1. The Biological Basis of Life
Chapter 3
The Biological Basis of Life

2. Chapter Outline The Cell DNA Structure DNA Replication
Protein Synthesis

3. Chapter Outline What is a Gene? Regulatory Genes Cell Division
Chromosomes, Mitosis, Meiosis
New Frontiers
Why It Matters

4. Focus Questions What is the biological basis of life?
Does it vary from species to species?
How do human beings fit into a biological continuum?

5. Genetics
The study of gene structure and action, and the patterns of inheritance of traits from parent to offspring.
Genetic mechanisms are the foundation for evolutionary change.

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

7. Cells

8. Structure of a Generalized Eukaryotic Cell

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

10. Cells
Life on earth can be traced back 3.7 billion years to single celled organisms, such as bacteria and blue-green algae.
Eukaryotic cells, cells with a nucleus, appeared 1.2 billion years ago.
A three-dimensional structure composed of carbohydrates, lipids (fats), nucleic acids, and proteins

11. Cell Nucleus
A discrete unit surrounded by a thin membrane, called the nuclear membrane.
Inside are two kinds of nucleic acids, molecules that contain genetic information that controls the cell’s function.

12. Molecules Structures made up of two or more atoms.
Molecules can combine with other molecules to form more complex structures.

13. Nucleic Acids
DNA (deoxyribonucleic acid)
RNA (ribonucleic acid)

14. Cytoplasm
Surrounds the nucleus and contains many other types of organelles involved in various activities, such as breaking down nutrients and converting them to other substances, storing and releasing energy, releasing waste, and manufacturing proteins in a process called protein synthesis.

15. Organelles
Mitochondria - oval structures enclosed within a folded membrane, containing their own distinct DNA, called mitochondrial DNA (mtDNA)
Ribosomes – roughly symmetrical and partly composed of RNA; essential in protein synthesis

16. Cells
Somatic cells – celllular components of body tissues, such as muscle, bone, skin, nerve, heart, and brain
Gametes – sex cells involved in reproduction and not important as structural components of the body
Egg cells produced in female ovaries
Sperm cells produced n male testes
Zygote – union of sex cells to form the potential of developing into a new individual; in this way gametes transmit genetic information from parent to offspring.

17. 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, comprising a double strand or double helix.
A nucleotide consists of a sugar, a phosphate, and one of four nitrogenous bases.

18. The DNA Molecule
James Watson (left) and Francis Crick in with their model of the structure of the DNA molecule.

19. 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)

20. Complementary
In genetics, referring to the fact that DNA bases form base pairs in a precise manner.
For example, adenine can bond only to thymine.
These two bases are said to be complementary because one requires the other to form a complete DNA base.

21. Part of a DNA Molecule

22. DNA Replication
Cells multiply by dividing, making exact copies of themselves and enabling organisms to grow and injured tissues to heal.
The DNA molecule is able to make copies of itself.

23. DNA Replication

24. Enzymes
Specialized proteins that initiate and direct chemical reactions in the body.
Replication begins when enzymes break the bonds between bases throughout the DNA molecule, separating two previously joined strands of nucleotides and leaving their bases exposed.

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

26. Proteins
Complex, three dimensional molecules that function through their ability to bind to other molecules
The protein hemoglobin, found in red blood cells, is able to bind to oxygen, which carries it throughout the body

27. 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.

28. Hemoglobin Molecule
Hemoglobin molecules are composed of four chains of amino acids (two “alpha” chains and two “beta” chains).
The red structures are the portions that bind to oxygen.

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

30. Amino Acids Small molecules that are the components of proteins.
Amino acids are the building blocks of protein.
Proteins differ according to number of amino acids and the sequence in which they are arranged

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

32. 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.

33. Codons
Triplets of messenger RNA bases that code for specific amino acids during protein synthesis.

34. Transfer RNA (tRNA)
The type of RNA that binds to amino acids and transports them to the ribosome during protein synthesis.

35. 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.

36. Transcription

38. Transcription The two DNA strands have partly separated.
Free messenger RNA (mRNA) nucleotides have been drawn to the template strand, and a strand of mRNA is being made.
Note that the mRNA strand will exactly complement the DNA template strand, except that uracil (U) replaces thymine (T).

39. 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.

40. What is a Gene?
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 the ability to produce vital protein and may lead to a new variety within the species, hence, evolution.

41. Recently, geneticists have learned that only some parts of genes, called exons, are actually transcribed into mRNA (most of the nucleotide sequences in genes are not expressed during protein synthesis.
Some noncoding sequences, called introns, are initially transcribed into mRNA and then clipped out.

42. Regulatory Genes
Genes that code for the production of proteins that can bind to DNA and modify the action of genes.
Many are active only during certain stages of development.

43. Homeobox Genes (Hox genes)
An evolutionarily ancient family of regulatory genes (highly conserved) that directs the development of the overall body plan and the segmentation of body tissues.

44. Vertebrae and Hox Genes
The cervical vertebrae (a) have characteristics that differentiate them from the thoracic vertebrae (b) attached to the ribs, and the lumbar vertebrae (c) of the lower back.
Hox genes determine the overall pattern of each type of vertebra and of each individual vertebra.

45. 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.

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

48. 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.

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

51. Types of Chromosomes Mammal females have two X 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.

52. 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.

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

54. Mitosis The cell is involved in metabolic activities.
DNA replication occurs, but chromosomes are not visible.

55. Mitosis
The nuclear membrane disappears, and double-stranded chromosomes are visible.

56. Mitosis
The chromosomes align themselves at the center of the cell.

57. Mitosis
The chromosomes split at the centromere, and the strands separate and move to opposite ends of the dividing cell.

58. Mitosis The cell membrane pinches in as the cell continues to divide.
The chromosomes begin to uncoil (not shown here).

59. Mitosis
After mitosis is complete, there are two identical daughter cells.
The nuclear membrane is present, and chromosomes are no longer visible.

60. Meiosis Cell division in specialized cells in ovaries and testes.
Meiosis involves two divisions and results in four daughter cells, each containing only half the original number of chromosomes.
These cells can develop into gametes.

61. Recombination
Sometimes called crossing over; the exchange of genetic material between partner chromosomes during meiosis.

62. Mitosis

63. Meiosis

64. Similar to the formal already present for the presentation of Mitosis
Meiosis is ultimately more important to understand, so it is even more deserving of a detailed presentation

66. 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.

67. Problems with Meiosis
In order for fetal development to occur normally, the meiotic process needs to be exact
If chromosomes or chromosome strands do not separate during either of the two divisions, serious problems can develop
Failure to separate is called nondisjunction

68. Polymerase Chain Reaction (PCR)
Allows 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 an individual DNA sequences.
Identify remains of victims of 911.
Exonerate people wrongly convicted of crimes.

69. 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 person.

70. Recombinant DNA Technology
A process in which genes from the cell of one species are transferred to somatic cells or gametes of another species.
Production of human gene products such as insulin
Genetic manipulation

71. Clones Organisms that are genetically identical to another organism.
The term may also be used in referring to genetically identical DNA segments, molecules, and cells.

72. Human Genome Project
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.
Scientists are still several years away from identifying the functions of many of the proteins produced by these genes.

73. Why It Matters
The latest developments in assessing the genetic sequences of chimpanzees and humans have confirmed similarities in genes that code for proteins and unanticipated differences in sequences that don’t code for proteins.
Tiny differences in protein-coding sequences may explain why humans are susceptible to diseases like cholera, malaria, and influenza while chimpanzees apparently are not.

74. Quick Quiz

75. 1. The entire sequence of DNA bases on the chromosome that code for a particular polypeptide chain is a(n)
ribosome.
amino acid.
gene.
polypeptide chain.

76. Answer: c
The entire sequence of DNA bases on the chromosome that code for a particular polypeptide chain is a gene.

77. 2. Which of the following is NOT true about RNA?
It is single stranded.
Some forms of RNA are involved with protein synthesis.
It has a different type of sugar than DNA has.
It contains the base thymine.

78. Answer : d The following is NOT true about RNA.
It contains the base thymine.

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

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

81. 4. A chromosomes is composed of _________________and __________.

82. Answer: a DNA molecule and proteins
A chromosome is composed of a DNA molecule and proteins.

83. 5. Somatic cell division is termed _________________ .

84. Answer: mitosis
Somatic cell division is termed mitosis.