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Unformatted text preview: Name:…………………………………………………………………………………………… 13.3 Gene Expression Gene expression = 2 processes 1- Transcription - to write down 2- Translation = yo convert into a different form Gene expression uses RNA to take information from DNA and turn it into amino acids DNA 2strands Deoxyribose Thymine 3 TYPES RNA : mRNA = Messenger RNA rRNA = ribosomal RNA tRNA = translationRNA RNA 1 strand Ribose Uracil Name ______________________________ Class ___________________ Date __________________ Skills Worksheet Active Reading Section: RNA and Gene Expression Read the passage below. Then answer the questions that follow. Like DNA, ribonucleic acid (RNA) is a nucleic acid—a molecule made of nucleotides linked together. RNA differs from DNA in three ways. First, RNA consists of a single strand of nucleotides instead of the two strands found in DNA. Second, RNA nucleotides contain the five-carbon sugar ribose rather than the sugar deoxyribose found in DNA nucleotides. And third, RNA has a nitrogenous base called uracil—abbreviated as U—instead of the base thymine (T) found in DNA. No thymine (T) bases are found in RNA. Like thymine, uracil is complementary to adenine whenever RNA base-pairs with another nucleic acid. SKILL: RECOGNIZING SIMILARITIES AND DIFFERENCES Read each question, and write your answer in the space provided. 1. In the spaces provided, write D if the statement is true of DNA. Write R if the statement is true of RNA. Write B if the statement is true of both DNA and RNA. r _____ a. consists of a single strand of nucleotides b _____ b. is made of nucleotides linked together d c. contains deoxyribose _____ r d. has the nitrogenous base uracil _____ r_____ b _____ d e. contains ribose f. is a nucleic acid _____ g. consists of a double strand of nucleotides b _____ h. contains a base that pairs with adenine An analogy is a comparison. In the space provided, write the letter of the term or phrase that best completes the analogy. _____ 2. RNA is to U as DNA is to a. C b. G c. T d. A Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Biology 11 DNA, RNA, and Proteins RNA polymerase RNA polymerase binds to the gene’s promoter. Genetics and Biotechnology Transcription 1 Promoter site on DNA 2 The two DNA strands unwind and separate. 3 C15 TEACHING TRANSPARENCY nucleotides are added. 3 Complementary RNA RNA Copyright © by Holt, Rinehart and Winston. All rights reserved. Genetics and Biotechnology Translation: Assembling Proteins TEACHING TRANSPARENCY C17 Copyright © by Holt, Rinehart and Winston. All rights reserved. Name CHAPTER 13 Class Date DNA, RNA, and Proteins SECTION 3 RNA and Gene Expression KEY IDEAS As you read this section, keep these questions in mind: • What is the process of gene expression? • What role does RNA play in gene expression? • What happens during transcription? • How do codons determine the sequence of amino acids that results after translation? • What are the major steps of translation? • Do traits result from the expression of a single gene? READING TOOLBOX Summarize After you read this section, make a flowchart showing the sequence of steps involved in the production of a protein from a DNA molecule. What Is Gene Expression? Gene expression is the process by which genes control the traits of an organism. The process of gene expression results in the production of proteins, as shown below. Nucleus DNA Cytoplasm Transcription RNA [email protected]<EHL>K 1. Identify What are the two main steps in gene expression? RNA Translation Protein Gene expression consists of two main steps: transcription and translation. In eukaryotic cells, like the one shown here, transcription occurs in the nucleus, and translation occurs in the cytoplasm. 8g^i^XVaI]^c`^c\ 2. Apply Concepts A DNA strand has the base sequence GCCATATTG. What is the complementary RNA sequence? Both transcription and translation involve RNA, or ribonucleic acid. Like DNA, RNA consists of nucleotide subunits linked together. RNA also has four bases and carries information. However, RNA differs from DNA in three ways: • RNA generally consists of a single strand of nucleotides. • RNA nucleotides contain the five-carbon sugar ribose instead of the sugar deoxyribose. • RNA nucleotides contain a base called uracil (U) instead of thymine. Like thymine, uracil is complementary to adenine. There are three main kinds of RNA. Each kind is described in the table on the next page. Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Reader 140 DNA, RNA, and Proteins Name Class SECTION 3 Date RNA and Gene Expression continued Type of RNA Description Messenger RNA (mRNA) produced during transcription; is complementary to a DNA strand Transfer RNA (tRNA) used during translation; attaches to an amino acid; contains a sequence of bases that are complementary to part of an mRNA strand Ribosomal RNA (rRNA) found in ribosomes; helps to bind amino acids together during translation [email protected]<EHL>K 3. Identify Which type of RNA is produced during transcription? What Is Transcription? The first stage of gene expression is transcription. During transcription, information in a particular region of DNA is copied into mRNA. A protein called RNA polymerase carries out transcription in three stages. Transcription 3 RNA polymerase KXcb8Yflk@k Find Word Roots Look up the word polymer in a dictionary. In a small group, talk about the most likely reason that proteins that produce DNA and RNA from free nucleotides are called polymerases. mRNA 1 2 3 1 RNA polymerase binds to a specific part of the gene called the promoter region. 2 The two DNA strands unwind and separate. [email protected]<EHL>K 4. Summarize What happens during transcription? 3 The RNA polymerase moves along the DNA strand. It adds complementary mRNA nucleotides to a growing mRNA strand as it moves. At the end of transcription, the RNA polymerase has produced an mRNA strand that is complementary to the DNA in the gene. You can think of a gene as a “sentence.” Each “word” in the sentence consists of a group of three bases called a codon. During transcription, the sentence of DNA codons is translated into a complementary sentence of mRNA codons. After transcription, the mRNA sentence moves from the cell nucleus to ribosomes in the cytoplasm. There, it is translated into proteins. Each mRNA codon either matches one amino acid or acts as a signal to start or stop translation. This system of paired codons and amino acids is called the genetic code. The figure at the top of the next page shows how to determine which amino acid a certain codon codes for. READING CHECK 5. Define What is a codon? Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Reader 141 DNA, RNA, and Proteins Name SECTION 3 Class Date RNA and Gene Expression continued Find the first base of the mRNA codon in this column. Follow that row to the column that matches the second base of the codon. Move up or down in that box until you match the third base of the codon with this column. #ODONSINM2.! [email protected]<EHL>K 6. Identify Which amino acid does the codon ACU code for? 7. Identify Give two examples of a stop codon. 3ECONDBASE &IRST BASE 5 5 555 55# 0HENYLALANINE 55! ,EUCINE 55' 5#5 5## 3ERINE 5#! 5#' 5!5 5!# 4YROSINE 5!! 3TOP 5!' 5'5 5'# #YSTEINE 5'! n3TOP 5'' n4RYPTOPHAN 5 # ! ' # #55 #5# ,EUCINE #5! #5' ##5 ### 0ROLINE ##! ##' #!5 #!# (ISTIDINE #!! 'LUTAMINE #!' #'5 #'# !RGININE #'! #'' 5 # ! ' !55 !5# )SOLEUCINE !5! !5'n3TART-ETHIONINE !!5 !#5 !## 4HREONINE !!# !SPARAGINE !#! !!! ,YSINE !#' !!' !'5 !'# 3ERINE !'! !RGININE !'' 5 # ! ' '55 '5# 6ALINE '5! '5' '#5 '## !LANINE '#! '#' ''5 ''# 'LYCINE ''! ''' 5 # ! ' ! ' # ! '!5 '!# '!! '!' !SPARTIC ACID 'LUTAMIC ACID ' 4HIRD BASE What Is Translation? READING CHECK 8. Describe What is the end result of translation? READING CHECK 9. Explain Does a particular trait result from the expression of a single gene? Translation is the second stage of gene expression. This process is shown in the figure on the next page. During translation, the “language” of mRNA (codons) is converted into the “language” of proteins (amino acids). Translation requires mRNA, tRNA, and rRNA. The result of translation is a complete polypeptide, or group of amino acids that forms a protein. How Are Genes Linked to Traits? Genes contain the information to produce proteins. Proteins, in turn, produce almost all the traits of an organism. However, the relationship between genes and the traits they affect is complex. Variations, mistakes, and other complex interactions can occur at each stage of DNA replication and gene expression. These interactions can cause the effects of a gene to change. A particular gene does not necessarily cause only one effect. Some genes are expressed only at certain times or under particular conditions. The protein a gene codes for may have many effects on an organism. In addition, a particular trait is not necessarily the result of only one gene. Some traits result from the expression of several genes. Several factors determine the final outcome of gene expression. They include the cell’s environment, the presence of other cells, and the timing of gene expression. Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Reader 142 DNA, RNA, and Proteins Name SECTION 3 Class Date RNA and Gene Expression continued Nuclear envelope Nuclear pore Codon 1 Anticodon tRNA U G A G U G A U G U G U G G C C U G U C G U A U G U After the mRNA strand leaves the nucleus, it binds to a ribosome and to a tRNA carrying the amino acid methionine. The anticodon on the tRNA binds to the codon on the mRNA. The mRNA codon AUG codes for the amino acid methionine. It is also the “start” codon, which tells the ribosome where to begin translation. Amino acid methionine An anticodon is a group of three nucleotides on a tRNA molecule. The anticodon is complementary to an mRNA codon. A tRNA with a particular anticodon carries only the amino acid that corresponds to the complementary codon. Ribosome mRNA 2 When the ribosome reaches a stop codon on the mRNA strand, no more amino acids are added to the chain. Looking CLoser Peptide bond As one ribosome moves further down the mRNA strand, another ribosome can begin to translate the mRNA again. In this way, many molecules of the same protein can be produced from a single strand of mRNA. tRNA A G U G U A G A U U C U U G G G C C C G U C G U A A U G U 4 The ribosome moves to the next codon on the mRNA. A tRNA with the complementary anticodon binds to the mRNA codon. The amino acid on this tRNA forms a peptide bond to the chain of amino acids attached to the previous tRNA. As the ribosome moves down the mRNA strand, more and more amino acids are added. A C C G U U U 3 A new tRNA arrives and binds to the next codon on the mRNA. A type of bond called a peptide bond forms between the methionine and the second amino acid. The bond between the first tRNA and the methionine is broken, and the first tRNA moves away from the ribosome. 11.  Describe  What causes translation to end? 12.  Identify  Where is the rRNA in the figure? 13.  Explain  How can the same mRNA strand be used to produce more than one polypeptide at the same time? Stop codon mRNA 10.  Explain  The first amino acid in most polypeptides is methionine. What is the reason for this? Newly made polypeptide A C C Large ribosomal subunit G The amino acid chain is released, and the ribosome and tRNA move apart. C A C A 5 Small ribosomal subunit A U A U U Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Reader 143 DNA, RNA, and Proteins Name Class Date Section 3 Review SECTION VOCABULARY codon in DNA and mRNA, a three-nucleotide sequence that encodes an amino acid or signifies a start signal or a stop signal gene expression the manifestation of the genetic material of an organism in the form of specific traits RNA ribonucleic acid, a natural polymer that is present in all living cells and that plays a role in protein synthesis transcription the process of forming a nucleic acid by using another molecule as a template; particularly the process of synthesizing RNA by using one strand of a DNA molecule as a template translation the portion of protein synthesis that takes place at ribosomes and that uses the codons in mRNA molecules to specify the sequence of amino acids in polypeptide chains 1. Define Write a definition of gene expression in your own words. 2. Describe What role does tRNA play in gene expression? 3. Apply Concepts Fill in the chart below to show how a DNA base sequence is converted into a sequence of amino acids. DNA codons TAC ACA CGA GGA GGG TCT AAA ATT mRNA codons tRNA anticodons Amino acids 4. Identify What are two things that can affect the result of gene expression? Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Reader 144 DNA, RNA, and Proteins Name ______________________________ Class ___________________ Date __________________ Skills Worksheet Directed Reading Section: RNA and Gene Expression In the space provided, write the letter of the description that best matches the term or phrase. _____ 1. ribonucleic acid (RNA) _____ 2. uracil _____ 3. transcription _____ 4. translation _____ 5. gene expression a. the entire process by which genes are used to build proteins/traits. b. a molecule made of linked nucleotides c. the process of reading instructions on an RNA molecule to put together the amino acids that make up a protein d. the process of transferring a gene’s instructions for making a protein to an RNA molecule e. a nitrogenous base used in RNA instead of the base thymine found in DNA Complete each statement by underlining the correct term or phrase in the brackets. 6. Transcription begins when [RNA / RNA polymerase] binds to the gene’s promoter. 7. RNA polymerase adds complementary [DNA / RNA] nucleotides as it “reads” the gene. 8. In eukaryotes, transcription takes place in the [nucleus / cytoplasm]. Read each question, and write your answer in the space provided. 9. What are two differences between transcription and DNA replication? _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 10. What determines where on the DNA molecule transcription begins and where it ends? _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor . Holt Biology 5 DNA, RNA, and Proteins Name ______________________________ Class ___________________ Date __________________ Directed Reading continued In the space provided, explain how the terms in each pair are related to each other. 11. RNA, messenger RNA _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 12. codons, genetic code _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ Study the following six steps in the synthesis of proteins. Determine the order in which the steps take place. Write the number of each step in the space provided. _____ 13. The codon following the start codon then receives the tRNA molecule with the complementary anticodon. The tRNA carries the amino acid specified by the codon. _____ 14. Steps 2–5 are repeated until a stop codon is reached. The newly made protein is released into the cell. _____ 15. The first tRNA detaches, leaves behind its amino acid, and moves away from the ribosome. _____ 16. Enzymes help form a peptide bond between the amino acids of adjacent tRNA molecules. _____ 17. The tRNA (with its growing protein chain) and mRNA move one codon down, and the next codon is ready to receive the next tRNA and its amino acid. _____ 18. An mRNA, the ribosome, and a tRNA carrying the amino acid methionine bind together. The tRNA bonds to the “start” codon AUG. Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor . Holt Biology 6 DNA, RNA, and Proteins Name ______________________________ Class___________________Date__________________ Quick Lab Genetic Code of Keratin Keratin is one of the proteins in hair. The gene for keratin is transcribed and translated by certain skin cells. The sequence below is part of the mRNA molecule that is transcribed from the gene for keratin. Analysis 1. Determine the sequence of amino acids that will result from the translation of the segment of mRNA above. Use the genetic code in Figure 13. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 2. Determine the anticodon of each tRNA molecule that will bind to this mRNA segment. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 3. Critical Thinking Recognizing Patterns Determine the sequence of nucleotides in the segment of DNA from which this mRNA strand was transcribed. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 4. Critical Thinking Recognizing Patterns Determine the sequence of nucleotides in the segment of DNA that is complementary to the DNA segment that is described in item 3. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Biology 1 DNA, RNA, and Proteins Genetics and Biotechnology Codons in mRNA First base U C A G UGU Cysteine UGC UGA – Stop UGG – Tryptophan G U C A G U C A G Third base C16 TEACHING TRANSPARENCY UAU Tyrosine UAC UAA Stop UAG CGU CGC Arginine CGA CGG A UCU UCC Serine UCA UCG CAU Histidine CAC CAA Glutamine CAG Second base C UUU Phenylalanine UUC UUA Leucine UUG CCU CCC Proline CCA CCG U CUU CUC Leucine CUA CUG U C A G U C A G AGU Serine AGC AGA Arginine AGG GGU GGC Glycine GGA GGG AAU Asparagine AAC AAA Lysine AAG GAU Aspartic Acid GAC GAA Glutamic GAG Acid ACU ACC Threonine ACA ACG GCU GCC Alanine GCA GCG AUU AUC Isoleucine AUA AUG – Start GUU GUC Valine GUA GUG Copyright © by Holt, Rinehart and Winston. All rights reserved. DNA: Cracking the Code A gene is like a long sentence which gives instructions on how to make part of a person. Each sentence consists of lots of three letter ‘words’. These words are written in a code, using only the letters A, T, C and G (abbreviations for the bases Adenine, Thymine, Cytosine and Guanine). Each word is called a codon, and codes for a piece of protein called an amino acid. These amino acid join together in a chain to form a protein, which determines something about you – for example your hair colour. The Genetic Code for Amino Acids TTT TCT TAT TGT Phe Tyr Cys TTC TC...
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