RNA and Protein Synthesis

Transcription

1 Name lass Date RN and Protein Synthesis Information and Heredity Q: How does information fl ow from DN to RN to direct the synthesis of proteins? 13.1 What is RN? WHT I KNOW SMPLE NSWER: RN is a nucleic acid that carries coded genetic information. WHT I LERNED SMPLE NSWER: RN contains the sugar ribose and the nitrogenous base uracil instead of thymine. It is usually a single strand. mrn molecules are made using DN as a template How do cells make proteins? SMPLE NSWER: The bases in DN, T,, and form a four-letter alphabet that writes the words of the genetic code. SMPLE NSWER: The genetic code is read in mrn codons, which are sequences of three bases that correspond to a single amino acid. Ribosomes use the sequence of codons to assemble amino acids into polypeptides What happens when a cell s DN changes? SMPLE NSWER: When DN changes, mistakes can be made. The organism may look or function differently. SMPLE NSWER: Mutations are heritable changes in genetic information. They can involve only one DN nucleotide or the whole chromosome. Mutations may or may not affect gene function How do cells regulate gene expression? SMPLE NSWER: ell proteins regulate gene expression. SMPLE NSWER: DN-binding proteins regulate genes by controlling transcription in prokaryotes. In eukaryotes, transcription factors control gene expression by binding DN sequences in the regulatory regions. hapter 13 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 193

2 Name lass Date 13.1 RN Lesson Objectives ontrast RN and DN. Explain the process of transcription. Lesson Summary The Role of RN RN (ribonucleic acid) is a nucleic acid like DN. It consists of a long chain of nucleotides. The RN base sequence directs the production of proteins. ltimately, cell proteins result in phenotypic traits. The main differences between RN and DN are: The sugar in RN is ribose instead of deoxyribose. RN is generally single-stranded and not double-stranded like DN. RN contains uracil in place of thymine. RN can be thought of as a disposable copy of a segment of DN. Most RN molecules are involved in protein synthesis. The three main types of RN are: Messenger RN (mrn) carries copies of instructions for polypeptide synthesis from the nucleus to ribosomes in the cytoplasm. Ribosomal RN (rrn) forms an important part of both subunits of the ribosomes, the cell structures where proteins are assembled. Transfer RN (trn) carries amino acids to the ribosome and matches them to the coded mrn message. RN Synthesis Most of the work of making RN takes place during transcription. In transcription, segments of DN serve as templates to produce complementary RN molecules. In prokaryotes, RN synthesis and protein synthesis takes place in the cytoplasm. In eukaryotes, RN is produced in the cell s nucleus and then moves to the cytoplasm to play a role in the production of protein. The following focuses on transcription in eukaryotic cells. The enzyme RN polymerase binds to DN during transcription and separates the DN strands. It then uses one strand of DN as a template from which to assemble nucleotides into a complementary strand of RN. RN polymerase binds only to promoters, regions of DN that have specific base sequences. Promoters are signals to the DN molecule that show RN polymerase exactly where to begin making RN. Similar signals cause transcription to stop when a new RN molecule is completed. RN may be edited before it is used. Portions that are cut out and discarded are called introns. The remaining pieces, known as exons, are then spliced back together to form the final mrn. Lesson 13.1 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 194

3 Name lass Date The Role of RN 1. omplete the table to contrast the structures of DN and RN. DN Sugar Number of Strands Bases deoxyribose 2, T,, and RN ribose usually 1,, and, but no T; contains (uracil) instead 2. On the lines provided, identify each kind of RN. transfer RN messenger RN ribosomal RN 3. The master plan of a building shows how to build and place important parts of the building, such as walls, pipes, and electrical outlets. On the building site, workers use copies of the master plan called blueprints to show them what to do. The master plan is kept in the office. Explain how mrn works like a blueprint in constructing proteins. The master plan is the DN molecule. The cell uses this molecule to prepare mrn blueprints. The mrn carries the instructions for protein synthesis from the nucleus to the ribosomes in the cytoplasm, where the proteins are built. Lesson 13.1 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 195

4 Name lass Date RN Synthesis For Questions 4 10, complete each statement by writing the correct word or words. 4. The process of using DN to produce complementary RN molecules is called transcription. 5. The sequence of bases in mrn complements the sequence in the DN template. 6. In eukaryotes, RN is formed in the nucleus and then travels to the cytoplasm. 7. The enzyme RN polymerase binds to DN during transcription. 8. RN polymerase binds to regions of DN called promoters, which are start signals for transcription. 9. Introns are portions of RN that are cut out and discarded. 10. Exons are spliced together to make the final mrn. 11. Sketch the sequence in which pre-mrn is edited after it is made on the DN template and before it is ready to function as mrn in the cytoplasm. Show the original DN, the pre-mrn, and the final mrn. Be sure to label exons and introns. Drawing should show a DN strand with introns and exons labeled. The introns and exons are contained in the pre-mrn strand, but introns are removed and exons spliced together to form the mrn. Drawing should resemble the figure in the textbook. 12. se the analogy of the master plan and blueprints used by builders to identify what represents messenger RN, where the ribosome is, and who performs the same kind of job as transfer RN. Explain your reasoning. The blueprints represent messenger RN because they carry instructions for the building from the office (the nucleus ) to the outside ( cytoplasm ). The ribosome is the job site where the building is being constructed. In the cell, proteins are built on the ribosome. The people at the job site are like transfer RN because they carry the building materials, such as bricks and blocks ( amino acids ) and match their placement to the instructions in the blueprint. Lesson 13.1 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 196

5 Name lass Date 13.2 Ribosomes and Protein Synthesis Lesson Objectives Identify the genetic code and explain how it is read. Summarize the process of translation. Describe the central dogma of molecular biology. Lesson Summary The enetic ode specific sequence of bases in DN carries the directions for forming a polypeptide, a chain of amino acids. The types and order of amino acids in a polypeptide determine the properties of the protein. The sequence of bases in mrn is the genetic code. The four bases,,,, and, act as letters. The code is read three letters at a time, so that each word is three bases long and corresponds to a single amino acid. Each three-letter word in mrn is known as a codon. Some codons serve as start and stop signals for protein synthesis. Translation Ribosomes use the sequence of codons in mrn to assemble amino acids into polypeptide chains. The process of decoding of an mrn message into a protein is translation. Messenger RN is transcribed in the nucleus and then enters the cytoplasm. On the ribosome, translation begins at the start codon. Each codon attracts an anticodon, the complementary sequence of bases on trn. Each trn carries one kind of amino acid. The match between the codon and anticodon ensures that the correct amino acid is added to the growing chain. The amino acids bond together, each in turn. The ribosome moves along the mrn, exposing codons that attract still more trns with their attached amino acids. The process concludes when a stop code is reached. The newly formed polypeptide and the mrn molecule are released from the ribosome. The Molecular Basis of Heredity Molecular biology seeks to explain living organisms by studying them at the molecular level, using molecules like DN and RN. The central dogma of molecular biology is that information is transferred from DN to RN to protein. ene expression is the way in which DN, RN, and proteins are involved in putting genetic information into action in living cells. The genetic code is generally the same in all organisms. Lesson 13.2 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 197

6 Name lass Date The enetic ode se the diagram to answer Questions 1 7. lanine Valine rginine Serine Lysine spartic acid sparagine lutamic acid Threonine Methionine lycine Isoleucine Phenylalanine Leucine 1. What are the words along the outside of the circle? They are the names of amino acids. rginine Serine lutamine Histidine Tyrosine 2. What can you find by reading this diagram from the inside out? the mrn codons for amino acids 3. For which amino acid is a codon? is a codon for lysine. 4. What is the codon for tryptophan? The codon for tryptophan is. 5. For which amino acid is a codon? is a codon for glycine. 6. What is a codon for alanine? codon for alanine is. 7. What are three other codons for alanine?,, Stop Proline ysteine Stop Tryptophan Leucine Lesson 13.2 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 198

7 Name lass Date Translation se the diagram to answer Questions What is the anticodon for leucine? 9. What is the codon for leucine? 10. List the amino acids in the order they would appear in the polypeptide coded for by this mrn. methionine, phenylalanine, lysine, leucine phenylalanine leucine lysine methionine mrn 11. What is the difference between transcription and translation? RN is produced from DN templates during transcription. In translation, that RN is read to form polypeptide chains. In a eukaryotic cell, transcription goes on in the nucleus and translation is carried out by ribosomes. 12. omplete the table to describe the steps in protein synthesis. Step Beginning of translation Description Translation begins when a ribosome attaches to an mrn molecule at a start codon. Transfer RN molecules carry amino acids to the mrn, where the anticodon matches the codon and ensures the placement of the correct amino acid. ssembly of polypeptide mino acids join one at a time onto the growing chain, and a trn floats away after it releases its amino acid. The ribosome moves along the mrn, binding a new trn molecule and the amino acid it carries. ompleting the polypeptide The process continues until a stop codon is reached, the polypeptide is complete, and the mrn is released from the ribosome. 13. Describe the role of rrn during translation. rrn molecules make up part of a ribosome. These molecules help hold ribosomal proteins in place and help locate the beginning of the mrn message. They may even carry out the chemical reaction that joins amino acids together. Lesson 13.2 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 199

8 Name lass Date The Molecular Basis of Heredity For Questions 14 18, write the letter of the correct answer on the line at the left. 14. The instructions for assembling proteins are contained in the. genes. B. ribosomes.. exons. D. introns. D 15. The central dogma of molecular biology is that information is transferred from. RN to protein to DN. B. DN to protein to RN.. protein to DN to RN. D. DN to RN to protein. B 16. n exception to the central dogma is. the infection of a virus by a bacteriophage. B. the ability of some viruses to transfer information from RN to DN.. the expression of different genes during different stages of development. D. the translation of the codon into the anticodon of trn. 17. The way in which DN, RN, and proteins are all involved in putting genetic information into action in living cells is called. translation. B. transcription.. gene expression. D. viral transfer. D 18. ll organisms are mostly the same in. the proteins they make on their ribosomes. B. how their proteins catalyze chemical reactions.. the size of their genes. D. the molecular biology of their genes. 19. Whether the organism is a pea plant or a human being, the information in the DN of the cell s nucleus directs synthesis of proteins in the cytoplasm. Why, then, are pea plants and human beings so different? They contain different DN, which directs the synthesis of different proteins. Those proteins form different structures and functions, making pea plant cells very different from human cells. Lesson 13.2 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 200

9 Name lass Date 13.3 Mutations Lesson Objectives Define mutations and describe the different types of mutations. Describe the effects mutations can have on genes. Lesson Summary Types of Mutations Mutations are heritable changes in genetic information. There are two categories of mutations: gene mutations and chromosomal mutations. ene mutations produce changes in a single gene. Point mutations involve only one or a few nucleotides. Substitutions, insertions, and deletions are all types of point mutations. In a substitution, one base is changed to a different base, which may affect only a single amino acid and have no effect at all. In insertions and deletions, one base is inserted or removed from the DN sequence. Insertions and deletions are called frameshift mutations because they shift the reading frame of the genetic message. Frameshift mutations can change every amino acid that follows the point of mutation and can have dramatic effects on the organism. hromosomal mutations produce changes in the number or structure of chromosomes. They include deletions, duplications, inversions, and translocations. Deletion involves the loss of all or part of a chromosome. Duplication produces an extra copy of all or part of a chromosome. Inversion reverses the direction of parts of a chromosome. Translocation occurs when part of one chromosome breaks off and attaches to another. Effects of Mutations enetic material can be altered by natural events or by artificial means. Errors can be made during replication. Environmental conditions may increase the rate of mutation. Mutagens are chemical or physical agents in the environment that cause mutations. The effects of mutations on genes vary widely: Some mutations have little or no effect. Some mutations produce beneficial variations. One example is polyploidy in plants, in which an organism has extra sets of chromosomes. Polyploid plants are often larger and stronger than diploid plants. Mutations can also produce proteins with new or altered functions that can be useful to organisms in different or changing environments. Some mutations negatively disrupt gene function or dramatically change protein structure. enetic disorders such as sickle cell disease can result. Lesson 13.3 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 201

10 Name lass Date Types of Mutations For Questions 1 8, match the term with its definition. Definition B 1. The change of one base to another in a DN sequence 2. change in one or a few nucleotides that occur at a single point in the DN sequence F 3. Part of one chromosome breaks off and attaches to another 4. heritable change in genetic information H 5. mutation that produces an extra copy of all or part of a chromosome 6. chromosomal mutation that reverses the direction of parts of a chromosome D 7. kind of mutation that can change every amino acid that follows the point of mutation E 8. The addition of a base to the DN sequence Term. mutation B. substitution. point mutation D. frameshift mutation E. insertion F. translocation. inversion H. duplication 9. omplete the table to describe the processes and outcomes of the different types of gene (point) mutations. Type Description Outcome Substitution One base is changed to a usually affects no more than a different base. single amino acid, and sometimes has no effect at all Insertion n extra base is inserted into the DN sequence. The effects can be dramatic. The groupings of bases shift in every codon that follows the mutation. Deletion base is removed from the DN sequence. The effects can be dramatic. The groupings of bases shift in every codon that follows the mutation. 10. Deletion can happen as a gene mutation or as a chromosomal mutation. What is the difference? In a gene mutation, a deletion happens when a base is removed from the DN sequence. In a chromosomal mutation, deletion involves the loss of all or part of a chromosome. Lesson 13.3 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 202

11 Name lass Date Effects of Mutations For Questions 10 17, write the letter of the correct answer on the line at the left. D B D B 10. The cellular machinery that replicates DN inserts an incorrect base. most of the time. B. about half the time.. roughly once in every million bases. D. roughly once in every 10 million bases. 11. Small changes in genes. disappear quickly. B. gradually accumulate over time.. prevent the next generation from developing. D. do not affect future generations. 12. possible mutagen is. an anticodon. B. translocation.. hemoglobin. D. ultraviolet light. 13. What happens when cells cannot repair the damage caused by a mutagen?. The DN base sequence changes permanently. B. The DN base sequence is not affected.. The organism is not affected. D. The organism is affected temporarily. 14. Which of the following most accurately summarizes the effects of mutations on living things?. Most mutations are harmful, but some have little effect. B. Many mutations have little or no effect, but some can be harmful or beneficial.. Most mutations are beneficial and a few are harmful. D. bout half of mutations are beneficial and half are harmful. 15. Mutations are important to the evolution of a species because they. happen over the long period of time that evolution requires. B. cut out and replace damaged or useless genes.. are a source of genetic variability. D. accelerate the transcription rate of DN. 16. ancer is the product of a mutation that. causes the uncontrolled growth of cells. B. changes the structure of hemoglobin in the blood.. brings about stunted growth and severe pain. D. causes a translocation in a pair of chromosomes. Lesson 13.3 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 203

12 Name lass Date B 17. Polyploidy is the condition in which. a piece of a chromosome breaks off and reattaches to another chromosome. B. an organism has an extra set of chromosomes.. a mutagen speeds the mutation rate. D. an insect develops a resistance to a pesticide. 18. In the space below, draw an example of a normal blood cell and an example of a sickle cell. Students drawings should look like those in the textbook. 19. gene that codes for one of the polypeptide chains of the blood protein hemoglobin lies on chromosome 11 in humans. substitution mutation in that gene causes the amino acid valine to be incorporated into hemoglobin in a place where glutamic acid would normally lie. The result is sickle cell disease. Explain how a change in a single base in DN can bring about such a serious disorder. single DN base-pair change in a gene can create an incorrect codon in the mrn molecule made from this DN. When the incorrect codon is read on the ribosome, the wrong amino acid (in this case valine rather than glutamic acid) is placed into the polypeptide. With the wrong amino acid sequence, the protein does not form or function properly. Lesson 13.3 Workbook opyright by Pearson Education, Inc., or its affiliates. ll Rights Reserved. 204