Unit 4: Cell Development and Replication, Part II: Gene Expression

Transcription

1 Name: Block: PKET 9 nit 4: ell Development and Replication, Part II: ene Expression Reading: hapter 9, plus 14.1 and 15.4 Date: Objectives: By the conclusion of this unit the student will be able to: 12. Define genes and explain their function and importance ( Explain the functions of DN, mrn, trn, rrn, and Proteins ( Explain what is meant by the genetic code, including the role of codons and anticodons ( List at least three functions that proteins have in cells ( List the structural differences between DN and RN ( Describe the process of RN synthesis during transcription ( Explain how the RN transcript is processed to become mrn ( Describe the process of translation ( Explain how proteins are transported and processed (post translational modifications( Describe the types of mutations (translation errors and how they can affect protein structure (9.7, Explain how all cells in an organism have the same DN but different cells manufacture different proteins and serve different functions (page 240, 14.1 Vocabulary: Transcription Translation Protein synthesis enetic ode Messenger RN Transfer RN Ribosomal RN Ribosome odon nticodon RN polymerase RN processing Initiation Elongation Termination Signal sequence Mutation Frameshift mutation Splicing Introns/Exons Promotor Transcription Factor Start and Stop codons oding strand Template strand Reading frame Point mutation Missense mutation Nonsense mutation entral Dogma 1

2 What%is%a%ene?%% % Figure'1:'Locating'a'ene' Define'gene:'' ' ' Figure'2:''Simplified,'ompletely'Fictional'hromosome'Map' ' Humans'have'23'pairs'of'chromosomes.''single'pair'is'shown'here.'' Why'pairs?'Because'one'set'of'genes'come'from'each'parent.' ' ' Relate'the'terms:'chromosome,'genes:'' gene'for'making'earwax' gene'for'eye'color' ' gene'for'hitchhiker s'thumb' gene'for'freckles' gene'for'dimples' ' ' Figure'3:'entral'Dogma'of'Molecular'Biology' ' rrows'in'this'diagram'show'a'transfer'of'information.'notice'that'proteins'are'the'final'product.'once' information'gets'into'the'form'of'protein,'it'cannot'get'out'again'' ' How'do'genes'code'for'life?''' 2

3 From%DN%to%Proteins%Web%Quest% % Log%on%to% questions%below.%% Optional:Foraquickreviewofthetopicswe vecoveredsofar,checkout %Tour%of%the% Basics.Hereyouwillfindquick,helpfultutorials: WhatisDN? Whatisagene? Whatisachromosome? Whatisaprotein? % Follow the links: Home Molecules of Inheritance RN the versitile molecule% 1.FillinthetablebelowtoexplainseveralsimilaritiesanddifferencesbetweenDNandRN. Similarities% Differences% Both%DN%and%RN%have % DN%has % RN%has % HowdoesthesingleBstrandednatureofRNallowforendlesspossibleshapesandfunctions? Molecules of Inheritance natomy of a ene 3.INYOROWNWORDS,describethefunctionofeachofthefollowingregionsofagene: % Promoter Switch(DNsequence Switch(Protein Startodon Exon Intron Stopodon 3

4 Molecules of Inheritance Proteins What is a protein% 4.Whatroledoreceptorproteinsplayinthesendingofnervesignalsthroughoutthebody? 5.Howdoproteinsrelatetotheuniqueshapeofnervecells? 6.Recallfromour ells unit:howdoesthefinishedproteinmigratetoitsultimatedestination? Whatorganellesareinvolved? Molecules of Inheritance Proteins Types of proteins 7.Matchthespecificproteintoitsfunction: Eggwhiteprotein;energysourcefordevelopingbird llowforcontraction(movementofmusclecells. luten B. Epidermal growth Foodsourceforgerminatingwheatplant factor (EF arryvessiclesaroundinsideacell. Myosin actin D. p53 PreventscellfromdividingwhenDNisdamaged E. ollagen Digestionofmilksugar F. DN Polymerase. Hemoglobin Strong,stretchyproteinfoundintendonsandligaments H. Ovalbumin I. ytochrome BuildsDNmolecules J. Lactase Transportsoxygeninredbloodcells K. Dyenin L. Insulin Energyproduction;partofelectrontransportchainin mitochondria Helpsdecreasebloodsugarafterameal;sugaristakenupbycells Woundhealing;initiatescelldivisioninskincells % % Home enetic Variation Test Neurofibromin ctivity in a ell 8.DescribethefunctionsofneurofibrominandtheRasprotein. 9.HowmightaDNmutationintheRasgeneortheNF1geneaffectthefunctionofthese proteins?(bespecific. 4

5 Home Molecules of Inheritance Proteins Prions % 10.Whatisaprion? 11.iveafewexamplesofprionBrelateddiseases. 12.Howdoprionscausespongiformdiseases?(Youwillfindthisinformationbywatchingthe slideshow. Home Molecules of Inheritance The Time of our Lives 13.WhatareircadianRhythms? 14.Whatpartofthehumanbrainisinvolvedin tellingtime?whatexternalcuesdoesthisbrain regionuse? 15.$$Per$and$tim$genescodeforPERandTIMproteinsinfruitflies.HowdothesePERandTIM proteinsworktogetherwithlkandyproteinstoserveasaninternalclockforthefly? twhattimesarelkandyproteinsfoundinthecell? WhatdoLKandYproteinsdowhentheyarefunctioning? twhattimesareper/timproteincomplexesfoundinthecell? WhateffectdoesthePER/TIMcomplexhaveontheLKandYproteins? 16.Ontheaxesbelow,graphtherelativelevelsofbothproteincomplexesthroughouta24Bhr Protein concentrations Min max period Y/LK complex PER/TIM complex 12am 4am 8am 12pm 4pm 8pm 12am Time 5

6 Biology Honors Why? ene Expression Transcription How is mrn synthesized and what message does it carry? DN is often referred to as a genetic blueprint. In the same way that blueprints contain the instructions for construction of a building, the DN found inside the nuclei of cells contains the instructions for assembling a living organism. The DN blueprint carries its instructions in the form of genes. In most cases the genes direct the production of a polypeptide, from which other more complex proteins, such as enzymes or hormones, may be constructed. These polypeptides and other molecules run the organism s metabolism and, in multicellular organisms, dictate what each cell s job is. So, what is the language of these instructions and how are they read and decoded by the cellular organelles? This activity will focus on the decoding of genes in eukaryotes. Model 1 Transcription 5 3 hromosome from a nondividing cell Template (reading strand Inside the Nucleus T RN polymerase and transcription factors Outside the Nucleus Direction of synthesis rowing strand of pre-mrn Free RN nucleotides Nuclear membrane 5 3 6

7 1. onsider the eukaryotic cell in Model 1. a. Where in the cell is the DN found? b. Where in the cell does transcription take place? 2. Refer to Model 1. a. What polymer is synthesized during transcription? b. What monomers are used to construct this polymer and where are they found? 3. ccording to Model 1, what enzyme is required for transcription? (Hint: Think about how enzymes are named. What ending is used for enzyme names? 4. Refer to Model 1. a. What is the base-pair rule for a DN strand matching an RN strand? b. ompare this base-pair rule with that of two DN strands. 5. Which strand of the DN contains the blueprint for the pre-mrn? 6. onsider Model 1. a. In which direction is the DN molecule read? b. The DN strand and pre-mrn strand are anti-parallel. With this in mind label the 3 and 5 ends of the pre-mrn strand in Model 1. c. In which direction is the pre-mrn molecule constructed? 7. Before printing presses were available, books had to be transcribed in order to share the information in them. onsider the definition of transcription and explain why the process in Model 1 is described using that word. 7

8 Biology Honors Model 2 mrn Processing Leading intron Exon Start codon Intron Pre-mRN Exon Inside the Nucleus Intron Exon Intron Outside the Nucleus 3 Methyl cap mrn Nuclear pore Poly- tail ompare the pre-mrn to the mrn leaving the nucleus in Model 1. a. What has been removed from the pre-mrn to make it into mrn? b. What has been added to the mrn that was not present in the pre-mrn, and where on the mrn strand are the additional items located? 13. Identify the structure through which the mrn leaves the nucleus. 14. The nucleotides on the mrn will be read in the next step to producing a polypeptide. What sequence of bases indicates the starting point for the polypeptide blueprint? 15. The m in mrn is short for messenger. Why is this molecule called messenger RN? 4 POIL ctivities for P* Biology 8

9 Read This Introns are sections of pre-mrn that are noncoding. That is, they don t provide useful information for the production of the polypeptide being synthesized. There is evidence that suggests these introns allow certain sections of DN to code for different polypeptides when different sections are removed. The removal of specific sections is triggered by a signal response in the cell. The portions of the pre-mrn that remain are called exons. The methyl cap (sometimes called the TP cap or 5 cap helps the mrn molecule move through the nuclear pore and attach to a ribosome, its final destination. mrn is a shortlived molecule. Once in the cytoplasm the mrn will be subject to exonucleases that immediately start removing individual nucleotides from the 3 end of a nucleic acid. The individual mrn nucleotides will then be free to be used again during the process of transcription. 16. The human genome contains about 25,000 genes and yet produces about 100,000 different polypeptides. Propose an explanation of how this is possible. 17. sing the information in the Read This box, develop a hypothesis to explain the advantage of the poly- tail added to the 3 end of the mrn. 18. Different mrn molecules can have poly- tails of different lengths. onsidering the purpose of adding the poly- tail (from the previous question, why are some tails longer than others? Justify your answer using complete sentences. 19. Summarize the steps of transcription. 9

10 Why? ene Expression Translation How do cells synthesize polypeptides and convert them to functional proteins? The message in your DN of who you are and how your body works is carried out by cells through gene expression. In most cases this means synthesizing a specific protein to do a specific job. First, mrn is transcribed from the DN code. Then, the mrn sequence is translated into a polypeptide sequence. Model 1 odons Model 2 Translation mino acid la His ncharged trn His harged trn Met Ser Leu Met Leu la Ser nticodon Ribosome 5 3 mrn Initiation Elongation Met Leu la Ser His H 2 O Release factor Termination 7. Refer to Model 2. a. What are the three stages of translation? b. Define each of the terms used in your answer to part a as they are used in everyday language. 10

11 8. ccording to Model 2, when the mrn leaves the nucleus, to which cellular organelle does it attach? 9. The mrn attaches to the organelle at the sequence. What is the significance of this sequence of nucleotides? 10. Describe the movement of the ribosome as translation occurs. Read This The ribosome is a large complex of ribosomal RN (rrn and proteins. It consists of two subunits. The smaller subunit binds to the mrn strand and the larger subunit holds the trn molecules in place while the covalent peptide bond is formed between the amino acids. Several ribosomes can attach to an mrn molecule simultaneously. This allows for many polypeptide chains to be synthesized at once. 11. The trn molecules in a cell are short sequences of nucleotides (about 80 bases that contain an anticodon and carry a specific amino acid. a. Find the trn in Model 2 that is carrying the Histidine (His. What sequence of nucleotides makes the anticodon on this trn molecule? b. What codon on mrn would match this anticodon? c. Verify that the codon you wrote in part b codes to Histidine by looking at the table in Model 1. d. What anticodon would be found on a trn molecule carrying lycine (ly? (Note: There are several correct answers here. 12. The t in trn is short for transfer. In a complete sentence, explain why this molecule is called transfer RN. 4 POIL ctivities for P* Biology 11

12 13. During elongation, how many trn molecules are held in the ribosome at the same time? 14. What will happen to the unattached trn once it has delivered its amino acid? 15. Describe two things that occur during termination as illustrated in Model Explain how the term translation applies to the synthesis of proteins from DN instructions. 17. The codons of mrn are a set of three nucleotides with four possible bases in combination. a. Show mathematically that there are 64 permutations possible when three bases are used. b. Show mathematically that two bases as a codon would not be sufficient to code for all 20 known amino acids. 12

13 Biology Honors Regulating ene Expression WHIH PROTEINS? HOW MNY OF EH? ene expression is controlled at many different stages along the way from DN to RN to protein It s important to have exactly the right amount of each protein for a cell to function normally. Different cells are specialized and must produce different proteins. POST-TRNLTIONL PROESSIN 1. New polypeptides must be folded Functional proteins have 1 o, 2 o, 3 o and 4 o structure The translated amino acid sequence is 1 o The new polypeptide is not functional, yet. WHT IDES FOLDIN? 2 o is spontaneous due to H-bond formation within backbone. hemical properties of amino acids 3 o structure haperone proteins help with tertiary and quaternary levels of folding 2. Proteins need modifications: new polypeptide may be cleaved, bound to other polypeptides and/or modified by the addition of functional groups. 3. Proteins must be delivered to their site of action: secreted by exocytosis, or delivered to membranes, cytoplasm or nucleus. 5 signal sequence 13

14 REVIEW: HOW PROTEIN IS BORN hromatin remodeling Transcription mrn processing mrn stabilization to some degree Translation Post translational modification Delivery to site of action * Proteins, like mrns have different lifespans. final factor in gene expression is how long the protein lasts PROTEOME >> ENOME enome: ll of the DN in a cell of an organism. Every cell in an organism has a nearly identical genome. Proteome: ll of the proteins in an organism. Humans have ~ 20,000 genes, but many times more proteins The old rule was One ene One Protein New Rule: One gene one, two, seven... many proteins PROTEOME >> ENOME Review Questions: 1. How do cells differentiate (specialize, when all cells in your body have the same exact DN? 2. What would happen to the level of gene expression in each of the following situations? The mature mrn is rapidly broken down after it has been synthesized. Transcription factors and histone modification allow for many mrn copies of a gene. protein resists being broken down in the cytoplasm, which results in a long lifespan for this protein. 3. What are chaperone proteins? What do they do? 4. How does the production of a cytoplasmic protein differ from production of a hormone? How does the cell know where to send these different proteins? 5. Describe two ways that a single mrn molecule may be used to build multiple different proteins. 14

15 Transcription and Translation Homework 1. Define codon and anticodon: Directions: sing your mino hart (Pink Sheet, fill out the organizer on page sing the sequence of the DN strand in the second column as a template, write the letter for the corresponding nucleotide in the mrn. 2. From position 11 thru 76, write the letter for the corresponding nucleotide in the trn anticodon. 3. Translate the codons in the mrn column into amino acids. Enter the three letter amino acid code in the final column. nalysis: 1. Why do the trn and amino acid columns start at position 11 and end at position 76? 2. Rewrite the first 10 nucleotides of the DN sequence in a straight line below. bove it write the letters of the nucleotides for the opposite DN strand. What is the relationship between the mrn sequence and the sequence of the DN strand that is not copied? 3. What is the relationship between the sequence of the trn anticodon and the sequence of the DN strand that is copied? 15

16 Mutations 4. hange the at position 31 to an. What effect does this change have on the amino acid sequence? What effect is this change in the DN likely to have on the protein? 5. Now change the same to a. What effect does this change have on the amino acid sequence? What effect is this change in the DN likely to have on the protein? 6. Now change the at position 37 to a T. What effect does this change have on the amino acid sequence? What effect is this change in the DN likely to have on the protein? STOP HERE. omplete the Mutations ard Sort ctivity before moving on. sing your newly filled-in mutations chart, categorize the mutations you categorized above and explain your answer. The mutation described in 4: The mutation described in 5: The mutation described in 6: 16

17 DN strand to Position be copied T T T T T 21 T 22 T 23 T T T T mrn trn anticodon amino acid 17

18 DN strand to Position be copied 44 T T T T T T T T T T 81 T T 84 T mrn trn anticodon amino acid 18

19 Mutations hart 19

20 ene, Proteins, and Disease dapted from BSS: The Human pproach, page Introduction: You have studied how a DN molecule can act as a template for its own replication. enetic information is used to build and maintain the physical characteristics of an organism. But how is the information in DN used within the cell to produce those characteristics? How is the message in the DN nucleotide sequence translated into a physical characteristic? In this activity you will model the relationship between DN and RN for a particular trait. You will also identify the connection between a DN sequence and the end protein product. The gene you will study is that for sickle-cell disease. (1 pt Transcription Translation Process and Procedure Part 1: Learning about Sickle-ell Disease 1. Read the attached Need to Know part 1 section on Hemoglobin and Red Blood ell bnormalities in Sickle-ell Disease (later in the packet p Read the essay Incomplete Dominance later in the packet (p 8. What might the phenotype be for a person with the genotype Hb Hb S? (1 pt 3. Discuss and record answers to the following questions. (0.5 pt each a. What medical symptoms might a person with sickle-cell disease experience? b. What problem in shape and behavior the red blood cells causes these symptoms to happen? c. What problem in the behavior of the hemoglobin molecules is associated with these changes in an individual s red blood cells? d. Think back to your knowledge of DN structure. What might be the molecular basis for the physical characteristics of sickle-cell disease (in other words what makes one person s DN for this gene different from another person s DN? 20

21 4. setheinformationgatheredto2illinthegenotypeandsections(6,(7,(8,(and(9ofbothpartsof yourseparateene(expression(planner.(don tjustusedrawingswritesomethingtoond takenoteof normal and sickle atthetopofthepagethesearethephysicalresultsofthe sicklefcellgene.nowlet slookattheunderlyingmolecularcauseforthesephysicaltraits.et astampbeforemovingon. Part 2: Modeling Transcription formation of mrn To begin this section, you must show the teacher you gene expression planner with parts 6, 7 and 8 filled in. 5. Write out the complimentary strand of DN using the sequence below. et a stamp before moving on to step 6. (1 pt ene: T T T omplimentary DN Strand: 6. The formation of an mrn is very similar to the process of DN replication. The enzyme RN polymerase opens up the DN double helix and starts building a new complementary strand. However, unlike DN replication, which uses both strands, RN polymerase only uses one strand of DN, called the template. lso, the new strand is made of RN nucleotides instead of DN nucleotides. 7. se the gene strand above as a template to write out a single mrn molecule. (The RN base uracil replaces the DN base thymine. fter RN polymerase forms the mrn strand, it detaches from the gene strand and the two DN strands reconnect. Remember - the DN molecule LWYS remains in the nucleus. Now the DN is safe in the nucleus and RN can go to the cytoplasm to assist in making protein. Record the sequence of your mrn strand in the space below. et a stamp before moving on to step 9. (1 pt ene: T T T mrn Strand: Part 3: Examining the DN sequence of Hemoglobin 8. Below are the sections of the DN sequences of a normal hemoglobin gene and the mutated gene that causes Sickle-cell disease. The sequences for these have been written in box 2 of your ene Expression Planner. In box 2, write the complementary DN sequence. Normal ene TTTT Mutated ene TTTTT 21

22 9. On your planner (both pages, in box 2, circle or draw an arrow to indicate the nucleotide(s in the sickle-cell sequence that differs from those in the normal sequence. 10.In(box(3,transcribethemessageintothemRNsequence.sethecomplementarysequence thatyourecordedreferbacktoyourprocedurefrompart2.howdidyouformthemrn there?dothesamethinghereheckwithyourteacherbeforemovingontothenextstep. 11.Refer to the genetic code diagram handout. se the table to determine the sequence of amino acids that would result from translating the mrn that you built from your complementary DN sequence. Put your resulting amino acid sequence into box 4 on your gene expression planner. To complete this step, you will need more information about the genetic code and how mrn is translated into protein. Refer to your notes from Section III of the reading guide (Textbook 12.3 and the genetic code chart below. 12.In box 4, draw a circle or arrow to indicate the amino acid(s in the sickle-cell protein sequence that differs from those in the normal sequence. 13.Read the attached Need to Know part 2 section (packet p 10 on The Sequence of mino cids Determines the Hemoglobin Molecule s Shape. se what you learn to fill in position 5 on your planner, also use what you have learned to add to positions 6, 7, and 8 if necessary. gain don t just draw se words to describe the differences 22

23 nalysis Questions (discuss with your groups while you answer these 1. How does the shape of the protein cause the symptoms of sickle-cell disease? 2. What ultimately controls the shape and function of proteins? 3. Explain how a mutation in a DN sequence affects a physical trait. How is the mutated message transferred through the process of transcription and translation? 4. The mutations you have looked at in this activity all occurred in the original DN sequence. How do you think they got there? 5. an you think of other ways mutations might occur? In other words, how might a protein be mutated if the DN is not? 6. The amino acid code is said to be redundant but not ambiguous. Look at your wheel and hypothesize what this means. Why might this be advantageous to life? 23

24 NEED TO KNOW PRT 1 Hemoglobin and Red Blood ell bnormalities in Sickle-ell Disease Each year, about one in 625 frican merican children is born with sickle-cell disease. This disease is caused by an abnormality in hemoglobin. Hemoglobin is the protein in red blood cells that carries oxygen to body cells. When the oxygen supply in the blood is low, these abnormal hemoglobin molecules clump together. Normal hemoglobin molecules remain separate. Figure 1 shows the difference between the behavior of sickle-cell hemoglobin and normal hemoglobin under conditions of low oxygen. In a person with sickle-cell disease, the clumping of the hemoglobin molecules at low oxygen levels causes the red blood cells to become long and rigid like a sickle instead of remaining round and flexible (Figure 2. That change in cell shape causes a variety of problem in the body. For example, as cells become sickled, they tend to block small blood vessels (Figure 3. This causes pain and damage to the areas that do not receive an adequate blood supply. The long-term effect of repeated blockages may permanently damage a person s internal organs. This includes the heart, lungs, kidneys, brain, and liver. For some people, the damage is so severe that they die in childhood. With good medical care, however, many people with sickle-cell disease can live reasonably normal lives. Sickle-cell disease is associated with the genotype Hb s Hb s. People who have this condition have two abnormal genes, one inherited from each parent. normal low oxygenlevel oxygenlevel normalhemoglobin normal low oxygenlevel oxygenlevel sicklehemoglobin Figure'1.'omparison'of'the'behavior'of' normal'and'sickle;cell'hemoglobin' under'condi?ons'of'low'oxygen. Figure'2.'omparison'of'the'shapes'of'abnormal'sickle;cell' (le6'and'normal'(right'red'blood'cells'under'condi?ons' of'low'oxygen. Figure'3.'omparison'of'movement'of'normal'(le6'and'sickle;cell' (right'red'blood'cells'through'blood'vessels. 24

25 NEED TO KNOW PRT 2 The Sequence of mino cids Determines the Hemoglobin Molecule s Shape Inside the environment of a red blood cell, a molecule of normal hemoglobin consists of four protein chains folded into a globular shape. The molecule remains folded in this manner because attractive forces occur between amino acids in different parts of the molecule s protein chains. change in the amino acid sequence can take place because of the single nucleotide mutation in the hemoglobin gene. This, however, has no effect on the molecule s overall shape when oxygen levels are normal. For that reason, sickle-cell hemoglobin behaves just like normal hemoglobin under such conditions. When oxygen levels are low, however, the change in a single amino acid alters the attractive forces inside the molecule. That causes molecules of sickle-cell hemoglobin to assume a different shape from those of normal hemoglobin. s Figure 4 shows, it is the change in molecule shape under low oxygen levels that causes sickle-cell hemoglobin to form the rigid rods characteristic of the condition. Don't forget to look at the figure and read the figure caption DON T FORET TO RED THE PTION BELOW Figure 4. Normal and sickle hemoglobin. The difference in behavior of sickle-cell hemoglobin is related to a change in shape that takes place at low oxygen levels. This shape change results from the amino acid valine replacing a glutamic acid. (a Molecules of normal hemoglobin will not associate with each other. This is because the bulge created by the glutamic acid is too large to fit into a pocket in another hemoglobin molecule. Molecules of sickle hemoglobin, however, will associate with each other. This is because the bulge created when valine replaces glutamic acid is small enough to fit into the pocket. (The size of the pocket does not change. (b Molecules of normal hemoglobin remain in solution, even under conditions of low oxygen. In contrast, molecules of sickle hemoglobin associate together to form rigid cells under low oxygen conditions. 25

26 DN Practice Questions Part I: Fill-in-the-Blank 1. Transcription occurs in/at the (what part of the cell?, and is when single-stranded DN is used as a template with which to build. Transcription is catalyzed by an enzyme called. 2. Translation occurs in/at the (what part of the cell?, and is when mrn is used as a template with which to build. 3. If you had 999 nucleotides (assume no non-coding sequences, you would expect a protein sequence of (how many? amino acids. Part II: Word Relationships In each of the following sets, one word does not belong. ircle the one that doesn t belong, and explain why it doesn t belong. 4. deoxyribose, phosphate, DN, uracil 5. amino acid, polypeptide, protein, transcription 6. ribose, RN, thymine, adenine 7. -T, -, -, - Replace the underlined definition with the correct vocabulary word. 8. The attraction between nitrogenous bases is the force that holds the two strands of DN together into one double helix molecule. 9. Each combination of three nucleotides on messenger RN specifies a specific amino acid that is to be placed in the polypeptide chain. 10. The RN that carries amino acids to the ribosomes is a single strand of RN that loops back on itself. 11. s a ribosome moves along a strand of messenger RN, each codon is paired with its three nucleotides on transfer RN that are complementary to the three nucleotides on messenger RN. Part III: Short nswer 12. s a scientist, you locate the following DN sequence. DN Sequence: TTT a. What will be the corresponding mrn sequence? b. What amino acid sequence would be expected to form from this mrn? 26

27 c. Imagine that a mutation caused the second amino acid to instead be sparagine (sn. (ll other amino acids remained the same. What kind of mutation do you hypothesize to be involved here? Why? Where exactly in the DN sequence do you think the mutation occurred? d. Imagine that a different mutation (of the original mrn sequence written in part b caused the second amino acid to instead be lutamine (ln, the third to instead be lanine (la, and the fourth to instead be Proline (Pro. What kind of mutation do you hypothesize to be involved here? Why? Where exactly in the DN sequence do you think the mutation occurred? Part IV: Matching 13. Match each description below to the correct nucleic acid molecule(s. (nswers may be re-used. Some questions will have more than one correct answer. stable molecule that stores genetic information. Remains protected in the nucleus. long with proteins, this molecule is used to build ribosomes. This messenger molecule brings a copy of a gene to the ribosome. This molecule is made during transcription. The monomers of this molecule are nucleotides. mutation in this molecule may be passed on to offspring. mutation in this molecule may result in production of a non-functional protein. single-stranded nucleic acid. nucleic acid in which complementary base pairing occurs. This molecule contains the sugar deoxyribose. Nitrogenous bases include cytosine and uracil. a.mrn b.trn c.rrn d.dn 14. Match the descriptions below to the correct processing or modification event. (nswers may be reused. Some questions will have more than one correct answer. Modification made to mrn before it leaves the nucleus; protects mrn molecule from being broken down by enzymes. The first few amino acids in the polypeptide act as a message, telling the cell where the protein should be delivered. One primary transcript (pre-mrn can be used to make multiple different proteins. haperone proteins assist with this as a polypeptide is being built. Expression of a gene is increased because more copies of its protein product accumulate in the cell. a. alternatesplicing b. poly7tail c. 5 cap(methyl guanine d. proteinfolding e. 5 signalsequence f. life7spanofmrn molecule g. life7spanof proteinmolecule

28 ene Expression Summary: Label each letter in the diagram with the following terms: anticodon mrn polypeptide codon amino acid ribosome trn 28

29 ut$outpages Objective13: Objective14: 29

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31 30 ut$outpages Objective16: Objective17:

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33 ut$outpages Objective18: Objective19:Translation 31

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35 32 ut$outpages OverviewofProteinSynthesis(Objectives17,19:

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37 Biology Honors ut$outpages Objective20:Post<translationalmodifications