1. Chapter 3 The Biological Basis of Life

2. Chapter Outline The Cell DNA Structure DNA Replication Regulatory Genes Protein Synthesis What is a Gene?

3. Chapter Outline Mutation: When Genes Change Chromosomes Karyotyping Chromosomes Cell Division New Frontiers Issue: Stem Cell Research: Promise and Controversy

4. The Cell Cells are the basic units of life. In some forms, such as bacteria, a single cell constitutes the entire organism. Complex life forms are made up of billions of cells. An adult human is made up of as many as 1,000 billion cells, all functioning in complex ways that promote the survival of the individual.

5. Cells Life on earth can be traced back 3.7 billion years in the form of prokaryotic cells. Prokaryotic cells are single celled organisms, such as bacteria and blue- green algae. Eukaryotic cells, structurally complex cells, appeared 1.2 billion years ago.

6. Bacterium Each one of these oval-shaped structures is a single- celled bacterium.

7. Structure of a Eukaryotic Cell The outer boundary of a cell is the cell membrane. Organelles are structures found in the cytoplasm: Mitochondria produce energy. Ribosomes manufacture protein The nucleus is surrounded by the cytoplasm and contains chromosomes.

8. Structure of a Eukaryotic Cell

9. Types of Cells Somatic cells are components of body tissue. Gametes are sex cells. Ova are produced in female ovaries. Sperm are produced in male testes. A zygote is the union between a sperm and an ovum.

10. Early DNA Researchers James Watson (left) and Francis Crick in 1953 with their model of the structure of the DNA molecule.

11. Question An adult human is made up of approximately how many cells? a) 1000 billion b) 10 million c) One trillion d) One billion

12. Answer: a An adult human is made up of approximately 1000 billion cells.

13. DNA Structure Cellular function and an organism’s inheritance depends on the structure and function of DNA. DNA is composed of two chains of nucleotides. A nucleotide consists of a sugar, a phosphate, and one of four nitrogenous bases.

14. Part of a DNA Molecule

15. DNA Structure Nucleotides form long chains. The two chains are held together by bonds formed on their bases with their complement on the other chain.  Adenine (A) is the complement of Thymine(T)  Guanine(G) is the complement of Cytosine(C)

16. The DNA Replication Process 1. Enzymes break the bonds between the DNA molecule. 2. Two nucleotide chains serve as templates for the formation of a new strand of nucleotides. 3. Unattached nucleotides pair with the appropriate complementary nucleotide

17. The DNA Replication Process 4. The result is two newly formed strands of DNA. 5. Each new strand is joined to one of the original strands of DNA.

18. DNA Replication

19. Hemaglobin Molecule

20. Hormones Substances (usually proteins) that are produced by specialized cells. Hormones travel to other parts of the body, where they influence chemical reactions and regulate various cellular functions.

21. Regulatory Proteins Proteins that can bind to DNA and modify the action of genes. Many are active only during certain stages of development. Amino acids  Small molecules that are the components of proteins.

22. Messenger RNA (Mrna) A form of RNA that’s assembled on a sequence of DNA bases It carries the DNA code to the ribosome during protein synthesis.

23. Proteins The major structural components of tissue. Enzymes are proteins that serve as catalysts, initiating chemical reactions in the body. Amino acids are the building blocks of protein. Proteins differ according to number of amino acids and the sequence in which they are arranged.

24. Protein Synthesis Ribosomes help convert the genetic message from the DNA into proteins. Messenger RNA (mRNA) carries the genetic message from the cell nucleus to the ribosome. Transfer RNA (tRNA),found in the cytoplasm, binds to one specific amino acid.

25. RNA and DNA RNA differs from DNA in three important ways: 1. It’s usually single-stranded. (This is true of the forms we discuss, but it’s not true for all.) 2. It contains a different type of sugar. 3. It contains the base uracil as a substitute for the DNA base thymine. (Uracil is attracted to adenine, just as thymine is.)

26. Question Which of the following is not true about RNA? a) It is single stranded. b) Some forms of RNA are involved with protein synthesis. c) It has a different type of sugar than DNA has. d) It contains the base thymine.

27. Answer : d The following is not true about RNA.  It contains the base thymine.

28. Characteristics of the DNA Code 1. The code is universal. The same basic messages apply to all life- forms on the planet, from bacteria to oak trees to humans. 2. The code is triplet. Each amino acid is specified by a sequence of three bases in the mRNA (the codon), which in turn is coded for by three bases in the DNA.

29. Characteristics of the DNA Code 3. The code is continuous—without pauses. 4. The code is redundant. While there are 20 amino acids, there are 4 DNA bases and 64 possible triplets or mRNA codons.

30. Protein Synthesis: Transcription The process of coding a genetic message for proteins by formation of mRNA. A portion of the DNA unwinds and serves as a template for the formation of a mRNA strand.

31. Transcription

32. Protein Synthesis: Translation The mRNA travels through the nuclear membrane to the ribosome. tRNAs arrive at the ribosome carrying their specific amino acids. The base triplets on the tRNA match up with the codons on the mRNA. As each tRNA line up in the sequence of mRNA codons their amino acids link to form a protein.

33. Assembly of an Amino Acid Chain in Protein Synthesis As the ribosome binds to the mRNA, tRNA brings a particular amino acid, specified by the mRNA codon, to the ribosome.

34. Assembly of an Amino Acid Chain in Protein Synthesis The tRNA binds to the first codon while a second tRNA–amino acid complex arrives at the ribosome.

35. Assembly of an Amino Acid Chain in Protein Synthesis The ribosome moves down the mRNA, allowing a third amino acid to be brought into position by another tRNA molecule. Note that the first two amino acids are now joined together.

36. Diagram of a DNA Sequence Being Transcribed

37. Genes A gene is the entire sequence of DNA bases responsible for the synthesis of a protein. A mutation occurs when the sequence of bases in a gene is altered. Mutations may interfere with an organisms ability to produce vital protein and may lead to a new variety within the species, hence, evolution.

38. Gene Structure The gene consists of exons and introns. Exons are DNA segments transcribed into mRNA that code for specific amino acids. Introns are DNA sequences not expressed during protein synthesis.

39. Homeobox Genes An evolutionarily ancient family of regulatory genes that directs the development of the overall body plan and the segmentation of body tissues.

40. Hox Genes The differences in these vertebrae are caused by Hox genes during embryonic development. The cervical (neck) vertebrae (a) have characteristics that differentiate them from the thoracic (b) and the lumbar vertebrae (c) of the lower back.

41. Universal Genetic Code The DNA code of all life on earth is composed of the same molecules and carries on similar functions. The universality of the genetic code implies a common ancestry for all life on the planet. Organisms differ according to the arrangement of the DNA.

42. Coding and Noncoding DNA

43. Sickle-cell Anemia A severe inherited hemoglobin disorder in which red blood cells collapse when deprived of oxygen. It results from inheriting two copies of a mutant allele. This allele is caused by a single base substitution in the DNA.

44. Gene Mutation Scanning electron micrograph of a normal, fully oxygenated red blood cell. Scanning electron micrograph of a collapsed, sickle shaped red blood cell that contains HBS.

45. Symptoms in People With Sickle-cell Anemia

46. Substitution of One Base at Position 6 Produces Sickling Hemoglobin

47. Chromosomes During Cell Division Scanning electron micrograph of human chromosomes during cell division. Note that these chromosomes are composed of two strands, or two DNA molecules.

48. Point Mutation A chemical change in a single base of a DNA sequence.

49. Chromatin The loose, diffuse form of DNA seen when a cell isn’t dividing. When it condenses, chromatin forms into chromosomes.  Chromosomes are discrete structures composed of DNA and protein found only in the nuclei of cells.  Chromosomes are visible under magnification only during certain phases of cell division.

50. Cell Division Cell division results in production of new cells. During cell division:  Cells are involved with normal cellular and metabolic processes.  The cell’s DNA becomes tightly coiled.  DNA is visible under a microscope as chromosomes.

51. Chromosome Structure A chromosome is composed of a DNA molecule and associated proteins. During normal cell functions, chromosomes exist as single-stranded structures. During cell division, chromosomes consist of two strands of DNA joined at the centromere. Since the DNA molecules have replicated, one strand of a chromosome is an exact copy of the other.

52. Chromosome Structure Centromere  The constricted portion of a chromosome.  After replication, the two strands of a double-stranded chromosome are joined at the centromere.

53. Chromosome Structure Locus  The position on a chromosome where a given gene occurs.  The term is sometimes used interchangeably with gene.

54. Chromosomes and Genetics Each species is characterized by a specific number of chromosomes.  Humans have 46 chromosomes. Chromosome pairs are called homologus:  These carry genetic information that influences the same traits.  They are not genetically identical.

55. Types of Chromosomes Autosomes - govern all physical characteristics except sex determination. Sex chromosomes - X and Y chromosome.  Mammal females have two X chromosomes.  Mammal males have one X and one Y chromosome.

57. Standard Chromosomal Complement in Various Organisms Organism Chromosome Number in Somatic Cells Chromosome Number in Gametes Human4623 Chimpanzee4824 Gorilla4824 Dog7839 Chicken7839

58. Standard Chromosomal Complement in Various Organisms Organism Chromosome Number in Somatic Cells Chromosome Number in Gametes Frog2613 Housefly126 Onion168 Corn2010 Tobacco4824

59. Karyotyping Chromosomes A karyotype is the chromosomal complement of an individual, or what is typical for a species.  Usually displayed in a photomicrograph, the chromosomes are arranged in pairs and according to centromere size and position. Physicians and genetic counselors routinely use karyotypes to help diagnose chromosomal disorders in patients, or in prenatal testing to identify chromosomal abnormalities in developing fetuses.

60. Alleles Alternate forms of a gene. Alleles occur at the same locus on paired chromosomes and thus govern the same trait. But because they’re different, their action may result in different expressions of that trait. The term is sometimes used synonymously with gene.

61. Karyotype of a Male Chromosomes arranged by size and position of the centromere, as well as by banding patterns.

62. Question There are basically two types of cells. They are: a) zygotes and nucleotides. b) cytoplasmic and nuclear. c) protein and mitochondrial. d) somatic and gametes.

63. Answer: d There are basically two types of cells. They are somatic and gametes.

64. Question The alternate form that a gene can take or the different expressions of a gene is a(n): a) karyotype. b) clone. c) allele. d) autosome.

65. Answer: c The alternate form that a gene can take or the different expressions of a gene is a(n) allele.

66. Mitosis Mitosis is cell division in somatic cells. Mitosis occurs during growth and repair/replacement of tissues. The result of mitosis is two identical daughter cells that are genetically identical to the original cell.

67. Steps in Mitosis 1. The 46 chromosomes line up in the center of the cell. 2. The chromosomes are pulled apart at the centromere. 3. The strands separate and move to opposite ends of the dividing cell. 4. The cell membrane pinches in and two new cells exist.

68. Mitosis

70. Meiosis Production of gametes (sex cells). 2 divisions result in 4 daughter cells. Each daughter cell contains 23 chromosomes. Resulting gamete may unite with another gamete to create a zygote. The zygote inherits the DNA, half from each parent, to develop and function normally.

71. Meiosis

73. Mitosis and Meiosis

74. Problems With Meiosis Nondisjunction occurs when chromosomes don’t separate during meiosis.  A gamete containing one less chromosome that fuses with a normal gamete will produce a zygote containing 45 chromosomes.  A gamete containing one extra chromosome that fuses with a normal gamete will produce a zygote containing 47 chromosomes.

75. Nondisjunction When chromosomes or chromosome strands don’t separate during either of the two divisions. The result is that one of the daughter cells receives two copies of the affected chromosome, while the other daughter cell receives none. If such an affected gamete unites with a normal gamete, the resulting zygote will have 45 or 47 chromosomes.

76. Question Which of the following is true for meiosis? a) It has only one division that duplicates the parent cell exactly. b) It produces gametes. c) When a mutation occurs it affects only the individual. d) It has no effect on evolution.

77. Answer: b The following is true for meiosis:  It produces gametes.

78. Examples of Nondisjunction in Sex Chromosomes Chromosomal Complement NameIncidenceManifestations XXXTrisomy X 1 per 1,000 female births Slight increase in sterility and mental impairment. In cases with more than three X chromosomes, mental retardation can be severe. XYY XYY syndrome 1 per 1,000 Affected males are fertile and tend to be taller than average.

79. Examples of Nondisjunction in Sex Chromosomes Chromosomal Complement NameIncidenceManifestations XO Turner syndrome 1 per 10,000 female births Short-stature, broad chests, webbed neck and sterility. Usually no mental impairment. Between 95 and 99% of affected fetuses die before birth.

80. Examples of Nondisjunction in Sex Chromosomes Chromosomal Complement NameIncidenceManifestations XXY Klinefelter syndrome 1 per 1,000 male births Reduced testicular development, reduced facial and body hair, breast development in half of all cases, reduced fertility.

81. Evolutionary Significance of Meiosis Meiosis and sexual reproduction are highly important evolutionary innovations. Meiosis increases genetic variation at a faster rate than mutation. Offspring in sexually reproducing species represent the combination of genetic information from two parents.

82. DNA Fingerprints Eight DNA fingerprints, one of which is from a blood sample left at an actual crime scene. The other seven are from suspects. By comparing the banding patterns, it is easy to identify the guilty party.

83. Polymerase Chain Reaction (PCR) Enables scientists to make of copies of DNA samples which can then be analyzed. Scientists use PCR to:  Examine nucleotide sequences in Neandertal fossils and Egyptian mummies  Identify DNA sequences unique to an individual.  Identify remains of victims of 911.  Exonerate people wrongly convicted of crimes and imprisoned for years.

84. Recombinant DNA Technology A process in which genes from the cell of one species are transferred to somatic cells or gametes of another species.

85. Nuclear Transfer Process a) The nucleus of an egg is drawn into a needle. b) The enucleated egg with only the cytoplasm remaining. c) The nucleus of a skin cell from the individual being cloned is injected into the egg. d) Electric shock causes the nucleus of the skin cell to fuse with the egg’s cytoplasm. e) The egg begins to divide, and a few days later the cloned embryo will be transferred into the uterus of a host animal.

86. Nuclear Transfer Process

87. Human Genome Project A genome is the entire genetic makeup of an individual or species. In humans, it’s estimated that each individual possesses 3 billion DNA nucleotides. Effort begun in 1990 to sequence the entire human genome, which consists of some 3 billion bases comprising approximately 25,000 to 30,000 genes. The goal was achieved in 2003.