University:
Campbell University
Course:
BIOL 342 | Genetics
Academic year:

2023
Views:

118

Pages:

10
Author:

Fletcher Wallace

From Gene to Protein - Transcription and Translation' How do genes influence our characteristics ? A gene is a segment of DNA that provides the instructions for making a protein. Proteins have many different functions that influence our characteristics. This chart shows an example. Gene in DNA -» Protein -» Another version of the gene provides instructions to make defective protein enzyme. -» JIBE Si -> One version of a gene provides instructions to make normal protein enzyme. Characteristic *fmJ Kwr —> * Normal enzyme makes the pigment molecule in skin and hair. Defective enzyme does not make this pigment F . Normal skin and hair -> color -» molecule. . :! Albinism ( very pale skin and hair) 1 How can a gene determine whether a person has albinism? (Give a molecular explanation.) ° cjjUX ; C^ — o vr O _OVvVJ6 - AZM^LV AjlJ ( CCMOAC VVVOKJ L HVQ. " WlO \ 'A How does a gene provide the instructions for making a protein? A two-step process: : DNA The first step is transcription of the gene in the DNA. Transcription produces messenger RNA (mRNA). i TRANSCRIPTION / ^ mRNA The second step is translation of the mRNA molecule. Translation produces proteins. TRANSLATION " —^iud.^. ,5 Cytoplasm i Protein 2a . Fill in the blanks in this figure to label the DNA, mRNA and protein molecules. 2b. DNA and RNA are polymers of nucleotides. The four nucleotides in DNA are A, T, four nucleotides in RNA are A, lv\ OAIA Transcription tp W • ti W IS! Mi1IM [SII M C . and (~7 . The . ( and (A 2c. A protein is a polymer of amino acids. Draw a circle around the amino acid Gly ( glycine ) in the protein. Wtfflpf r Translation i- 3a. During transcription, the sequence of nucleotides in a gene in the DNA is copied to a corresponding - C cfjLQ in mRNA. sequence of 1WC: ( ; \ TcA 3b. During translation, the sequence of nucleotides in mRNA determines the sequence of Q. WVl AD CLC,i in the protein. The sequence of amino acids determines the structure and function of the protein. rJK t . 4a Which process takes place in the nucleus ? . translation transcription 4b Explain why this process must occur in the nucleus. DMA fS \ oc_ofatxl kjL-'XJL Transcription . 5 Why does a cell need to carry out transcription in order to make a protein? \S +o o ^° { jLaAJt VKJL- ' ; wicucb. in ordjux 4T> l 0-A/ \A C -£LJCM- bkx (M \ooSo WVJL AVJ-'&k so CO , pov^ 6. In this activity, you will model how a cell carries out transcription and translation to make the , ' ‘ beginning of the hemoglobin molecule. What type of molecule is hemoglobin? v\ During transcription, the enzyme RNA polymerase: • separates the two strands of a DNA • double helix * ‘ ncorr ck ^ • . do&i U‘s uses a gene in one DNA strand as a guide to make an mRNA molecule. * r RNA polymerase jf % 1 1 jg I I I . 7 In the figure: - Write enzyme next to the name of the enzyme. - Trace the outlines of the DNA molecule. RNA polymerase adds one nucleotide at a time to the growing mRNA molecule. Each DNA nucleotide in the gene is matched with a complementary RNA nucleotide which has a matching shape and charge distribution. RNA nucleotides •i • cm : .4 rum 11 i to c m r u c c C\ A > To model the process of transcription, your group will need a page showing an RNA polymerase molecule inside a nucleus, a paper strip showing a single strand of DNA labeled "Beginning of Hemoglobin Gene", RNA nucleotides and tape. One of you will be the RNA polymerase. Another group member will be the cytoplasm which surrounds the nucleus and supplies the ' nucleotides which are used to make the mRNA molecule. ' > RNA polymerase: Insert the "Beginning of Hemoglobin Gene" DNA molecule through the slot in the RNA polymerase diagram so the first two nucleotides of the gene are on the dashes labeled DNA. Your RNA polymerase should look like this figure. ( Note: A real RNA polymerase molecule and DNA and RNA nucleotides are much smaller than the nucleus.) i 'Y fM+i f y i v i p s f e y s l OfriwttiJtjp Si •Tr «inV.iI,:.»s?i. (JJ ' Q< * Q Ur : j M!3‘. ^ .i •• •' I: v. i r ‘ * W1» •t ' r .: » VIVNV V*»^ ••*iv v * * » V " yzx . <2 r • h- r- - * vvw "r w^ 1 IM v*'# '" * ' 1 ^'HlW V M —*• > > r -: ; i . * *** » • Nucleus SF i k polymerase % as ft tsm &m • w ere e syme forms Vcovalentbond ^ between ^ nucleotides vv ww II > Cytoplasm: Use the base-pairing rules to choose > an RNA nucleotide that is complementary to the first DNA nucleotide. Give this nucleotide to the RNA polymerase person. RNA polymerase: Put the first RNA nucleotide in the box labeled RNA nucleotide. > Cytoplasm: Give > > the next RNA nucleotide ( complementary to the next DNA nucleotide) to the RNA polymerase person. RNA polymerase: Put this nucleotide in the box labeled "next RNA nucleotide". Join the two RNA nucleotides together with transparent tape; the tape represents the covalent bond between these two nucleotides in the growing mRNA molecule. Then, move the DNA molecule and the mRNA molecule one space to the left. these last two steps as often as needed to complete transcription of the beginning of the hemoglobin gene, adding one nucleotide at a time to the mRNA molecule. Repeat WhaJr /s /Ai rnfhjj 4 S&uovici a i 7tTO/rtSC' Xs jhd CM rJcAuhj r, T , ( 6 r 10. The first column of this table describes DNA replication. Fill in the blanks in the second column to summarize the differences between DNA replication and transcription. Transcription DNA replication 1 The whole chromosome is replicated. 3ex )& is transcribed. mRNA is made. DNA is made. DNA is double-stranded. -stranded. mRNAis RAJA polymerase is the enzyme which carries DNA polymerase is the enzyme which carries out DNA replication. out transcription. T = thymine is replaced by _ so A in DNA pairs with T = thymine is used in DNA, so A pairs with T in DNA. = uracil in RNA, in mRNA. . 11 Fill in the blanks to describe the similarities between transcription and DNA replication. Both transcription and DNA replication produce nucleic acids which are polymers of A.u/ ieoWlcs, ( C, G, A, and T or U). Both processes depend on a 1^ Vi dP . at a time To determine which nucleotide is added enzyme which adds one Du ^, * 0 next, both transcription and DNA replication use the nucleotide sequence in a bft.Se,- paAn AG the strand and rules. . 12a. Fill in the blanks to label each type of molecule in the figure. 12b. Name the process shown in the figure and explain how this process occurs. Include in your answer each of the molecules shown and these words and phrases: gene, base-pairing rules, one at a time . P r? ( r i $0Y -/Wylotfo#- jpo£ui - V '1 ' routed OLctd oYlt riuC' ljLo/ cA/ y' ' Afou Ao WlaJu a&- & MA.' r y&cAo - a m 4 Translation . 13 To show how translation follows transcription, fill in the blanks and box in this figure. Sene fn DNA m i How can four different types of nucleotide in mRNA provide a different code for each of the 20 different types of amino acids in proteins ? The answer is that the mRNA code for each type of amino acid is a sequence of three nucleotides called a codon. l m Transcription : I CoclM 14. In the figure, circle the mRNA codon that codes for the amino acid Gly ( glycine ). 1 Jiis i< A Translation requires two types of RNA: mRNA and transfer RNA = tRNA . tRNA molecules bring the correct amino acid for each codon in the mRNA. There are multiple different types of tRNA, each with a different anticodon. Each tRNA anticodon has three nucleotides that are matched by the base-pairing rules to the three nucleotides in the mRNA codon for a specific amino acid. . 15 What is the tRNA anticodon for the amino acid Gly (glycine) ? 16. For each type of tRNA, there is a specific enzyme that attaches the correct amino acid for the anticodon in that tRNA. These enzymes are needed for step ^ in the figure below. (1/2/3/4) 0 Translation takes place in ribosomes ( tiny structures inside cells ). Inside the ribosome, a codon in an mRNA molecule is matched by the base-pairing rules with an anticodon in a tRNA ( step 3). This tRNA brings the next amino acid to be added to the growing protein molecule. Translation . 1 tRNA and amino acids float freely in cytoplasm /o0 mmm 4. Amino acids are joined together to make a protein . . 17 In the ribosome, circle a codon in the mRNA and the complementary anticodon in a tRNA molecule. 2. Enzymes bind each tRNA to the appropriate amino acid for that tRNA‘s anticodon isii; . WB m S ft f fl l|8M|BBly 3. Using the base-pairing rules, each mRNA codon is matched with the anticodon in a tRNA The tRNA brings the right amino acid for that mRNA codon. mRNA Each amino acid is joined to the previous amino acid in the growing protein molecule ( step 4). . . ^ ribosome The ribosome moves along the mRNA, adding one amino acid at a time to produce the protein coded for by the mRNA. 18 Use an arrow to show where the next amino acid will be added to the growing protein molecule. . 19 What part of translation depends on the base-pairing rules ? CocAoH sTY \ CcW^ 6S CLtA Vl'cocitD / Translation Modeling Procedure In this section you will simulate the steps in translation to produce the beginning of a hemoglobin protein. One of you will be the ribosome, and another will be the cytoplasm. > Preparation To model translation, you will need a page showing a ribosome, tRNA molecules, amino acids, the mRNA you made during your simulation of transcription, and a strip labeled "Second Part > ofmRNA". > Cytoplasm: Tape the CUG end of the mRNA you made to the ACU end of the Second Part of mRNA strip. . 20 For tRNA to do its job, each tRNA molecule must be attached to the correct amino acid that ' corresponds to the anticodon in that type of tRNA. To know which amino acid should be attached to eacmtRNA molecule, use the base-pairing rules to complete this table . Amino acid Anticodon in tRNA molecule that carries this amino acid mRNA codon amic acid (Glu) Valine ( Val) GhC GWC CAc CUG GAG GUG Proline Leucine ( (Pro) Threonine (Thr) Histidine (His) UGA 6uA A A' JSACT ecu Cytoplasm: Use this table to matplfeach model tRNA molecule with the correct amino acid for > that type of tRNA. Tape the fnino acidTothe tRNA very lightly, because they will only be joined temporarily and wiffsoon separate. ^ Note: Each mod KRNA molecule only shows the three nucleotides of the anticodon and the ^ the amino acid. A real tRNA molecule has, many more nucleotides. Similarly, a binding siteidr s' has. real mRI A molecule has many more nucleotides than your strip V . . A n\ ^ X . X 21 You. arrange the amino acids in the correct sequence; then he tapes together all six amino acids. carry out Ex- lain why this would not be a good simulation of the actual sequence of steps used to X . (Hint: See page 5.) - ^ Atranslation 1 T}\A^.O VI i AjL - PhD )iUjL ~ C_ * 6 Modeling the Steps in Translation > > > Ribosome: Insert the mRNA through the slot in the model ribosome, with the first three nucleotides of the mRNA in the " codon " position and the next three nucleotides in the "next codon" position. Cytoplasm: Use the base-pairing rules to supply the tRNA that has the correct anticodon to match the first codon in the mRNA. Ribosome: Place this tRNA with its amino acid in position. Your model ribosome should look like this: Ribosome place where ribosome forms covalent bond between amino acids o -t Valine IliMJ I Ip tRNA with next amino acid slot m pus? in m ; iHl “* * \ % . . \ ylVrAV VAVMVWWAV<\TMVVAVWV/ ' ^ VSMWNWmHM 1 codon next codon In mRNA~ . "* i mRNA . 22 In the above diagram, put a rectangle around the anticodon in the tRNA. Use an arrow to indicate the amino acid. > > > > Cytoplasm: Supply the tRNA position. that has the correct anticodon to match the codon in the "next codon " Ribosome: Place the tRNA in position. Tape the two amino acids together to represent the covalent bond between these two amino acids. Detach the amino acid on the left from its tRNA. Ribosome: Move the mRNA and matching tRNAs with amino acids one codon to the left. Release the tRNA on the left to the cytoplasm. Repeat these three steps until you have attached all six amino acids to form the beginning portion of the hemoglobin protein. u ** J ( lAjkctA / 5 rU Hru / U eutot / LO rf 23. Why does axell need tRNA to makers protein? Explain the function of tRNA and how tRNA and mRNA work together to put the right amino acids in the right sequence as the protein is made. i\ brf /vop ' amWio CD cl Ao fkc m CLC\ ~ frt K / \$ /T IOIAJCA/ etc n . . 24 Explain why it makes sense to use the-word translation to describe protein synthesis and why it would not make sense to use the word translation to describe mRNA synthesis. tn PMA fo idM A /UU' UO'fi 'ctzA ' 0\/ 4 AAl/J/Slhv ). sIn \ iM t )/ i r /7 s ' JsJ . £o 25 Why does a cell need to carry out transcription before translation? hxaJ ' Lc code can sl&eud^ Ci Lc. t'VictcljL - ^ . r /boSorvUL / 26a Fill in the blanks to label each type of molecule in this figure . 26b. Name the process shown in the figure and explain each step in this process. Include in your answer each of the molecules shown and these words and phrases: anticodon, base-pairing rules, codon, ribosome, sequence of amino acids. erf ibi riboScnouL the mKKiA codo ^S fftAtckuJ to i fta flu a'rficcclo ^ O-C u Q f f v bcu)-t ~'P ot-^vhs WIM 'd b^ ivtoJ Am cowed OJsvriYio cLu be> YAP y' lbosoonji ouid - i p c i c j c k. bkn-vY ivc Jjijcc io rvicoko ) ^ Understanding How the Gene for Sickle Ceil Hemoglobin Results in Sickle Cell Anemia Different versions of the same gene are called different alleles. These different alleles share the same general sequence of nucleotides, but they differ in at least one nucleotide in the sequence. 27a. Complete this flowchart to show how different alleles can result in different characteristics. In the DNA, different alleles of a gene have a different sequence of fW ^ dnobl' Aj^ ! franspripj-ioin N/ different sequence of AAAC- si / different sequence of OLmi A' sn Ludieblb inmRNA j-ra /isforfrfan (3ooidJ in a protein \^ ' T different structure and function of the protein si' different characteristics 27b. Label the arrow that represents transcription and the arrow that represents translation. 8 Next, you will analyze how different alleles of the hemoglobin gene can result in sickle cell anemia vs. normal health. 28. Using the table below, compare the nucleotide sequence in the "Beginning of Normal Hemoglobin Gene" vs. the "Beginning of Sickle Cell Hemoglobin Gene". What is the only difference? iitmeJl - T 5tMt Cell ~ A Beginning of Normal Hemoglobin Gene CACGTAGACTGAGGACTC Transcription produces : codonl Translation produces: amino acid 2 acid 1 codon 4 amino acid 3 codon 5 codon 6 amino acid 4 acid 6 acid 5 nic UforttM Mi /U bluhi Aold htshdt Ai Beginning of Normal Hemoglobin Protein / ' CACGTAGACTGAGGACFC 6 Ub au CUG kOX CCU Gel 6 Beginning of Sickle Cell Hemoglobin Gene Transcription produces : Beginning of Sickle Cell Hemoglobin mRNA Translation produces: codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 amino amino amino acid 2 amino acid 4 amino acid 1 amino acid 3 acid 5 acid 6 fodUkl hfrftot IOUOIM Jfauvwk Beginning of Sickle Cell Hemoglobin Protein 29 Complete the above table. ('y codon 3 CUG AGU CCU. bAG GUG OAU amino amino amino Beginning of Normal Hemoglobin mRNA . codon 2 \ UcC OjCkA co ^\t^^t blfi^n^§g ^4x 4Telpjwi^h'J^anslation.)Codon okact ^ . ' § ) , 30 Compare the amino acid sequence for the beginning of sickle cell hemoglobin vs. the beginning of normal hemoglobin. What difference do you observe ? X arfn‘no CJl Sickle cell hemoglobin and normal hemoglobin differ in only a single amino acid out of more than 100 amino acids in the complete hemoglobin protein. This difference in a single amino acid results in the different properties of sickle cell hemoglobin compared to normal hemoglobin. Hemoglobin is carried inside red blood cells. Normal hemoglobin dissolves in the watery cytosol of red blood cells. Sickle cell hemoglobin is less soluble in the cytosol because: Valine (Val) is much less water-soluble than glutamic acid (Glu). Amino acid 6 is in a crucial location on the outer surface of the hemoglobin protein. The chart on the next page shows how the lower solubility of sickle cell hemoglobin results in the symptoms of sickle cell anemia. • • A r Genes in DNA 2 copies of the allele that codes for normal hemoglobin (SS) -- Protein Normal hemoglobin dissolves in the cytosol of red blood cells. r\ » m I Characteristics Disk-shaped red blood cells can squeeze through the smallest blood vessels -> normal health ft -# h -I A a If sickle cell hemoglobin clumps in long rods -» sickle-shaped red blood cells -> clogged small blood vessels + fragile red blood cells , damage to body organs pain -> + anemia = sickle cell anemia Sickle cell hemoglobin can clump in long rods in red blood cells. 2 copies of the allele that codes for sickle cell hemoglobin (ss) . 31b. Use the letter for each of the following statements to label the box or boxes in the flowchart that 31a Circle the arrows in the chart that represent transcription + translation. illustrate this statement. A. Normal hemoglobin dissolves in the watery cytosol of red blood cells. The disk-shaped red blood cells can squeeze through the smallest blood vessels so blood flow is normal. B. If a person inherits two copies of the sickle cell hemoglobin allele and produces only sickle cell hemoglobin, then the sickle cell hemoglobin molecules tend to clump together in long rods inside red blood cells. C. These hemoglobin rods can result in sickle-shaped red blood cells which can block blood flow in smallblood vessels; this causes pain and damage to body organs. Sickle-shaped red blood cells don't last as long as normal red blood cells; when the body can't produce enough replacement red blood cells, this results in anemia. . 32 Considering that we are all made up of the same 4 nucleotides in our DNA, the same 4 nucleotides in our RNA, and the same 20 amino acids in our proteins, why are we so different from each other? For example, why do some people have sickle cell anemia and others don't ? i . icM' in ] By Drs Ingrid Waldron and Jennifer Doherty, Department of Biology, University of Pennsylvania, Copyright, 2017. Teachers are encouraged to copy this Student Handout for classroom use A Word file (which can be used to prepare a modified version if desired) arid Teacher Preparation Notes with instructional suggestions and background biology are available at http:/ / serendipstudio ore/ sd edu/waldron/#trans . . . 10

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