CHAPTER 1. DNA: The Hereditary Molecule SECTION D. What Does DNA Do? Chapter 1 Modern Genetics for All Students S 33

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1 HPER 1 DN: he Hereditary Molecule SEION D What Does DN Do? hapter 1 Modern enetics for ll Students S 33

2 D.1 DN odes For Proteins PROEINS DO HE nitty-gritty jobs of every living cell. Proteins are the molecules that give structure and shape to living cells and that carry out all of the chemical reactions necessary for life. he importance of DN is that it contains the information that is used to make all of the proteins on which life depends. he proteins whose structures are specified by our DN do more than carry out all of the reactions necessary to keep our cells alive; they also digest our food for us, influence how we will respond to infections, and determine what color our eyes, hair and skin will be. Proteins are made of long strings of individual building blocks known as amino acids. mino acids come in 20 different kinds that are all slightly different from one another chemically. It is not important for us to understand the details of the chemical differences that distinguish these 20 kinds of amino acids. But it is important to realize that because of these differences, the structure and function of every protein depends on the sequence in which the various kinds of amino acids are strung together. protein may contain many hundred amino acids. But if just one of these amino acid is changed, the function of the protein might change drastically. gene, which is a functional unit of DN, carries coded information indicating the precise sequence in which amino acids should be strung together to make one particular kind of protein that will play one particular role in the life of the cell. he elongated shape of collagen protein, shown in this molecular model, allows collagen to provide structural support to cells and organs. ntibodies, such as this human immunoglobulin, recognize and attack viruses, bacteria, and other foreign substances. hapter 1 Modern enetics for ll Students S 34

3 D.1 here are several different categories of proteins. Most proteins function as enzymes to regulate the speed of particular chemical reactions. Every cell contains hundreds of different enzymes that work together to release energy from food molecules and to use energy to build new cellular materials. ll enzymes are proteins. But not all proteins are enzymes. Structural proteins, as the name implies, provide structural support inside and outside cells and for the body as a whole. Defense proteins are an assortment of proteins in the blood that recognize and fight off foreign invaders, such as bacteria and viruses. ransport proteins are used to carry various molecules into and out of cells as well as through the body. he table on the next page gives a few examples of these and other kinds of proteins. Every aspect of life depends on proteins. In the next set of activities, you will learn about the processes a cell uses to convert the coded information in a bit of DN (a gene) into a particular kind of protein. hapter 1 Modern enetics for ll Students S 35

4 D.1 FEW HUMN PROEINS ND HEIR FUNIONS Protein ype What it does hemoglobin a red, iron-containing, makes your blood red transport protein picks up oxygen from the air in your lungs and releases it to cells elsewhere in your body if you don t make enough hemoglobin, or you make a type that doesn t carry oxygen well, you will be anemic insulin a hormone tells your cells when to remove sugar from your blood after a meal if you don t make enough insulin, or if your cells do not respond to it well, the concentration of sugar in your blood will get too high, and you will have diabetes antibody a defense protein fights infections from bacteria and viruses vaccination triggers production of antibodies that will fight a particular kind of infection if you couldn t make any antibodies, you would have been dead long ago! lactase an enzyme in your digestive tract digests lactose (milk sugar) in milk and dairy products into simpler sugars if you don t make enough lactase, you get diarrhea when you drink milk or eat ice cream or other diary products but you can buy lactase pills to swallow before eating dairy products collagen a structural protein provides the tough structural framework of your skin, bones, tendons, and cartilage keratin a structural protein provides the resistant outer layer of your skin and the tough structural material of your hair and nails myosin a structural protein uses energy derived from food and works that is also an enzyme together with actin to cause muscles to contract you can increase the myosin content of your muscles with exercise hapter 1 Modern enetics for ll Students S 36

5 How DN odes For Proteins Reprinted with permission from onick, L. and Wheelis, M. (1991). he artoon uide to enetics. New York: Harper ollins Publishers hapter 1 Modern enetics for ll Students S 37

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15 Name Date Hour QUESIONS ON HOW DN ODES FOR PROEINS FER YOU HVE read about protein synthesis in your excerpt from the artoon uide to enetics, answer the following questions. 1. What is the relationship between genes and proteins? 2. How does RN differ from DN? 3. What is the molecule that carries the information from a gene to the place where a protein will be made? 4. What is the process by which such a molecule is made? 5. What is the enzyme that mediates the process named above? 6. What is the structure on which proteins are made? 7. How many bases form one word of the RN message? 8. What is the technical name for such a group of bases found on mrn? 9. What is another term for protein synthesis? 10. What is the group of molecules that translates the genetic code? 11. What is an anticodon? 12. t the tail end of each trn molecule, an attaches the appropriate molecule to the trn. 13. What happens when two trns are side by side on a ribosome? 14. he first codon on an mrn always is. 15. his codes for the amino acid called. hapter 1 Modern enetics for ll Students S 47

16 D.3 he ene Expression Dance S YOU HVE RED in your excerpt from the artoon uide to enetics, three kinds of RN molecules cooperate to convert the coded information in DN (a gene) into a protein with a particular sequence of amino acids. he process in which the nucleotide sequence of a gene (DN) is used to specify the amino acid sequence of a protein is called gene expression, and it consists of two major phases: 1) transcription, in which a messenger RN (mrn) molecule that is complementary in nucleotide sequence to the gene is synthesized, and 2) translation, in which the message carried by that mrn molecule is used to synthesize the corresponding protein. In this exercise, your class will perform a simulation of these two processes. MERILS Your teacher will hand out the gene-expression flash cards that you will use in this dance. PROEDURE Your teacher will instruct you how to perform the dance. mrn DN 4 U mrn U DN DN 2 DN 7 U codes Isoleucine Methionine U U mrn protein U U Histidine lutamine hapter 1 Modern enetics for ll Students S 48

17 D.4 Name Date Hour Paper Proteins: Models for Simulating ene Expression MERILS For each student or pair of students: 1 set of paper-protein puzzle pieces PROEDURE Follow the directions below to model the processes of transcription and translation, and to make a paper protein. DN Figure 1 1. Place the DN strip on the desk so that the letters read properly for you (fig. 1). mrn 2. Working from left to right, find the mrn pieces that match the DN and line them up (fig. 2). What is the process in which an mrn molecule that is complementary to a DN molecule is produced? DN Figure 2 (nswer question 2 here) 3. Separate the mrn from the DN to simulate the mrn moving out of the nucleus to a ribosome in the cytoplasm of the cell. Leave the mrn pieces lined up next to one another(fig. 3). mrn U Figure 3 U U U 4. Match each of the trn pieces to the amino acid piece that fits with it (fig. 4). Lay them out so that all of them are visible. trn mino cid U Methionine Figure 4 hapter 1 Modern enetics for ll Students S 49

18 D.4 Name Date Hour 5. Search for the trn that will base pair with the first codon of the mrn (the one on the left-hand end). Move the trn with its attached amino acid into place in the mrn (fig. 5). ontinue with the second codon, and so forth. What is the name for this process in which a protein is produced that has an amino acid sequence specified by an mrn molecule? mrn trn mino cid U U Methionine Figure 5 U U U (nswer question 5 here) 6. Now pull the string of six amino acids away from the trn (fig. 6). hese six amino acids represent a new protein. (However, real proteins always contain many more amino acids than this, sometimes more than a thousand.) mino cid Methionine Figure 6 fter you have completed these steps, use the model pieces to explain the two component processes of gene expression to another student. hen write out the steps in your own words. You may refer to your notes or a book to check for scientific accuracy. hapter 1 Modern enetics for ll Students S 50

19 D.5 Name Date Hour Using the enetic ode to ranslate an mrn HE HER OF the regular and predictable relationship between the sequence of nucleotides in any gene and the sequence of amino acids present in the protein for which that gene is said to code is a fixed set of nucleotide-to-amino acid relationships that is known as the genetic code. Just as the Morse code can be printed in the form of a table indicating which letter of the English alphabet is specified by each combination of dots and dashes, the genetic code is usually printed in the form of a table indicating what kind of amino acid is specified by each possible mrn codon. o the right is a DN coding sequence that codes for part of the hemoglobin molecule. omplete the mrn strand following base-pairing rules. hen use the mrn enetic ode able on the next page to determine the amino acid sequence for which this piece of a gene codes. DN mrn mino cid ongratulations! You have just synthesized the first part (12 amino acids) of the protein called ß-globin, which is part of the hemoglobin molecules that make your blood red and carry oxygen to cells throughout your body. (Each real ß-globin molecule actually consists of a string of 147 amino acids.) hapter 1 Modern enetics for ll Students S 51

20 D.5 mrn ENEI ODE BLE 1st base 2nd base U U UUU = phe UU = ser UU = tyr UU = cys U UU = phe U = ser U = tyr U = cys UU = leu U = ser U = stop U = stop UU = leu U = ser U = stop U = trp 3rd base ala arg asn asp cys gln glu gly mino cid bbreviations = alanine = arginine = asparagine = aspartic acid = cysteine = glutamine = glutamic acid = glycine UU = leu U = pro U = his U = arg U U = leu = pro = his = arg U = leu = pro = gln = arg his ile leu lys = histidine = isoleucine = leucine = lysine U = leu = pro = gln = arg UU = ile U = thr U = asn U = ser U U = ile = thr = asn = ser U = ile = thr = lys = arg met = methionine phe = phenylalanine pro = proline ser thr trp tyr = serine = threonine = tryptophan = tyrosine U = met = thr = lys = arg val = valine UU = val U = ala U = asp U = gly U U = val = ala = asp = gly U = val = ala = glu = gly U = val = ala = glu = gly hapter 1 Modern enetics for ll Students S 52

Basic concepts of molecular biology

Basic concepts of molecular biology Gabriella Trucco Email: gabriella.trucco@unimi.it Life The main actors in the chemistry of life are molecules called proteins nucleic acids Proteins: many different