3. Table of Contents – pages iv-v Unit 1: What is Biology? Unit 2: Ecology Unit 3: The Life of a Cell Unit 4: GeneticsGenetics Unit 5: Change Through Time Unit 6: Viruses, Bacteria, Protists, and Fungi Unit 7: Plants Unit 8: Invertebrates Unit 9: Vertebrates Unit 10: The Human Body

4. Table of Contents – pages iv-v Unit 1: What is Biology? Chapter 1: Biology: The Study of Life Unit 2: Ecology Chapter 2: Principles of Ecology Chapter 3: Communities and Biomes Chapter 4: Population Biology Chapter 5: Biological Diversity and Conservation Unit 3: The Life of a Cell Chapter 6: The Chemistry of Life Chapter 7: A View of the Cell Chapter 8: Cellular Transport and the Cell Cycle Chapter 9: Energy in a Cell

5. Table of Contents – pages iv-v Unit 4: GeneticsGenetics Chapter 10: Mendel and Meiosis Chapter 11: DNA and GenesDNA and Genes Chapter 12: Patterns of Heredity and Human Genetics Chapter 13: Genetic Technology Unit 5: Change Through Time Chapter 14: The History of Life Chapter 15: The Theory of Evolution Chapter 16: Primate Evolution Chapter 17: Organizing Life’s Diversity

6. Table of Contents – pages iv-v Unit 6: Viruses, Bacteria, Protists, and Fungi Chapter 18: Viruses and Bacteria Chapter 19: Protists Chapter 20: Fungi Unit 7: Plants Chapter 21: What Is a Plant? Chapter 22: The Diversity of Plants Chapter 23: Plant Structure and Function Chapter 24: Reproduction in Plants

7. Table of Contents – pages iv-v Unit 8: Invertebrates Chapter 25: What Is an Animal? Chapter 26: Sponges, Cnidarians, Flatworms, and Roundworms Chapter 27: Mollusks and Segmented Worms Chapter 28: Arthropods Chapter 29: Echinoderms and Invertebrate Chordates

8. Table of Contents – pages iv-v Unit 9: Vertebrates Chapter 30: Fishes and Amphibians Chapter 31: Reptiles and Birds Chapter 32: Mammals Chapter 33: Animal Behavior Unit 10: The Human Body Chapter 34: Protection, Support, and Locomotion Chapter 35: The Digestive and Endocrine Systems Chapter 36: The Nervous System Chapter 37: Respiration, Circulation, and Excretion Chapter 38: Reproduction and Development Chapter 39: Immunity from Disease

9. Unit Overview – pages 250-251 Genetics Mendel and Meiosis DNA and Genes Patterns of Heredity and Human Genetics Genetic Technology

10. Chapter Contents – page viii Chapter 11 DNA and GenesDNA and Genes 11.1: DNA: The Molecule of HeredityDNA: The Molecule of Heredity 11.1: Section CheckSection Check 11.2: From DNA to ProteinFrom DNA to Protein 11.2: Section CheckSection Check 11.3: Genetic ChangesGenetic Changes 11.3: Section CheckSection Check Chapter 11 SummarySummary Chapter 11 AssessmentAssessment

11. Chapter Intro-page 280 What You’ll Learn You will relate the structure of DNA to its function. You will explain the role of DNA in protein production. You will distinguish among different types of mutations.

12. 11.1 Section Objectives – page 281 Analyze the structure of DNA Section Objectives: Determine how the structure of DNA enables it to reproduce itself accurately.

13. Section 11.1 Summary – pages 281 - 287 Although the environment influences how an organism develops, the genetic information that is held in the molecules of DNA ultimately determines an organism’s traits. DNA achieves its control by determining the structure of proteins. What is DNA?

14. Section 11.1 Summary – pages 281 - 287 All actions, such as eating, running, and even thinking, depend on proteins called enzymes. Enzymes are critical for an organism’s function because they control the chemical reactions needed for life. What is DNA? Within the structure of DNA is the information for life—the complete instructions for manufacturing all the proteins for an organism.

15. Section 11.1 Summary – pages 281 - 287 In 1952 Alfred Hershey and Martha Chase performed an experiment using radioactively labeled viruses that infect bacteria. These viruses were made of only protein and DNA. DNA as the genetic material

16. Section 11.1 Summary – pages 281 - 287 Hershey and Chase labeled the virus DNA with a radioactive isotope and the virus protein with a different isotope. DNA as the genetic material By following the infection of bacterial cells by the labeled viruses, they demonstrated that DNA, rather than protein, entered the cells and caused the bacteria to produce new viruses.

17. Section 11.1 Summary – pages 281 - 287 DNA is a polymer made of repeating subunits called nucleotides. Nucleotides have three parts: a simple sugar, a phosphate group, and a nitrogenous base. Phosphate group Sugar (deoxyribose) Nitrogenous base The structure of nucleotides

18. Section 11.1 Summary – pages 281 - 287 The phosphate group is composed of one atom of phosphorus surrounded by four oxygen atoms. The simple sugar in DNA, called deoxyribose (dee ahk sih RI bos), gives DNA its name—deoxyribonucleic acid. The structure of nucleotides

19. Section 11.1 Summary – pages 281 - 287 A nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen. In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Adenine (A) Guanine (G)Thymine (T) Cytosine (C) The structure of nucleotides

20. Section 11.1 Summary – pages 281 - 287 Thus, in DNA there are four possible nucleotides, each containing one of these four bases. The structure of nucleotides

21. Section 11.1 Summary – pages 281 - 287 Nucleotides join together to form long chains, with the phosphate group of one nucleotide bonding to the deoxyribose sugar of an adjacent nucleotide. The phosphate groups and deoxyribose molecules form the backbone of the chain, and the nitrogenous bases stick out like the teeth of a zipper. The structure of nucleotides

22. Section 11.1 Summary – pages 281 - 287 In DNA, the amount of adenine is always equal to the amount of thymine, and the amount of guanine is always equal to the amount of cytosine. The structure of nucleotides

23. Section 11.1 Summary – pages 281 - 287 In 1953, Watson and Crick proposed that DNA is made of two chains of nucleotides held together by nitrogenous bases. The structure of DNA Watson and Crick also proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring. Because DNA is composed of two strands twisted together, its shape is called double helix.

24. Section 11.1 Summary – pages 281 - 287 The importance of nucleotide sequences Chromosome The sequence of nucleotides forms the unique genetic information of an organism. The closer the relationship is between two organisms, the more similar their DNA nucleotide sequences will be.

25. Section 11.1 Summary – pages 281 - 287 The importance of nucleotide sequences Scientists use nucleotide sequences to determine evolutionary relationships among organisms, to determine whether two people are related, and to identify bodies of crime victims.

26. Section 11.1 Summary – pages 281 - 287 Replication of DNA Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes. The DNA in the chromosomes is copied in a process called DNA replication. Without DNA replication, new cells would have only half the DNA of their parents.

27. Section 11.1 Summary – pages 281 - 287 Replication of DNA DNA Replication

28. Section 11.1 Summary – pages 281 - 287 Replication of DNA Click this image to view movie

29. Section 11.1 Summary – pages 281 - 287 DNA is copied during interphase prior to mitosis and meiosis. It is important that the new copies are exactly like the original molecules. Copying DNA

30. Section 11.1 Summary – pages 281 - 287 Copying DNA Original DNA Original DNA Strand Free Nucleotides New DNA molecule New DNA Strand New DNA molecule

31. Section 1 Check Question 1 What importance did the experiment performed by Alfred Hershey and Martha Chase have in determining what genetic material was? Many scientists believed protein was the genetic material. However, an experiment using radioactively labeled viruses allowed Hershey and Chase to provide convincing evidence that DNA is the genetic material. Answer

32. Section 1 Check Question 2 Which of the following is NOT a component of DNA? D. proteins C. nitrogenous bases B. phosphate groups A. simple sugars The answer is D.

33. Section 1 Check Question 3 Which of the following correctly comprises a complimentary base pair? D. cytosine – thymine C. guanine – adenine B. thymine – guanine A. adenine – thymine The answer is A.

34. Section 2 Objectives – page 288 Section Objectives Sequence the steps involved in protein synthesis. Relate the concept of the gene to the sequence of nucleotides in DNA.

35. Section 11.2 Summary – pages 288 - 295 The sequence of nucleotides in DNA contain information. Genes and Proteins This information is put to work through the production of proteins. Proteins fold into complex, three- dimensional shapes to become key cell structures and regulators of cell functions.

36. Section 11.2 Summary – pages 288 - 295 Some proteins become important structures, such as the filaments in muscle tissue. Other proteins, such as enzymes, control chemical reactions that perform key life functions—breaking down glucose molecules in cellular respiration, digesting food, or making spindle fibers during mitosis. Genes and Proteins

37. Section 11.2 Summary – page 288 - 295 Thus, by encoding the instructions for making proteins, DNA controls cells. In fact, enzymes control all the chemical reactions of an organism. Genes and Proteins

38. Section 11.2 Summary – page 2888- 295 You learned earlier that proteins are polymers of amino acids. The sequence of nucleotides in each gene contains information for assembling the string of amino acids that make up a single protein. Genes and Proteins

39. Section 11.2 Summary – pages 288 - 295 RNA like DNA, is a nucleic acid. RNA structure differs from DNA structure in three ways. First, RNA is single stranded—it looks like one-half of a zipper —whereas DNA is double stranded. RNA

40. Section 11.2 Summary – pages 288 - 295 The sugar in RNA is ribose; DNA’s sugar is deoxyribose. Ribose RNA

41. Section 11.2 Summary – pages 288 - 295 Both DNA and RNA contain four nitrogenous bases, but rather than thymine, RNA contains a similar base called uracil (U). Uracil forms a base pair with adenine in RNA, just as thymine does in DNA. Uracil Hydrogen bonds Adenine RNA

42. Section 11.2 Summary – pages 288 - 295 DNA provides workers with the instructions for making the proteins, and workers build the proteins. The workers for protein synthesis are RNA molecules. RNA

43. Section 11.2 Summary – pages 288 - 295 DNA provides workers with the instructions for making the proteins, and workers build the proteins. The workers for protein synthesis are RNA molecules. They take from DNA the instructions on how the protein should be assembled, then— amino acid by amino acid—they assemble the protein. RNA

44. Section 11.2 Summary – pages 288 - 295 There are three types of RNA that help build proteins. Messenger RNA (mRNA), brings instructions from DNA in the nucleus to the cell’s factory floor, the cytoplasm. On the factory floor, mRNA moves to the assembly line, a ribosome. RNA

45. Section 11.2 Summary – pages 288 - 295 The ribosome, made of ribosomal RNA (rRNA), binds to the mRNA and uses the instructions to assemble the amino acids in the correct order. RNA

46. Section 11.2 Summary – pages 288 - 295 Transfer RNA (tRNA) is the supplier. Transfer RNA delivers amino acids to the ribosome to be assembled into a protein. RNA Click image to view movie

47. Section 11.2 Summary – pages 288 - 295 Transcription In the nucleus, enzymes make an RNA copy of a portion of a DNA strand in a process called transcription.

48. Section 11.2 Summary – pages 288 - 295 Transcription

49. Biochemists began to crack the genetic code when they discovered that a group of three nitrogenous bases in mRNA code for one amino acid. Each group is known as a codon. A code is needed to convert the language of mRNA into the language of proteins. The Genetic Code

50. Section 11.2 Summary – pages 288 - 295 Sixty-four combinations are possible when a sequence of three bases is used; thus, 64 different mRNA codons are in the genetic code. The Genetic Code

51. Section 11.2 Summary – pages 288 - 295 The Genetic Code The Messenger RNA Genetic Code First Letter Second Letter U U C A G Third Letter U C A G U C A G U C A G U C A G C A G Phenylalanine (UUU) Phenylalanine (UUC) Leucine (UUA) Leucine (UUG) Leucine (CUU) Leucine (CUC) Leucine (CUA) Leucine (CUG) Isoleucine (AUU) Isoleucine (AUC) Isoleucine (AUA) Methionine; Start (AUG) Valine (GUU) Valine (GUC) Valine (GUA) Valine (GUG) Serine (UCU) Serine (UCC) Serine (UCA) Serine (UCG) Proline (CCU) Proline (CCC) Proline (CCA) Proline (CCG) Threonine (ACU) Threonine (ACC) Threonine (ACA) Threonine (ACG) Alanine (GCU) Alanine (GCC) Alanine (GCA) Alanine (GCG) Tyrosine (UAU) Tyrosine (UAC) Stop (UAA) Stop (UAG) Histadine (CAU) Histadine (CAC) Glutamine (CAA) Glutamine (CAG) Asparagine (AAU) Asparagine (AAC) Lysine (AAA) Lysine (AAG) Aspartate (GAU) Aspartate (GAC) Glutamate (GAA) Glutamate (GAG) Cysteine (UGU) Cysteine (UGC) Stop (UGA) Tryptophan (UGG) Arginine (CGU) Arginine (CGC) Arginine (CGA) Arginine (CGG) Serine (AGU) Serine (AGC) Arginine (AGA) Arginine (AGG) Glycine (GGU) Glycine (GGC) Glycine (GGA) Glycine (GGG)

52. Section 11.2 Summary – pages 288 - 295 Translation: From mRNA to Protein The process of converting the information in a sequence of nitrogenous bases in mRNA into a sequence of amino acids in protein is known as translation. Translation takes place at the ribosomes in the cytoplasm. In prokaryotic cells, which have no nucleus, the mRNA is made in the cytoplasm.

53. Section 11.2 Summary – pages 288 - 295 Translation: From mRNA to Protein In eukaryotic cells, mRNA is made in the nucleus and travels to the cytoplasm. In cytoplasm, a ribosome attaches to the strand of mRNA like a clothespin clamped onto a clothesline.

54. Section 11.2 Summary – pages 288 - 295 For proteins to be built, the 20 different amino acids dissolved in the cytoplasm must be brought to the ribosomes. This is the role of transfer RNA. The role of transfer RNA

55. Section 11.2 Summary – pages 288 - 295 Each tRNA molecule attaches to only one type of amino acid. Amino acid Chain of RNA nucleotides Transfer RNA molecule Anticondon The role of transfer RNA

56. Section 11.2 Summary – pages 288 - 295 Translation

57. Section 11.2 Summary – pages 288 - 295 The role of transfer RNA Ribosome mRNA codon

58. Section 11.2 Summary – pages 288 - 295 Usually, the first codon on mRNA is AUG, which codes for the amino acid methionine. AUG signals the start of protein synthesis. When this signal is given, the ribosome slides along the mRNA to the next codon. The role of transfer RNA

59. Section 11.2 Summary – pages 288 - 295 tRNA anticodon Methionine The role of transfer RNA

60. Section 11.2 Summary – pages 288 - 295 A new tRNA molecule carrying an amino acid pairs with the second mRNA codon. Alanine The role of transfer RNA

61. Section 11.2 Summary – pages 288- 295 The amino acids are joined when a peptide bond is formed between them. Alanine Methionine Peptide bond The role of transfer RNA

62. Section 11.2 Summary – pages 288 - 295 A chain of amino acids is formed until the stop codon is reached on the mRNA strand. Stop codon The role of transfer RNA

63. Section 2 Check What are the three chemical differences between RNA and DNA? Question 1 Answer RNA consists of a single strand of nucleotides whereas DNA is a double strand. RNA contains ribose as its sugar and DNA contains deoxyribose as its sugar. Uracil in RNA replaces thymine in DNA as the nitrogenous base.

64. Section 2 Check What is the role of rRNA in protein synthesis? Question 2 Answer Ribosomal RNA binds to messenger RNA and assembles the amino acids in the order needed for the protein to be synthesized.

65. Section 2 Check Which regions of the mRNA travel to the ribosome; introns, exons, or both? Question 3 Answer Only exons, which contain coding information, travel to the ribosome. Introns, noncoding nucleotide sequences, do not travel to the ribosome.

66. Section 2 Check What is an anticodon, and what does it represent? Question 4 Answer An anticodon is a sequence of three nucleotides on the tRNA molecule that binds to a codon of the mRNA strand.

67. 11.3 Section Objectives – page 296 Categorize the different kinds of mutations that can occur in DNA. Section Objectives: Compare the effects of different kinds of mutations on cells and organisms.

68. 11.3 Section Summary 6.3 – pages 296 - 301 Organisms have evolved many ways to protect their DNA from changes. Mutations In spite of these mechanisms, however, changes in the DNA occasionally do occur. Any change in DNA sequence is called a mutation. Mutations can be caused by errors in replication, transcription, cell division, or by external agents.

69. 11.3 Section Summary 6.3 – pages 296 - 301 Mutations can affect the reproductive cells of an organism by changing the sequence of nucleotides within a gene in a sperm or an egg cell. Mutations in reproductive cells If this cell takes part in fertilization, the altered gene would become part of the genetic makeup of the offspring.

70. 11.3 Section Summary 6.3 – pages 296 - 301 Mutations in reproductive cells The mutation may produce a new trait or it may result in a protein that does not work correctly. Sometimes, the mutation results in a protein that is nonfunctional, and the embryo may not survive. In some rare cases a gene mutation may have positive effects.

71. 11.3 Section Summary 6.3 – pages 296 - 301 What happens if powerful radiation, such as gamma radiation, hits the DNA of a nonreproductive cell, a cell of the body such as in skin, muscle, or bone? If the cell’s DNA is changed, this mutation would not be passed on to offspring. However, the mutation may cause problems for the individual. Mutations in body cells

72. 11.3 Section Summary 6.3 – pages 296 - 301 Mutations in body cells Damage to a gene may impair the function of the cell. When that cell divides, the new cells also will have the same mutation. Some mutations of DNA in body cells affect genes that control cell division. This can result in the cells growing and dividing rapidly, producing cancer.

73. 11.3 Section Summary 6.3 – pages 296 - 301 A point mutation is a change in a single base pair in DNA. A change in a single nitrogenous base can change the entire structure of a protein because a change in a single amino acid can affect the shape of the protein. The effects of point mutations

74. 11.3 Section Summary 6.3 – pages 296 - 301 The effects of point mutations Normal Point mutation mRNA Protein Stop mRNA Protein Replace G with A

75. 11.3 Section Summary 6.3 – pages 296 - 301 Frameshift mutations What would happen if a single base were lost from a DNA strand? This new sequence with the deleted base would be transcribed into mRNA. But then, the mRNA would be out of position by one base. As a result, every codon after the deleted base would be different.

76. 11.3 Section Summary 6.3 – pages 296 - 301 Frameshift mutations mRNA Protein Frameshift mutation Deletion of U

77. 11.3 Section Summary 6.3 – pages 296 - 301 Frameshift mutations This mutation would cause nearly every amino acid in the protein after the deletion to be changed. A mutation in which a single base is added or deleted from DNA is called a frameshift mutation because it shifts the reading of codons by one base.

78. 11.3 Section Summary 6.3 – pages 296 - 301 Changes may occur in chromosomes as well as in genes. Alterations to chromosomes may occur in a variety of ways. Structural changes in chromosomes are called chromosomal mutations. Chromosomal Alterations

79. 11.3 Section Summary 6.3 – pages 296 - 301 Chromosomal mutations occur in all living organisms, but they are especially common in plants. Few chromosomal mutations are passed on to the next generation because the zygote usually dies. Chromosomal Alterations

80. 11.3 Section Summary 6.3 – pages 296 - 301 In cases where the zygote lives and develops, the mature organism is often sterile and thus incapable of producing offspring. When a part of a chromosome is left out, a deletion occurs. Deletion A B C D E F G HA B C E F G H Chromosomal Alterations

81. 11.3 Section Summary 6.3 – pages 296 - 301 When part of a chromatid breaks off and attaches to its sister chromatid, an insertion occurs. The result is a duplication of genes on the same chromosome. Insertion A B C D E F G H A B C B C D E F G H Chromosomal Alterations

82. 11.3 Section Summary 6.3 – pages 296 - 301 When part of a chromosome breaks off and reattaches backwards, an inversion occurs. Inversion A B C D E F G H A D C B E F G H Chromosomal Alterations

83. 11.3 Section Summary 6.3 – pages 296 - 301 When part of one chromosome breaks off and is added to a different chromosome, a translocation occurs. A B E F DCBX A W C H G G E H D F W XYZYZ Translocation Chromosomal Alterations

84. 11.3 Section Summary 6.3 – pages 296 - 301 Some mutations seem to just happen, perhaps as a mistake in base pairing during DNA replication. These mutations are said to be spontaneous. However, many mutations are caused by factors in the environment. Causes of Mutations

85. 11.3 Section Summary 6.3 – pages 296 - 301 Any agent that can cause a change in DNA is called a mutagen. Mutagens include radiation, chemicals, and even high temperatures. Forms of radiation, such as X rays, cosmic rays, ultraviolet light, and nuclear radiation, are dangerous mutagens because the energy they contain can damage or break apart DNA. Causes of Mutations

86. 11.3 Section Summary 6.3 – pages 296 - 301 Causes of Mutations The breaking and reforming of a double- stranded DNA molecule can result in deletions. Chemical mutagens include dioxins, asbestos, benzene, and formaldehyde, substances that are commonly found in buildings and in the environment. Chemical mutagens usually cause substitution mutations.

87. 11.3 Section Summary 6.3 – pages 296 - 301 Repairing DNA Repair mechanisms that fix mutations in cells have evolved. Enzymes proofread the DNA and replace incorrect nucleotides with correct nucleotides. These repair mechanisms work extremely well, but they are not perfect. The greater the exposure to a mutagen such as UV light, the more likely is the chance that a mistake will not be corrected.

88. Section 3 Check Any change in DNA sequences is called a _______. Question 1 D. translation C. transcription B. mutation A. replication The answer is B.

89. Section 3 Check Which is more serious, a point mutation or a frameshift mutation? Why? Question 2 Answer A frameshift mutation is more serious than a point mutation because it disrupts more codons than a point mutation.

90. Section 3 Check Why are chromosomal mutations rarely passed on to the next generation? Question 3 Answer Few chromosomal changes are passed on to the next generation because the zygote usually dies. If the zygote survives, it is often sterile and incapable of producing offspring.

91. Chapter Summary – 11.1 Alfred Hershey and Martha Chase demonstrated that DNA is the genetic material. DNA: The Molecule of Heredity Because adenine can pair only with thymine, and guanine can pair only with cytosine, DNA can replicate itself with great accuracy.

92. Chapter Summary – 11.1 DNA: The Molecule of Heredity DNA, the genetic material of organisms, is composed of four kinds of nucleotides. A DNA molecule consists of two strands of nucleotides with sugars and phosphates on the outside and bases paired by hydrogen bonding on the inside. The paired strands form a twisted-zipper shape called a double helix.

93. Chapter Summary – 11.2 Genes are small sections of DNA. Most sequences of three bases in the DNA of a gene code for a single amino acid in a protein. From DNA to Protein Messenger RNA is made in a process called transcription. The order of nucleotides in DNA determines the order of nucleotides in messenger RNA.

94. Chapter Summary – 11.2 From DNA to Protein Translation is a process through which the order of bases in messenger RNA codes for the order of amino acids in a protein.

95. Chapter Summary – 11.3 Genetic Changes A mutation is a change in the base sequence of DNA. Mutations may affect only one gene, or they may affect whole chromosomes. Mutations in eggs or sperm affect future generations by producing offspring with new characteristics. Mutations in body cells affect only the individual and may result in cancer.

96. Chapter Assessment Question 1 How does DNA control the structures and functions of a cell? Answer DNA determines the structure of proteins. Some proteins become important cell structures. Other proteins, such as enzymes, control chemical reactions that perform key life functions.

97. Chapter Assessment Question 2 The process through which the order of bases in messenger RNA codes for the order of amino acids in a protein is: D. point mutation C. replication B. translation A. transcription The answer is B.

98. Chapter Assessment Question 3 Why would scientists use nucleotide sequences to identify bodies of crime victims? Answer In comparing nucleotide sequences in the DNA of a crime victim with nucleotide sequences from a possible close relative of the crime victim, scientists can determine if the two are related.

99. Chapter Assessment Question 4 What happens when a stop codon is reached during translation? Answer When a stop codon is reached, translation ends and the amino acid strand is released from the ribosome.

100. Chapter Assessment Question 5 A ________ bond forms between adjacent amino acids during translation. D. peptide C. hydrogen B. phosphate A. nucleotide The answer is D.

101. Chapter Assessment Question 6 What is the difference between a purine and a pyrimidine? Answer A purine is a double-ringed nitrogenous base. A pyrimidine is a single-ringed nitrogenous base.

102. Chapter Assessment Question 7 Why is DNA replication important to cell division? Answer Without DNA replication, new cells would have only half the DNA of their parents. Species could not survive and individuals could not grow or reproduce successfully.

103. Chapter Assessment Question 8 At the beginning and end of replication, which of the following are instrumental in breaking and bonding the hydrogen bonds between bases? D. enzymes C. nucleotides B. purines A. pyrimidines The answer is D.

104. Chapter Assessment Question 9 What is the role of mRNA in protein synthesis? Answer The messenger RNA acts as a genetic message, providing the complete information, in sequences of codons, for the building of a protein.

105. Chapter Assessment Question 10 The DNA sequences of a parrot _________. D. contain exactly the same nucleotides as those of a beetle C. are exactly the same as those of a human B. are more similar to a fern than a dog A. are more similar to those of a clam than a robin The answer is D.

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107. End of Chapter 11 Show