PROTEIN

SYNTHESIS

Teacher's Guide

Protein SynthesisTeacher's Guide

The programs are broadcast by TVOntario, thetelevision service of The Ontario EducationalCommunications Authority. For broadcast datesconsult the appropriate TVOntario schedule. Theprograms are available on videotape. Orderingi nformation for videotapes and this publicationappears on page 25.

Canadian Cataloguing in Publication Data

Rosenberg, Barbara L.Protein synthesis

The Series

Producer/ Director: David ChamberlainWriter: Alan RitchieNarrator. James MoriartyConsultant: Hubert DollarAnimation: Animation Drouin Inc.

The Guide

Project leader: David ChamberlainWriter: Barbara L. RosenbergEditor: Loralee CaseDesigner: John RandleConsultant: H. Murray Lang

Contents

Program 1:Protein: The Stuff of Life .................... 1

Program 2:DNA: The Molecule of Heredity .............. 8

Program 3:DNA Replication: The Repeating Formula ...... 12

Program 4:RNA Synthesis: The Genetic Messenger ....... 15

Program 5:Transfer RNA: The Genetic Messenger ........ 19

Program 6:Ribosomal RNA: The Protein Maker ........... 22

To be used with the television program, Proteinsynthesis.Bibliography: p.I SBN 0-88944-080-8

1. Protein synthesis (Television program) 2. Proteinbiosynthesis. 3. Protein biosynthesis - Study andteaching (Secondary)

QP551.R671985 574.19'296 C85-093027-8

©Copyright 1985 by The Ontario EducationalCommunications AuthorityAll rights reserved.

Printed in Canada.

Protein: The Stuff of LifeObjectivesStudents should be able to:

1. Recognize that each species manufactures its own uniqueproteins.

2. Cite an example of protein specificity in the human body.3. List the different functions of proteins and cite examples for each.4. Describe the basic components found in protein.5. Draw the molecular structure of some common amino acids.6. Illustrate the formation of a peptide bond between two amino

acids.7. Explain why, an infinite variety of protein molecules is possible.8. Develop the concept of the significance of protein for the survival

of the cell and the organism as a whole.

Program DescriptionEach cell contains hundreds of different proteins, and each kind ofcell contains some proteins that are unique to it. Not only does everydifferent species of plant and animal synthesize protein peculiar tothat species, but every individual likely produces some proteinmolecules slightly different from those of every other individual. Thedegree of difference in the proteins of two species depends uponthe evolutionary relationship of the forms involved. Organisms lessclosely related by evolution have proteins that differ more markedlythan those of closely related forms.

The protein specificity of an individual is particularly evident in thei mmunological reactions of animals, by which foreign proteins areprevented from remaining permanently in the body of the organism.The body manufactures specific protein -antibodies. The surfacefeatures of the antibody complement the surface irregularities of theforeign protein. As a result the antibody binds to the foreign proteinand disposes of it.

The types and functions of proteins are extremely varied. Proteinsare found as enzymes - catalysts that make chemical reactions ofliving matter possible. An example is amylase, which begins to breakdown starch in the mouth. Muscles, responsible for the movement ofliving organisms, are largely composed of ordered protein molecules,

actin and myosin. Transport proteins are responsible for carryingmany materials through the circulatory system. Haemoglobintransports oxygen and carbon dioxide in the blood. Interaction of anumber of different proteins results in the clotting of blood.Antibodies can recognize and inactivate virtually any foreignsubstance that gains access to the body. Hormones, which regulateand coordinate bodily functions, are proteins. Major structural andprotective material in animals is made up of protein. Collagen andelastin provide the strength and resilience of connective tissuessuch as skin and ligaments. Keratin i s a major protein found in hairand nails. Lastly, proteins also serve as food reserves, as inovalburain (egg white) and casein, a major protein found in milk.

Proteins are macromolecules (polypeptides) containing atoms ofcarbon, hydrogen, oxygen, nitrogen, and often sulfur. Trace amountsof phosphorus, copper, and zinc may also be found. Proteins arecomposed of a linear arrangement of amino acids, the buildingblocks of protein, bonded together in long chains varying in lengthfrom less than 100 to more than 50 000 amino acids. An amino acidcontains a carbon atom which is attached by covalent bonds: ahydrogen atom; an amino (NH2) group; a carboxyl group (COOH); and"something else" - an "R" group that establishes which particularamino acid it is. Amino acids are joined together in peptide linkagesto form polypeptides. Peptide bond formation involves the elimina-tion of a water molecule between each pair of amino acid groups.

Not only do different proteins vary in length, they also vary inshape because each type of protein contains specific numbers andkinds of amino acids arranged in particular sequences. Consequent-l y, each type of protein molecule has a unique chain of amino acidsand a unique shape. For example, the molecules of fibrous proteinsare long and threadlike. They have special functions, such as bindingbody parts together or forming the fine threads of a blood clot.Globular proteins are coiled or folded into compact masses;enzymes are usually of this type. Considering that there are 20commonly occurring amino acids and that proteins may consist ofthousands of these units, the possible number of differentsequences of amino acid units, and hence the number of differentprotein molecules, is staggeringly large. An almost infinite variety ofprotein molecules is possible.

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Although the difference between two proteins may be as slight asthe replacement of a single amino acid in a chain of several hundred,it may lead to profound consequences within the organism. Incorrectsequencing of the protein insulin results in the condition known asdiabetes mellitus.

The synthesis of protein is perhaps the most significant synthesiscarried on by the cell. Since enzymes are proteins, protein synthesiscontrols the nature of the enzymes produced. Enzymes in turndetermine the reactions the cell can perform. These reactionscontrol the substances that can be synthesized or degraded, and thesubstances produced and stored determine the structure andfunction of the cell. The structure and function of the cells in turncontrol the nature of the entire organism.

Before ViewingProgram 1 may stand alone as an introduction to proteins in abiochemistry unit. When used as part of the unit on proteinsynthesis, the structure of amino acids should be reviewed as wellas the formation of peptide bonds. Functions of proteins should alsobe reviewed at this time.

You may want to perform Activity 1 now to introduce students tothe fact that many of the foods we eat contain protein. You may alsochoose to do similar experiments from any of the resource materiallisted in Activity 1.

Figure 1

After ViewingThe vital role of proteins in the maintenance and continuation ofliving organisms should be stressed. Examples of specific aminoacids may be drawn on the board to illustrate basic differencesamong them. Common examples to use are glycine, alanine, andl eucine. Refer to Figure 1 for their chemical compositions.

The amino acid sequence for insulin (a protein that causes adecrease in the level of blood sugar) could also be placed on anoverhead to explain that an incorrect sequencing could be

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Drawing a small portion of the amino acidsequence for insulin with the peptidelinkages illustrates a growingpolypeptide (Figure 2).

Figure 2

disastrous (Figure 3). This figure shows a sequence of amino acidsin the insulin molecule. The molecule consists of two polypeptidechains held together by two disulfide bridges.

Figure 3

anemia. Figure 4 shows the N-terminal portions of normalhaemogiobin and sickle-cell haemoglobin.

Figure 4

The amino acid residue in one of the protein chains of haemoglobini s glutamic acid. Certain individuals inherit a gene that results in thereplacement of this glutamic acid by another amino acid, valine. As aresult, the individual suffers from a chronic disease known assickle-cell anemia. Figure 4 shows the N-terminal portions of normalhaemoglobin and sickle-cell haemoglobin.

Activities 2, 3, and 4 can be performed at this time.

Although not mentioned in the program, you may wish to discussthe classic example of haemoglobin as well (Figure 4). The aminoacid residue in one of the protein chains of haemoglobin is glutamicacid. Certain individuals inherit a gene that results in the replace-ment of this glutamic acid by another amino acid, valine. As a result,the individual suffers from a chronic disease known as sickle-cell

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ActivitiesActivity 1(a): Identificationof ProteinsThe purpose of this activity is to informstudents that various foods we eat containproteins.

Apparatus10% solution egg albumin1 % solution gelatinMilkChicken bouillonDistilled water0.02M copper sulfate solution6M sodium hydroxideConcentrated nitric acidTest tubesTest tube rack10 mL graduated cylinderEye dropper

MethodBiuret Test1. Label the test tubes with the names of the

solutions to be tested; include distilled wateras a control sample.

2. To 2 mL of each solution add 2 mL of 6Msodium hydroxide and four drops of 0.02Mcopper sulfate solution. Gently shake thetubes to mix the solutions.

3. The appearance of a violet or violet-pink colorindicates the presence of proteins andspecifically the presence of peptide bondsbetween the amino acids.

Xanthoproteic Test1. Label the test tubes with the names of the

solutions to be tested.2. To 1 mL of each solution add five to ten drops

of concentrated nitric acid. CAUTION: Nitricacid is corrosive.

3. The appearance of a yellow color indicatesthe presence of proteins and specifically thepresence of the benzene nucleus.

Observations

Record the results in chart form.Type of test:Sample1.

2.

3.

4.

5.

Discussion1. Explain which test

proteins.2. Compare and contrast coagulation and

denaturation and name several agentsinvolved in these reactions.

3. Describe the functions of proteins.4. What is a polymer?

Activity 1(b): Identificationof Proteins

is the better test for

For a very simple and quick experiment1. Put 3 cm of water in a test tube. Add 1/8

teaspoon of gelatin powder. Shake well.2. Add six drops of Biuret solution. Notice how

the color of the Biuret solution changes fromblue to violet. (A violet color indicates thepresence of proteins.)

3. As an alternative, use 1/8 teaspoon of driedegg white instead of gelatin, or finelychopped hard-boiled egg white. If usinghard-boiled egg white the solution should beheated.

Observations Interpretation

Other experiments in the identification ofproteins may be found in McCormack et al,Biology Laboratory Manual, p.193; Feldman,Experiments in Biological Design, p. 52; andAbramoff and Thomson, Investigations of Cellsand Organisms, p. 49. (Refer to FurtherReading.)

Activity 2: What Is the Nature ofthe Protein Molecule?If the equipment is available, try thisexperiment. The chemical extraction proce-dures are particularly clear cut and easy.Proteins as well as nucleic acids are obtained.(The nucleic acids can be used later followingProgram 4.) Students will also be introduced tocentrifugation and chromatography, proceduresthat are widely used in biochemical research.The organism involved is Saccharomycescerevisiae, obtained commercially as baker'syeast.

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Apparatus (for each group)10 g moist baker's yeast30 mL trichloroacetic acid (TCA) 5% solution30 mL sodium chloride 10% solution100 mL ethyl alcohol 95%5 mL pancreatic enzyme in buffer solution5 mL phosphate buffer solution without enzymeTwo crystals thymol35 mL isopropanol5 mL formic acid20 g fine sandEight capillary tubes or toothpicksThree centrifuge tubesTwo test tubesOne mortar and pestleOne sheet of Whatman No. 1 chromatographic

Figure 4

paper (15 cm x 15 cm)One 1 L jar with lid.

Apparatus (for class)111 L jars with lidsOne or two centrifugesCellophane tapeSolutions of amino acids: alanine, aspartic acid,

histidine, lysine, methionine1 L ninhydrin reagentWater bathIce bathRefrigeratorOven or electric iron

Method

Refer to Figure 4.

CAUTION: Ninhydrin must only be used byteachers with a knowledge of carcinogenicmaterials and the proper use, safe storage,and safe disposal of the chemical.

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Step 1Disrupting the yeast cells and separatingglycogen from protein and nucleic acid

Flow Chart1. To 10 g of washed baker's yeast in a mortar, add twice as much sand; grind thoroughly for five

minutes. Add 30 mL of 5% TCA and grind two to three minutes more. Let the sand settle. Pouroff the milky suspension into a 50 mL plastic centrifuge tube. Centrifuge for five minutes.

Precipitate(Nucleic acids, proteins)

Supernatant(glycogen - discard)

Step 2Separating protein and nucleic acid

2. Add the precipitate to 15 mL of 10% sodium chloride solution. Stir and heat in a boiling waterbath for 10 minutes. Store in a refrigerator until the next class.

3. Centrifuge three minutes.

Precipitate(coagulated proteins)

Supernatant(nucleic acids)

Step 3Hydrolyzing protein

4. Measure out small portions of the precipitate(about the size of a small pea) into each oftwo labelled test tubes. To one test tube add4 mL of a solution of pancreatic enzyme inphosphate buffer and a crystal of thymol.Swirl the tube to suspend its contents. To theprotein in the other tube add 4 ml- of bufferwithout enzyme and add thymol. This tubeserves as a control. Label both tubes andstore until the next class.

5. Pour supernatant into another centrifugetube. Precipitate the nucleic acids by adding30 mL of ethyl alcohol; stir and cool severalminutes in an ice bath. Store in therefrigerator for use after viewing Program 4.

Hydrolyzed(proteins)

Unhydrolyzed(proteins)

Step 4Preparing chromatographic equipment foranalysis of amino acid

6. Touch the paper only along the edges. Using a sharp pencil, draw a fine line parallel to one sideof the filter paper about 1.5 cm from the edge to serve as the bottom of the chromatogram.Allow a margin of about 1.5 cm on each side of the paper, and place eight pencil dots evenlyspaced between the margins along the line.

Step 5Running the chromatogram

7. Spot one solution per dot of the amino acids, the hydrolyzed protein, and the unhydrolyzedcontrol. (See Figure 4). The remaining place is for an unknown amino acid selected by theteacher. Using a different, capillary tube (or a toothpick) for each solution, place a drop (about3 mm) on the paper. Allow it to dry, and repeat the process twice for each of the amino acid

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Step 6Analyzing the chromatogram

solutions and four times for the hydrolyzed and unhydrolyzed protein samples. Roll the paper asshown in Figure 4 and lower it into the solvent (10 parts formic acid, 70 parts isopropanol, 20parts water). (There should be enough solvent to cover the bottom of the jar.) Allow the solventto run up the paper to within a centimetre of the top. Remove the paper and make a pencil lineat the solvent front. Place the paper in a safe place to dry.

8. Wearing plastic gloves, dip the paper into the ninhydrin reagent and let it dry again. (CAUTION:Ninhydrin reagent is a poisonous carcinogen. Use only in a fume cupboard.) Heat the paper in awarm oven (30°C) or place between two sheets of clean filter paper and heat with an electrici ron for a few minutes until colored spots appear. Ninhydrin reacts with amino acids, formingblue or pinkish-blue spots. Outline the spots with a pencil. Determine the R F value of eachamino acid and record it.

For further details about this experiment, referto BSCS, Laboratory Block: The MolecularBasis of Metabolism, pp. 6-16. (See FurtherReading).

DiscussionThe ratio of the distance the solvent has movedi s called the R F. The R F of a substance underparticular conditions is important information inidentifying the substance. Two substances withthe same R F i n a number of solvents areprobably 'identical. The R F can be expressed asfollows:

distance of flow of known orR F = unknown compound

distance of flow of solvent

The R F i s usually written as a decimal and isalways less than one. Explain to students theprinciple involved in paper chromatography.

Activity 3: Amino AcidComposition of an UnknownThis lab exercise investigates the occurrenceof amino acids as an indication of proteinmetabolism within the body. The presence ofamino acids is once again tested for by usingpaper chromatography. The experiment can be

found in BSCS, Biological Science, An Inquiryinto Life, Student Laboratory Guide, (2nd ed.),I nquiry 6-2. (See Further Reading.)

Activity 4: Review1. Describe an example of protein specificity in

the human body.2. Describe the different roles that proteins play

within the body. Give examples.3. List the different elements found in all

proteins. What other elements may be foundi n proteins?

4. Draw the molecular structures for glycineand alanine. What is the basic differencebetween the two?

5. How does a peptide linkage occur'? Whatsubstance is formed during this process?

6. There are millions of different proteins in theliving world. How is this possible?

Further ReadingAbramoff, P and R. Thomson. Investigations of

Cells and Organisms: A Laboratory Study inBiology. Englewood Cliffs, New Jersey:Prentice Hall, 1968.

Benson, G.D. et al. Investigations in Biology.Toronto: Addison Wesley,1977.

BSCS. Laboratory Block: The Molecular Basisof Metabolism. Colorado: Raytheon Educa-tion Co., 1968.

BSCS. Biological Science: An Inquiry Into Life.Student Laboratory Guide. 2nd ed. New York:Harcourt, Brace and World, 1968.

Feldman. Experiments in Biological Design.New York: Holt, Rinehart and Winston,1965.

I ngram,,P.J. Biosynthesis of Macromolecules.2nd ed. Menlo Park, California:WA. Benjamin, 1972.

Kimball, J. Biology. 5th ed. Reading,Massachusetts: Addison-Wesley, 1983.

McCormack, J. et al. Biology LaboratoryManual. Glenview, Ilinois: Scott, Foresman,1980.

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DNA: The Molecule of Heredity

ObjectivesStudents should be able to:

1. State where the "blueprint," or genetic information, is stored.2. Describe the general structure of a DNA molecule.3. Describe the composition of a nucleotide.4. Differentiate between purines and pyrimidines.5. State the specific base pairing that occurs within the DNA

molecule.6. State what constitutes the genetic code.7. Recognize that DNA carries a code that specifies the primary

structure for all proteins in the body of an organism.

Program DescriptionWe resemble our parents because we inherit "genetic traits" fromthem. What is actually passed on is genetic information - instruc-tions for carrying out life processes. This genetic information, or"blueprint," is located in DNA molecules found in the geneslocated in the chromosomes inside the nucleus of the parents' sexcells and is then passed from cell to cell by mitosis as the childdevelops. The "blueprints" direct the developing cells to constructspecific protein molecules, which in turn function as structuralmaterials, enzymes, or other vital substances.

To find out how DNA could serve its genetic functions - storingand replicating information - a model was built to explain all thei nformation known about DNA. DNA is an exceedingly longmolecule, very thin, yet rather rigid. It is composed of two strands ofpolynucleotides coiled around each other in a helical manner andheld together by hydrogen bonds between pairs of nucleotide bases.

A nucleotide consists of a 5-carbon sugar, deoxyribose; aphosphate group attached to the 5-carbon atom of the sugar; and anitrogen-containing ring structure called a base. The base of a DNAnucleotide can be one of four kinds: adenine (A) and guanine (G),which are purines, and thymine (T) and cytosine (C), which arepyrimidines. The backbone of each of these two chains is composedof alternating deoxyribose sugar residues and phosphoric acidmolecules; it is uniform throughout the enormous length of the

molecule and apparently carries no genetic information. The purineor pyrimidine base bonded to each pentose sugar projects intowards the axis of the helix. One purine base and one pyrimidinebase bond together and hold the chains together. The resultingstructure is something like a ladder or zipper in which the outer railsrepresent the sugar and phosphate backbones of the two strandsand the crossbars, or "teeth of the zipper," represent the organicbases. In addition, the molecular ladder is twisted to form a double.helix, or corkscrew, effect.

The DNA strand consists of nucleotides arranged in a particularsequence. Moreover, the nucleotides of one strand are paired in aspecial way with those of the other strand. Only certain bases will fitand bond their nucleotides together. One purine and one pyrimidinejust fill the available space between the two chains. Specifically,adenine will only bond with a thymine and a cytosine will only bondwith a guanine. As a consequence of such base pairing, a DNAstrand possessing the base sequence A, G, C, T would have to bebonded to a second strand with the complementary base sequenceT, C, G, A. It is the particular sequence of base pairs that encodes thegenetic information held in the DNA molecule. A single DNAmolecule may contain from hundreds of thousands to close to 100million base pairs in endless possible sequences. The order ofthese sequences constitutes the genetic code for the constructionof protein.

Before ViewingAs an introduction you might ask students to consider why humansgive birth to humans, cats give birth to cats, and birds give birth tobirds. What makes it possible for characteristics to be carried onfrom one generation to the next?

You may wish to complete Activity 1 at this time. In this exercisestudents will use a specific staining procedure to determine whereDNA is located in the cells.

After ViewingThe molecular structures of adenine, guanine, thymine, and cytosinecould be drawn on the board, making note of the differences

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between the purines and pyrimidines. Refer to Figure 1. CompleteActivities 2, 3, 4, 5, and 6.

Figure 1

ActivitiesActivity 1: Where Is DNA Located?Place several onions in water a week prior toperforming this lab exercise. Before the lab cutoff 1 cm of the root tips that grew out from theonions avid fix them in acetic acid, rinse indistilled water, and hydrolyze in hydrochloric acid.

ApparatusOnion root tips - fixedSchiff's reagentSodium bisulfiteAcetic acidBeakersForcepsMicroscopeSlidesCover slipsMedicine droppersCheeseclothRubber band

MethodRefer to Figure 2.1. Place the root tips in the beaker and cover

the beaker with cheesecloth. Wash the roottips in running tap water for five to tenminutes to remove the acid.

2. Pour off the excess water and then addenough of the Schiff's reagent to cover theroot tips.

3. Leave the root tips in the dye for 20 minutes.They should turn a purple color. If they don't,l et them stand until the tips are stained, thenremove all excess dye by washing the tipsunder tap water for three to five minutes.

4. Add enough sodium bisulfite to cover theroot tips and leave them in this solution forone to two minutes. This bleaches all parts ofthe cell that do not contain DNA.

5. After bleaching, remove the root tips fromthe beaker and place them on a microscopeslide. Add a drop of acetic acid.

6. Add a cover slip, and with a pencil gently rollthe preparation to squash the root tips and

Figure 2

Schiff's reagent

Cheesecloth

Rubber band

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separate the cells.7. Examine the slide under the microscope, first

with low power and then with high power.The dye stains the DNA in the cell purple.The longer staining period and the washingprovide a better delineation of the DNA.

Discussion1. In what part of the cell is DNA located?2. What is the color of the cytoplasm?3. Can you identify individual chromosomes in

any of the cells?4. Are there any cells i n the process of

dividing?

Activity 2: Structure of DNAApparatus

Tracing paperPencilScissorsTape that can be written on

MethodMake copies of each of the nucleotides shownhere and have students build the DNAmolecule.

Discussion1. How can the models be arranged so that

the width of the total structure is always thesame?

2. What nucleotides will "fit" next to thethymine nucleotide? To the guaninenucleotide?

3. What "fits" are possible for the adeninenucleotide? For the cystine nucleotide?

4. What characteristics of the models deter-mined your answers in 2 and 3?

5. From observations of shape and size alone,you know that adenine could pair witheither thymine or cytosine. But does it pairwith one or the other, or both, in a real DNAmolecule?

6. If adenine always pairs with cytosine, howshould the relative amounts of adenine andcytosine compare in a DNA molecule?

7. If adenine always pairs with thymine, whatrelative amounts of these bases would youexpect to find?

8. If adenine sometimes pairs with cytosineand sometimes with thymine, what relativeamounts of adenine, compared to theamount of the other two, would you expectto find?

9. What do you notice about the percentage ofany single base in the different kinds ofcells? Consider the following data.

Amount of DNA Found in Human Cells

10. (a) Which bases pair together in humanDNA? Use examples from the data toexplain your answer.

(b) Would the same pattern of pairing holdtrue for all organisms? Explain.

Activity 3: What Is the MolecularBasis of Heredity?This dry lab can be found in Abramoff andThomson, Investigations of Cells and Organ-isms, Exercise 60. (Refer to Further Reading.)You may wish to use it to reinforce thestructure of the DNA molecule and as a lead-into Program 3.

Tissue Adenine Guanine Thymine CytosineThymus cells 30.9 19.9 29.4 19.8

Spleen cells 29.2 21.0 29.4 20.4Liver cells 30.3 19.5 30.3 19.9Sperm cells 30.7 19.3 31.2 18.8

Activity 4: Extracting DNA fromCellsIf time and equipment allows, you may wish totry this experiment in McCormack et al, BiologyLaboratory Manual, p. 39. This is a biochemicalprocedure illustrating how biochemists extractand study chemical substances found in livingorganisms. It involves a 24-hour nutrient brothculture of E, coli. After centrifugation the DNAstrands are lifted out of the test tube andobserved under blue light. A wet amount of theextracted DNA can then be prepared andviewed under the microscope.

Activity 5: ReportsMany people were involved in the researchleading to the structural model of DNAproposed by Watson and Crick. Have studentsinvestigate the contributions of one of thefollowing and write a brief report: FriedrichMeescher (1844-1895); Albrecht Kossel (1835-1927); Phoebus Aaron Levene (1869-1940);Alexander Todd (1907-); Oswald Avery (1877-1955); Heinz Fraenkel-Conrat (1910-); andRosalind Franklin (1920-1958).

Activity 6: Review1. Where are the master instructions for protein

synthesis located in a cell?2. DNA is described as a zipper and a

corkscrew. Unwound it looks like a ladder. Ofwhat substances are the rails and rungscomposed?

3. What is the composition of each of the fournucleotides?

4. What is the basic difference between apurine and a pyrimidine? Draw the structures.

5. What are the four possible combinations inthe base pairing?

6. What is the significance of the complemen-tary base pairing?

7. What is the function of DNA in the cell?

Further ReadingAbramoff, P and R. Thomson. Investigations

of Cells and Organisms. Englewood Cliffs,New Jersey: Prentice-Hall, 1968.

"Biopolymer Models of Nucleic Acids." Journalof Chemical Education. March 1979. Vol. 56.

168.p.Frankel, E. DNA: The Ladder of Life. 2nd ed.

New York: McGraw-Hill, 1979.

Lessing, L. DNA: At the Core of Life Itself. NewYork: Macmillan, 1967.

McCormack, J. et al. Biology LaboratoryManual. Glenview, Illinois: Scott, Foresman,1980.

Watson, J. The Double Helix. New York:Atheneum, 1969.

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DNA Replication: The Repeating FormulaObjectivesStudents should be able to:

1. Describe the structure of a DNA molecule.2. State what is meant by compiementarity3. Draw the molecular structures for the four bases and explain the

i mportance of hydrogen bonds in DNA.4. State at what point during cell division DNA replication occurs.5. Describe the basic steps involved in DNA replication.

Program DescriptionThe rails of the DNA molecule are made up of sugar moleculesbonded to phosphoric acid molecules; the rungs are made up ofnitrogenous bases - a purine (adenine or guanine) bonded with apyrimidine (thymine or cytosine). The specific sequencing of thebase pairs builds the genetic code, the "blueprint" necessary for thesynthesis of protein.

An important question now arises: How is the genetic code read,or how is the DNA decoded to make an exact copy of itself? The keyto the copying is in the architecture of the DNA molecule. The

; nucleotides of one strand are paired in a special way with those ofthe other strand. Only certain bases will fit and bond their nucleo-tides together. One purine and one pyrimidine just fill the availablespace between the two chains. The shape of the cytosine moleculei s such that a stable set of three hydrogen bonds could only beformed between it and guanine, and vice versa. Similarly, the shapeof the thymine molecule is such that the most stable set ofhydrogen bonds (two) would be formed between it and adenine, andvice versa. This complementarity is essential to the accuratereplication of DNA.

Molecular replication occurs during the process of cell division(mitosis) and enables the "blueprints" for creating proteins to bepassed on from organism to organism. DNA replication begins withan "unzipping" of the "parent" molecule. The hydrogen bondsbetween the base pairs are broken by a special enzyme and the twohalves of the molecule unwind. The exposed strands now bond withcomplementary free-floating nucleotides in the nucleus. The growing

chain of nucleotides is then linked together by the bonding of thesugar and adjacent phosphoric acid molecules. At the end of theprocess there are two DNA molecules; half of each is derived fromthe parent molecule; the other half is the new DNA. The two newDNA molecules will exactly .resemble the original one. Theduplicated double helix molecules can then be distributed, one toeach of the products of cell division. In this way cell continuity aswell as the continuity of the organism as a whole is ensured.

Before ViewingThe structure of the DNA molecule should be reviewed. It isimportant to stress that it is the "blueprint" necessary for thecontinuation of the organism. Since students were exposed to thestructures of the nitrogenous bases in Program 2, you might take thetime now to review the structures and discuss the hydrogen bondingthat occurs between specific base pairs. Refer to Figure 1.

Figure 1

Thymine

After Viewing Cytosine

It is important for students to understand that the molecular shapeof the DNA molecule is of immense consequence. Consider a singlepolynucleotide strand, a small portion of the DNA molecule. In thecourse of random molecule motion, the free-floating nucleotideswithin the nucleus would impinge against the base molecules of theDNA strand. Sooner or later a thymine residue would come intoopposition with an adenine residue in the chain. A pair of hydrogenbonds would be formed, and this thymine nucleotide would bebound to the DNA strand. In the same way the free-floating cytosinenucleotide would be bound to the guanine residue, an adeninenucleotide to the thymine residue, and a guanine nucleotide to thecytosine residue. The sequence of nucleotides bound to the DNAstrand would be in the proper configuration to allow for esterlinkages to form, between the sugar and phosphate residues ofadjacent molecules. In this way, in spite of the essential randomnessof molecular collisions and the reactions resulting from them, apolynucleotide strand of specific structure would be built. Activities1, 2, and 3 should be completed now.

ActivitiesActivity 1: DNA - How Does ItMake Copies of Itself?1. Use the patterns shown here to make parts

of a DNA molecule. Trace and cut out thefollowing number of parts: 16 Ss, 12 Ps, 4 Gs,4 Ts, 4 As, 4 Cs.

2. Build a model of a segment of a DNAmolecule. The segment should contain fiverungs. Some pieces will be left over; this isthe way it might be in a real cell. There wouldbe a strand of DNA in the nucleus and many

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"spare parts" circulating in the cell. Refer toFigure 2.

3. Once the model has been made, carefullyseparate it down the centre so that there aretwo parts. Refer to Figure 3. Use the "spareparts" to make a new strand of DNA bymatching the extra pieces to each of the twohalves.

Discussion

1. Compare the two strands of DNA. Howclosely alike are they?

2. Explain how DNA makes copies of itself.

Activity 2: Bacteria, Pneumonia,and DNAThis is a "dry" lab in which students are ledstep by step to a conclusion as they interpretdata from experiments where mice are injectedwith pneumococcus cells. Students shouldanswer the discussion questions at the end ofeach experiment before reading about the nextexperiment. From these experiments studentsshould understand that DNA is the source ofhereditary instructions. The activity.i s found inBSCS, Biological Science - A Molecular

Approach, I nvestigation 8-A. (Refer to FurtherReading.)

Activity 3: Review1. What is the importance of hydrogen bonds in

the explanation of the DNA model?2. Define complementanty and its significance

with respect to DNA.3. Illustrate the bonding patterns that occur

between specific base pairs.4. At what point during cell division does DNA

replicate? Why?5. Discuss the basic steps involved in DNA

replication.

Figure 2

Figure 3

Further ReadingBSCS. Biological Science - A Molecular

Approach. 4th ed. Lexington, Massachusetts:D.C. Heath, 1980.

"Genetic Repair." Sciquest. January 1981.

I ngram, D.J. Biosynthesis of Macromolecules.2nd ed. Menlo Park, California:W.A. Benjamin, 1972.

Lessing, L. DNA: At the Core of Life Itself.New York: Macmillan, 1967.

Sagre, A. Rosalind Franklin and DNA. New York:Norton, 1975.

"Selfish DNA." Sciquest. January 1981.

"The Teaching of DNA Replication in Schools:Thirty Years on, Thirty Years Out of Date?"Journal of Biological Education. Vol. 18.September 1984. p. 25.

Watson, J. The Double Helix: A PersonalAccount of the Discovery of the Structure ofDNA. New York: Atheneum,1968.

RNA Synthesis: The Genetic MessengerObjectivesStudents should be able to:

1. List seven differences between DNA and RNA.2. List and state the functions of the three types of RNA.3. Explain how a messenger RNA (mRNA) molecule is made from

DNA.4. Identify mRNA as a complementary copy of DNA.5. Define the terms codon, terminator codon, and initiator codon.6. State the significance of the codon AUG.7. State the significance of the "poly-A" tail.8. State where protein synthesis occurs.

Program DescriptionAlthough DNA molecules are located in the chromosomes of a cell'snucleus, protein synthesis occurs in the cytoplasm. Therefore thegenetic information must be transferred from the nucleus into thecytoplasm. This transfer of information is the function of mRNA. Thedifferences between DNA and RNA are described in the program.

The ribonucleic acids are classified into three groups:

(a) mRNA, the template for protein synthesis:(b) tRNA, whose function is to act as the amino acid-adaptor

molecule carrying specific amino acids into their specific placeson the protein synthesizing template; and

(c) rRNA, which controls the manufacturing process.

acid. For example, GCU codes for alanine, GGA for glycine, and CACfor histidine.

The minimum coding relationship between nucleotides and aminoacid is three nucleotides per amino acid. Four different kinds ofnucleotides taken three at a time provide for 64 combinations(43 -64). All but three of the 64 combinations code for one or anotheramino acid, and as many as six different nucleotide triplets mayspecify the same amino acid. The three codons which are notspecific for any amino acid are called terminators. Terminator tripletssignal the end of the polypeptide chain and cause the protein chainto become detached from the ribosome..UAG is an example of aterminator codon. The nucleotide triplet AUG is also unique. It is theinitiator codon as well as the codon for the amino acid methionine.How the correct AUG is selected for initiation is not known, butonce the correct AUG has been located the subsequent nucleotidesare read in groups of three.

Many RNA molecules are synthesized within the nucleus. Thoseinvolved in protein synthesis will have a long string of adenineresidues (100-200 poly-A) attached to the end of the mRNA molecule.This poly-A tail is retained as the molecule enters the cytoplasm. Thelonger the tail, the more stable the molecule. Perhaps the length ofthe tail in some way determines how many times that particularmRNA will be translated.

Once in the cytoplasm mRNA links up with a ribosome. It is herethat the genetic instructions carried by mRNA are received and, withthe assistance of tRNA, translated into functional proteins.

As mRNA is produced, a double-stranded section of a DNAmolecule seems to unwind and pull apart. A molecule of mRNA isthen formed of nucleotides that are complementary to thosearranged along the exposed strand of DNA. In this way the mRNAmolecule that contains the information for arranging the amino acidof a protein molecule in the sequence dictated by the DNA "masterinformation" is synthesized. Once formed, mRNA molecules canmove out of the nucleus into the cytoplasm. Once the genetic codehas been transcribed to mRNA, the message can then be read threenucleotides at a time. The triplet code with three adjacent nucleotidebases is termed a codon and is responsible for a specific amino

Before ViewingEmphasize once again the fact that DNA is a huge macromoleculeformed by thousands of nucleotide units. There are four differentnucleotides depending on the nitrogenous base each contains, andthese four nucleotides are linked in a specific sequence within eachDNA molecule. The essential feature of DNA is that it is a self-duplicating molecule; it is the basis of life.

Evidence clearly indicates that the four different nucleotides actas the letters of the alphabet and are used to encode the informationnecessary for the synthesis of protein and hence for control of the

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cell. Since the DNA molecule can build exact replicas of itself, thegenetic code can be copied and recopied so that each cell arisingfrom the original parent cell may possess a copy of instructions thatdetermine its nature.

After ViewingDiscuss the basic differences between DNA and RNA and havestudents complete the following chart.

The other point to be stressed is that if the sequence of the DNAbases is, for example, A, T, G, C, G, T, A, A, C, then the complemen-tary bases in the developing mRNA molecule would be U, A, C, G, C,A, U, U, G. Thus the sequence allows for the genetic information tobe carried to the ribosome and to be translated by tRNA, which willbe introduced in Program 5. Activities 1, 2, and 3 may be completedat this time.

"The mitochondria and chloroplasts have their own DNA separate from the DNA ofthe nucleus.

ActivitiesActivity 1:Extraction of DNA and RNAThis exercise involves the extraction of bothDNA and RNA from plant tissues and the identi-fication of three of the four nitrogen bases bymeans of paper chromatography. It is similar toActivity 2 except that geranium leaves are usedinstead of yeast. The technique for chromato-graphy is also less involved but the overallexperiment is not as effective. The exercise canbe found in Benson et al, Investigations inBiology, Investigation 9. A similar activity can befound in BSCS, Biological Science. An inquiryinto Life, Inquiry 8-1. (Refer to Further Reading.)

Activity 2: What Is theNature of Nucleic Acids?The yeast extract contains both RNA and DNA,but there is much more RNA. That is why thisexperiment is done in this program rather thani n Program 2: DNA.

Apparatus (for each group)

l mL bromthymol blueOne sheet Whatman No. 1 chromatogrampaper (15 cm x 15 cm)One 1 L jar and lidSix capillary tubes or toothpicks10 mL acetic acid30 mL butanolCellophane tapeI ndividual solutions of adenine, guanine,cytidine monophosphate (CMP), and uridinemonophosphate (UMP)A mixture of adenine, guanine, cytidinemonophosphate, and uridine monophosphateOne or two clinical-type centrifugesRefrigeratorWater bath

5 mL 1M sulfuric acid5 mL barium hydroxide

Pentose sugar Deoxyribose RiboseStructure Double helix Single helixSize Large molecule

(can be thousands ofnucleotides long)

Smaller molecule(transcribes only a sectionof the total DNA molecule)

Amount Few molecules in cell Many molecules in cellWhere Nucleus' Nucleus and cytoplasmKinds One type 3 types - mRNA, tRNA,

rRNANitrogenous bases Adenine, guanine,

thymine, cytosineAdenine, guanine, uracil .cytosine

FLOW CHARTStep 1 1. Centrifuge the alcohol-nucleic acids from Program 1, Activity 2, Step 2 (4) for three minutes.Hydrolyzing nucleic acid

Precipitate (nucleic acids) Supernatant (discard)

2. Dissolve the precipitate in 2 mL of sulfuric acid, CAUTION: Sulfuric acid is a strong oxidant.Transfer half the solution to a small test tube and heat in a boiling water bath for an hour (or asnear an hour as convenient - 30 to 60 minutes.) During heating, maintain the volume by addingwater. Transfer the unheated half of the sulfuric acid solution to another test tube. Label both.Neutralize both portions of the solution with barium hydroxide, using a drop of bromthymol blueas an indicator. Add barium hydroxide to the acid solution drop by drop until the indicator turnsblue. Do not add more barium hydroxide than is required to produce a color change. Bariumsulfate precipitates; ignore it. The sample that is not heated should be neutralized as soon asthe precipitate is dissolved. Store the test tubes i n the refrigerator for the next period.

Step 2 3. Refer to Program 1, Activity 2, Step 4 (6) and Step 5 (7) and to Figure 1 in that program. PreparePreparing chromatographic equipment and a the jar and sheet as before. Put on at least five superimposed spots of each of the test subchromatogram sheet stances. These should include adenine, guanine, CMP, UMP, a mixture of these four, the nucleic

acid hydrolysate, and the unhydrolyzed sample. Pour enough of the solvent to cover the bottomStep 3 of the jar. (The solvent should be 15 parts acetic acid, 60 parts butanol, and 25 parts water.) LetRunning the chromatogram the chromatogram develop as before. Remove the paper when the solvent nears the top and let

it dry.Step 4 4. When the paper is dry examine it under ultraviolet light in a dark room. The spots containing theAnalyzing the chromatogram bases will appear dark against a blue background. CAUTION: Do not look at ultraviolet light or

its reflections unless you are wearing protective glasses. Serious damage can be done to youreyes.

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Discussion1. Use the R F values of the known bases to

identify the bases of the hydrolyzed nucleicacids. Record the R F values of allsubstances.

2. What are the chemical, structural, andfunctional differences between DNA andRNA?

3. Explain the principle involved in paperchromatography.

Activity 3: Review1. List seven differences between DNA and

RNA.2. What are the three kinds of RNA and what

are their functions?3. How does mRNA become a pattern for

protein synthesis?4. An "unzipped" DNA strand exposes the

following nucleotides: ATGGCATTGAC.What mRNA sequence will form?

5. Define the following: codon, terminatorcodon, initiator codon.

6. Where in the cell does protein synthesisoccur?

Further ReadingBenson, G.D. et al. Investigations in Biology.

Toronto: Addison-Wesley, 1977.

BSCS. Laboratory Block: The MolecularBasis of Metabolism. Colorado: RaytheonEducation Co., 1968.

BSCS. Biological Science: An Inquiry into Life.Student Laboratory Guide. 2nd ed. New York:Harcourt, Brace and World, 1968.

Ingram, D.J. Biosynthesis of Macromolecules.2nd ed. Menlo Park, California:W.A. Benjamin, 1972.

Temin, H.M. "RNA-Directed DNA Synthesis."Scientific American. January 1972. p. 24.

Travers, A.A. Transcription of DNA.Oxford Biology Reader. 2nd ed. London:Oxford University Press, 1977.

Transfer RNA: The' Genetic Messenger

ObjectivesStudents should be able to:

1. Explain the role of the endoplasmic reticulum.2. Name the building blocks of proteins.3. Describe the structure of the tRNA molecule.4. State the function of tRNA.5. Define the terms anticodon and acceptor codon.6. Identify how a particular tRNA attaches to a particular place on the

mRNA.7. State how a triplet of bases in the mRNA determines the specific

amino acid.8. Discuss the role of the ribosome in protein synthesis.

Program DescriptionMost cells contain an extensive system of tubules with thinmembranes called endoplasmic reticulum. Associated with theendoplasmic reticulum are ribosomes, and it is here that proteinsynthesis occurs. Before a protein molecule can be synthesized, thecorrect amino acids must be present in the cytoplasm to serve asbuilding blocks. Furthermore, these amino acids must be positionedi n the proper locations along a strand of mRNA. The positioning ofthe amino acid molecules is the function of transfer RNA (tRNA).Since at least 20 different amino acids are involved in proteinsynthesis, there must be at least 20 different kinds of tRNAmolecules to serve as guides. Each kind of tRNA moleculerecognizes and binds to one kind of amino acid.

Transfer RNA molecules are polynucleotide chains of some 75 to85 nucleotides. Many of these nucleotides containing the regularnitrogenous bases link two portions of the chain in a double helixsimilar to that of the DNA molecule. Because of this several loopsare formed in the chain. The nucleotide sequences for the tRNAmolecules vary widely, but all molecules of tRNA have an unlinkedcodon at one end - the acceptor end of the tRNA molecule. Theamino acid is attached at this end. In each case, the amino acid isactivated and attached to the appropriate tRNA molecule by meansof an activating enzyme specific for that amino acid. Energy of

activation is supplied by ATP The tRNA then ferries the amino acid tothe ribosome. One portion of the nucleotide sequence in the tRNArepresents the anticodon, an unpaired nucleotide-triplet complemen-tary to the codon in mRNA that specifies that amino acid. Thenucleotides on the anticodon bond to the complementary nucleo-tides on the mRNA strand. In this way the tRNA carries its aminoacid to a correct position on a mRNA strand. The ribosome thenmoves onto the next codon and the tRNA for the next amino acid .links up with the specific codon on the mRNA. The preceding aminoacid is linked to the incoming one by a peptide bond, and its tRNA isreleased and is available to pick up another amino acid. As a result,amino acids are placed in the sequence needed to form a particularprotein molecule. Once the polypeptide chain is completed, the pro-tein is then released and becomes a separate functional molecule.

By knowing the nucleotide sequence of a particular protein onecan trace its protein structure back to its DNA "blueprint" and canreconstruct an exact copy of the DNA molecule.

The role of the ribosome is to provide the proper orientation of theamino acid-transfer RNA, the messenger RNA, and the growing poly-peptide chain so that the genetic code on the template, or mRNA,can be read accurately to ensure that the correct protein is formed.

Before ViewingIt may be wise at this time to introduce the structure of the tRNAmolecule. The program depicts the molecule as an "L" shape.However, most texts illustrate tRNA as a "clover leaf." An acetateoutline such as Figure 1, which shows methionine - tRNA isolatedfrom E. coli, may be used to point out exactly where the anticodonand the acceptor codon are located. There may be a slight dis-crepancy between the guide and the program as to the descriptionof the acceptor codon. All tRNAs end in the unpaired nucleotidesACC, and it is the arrangement of the nucleotides within themolecule in combination with a specific enzyme that recognizes thespecific amino acid that will attach to the specific tRNA. The

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After ViewingStress once again the fact that the function of the tRNA molecule isto act as an acceptor for an activated amino acid and as an adaptorfor carrying the amino acid to the site of protein synthesis in themRNA template in the ribosome, ensuring that the correct aminoacid is placed on the correct coding site. Activities 1, 2, and 3 shouldbe completed now

program suggests that the triplet codon at the acceptor end isspecific for a particular amino acid. Specific base pairings can alsobe mentioned, pointing out to students the formation of a doublehelix similar to the DNA molecule.

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AC ivi'tiesActivity 1: Reconstruction of theDNA "Blueprint"This activity reinforces the concepts oftranscription and translation. Refer to Figure 3in Program 1 for the amino acid sequence ofinsulin. A chart of the nucleotide triplets for the

Activity 2: What Controls theSynthesis of Large Molecules in aLiving Cell?This investigation is presented as a "dry" lab.The discussion questions concerning the datashould l ecid students to the conclusion that foreach enzyme (protein) in Neurospora presentand functioning in the synthesis of amino acidsor vitamins, there is a particular gene or groupof genes responsible for its formation. This labis extremely helpful to the students' under-standing of the gene-enzyme relationship: thatDNA directs the synthesis of the enzyme, aprotein necessary for the formation of specificsubstances in the organism. The investigationis found in BSCS, Biological Science - AMolecular Approach, Investigation 9-C. (Refer toFurther Reading.)

specific amino acids can be found in Kimball'sBiology, p. 256. (See Further Reading.) Havestudents trace part of the protein structure ofi nsulin back to its DNA "blueprint."

Activity 3: Review1. What is the function of the endoplasmic

reticulum?2. Name the building blocks of protein.3. Draw a simplified model of the tRNA

molecule.4. What is the function of tRNA?5. Define anticodon and acceptor codon.6. How many different kinds of tRNA must

exist in a cell? Explain.7. (a) Distinguish between transcription and

translation.(b) Where do each occur?

Further ReadingAsimov, I. The Genetic Code. New York: New

American Library, 1962.

Beadle, G. and M. Beadle. Language of Life:An Introduction to the Science of Genetics.New York: Doubleday,1966.

Bouk, E. The Code of Life. New York: ColumbiaUniversity Press, 1965.

BSCS. Biological Science - A MolecularApproach. 4th ed. Lexington, Massachusetts:D.C. Heath, 1980.

I ngram, D.J. Biosynthesis of Macromolecules.2nd ed. Menlo Park, California:WA. Benjamin, 1972.

Kimball, J.W. Biology. 5th ed. Reading,Massachusetts: Addison-Wesley, 1983.

"The Teaching of Protein Synthesis - AMicrocomputer Based Method" Journalof Biological Education. Vol. 17. Fall 1983.pp. 222-24.

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Ribosomal RNA: The Protein MakerObjectivesStudents should be able to:

1. Describe the structure and state the function of the ribosome.2. State what factors must be present in order for peptide initiation

to occur.3. Identify how a particular tRNA attaches to a particular place on

mRNA.4. Describe the initiation process.5. Describe how a chain of amino acids attached to tRNA molecules

becomes linked together.6. Explain the cause and effect of a mutation.

Program DescriptionThe machinery for the assemblage of a protein is in the ribosome,the key building block being ribosomal RNA (rRNA). The ribosome iscomposed of two subunits - a smaller subunit containing one RNAmolecule and 21 proteins and a larger subunit containing two RNAmolecules and 34 proteins.

Peptide initiation includes the formation of a complex betweenthe smaller subunit, mRNA, tRNA, GTP (energy necessary forsynthesis), and three distinct initiation factors, F 1 , F2 , and F3 . Thenext step appears to be the attachment of the larger subunit.Transfer RNA, with its specific amino acid, now binds to a specificsite on the ribosome, the "R" site. At this point the anticodon oftRNA binds to the codon on mRNA (usually AUG) that starts everymessage. Stresses in the molecular bonds between the codon andthe anticodon cause the tRNA to "flip over." This ensures properbinding. The tRNA is then translocated to a second site, the "P" site,on the ribosome. Now there is the addition of the next aminoacid-tRNA added to the first site on the ribosome, which wasrecently vacated. In other words, the new tRNA is capable of basepairing with the next mRNA codon at the "R" site. This tRNA nowflips sideways and the two amino acids are aligned. The precedingamino acid is linked to the incoming one by a peptide bond. Theproduct is located at this point on the "R" site. The tRNA on the "P"site is now released and a shift of the new peptidyl-tRNA from the

"R" site to the "P" site on the ribosome occurs. Also at this point,the ribosome has moved along the mRNA by three nucleotides, orone codon. Everything is "now ready for the addition of a furthertRNA, and the cycle repeats itself. This process is repeated againand again until the protein is completed.

The program ends by briefly summarizing the role of the ribosomei n engineering the correct link-up between mRNA and tRNA. There isa brief mention of mutations, alterations in the DNA code that mayeventually result in the evolution of a new organism.

Before ViewingHave students review the structure of the tRNA molecule and therole played by the ribosome in the synthesis of protein molecules.

After ViewingThe program describes the building of the polypeptide in generalterms. It might be easier for students to understand the concepts ofpolypeptide formation if the process is divided into three phases:i nitiation, elongation, and termination. This is described on page 254of Kimball's Biology. (Refer to Further Reading.)

There is a slight discrepancy dealing with the initiation process.The program states that the tRNA initially binds to the "R" site. Inmost texts this is listed as the "A" site. The tRNA is then trans-l ocated to the "P" site. To put things into perspective, you maywant to use a chalkboard or acetate outline of the formation of poly-peptides similar to Figure 1.

It may be of interest at this time to discuss mutations. Althoughmost mutations seem to be harmful to the cell or organism,occasionally one occurs that has a slight new advantage over othersof its species. By reproduction the new mutant organism may passthe advantageous gene into the population of that particular species.This can open a pathway toward evolution into a new species. Thisidea can then be followed up in Activities 1 and 2.

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ActivitiesActivity 1: How Can MutantStrains of Bacteria Be Isolated?Because of the importance of bacterialresearch in the areas of biochemistry, genetics,and medicine, students should be introducedto the basic bacteriological techniques oftransferring and culturing. The work withbacteria introduces the idea that mutations arechanges in the biochemistry of an organismand do not necessarily produce a visiblechange. Students innoculate agar media withbacteria and observe the growth pattern of thebacteria in the presence of antibiotics. Uponcompletion of this activity students should beable to relate the meaning of mutations to thechanges that occur to the code of the geneticmaterial within the cell. This investigation canbe found in BSCS, Biological Science - AMolecular Approach, Investigation 9-A. (Refer toFurther Reading.)

Activity 2: Effects of Radiation onMicroorganismsUnderstanding some of the useful, as well asthe harmful, effects of radiation is important inour modern age. Cancer treatment and foodpreservation by radiation are possible becauseof the lethal effect of the rays on the exposedcells. In this activity, students will haveexperimental evidence of the killing effect ofultraviolet light on yeast cells. The investigationcan be found in BSCS, Biological Science - AMolecular Approach, Investigation 9-B. (Refer toFurther Reading.)

Activity 3: Genetic EngineeringConsiderations as to the handling of thisbioethical issue are in order. Once the transfer

of genetic information is fully understood, therei s no technical reason why humans cannotaffect the process. It might soon be possible,for example, to correct the genetic code for anindividual who has a genetic disease, such assickle-cell anemia or phenylketonuria. Tamper-ing with the transfer of genetic information iscalled genetic engineering. Have students forma debate on this topic. Questions to considerare: Do scientists think it is possible toeventually "build babies to order"? Do youthink this is a good idea? Why or why not?What are the arguments for and against geneticengineering?

Activity 4: Research PaperHave students prepare a report on a hereditarydisease such as PKU, cystic fibrosis, diabetes,Huntington's Chorea, Down's syndrome,TaySachs disease, sickle-cell anemia, or cleftpalate. Their reports should discuss the causes,symptoms, detection, and treatment of thedisease.

Activity 5: Review1. Describe the structure and state the function

of the ribosome.2. What factors are necessary in order to

initiate polypeptide formation?3. Describe where the initiator tRNA binds to

the ribosome. How does the tRNA bind tomRNA?

4. Describe the elongation process and theformation of the polypeptide.

5. Describe the role of the DNA code, codons,and anticodons relative to RNA, ribosomes,and amino acids.

6. Explain the result of errors in the transfer ofgenetic information.

Further ReadingBrown, D.D. "The Isolation of Genes." Scientific

American. July 1975. p. 24.

BSCS. Biological Science - A MolecularApproach. 4th ed. Lexington, Massachusetts:D.C. Heath, 1980.

I ngram, D.J. Biosynthesis of Macromolecules.2nd ed. Menlo Park, California:W.A. Benjamin, 1972.

Kimball, J. Biology. 5th ed. Reading,Massachusetts: Addison Wesley,1983.

Kornberg, A. DNA Synthesis. San Francisco:W.H. Freeman, 1974.

Patt, D.A., and G.R. Patt. An Introduction toModern Genetics. Reading, Massachusetts:Addison-Wesley, 1975.

Pines, M. Inside the Cell. The New Frontier ofMedical Science. U.S. Dept. of Health,Education and Welfare. DHEW PublicationNo. (NIH) 78-1051.

United StatesTVOntario U.S. Sales Office901 Kildaire Farm RoadBuilding ACary, North Carolina27511Phone: 800-331-9566Fax: 919-380-0961E-mail: ussales@tvo.org

Videotape BPNProgram 1: Protein: 248901

The Stuff of Life

Program 2:DNA: The Molecule 248902of Heredity

Program 3: DNA Replication: 248903The Repeating Formula

Program 4: RNA Synthesis: 248904The Genetic Messenger

Program 5: Transfer RNA: 248905The Genetic Messenger

Program 6: Ribosomal RNA: 248906The Protein Maker

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OrderingInformationTo order the videotapes or thispublication, or for additional information,please contact one of the following:OntarioTVOntario Sales and LicensingBox 200, Station QToronto, Ontario M4T 2T1(416) 484-2613