Teacher Preparation Notes for "From Gene to Protein Transcription and Translation" 1

Transcription

1 Teacher Preparation Notes for "From ene to Protein Transcription and Translation" 1 In this hands-on, minds-on activity students learn (1) how genes provide the instructions for making a protein via transcription and translation and (2) how genes influence characteristics such as albinism and sickle cell anemia. Students use simple paper models to simulate the molecular processes of transcription and translation. This activity also includes multiple figures, brief explanations and questions, together with four recommended videos. You can use this activity to introduce students to transcription and translation or to reinforce and enhance student understanding. If you plan to use this activity to introduce transcription and translation, the activity will probably require four 50-minute periods. If your students already have a basic understanding of transcription and translation, you may be able to complete the activity in two 50-minute periods. This activity is intended for students who have been introduced to: the structure and function of proteins and DN (Key concepts and relevant learning activities are provided in "nderstanding the Functions of Proteins and DN" ( DN replication and the base-pairing rules (For this purpose we recommend the analysis and discussion activity, "DN Structure, Function and Replication" ( or the hands-on activity, "DN" ( If you prefer an analysis and discussion version of this activity which omits the paper models, see From ene to Protein via Transcription and Translation ( These Teacher Preparation Notes include: Learning oals (pages 1-3) Supplies (page 3) Recommendations for Implementation and Background Biology o eneral Information and Recommendations for Implementation (including Recommended Sequence) (page 4-5) o Transcription and Translation Background Biology and Recommendations for Discussion (pages 5-9) o Transcription and Translation Modeling Procedures (pages 9-10) o Sickle Cell Hemoglobin and Sickle Cell nemia (pages 11-13) Related Learning ctivities (page 13) Templates for Making Needed Supplies (pages 14-20) Learning oals In accord with the Next eneration Science Standards: 2 Students will gain understanding of the following Disciplinary Core Ideas 1 By Drs. Ingrid Waldron and. Jennifer Doherty, Department of Biology, niversity of Pennsylvania, These Teacher Preparation Notes and the related Student Handout are available at We thank my Dewees, Jenkintown High School, Erica Foley and Lori Spindler for helpful suggestions and NancyLee Bergey, niversity of Pennsylvania School of Education, Holly raham, Central Bucks High School South, and Mr. Ippolito, Port Chester High School, for sharing helpful activities which provided us with many useful ideas. 2

2 LS1., Structure and Function, including "enes are regions in the DN that contain the instructions that code for the formation of proteins, which carry out most of the work of cells." LS3. and LS3.B, Inheritance and Variation of Traits, including "DN carries instructions for forming species characteristics." Students will engage in Science Practices, including construct explanations and "use multiple types of models to provide mechanistic accounts and/or predict phenomena, and move flexibly between model types " This activity provides the opportunity to discuss the Crosscutting Concepts: Structure and function, including Students model complex and microscopic structures and systems and visualize how their function depends on the shapes, composition, and relationships among its parts." Cause and effect: Mechanism and explanation, including understanding causal relationships by examining what is known about smaller scale mechanisms within the system. This activity helps to prepare students to meet Performance Expectations HS-LS1-1, "Construct an explanation based on evidence for how the structure of DN determines the structure of proteins which carry out the essential functions of life through systems of specialized cells." HS-LS3-1, "sk questions to clarify relationships about the role of DN and chromosomes in coding the instructions for characteristic traits passed from parents to offspring." Specific Learning Objectives enes influence our phenotype by the following sequence of steps: nucleotide sequence in the DN of a gene nucleotide sequence in messenger RN (mrn) transcription amino acid sequence in a protein translation structure and function of the protein (e.g. normal hemoglobin vs. sickle cell hemoglobin) person's characteristics or traits (e.g. normal health vs. sickle cell anemia) Transcription is the process that copies the message in a gene into a messenger RN (mrn) molecule that will provide the instructions for making a protein molecule. The sequence of nucleotides in a gene in the DN determines the sequence of nucleotides in the mrn molecule. Each DN nucleotide is matched with a complementary mrn nucleotide in accord with the base-pairing rules: C pairs with and pairs with (in RN) or T (in DN). To make the mrn molecule, the enzyme RN polymerase adds the complementary nucleotides one at a time to the growing mrn molecule, using the base-pairing rules to match complementary nucleotides. 2

3 comparison between transcription and DN replication shows: Similarities Differences - Both processes use a DN strand together - single gene is transcribed into an mrn with the base-pairing rules to determine molecule, whereas the whole chromosome is which nucleotide is added next. replicated. - Both processes produce a polymer of - Transcription produces a single-stranded nucleotides (a nucleic acid). mrn molecule, whereas replication produces - Both transcription and replication are a double-stranded DN molecule. carried out by a polymerase enzyme which - The enzyme for transcription is RN adds nucleotides one at a time. polymerase, whereas the enzyme for DN replication is DN polymerase. - Thymine in DN is replaced by uracil in RN. Translation is the process that makes proteins. mrn carries the genetic message from the nucleus to the ribosomes where proteins are synthesized. The sequence of nucleotides in an mrn molecule specifies the sequence of amino acids in a protein. The sequence of amino acids determines the structure and function of the protein. Each triplet codon in the mrn codes for a specific amino acid in the protein. The triplet codon in mrn is matched by a complementary triplet anti-codon in a transfer RN (trn). For each type of trn, there is a specific enzyme that attaches the correct amino acid for the anticodon in that trn. Thus, different types of trn bring the right amino acids for each position in the protein as the protein is synthesized by the ribosome. The ribosome adds amino acids one at a time to the growing protein in accord with the instructions from the codons in the mrn. Supplies For each group of 2-4 students, use the templates shown beginning on page 14 of these Teacher Preparation Notes to make: a page labeled Nucleus and a page labeled Ribosome (To encourage accurate modeling, we recommend that you cut out the 4 mm x 30 mm slots in the nucleus and ribosome pages and have your students insert the DN and RN molecules through these slots so that initially only the beginning of the DN or RN molecule can be seen. We recommend printing these on different colored card stock or heavy paper. The nucleus and ribosome pages can be reused in multiple classes.) the following items can be prepared as disposable items or laminated for reuse in multiple classes: DN molecule (cut the page in strips) Second part of mrn strip (a different color from the DN; cut the page in strips) 9 RN nucleotides (the same color as the mrn; each student group will need 1, 2 C, 3, and 3 ) 6 trn molecules (the same color as the mrn; cut each trn rectangle to include the three nucleotides and the words "amino acid" directly above these nucleotides; one of each type of trn for each student group) 6 amino acids (on a different color paper; one of each amino acid for each student group) transparent tape Depending on your students, you may want to prepare a packet with all the supplies for each student group or you may want to dole out supplies as needed for each step in the simulation and have the 9 RN nucleotides, the 6 trn molecules and the 6 amino acids for each student group in three separate small envelopes. 3

4 Suggestions for Implementation and Background Biology eneral Information and Recommendations for Implementation In the Student Handout, numbers in bold indicate questions for the students to answer and indicates a step in the modeling procedure for the students to do. The PDF of the Student Handout shows the correct format; please check this if you use the Word document to make revisions. We recommend that you have your students work in pairs or in groups of four to model transcription and translation and also to answer the questions. Each student should have a specific role in the modeling procedures. For example, in a group of four students modeling transcription, one should act as the RN polymerase, one should read the instructions for the RN polymerase, one should act as the cytoplasm, and one should read the instructions for the cytoplasm (see page 3 of the Student Handout). key is available upon request to Ingrid Waldron (iwaldron@sas.upenn.edu). The following paragraphs provide additional instructional suggestions and background information some for inclusion in your class discussions and some to provide you with relevant background that may be useful for your understanding and/or for responding to student questions. Recommended Sequence for Implementation 1. To stimulate student interest and get your students thinking about the topic, have your students discuss the initial question, "How do genes influence our characteristics?" Then, use the information and questions on page 1 and the top of page 2 of the Student Handout to help students understand the overall process by which genes influence characteristics and how transcription and translation contribute to this process. This introductory section will provide a useful framework for the more detailed information in the following sections and will help students to understand why it is important to learn about transcription and translation. You may also want to show your students the 5-minute video What is DN and how does it work? ( This video provides a good introduction and overview, which can provide a helpful context for learning about transcription and translation. 2. Students learn how transcription occurs, using the information on page 2 of the Student Handout and questions 5-9. Show the basic version of the animation of transcription produced by the Howard Hughes Medical Institute ( This animation provides a dynamic simulation of the basic process of transcription and also illustrates the amazing rapidity of the process; RN polymerase adds about 50 nucleotides per second to the growing mrn molecule. 3. Have students model transcription by carefully following the instructions on page 3 of the Student Handout; try to make sure that each group of students carries out each step in the procedure to ensure accurate understanding of the process of transcription. 4. Have students answer questions and discuss their answers. Then, have students consolidate their understanding of transcription by answering question 12 and discussing their answers; recommended approaches to this question are provided on page 8 of these Teacher Preparation Notes. 5. Students learn how translation occurs, using the information on page 5 of the Student Handout and questions You may want to show the simplified animation of translation, available at We recommend that you show the basic version of the animation of translation available at 4

5 to provide a dynamic overview of the process. You may want to pause the animation and have students compare the animation with the figure on the bottom of page 5 of the Student Handout. You also may want to mention that a ribosome adds about 2-20 amino acids per second in eukaryotes and bacteria, respectively. 6. Have students model translation by carefully following the instructions on pages 6-7 of the Student Handout. s they model translation, they should answer questions Have students answer questions and discuss their answers. Then, have students consolidate their understanding of translation by answering question 26 and discussing their answers; recommended approaches to this question are provided on page 8 of these Teacher Preparation Notes. 8. The last section revisits the question of how different alleles result in different versions of a protein which in turn can result in different characteristics. s you discuss question 27, you may want to review the example of albinism vs. normal skin and hair color (see page 11 of these Teacher Preparation Notes). To analyze the sickle cell anemia example, have students answer questions 28-30, and discuss their answers. Then, discuss the information on the bottom of page 9 and the top of page 10 of the Student Handout, have students answer questions 31-32, and discuss their answers. We recommend that during this section you show the sickle cell anemia video ( This activity includes multiple simplifications. For example, the definition of a gene at the top of page 1 of the Student Handout ignores multiple complexities, including the facts that many genes code for more than one polypeptide and many genes code for RN that has different functions from mrn. The chart on the top of page 1 of the Student Handout does not include the fact that the allele for albinism is recessive, so only an individual who is homozygous for this allele will be an albino. n allele that codes for a nonfunctional protein is often recessive, because a single copy of the allele that codes for the normal functional protein results in the production of enough normal protein to produce a normal phenotype. If your students are already familiar with the concepts of recessive alleles and homozygous vs. heterozygous individuals, we recommend that you include this information in your discussion of albinism. Otherwise, we recommend that you postpone discussion of these terms to our enetics activity ( The type of albinism discussed in this activity is called oculocutaneous albinism because the melanin deficiency results in vision problems as well as pale skin and hair color. This type of albinism is due to a defect in the tyrosinase enzyme which catalyzes the first step in the production of melanin ( Transcription and Translation Background Biology and Recommendations for Discussion Question 5 is intended to help students remember how transcription fits in the overall framework of protein production. We have found that it is important to repeatedly remind students of this overall framework so they don t get lost in the details of the specific processes. The figure on page 2 of the Student Handout labels the template strand (i.e. the DN strand that is transcribed). If your students ask how the RN polymerase is directed to transcribe a gene in the template strand of the DN double helix, you can explain the role of the promoter in initiating transcription. 5

6 You can use this figure if your students need a refresher about DN structure or why the rules that describe which nucleotides are complementary are called the base-pairing rules. Your discussion of transcription and the base-pairing rules provides a good opportunity to discuss the Structure and Function Crosscutting Concept, including Students model complex and microscopic structures and systems and visualize how their function depends on the shapes, composition, and relationships among its parts." ( To help students understand how the mrn separates from the DN during transcription, you may want to remind your students that the bonds within each DN or RN strand are covalent bonds, but base-pairing involves weaker hydrogen bonds which are more readily broken. (There are many many hydrogen bonds connecting the two strands of a DN molecule, which is why the bonds between the two DN strands are quite stable.) During transcription in a cell, multiple RN nucleotides are constantly entering and leaving the RN polymerase. For each DN nucleotide, only the complementary RN nucleotide that has the right shape and charges to form multiple hydrogen bonds with that specific DN nucleotide will remain in place and be covalently bonded to the preceding RN nucleotide. Similarly, for translation, trn molecules enter the ribosome at random; non-matching trn will enter and then leave the ribosome; when a trn with an anti-codon that is complementary to the mrn codon enters the ribosome, the amino acid carried by that trn will be covalently bonded to the growing polypeptide. On page 4 of the Student Handout, students compare transcription to DN replication. If you would like to show your students a figure to remind them about the process of DN replication, you could use one of these figures. DN Replication (not showing the enzymes involved) 6

7 The Student Handout section on translation begins with a review of the overall sequence of transcription and translation, to ensure that students are clear about where translation fits in the overall sequence from gene to protein. s you discuss codons, it may be helpful to make an analogy between using different combinations of the 4 nucleotides to code for each of the 20 different types of amino acids and using different combinations of 26 letters to make thousands of different words. One big difference is that each codon is exactly 3 nucleotides long, whereas the number of letters in a word is variable. There are 4 x 4 x 4 = 64 codons, compared to only 20 amino acids; as would be expected, there are multiple codons for each amino acid (with one exception which also is the start codon) and there also are three stop codons. s you introduce translation, you may want to explain why translation is more complex than transcription. In transcription, the shape and chemical structure of each mrn nucleotide matches the shape and chemical structure of the complementary DN nucleotide. In contrast, in translation, the shape and chemical structure of each amino acid does not match the shape and chemical structure of the corresponding mrn codon. This explains the need for: trn molecules, each of which has an anticodon that is complementary to an mrn codon, and enzymes that attach the correct amino acid for the anticodon in each type of trn. These enzymes and the trn molecules play crucial roles in translating from the nucleotide sequence in mrn to the amino acid sequence in proteins. The enzyme that binds each trn to the appropriate amino acid forms a covalent bond between the trn and amino acid. 3 Inside the ribosome there is a ribozyme (RN enzyme) that transfers the amino acid from the trn to the growing polypeptide chain. This ribozyme breaks the covalent bond between the trn in the P site and its amino acid and simultaneously forms a new covalent peptide bond between this amino acid and the next amino acid in the growing polypeptide chain. ( Ribosomes have three sites for trns, including the sites shown in the ribosome page used for modeling translation and a third site (to the left) where the trn that has lost its amino acid is located before it exits the ribosome. 3 simulation of this enzyme in action is available at 7

8 In humans, there are 48 different types of trn, compared to 61 different codons for amino acids in mrn. Some types of trn have anti-codons that are able to match with two different codons that have the same first two nucleotides but differ in the third nucleotide (both are codons for the same amino acid). The figure shows how a trn molecule folds into an upside down L shape. ( ) To encourage students to actively synthesize their own basic understanding of transcription and translation, we strongly recommend having your students complete questions 12 and 26 (on pages 4 and 8 of the Student Handout), perhaps as a homework assignment if you do not have time during class. If you feel that these questions will be too challenging for your students, we have several suggestions to help your students succeed. If your students have trouble learning vocabulary, you may want to precede questions 12 and 26 with questions that ask for definitions of the terms listed (or perhaps a matching question in which you provide your preferred definitions for these terms). You may want to review the animation of transcription ( immediately before the students answer question 12 and review the animation of translation ( immediately before the students answer question 26. s an introduction to these questions, you may want to provide concept maps for your students to complete (see ion_translation_lessonplan.pdf for an example). You could provide the beginning of a first sentence to help your students get started. It may be helpful to have your students try to answer each of these questions individually and then work in groups of 2-4 students to develop a consensus answer which each group would share with the whole class. fter class discussion of questions 12 and 26, we recommend that you have each student revise his/her answers to the question so he/she can consolidate an accurate understanding of transcription and translation. To ensure that students develop a good understanding of the basic processes of transcription and translation, this activity omits many complexities. For example, the Student Handout does not mention: the initiation and termination phases of transcription and translation since we have focused exclusively on the elongation phase introns, exons and splicing how polypeptides fold and may combine with other polypeptides to form proteins transcription produces multiple copies of mrn from a gene, and multiple ribosomes move along an mrn molecule, producing multiple copies of the polypeptide 8

9 differences in the rate of transcription of specific genes in different types of cells, corresponding to the differences in the types of proteins in different types of cells (e.g. hemoglobin abundant in red blood cells and the enzyme for making melanin abundant in melanocytes in the skin) a standard genetic code chart or codon wheel. (Our preference is to use the abbreviated chart on page 6 of the Student Handout, so students can concentrate on understanding the process of translation, and then, if desired, practice using the codon wheel in a separate activity. For example, in the analysis and discussion activity, "The Molecular Biology of Mutations and Muscular Dystrophy" ( students review transcription and translation, use a codon wheel to analyze different types of mutations, and evaluate which types of mutation result in the more severe Duchenne muscular dystrophy vs. the milder Becker muscular dystrophy.) If your students already have a good grasp of the basics of transcription and translation, you may want to include some of these additional complexities. Transcription and Translation Modeling Procedures We find that, at each step in the modeling procedure, you have to be very explicit in your instructions in order to prevent students from racing ahead in ways that undermine the learning goals. You may want to: demonstrate the steps in the modeling procedure require your students to check off each arrow head for each step in the modeling procedure and also answer any questions before moving on to the next step. You may want to view an animation which summarizes the modeling procedure (available at prepared by Erik Johnson, River Valley High School). To use this modeling activity to facilitate student understanding of how transcription takes place, students should add each nucleotide one at a time, mimicking the actual activity of RN polymerase. During transcription, some students will want to lay out all the mrn nucleotides and tape them together all at once; this is more efficient in getting the task done, but less effective in modeling and understanding the real biological process. Similarly, during translation, the students should mimic the actual function of the ribosome by bringing in one trn with amino acid at a time. sing the slots in the nucleus and ribosome pages helps to encourage students to do the modeling correctly. To help your students understand why RN polymerase adds nucleotides one at a time, you may want to point out that a typical protein has hundreds of amino acids so a typical mrn has hundreds or thousands of nucleotides. Have your students think about the problems that would arise if natural selection or a molecular biologist tried to design an enzyme that could simultaneously arrange and join together the whole sequence of hundreds or thousands of nucleotides in an mrn molecule. Similarly, to help your students understand why ribosomes add amino acids one at a time, you may want to have your students think about the problems of trying to design a ribosome that could simultaneously arrange and bond together the whole sequence of amino acids in a protein, especially considering that there are many thousands of different types of proteins in a cell. 9

10 Page 7 of the Student Handout has a diagram which shows the students how their model ribosome should look after the first few steps in modeling translation. The following diagrams show how the model ribosome should look during the next few steps. The line between the amino acids represents the tape which represents the covalent peptide bonds. additional nucleotides in mrn additional nucleotides in mrn This activity includes several different types of models of transcription and translation. model is a simplified representation of a real world phenomenon. Like all models, the models in this activity involve simplifications which help to clarify important points but also limit the accuracy of the models as representations of the actual complex biological processes. Different types of models serve different purposes for learning about and understanding the processes of transcription and translation. The flow charts on page 1 of the Student Handout provide a basic framework that provides a context for understanding the complexities that follow. The diagrams on page 2 and the bottom of page 5 show more specifics of how transcription and translation are accomplished in the cell. The recommended animations illustrate the dynamic nature of these processes. Finally, the actual modeling procedures help to engage students in actively mimicking and understanding these processes. We recommend that you discuss with your students the Crosscutting Concept, Structure and function, including Students model complex and microscopic structures and systems and visualize how their function depends on the shapes, composition, and relationships among its parts." 10

11 Sickle Cell Hemoglobin and Sickle Cell nemia This section of the Student Handout begins with a question that reviews transcription and translation. s you discuss question 27, you may want to review the example of albinism vs. normal skin and hair color, perhaps using the following illustrated version of the chart in question 27a. In this context, you can remind students that the sequence of amino acids determines how a protein folds and functions. 11

12 In this section of the activity, students analyze how transcription and translation of the beginning of the gene for the beta globin polypeptides in the hemoglobin tetramer protein. We ignore the gene for the alpha globin polypeptides; that gene is the same in normal and sickle cell hemoglobin. s discussed in the Student Handout, the lower solubility of nonpolar valine in the watery cytosol of the red blood cell (compared to the high solubility of ionic glutamic acid) contributes to the tendency of sickle cell hemoglobin to clump together in long rods inside the red blood cells. This difference in the solubility of amino acid 6 is crucial because amino acid 6 is in a key location on the outside of the hemoglobin molecule (labeled sickle cell mutation in the figure). The analysis of the molecular biology of sickle cell anemia provides the opportunity to discuss the Crosscutting Concept, Cause and effect: Mechanism and explanation, including understanding causal relationships by examining what is known about smaller scale mechanisms within the system. In the Student Handout, we summarize the effects of homozygous sickle cell alleles, which result in sickle cell anemia. Even in a person who has severe sickle cell anemia, most red blood cells are not sickled most of the time. The degree of clumping of sickle cell hemoglobin into rods varies, depending on factors such as differences in dehydration, oxygen levels in the blood, and multiple genetic factors. Dehydration increases the concentration of hemoglobin in red blood cells which increases the tendency of sickle cell hemoglobin to clump into rods. The resulting sickled red blood cells can block some of the small blood vessels, which can cause pain and organ damage (called a sickling crisis). n infection that induces vomiting and diarrhea can result in dehydration which can cause a sickling crisis. However, the causes of most sickling crises are unknown. The severity of sickle cell anemia in different individuals varies from relatively mild sickle cell anemia with few sickling crises and nearly normal health and survival to severe sickle cell anemia with frequent sickling crises, significant organ damage and early death. The majority of people with sickle cell anemia have an intermediate severity. One factor that contributes to variation in the frequency of sickling crises is that some people with sickle cell anemia spontaneously produce relatively high levels of fetal hemoglobin (which contains gamma globin instead of beta globin polypeptides), and fetal hemoglobin inhibits clumping of sickle cell hemoglobin. Hydroxyurea, which increases the production of fetal hemoglobin, is one treatment for sickle cell anemia. good summary of the medical aspects of sickle cell anemia, including symptoms, diagnosis and treatment is available at 12

13 n individual who is heterozygous for the sickle cell allele (called sickle cell trait) rarely has symptoms of sickle cell anemia because each red blood cell contains both normal and sickle cell hemoglobin and the normal hemoglobin generally prevents clumping of the sickle cell hemoglobin. thletic associations recommend testing for sickle cell trait and, for athletes who have sickle cell trait, taking appropriate precautions to prevent extreme exertion and dehydration in order to reduce the small but significant risk of exercise-related sudden death. Harmful health effects of sickle cell trait are rare, and life expectancy is not detectable reduced. Sickle cell trait has beneficial health effects in areas where malaria is prevalent; individuals with sickle cell trait have less serious malaria infections because the malaria parasite doesn't grow as well in their red blood cells. In discussing question 32, you may want to point out that our bodies are made up of roughly 100,000 different types of proteins and each protein is made up of hundreds or thousands of amino acids. Thus, there are many many opportunities for variation in proteins and phenotypic characteristics. Related Learning ctivities "Molecular Biology: Major Concepts and Learning ctivities" (available at is an overview that reviews key concepts and learning activities. Topics covered include basic understanding of the important roles of proteins and DN, DN structure and replication, and the molecular biology of how genes influence traits, including transcription, translation, and the molecular biology of mutations. To help students understand the relevance of these molecular processes, the suggested learning activities link alleles of specific genes to human characteristics such as albinism, sickle cell anemia and muscular dystrophy. Several possible follow-up activities are suggested, including "The Molecular Biology of Mutations and Muscular Dystrophy" (available at 13

14 Nucleus RN polymerase place where enzyme forms covalent bond between nucleotides RN nucleotide next RN nucleotide slot DN cytoplasm around the nucleus

15 Ribosome place where ribosome forms covalent bond between amino acids trn with amino acid trn with next amino acid slot codon next codon mrn

16 Beginning of hemoglobin gene - 8 sets Beginning of Hemoglobin ene Beginning of Hemoglobin ene Beginning of Hemoglobin ene Beginning of Hemoglobin ene Beginning of Hemoglobin ene Beginning of Hemoglobin ene Beginning of Hemoglobin ene Beginning of Hemoglobin ene C C T C C C T C C C T C C C T C C C T C C C T C C C T C C C T C

17 Second Part of mrn - 8 sets C C C Second Part of mrn C C C Second Part of mrn C C C Second Part of mrn C C C Second Part of mrn C C C Second Part of mrn C C C Second Part of mrn C C C Second Part of mrn C C C Second Part of mrn

18 RN neuclotides - 8 sets C C C C C C C C C C C C C C C C

19 trn molecules - 2 sets mino cid mino cid mino cid C C C C mino cid mino cid mino cid C C C C mino cid mino cid mino cid C mino cid mino cid mino cid C

20 amino acids - 4 sets Leucine Histidine Valine Leucine Histidine Valine Leucine Histidine Valine Leucine Histidine Valine Threonine Threonine Threonine Threonine Proline Proline Proline Proline lutamic cid lutamic cid lutamic cid lutamic cid