have a copy of the gene that provides instructions for making lactase his body would not be able to make the protein. Proteins are large molecules made of smaller building blocks called amino acids. People need to eat 20 essential amino acids so they can build their own proteins. If a person does not get a particular amino acid in his diet, he would not be able to build proteins. (It would be like trying to write a sentence without the letter e ) DNA codes for messenger RNA which uses a sequence of 3 nucleotides, called a codon, to specify a certain amino acid. By putting together all of the amino acids coded for by a gene in the correct sequence, the cell can build a specific protein. A ribosome is like a work bench where amino acids are put together to make a protein. What do mutations do? If a change in the DNA occurs, the amino acid sequence in a protein may change. This may not seem like a big deal, but it can have serious consequences. A change in only one nucleotide in the human gene for hemoglobin causes a change in the amino acid sequence and structure of the protein. As a result, the red blood cells of the person have a sickled shape that makes them get caught in blood vessels. The person with sickle-cell anemia suffers from pain tissue death, and may even die--- because of one tiny change in the nucleotide of one gene!

5 1. Make a small change in the sense strand of your original DNA molecule. Change the nucleotide sequence from T-A-G-G-G-G-C-T-T-C-T-T to T-A-G-G-G-G-C-T-T-T-T-T. 2. Use the new mutated DNA to build an m-rna molecule. 3. Do the new m-rna codons match with any of the t-rna anticodons you have? Can you complete your protein? What is genetic engineering? Scientists have learned how to use enzymes as chemical scissors to cut up DNA into short sequences of nucleotides. They can then reassemble the nucleotides in any order, creating designer genes. Genes from one organism can be snipped out and added to the genes of another organism using the process called recombinant DNA for example, the gene for human growth hormone is being added to pigs cells to make the pigs grow fatter. The human insulin gene has been inserted into bacteria so they make large quantities of human insulin for diabetics. What are the pros and cons of genetic engineering? Genetic engineering may make it possible to treat genetic diseases like sickle cell anemia. If the mutant gene can be replaced with the normal gene for hemoglobin, the person would be able to produce normal hemoglobin and would no loner suffer from sickle cell anemia. Genetic engineering poses some dangers to the environment. The Monsanto chemical company has genetically engineered the terminator gene that selectively programs a plant s DNA to kill its own embryos, making the seeds sterile. This genetic engineering process interferes with a plant s natural biology and prevents farmers from saving seeds to start next year s crops, forcing them to buy new seed annually. To explore the pros and cons of genetic engineering go to the website:

II. DNA Deoxyribonucleic Acid Located in the nucleus of the cell Codes for your genes Frank Griffith- discovered DNA in 1928

II. DNA Deoxyribonucleic Acid Located in the nucleus of the cell Codes for your genes Frank Griffith- discovered DNA in 1928 HEREDITY = passing on of characteristics from parents to offspring I. DNA, Chromosomes, Chromatin, and Genes DNA = blueprint of life (has the instructions for making an organism) Chromatin= uncoiled DNA