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Chapter 3

Chapter 3. The Biological Basis of Life. Chapter Outline. The Cell DNA Structure DNA Replication Protein Synthesis Cell Division: Mitosis and Meiosis New Frontiers. The Cell. Cells are the basic units of life in all living organisms.

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Chapter 3

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  1. Chapter 3 The Biological Basis of Life

  2. Chapter Outline • The Cell • DNA Structure • DNA Replication • Protein Synthesis • Cell Division: Mitosis and Meiosis • New Frontiers

  3. The Cell • Cells are the basic units of life in all living organisms. • Complex life forms, such as plants and animals, are made up of billions of cells. • The cells of all living organisms share many similarities as a result of their common evolutionary past.

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

  5. 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.

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

  7. 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.

  8. 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)

  9. 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

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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Cell Division: Mitosis and Meiosis • 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.

  19. 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.

  20. Chromosomes and Genetics • Each species is characterized by a specific number of chromosomes. • Humans have 46 chromosomes. • Chromosome pairs are called homologus. • Homologous chromosomes carry genetic information influencing the same traits. • Homologous chromosomes are not genetically identical.

  21. 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.

  22. 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.

  23. 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.

  24. 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.

  25. 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.

  26. Problems With Meiosis • Errors in meiosis may lead to miscarriage. • 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.

  27. Abnormal Numbers of Chromosomes • Down's syndrome occurs because of three copies of chromosome #21. • Problems include mental retardation, heart defects and respiratory infections. • Nondisjunction may occur in the X and Y chromosomes and result in sterility.

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