1. Copyright © 2009 Pearson Education, Inc. Lectures by Gregory Ahearn University of North Florida Chapter 8 The Continuity of Life: How Cells Reproduce

2. Copyright © 2009 Pearson Education Inc. 8.1 Why Do Cells Divide?  Cells reproduce by cell division. One cell gives rise to two or more cells, called _______________ cells. Each daughter cell receives a complete set of heredity information—from the parent cell—and about half of the cytoplasm.

3. Copyright © 2009 Pearson Education Inc. 8.1 Why Do Cells Divide?  Cell division transmits hereditary information to each daughter cell. The hereditary information in each cell is deoxyribonucleic acid (DNA). DNA is contained in ________________. A molecule of DNA consists of smaller subunits called _____________.  Segments of different lengths along a DNA molecule are the units of inheritance called genes.  Each gene spells out the instructions for making the proteins of the cell.

4. Copyright © 2009 Pearson Education Inc. Fig. 8-1 nucleotide phosphate base sugar A single strand of DNAThe double helix (a)(b) A C A T A A A T T T GC A T CG G G C C  The four bases are adenine (A), thymine (T), guanine (G), and cytosine (C).  The nucleotides are held together by __________ bonding between the bases.

5. Copyright © 2009 Pearson Education Inc. 8.1 Why Do Cells Divide?  When a cell divides, it first ____________ its DNA, and each copy is transferred into each daughter cell.  Cell division is required for growth and development. Cell division in which the daughter cells are genetically identical to the parent cell is called __________ cell division. After cell division, the daughter cells may grow and divide again, or may differentiate, becoming specialized for specific functions. The repeating pattern of division, growth, and differentiation followed again by division is called the cell cycle.

6. Copyright © 2009 Pearson Education Inc. 8.1 Why Do Cells Divide?  Most multicellular organisms have three categories of cells. Stem cells: retain the ability to divide and can differentiate into a variety of cell types Other cells capable of dividing: typically differentiate only into one or two different cell types Permanently differentiated cells: differentiated cells that can never divide again

7. Copyright © 2009 Pearson Education Inc. 8.1 Why Do Cells Divide?  Cell division is required for sexual and asexual reproduction. Sexual reproduction in eukaryotic organisms occurs when offspring are produced by the fusion of gametes (sperm and eggs) from two adults. Gametes are produced by __________ cell division, which results in daughter cells with exactly half of the genetic information of their parent cells. Fertilization of an egg by a sperm results in the restoration of the full complement of hereditary information in the offspring.

8. Copyright © 2009 Pearson Education Inc. 8.1 Why Do Cells Divide?  Reproduction in which offspring are formed from a single parent, without having a sperm fertilize an egg, is called __________ reproduction. Asexual reproduction produces offspring that are genetically identical to the parent. Examples of asexual reproduction occur in bacteria, single-celled eukaryotic organisms, multicellular organisms such as Hydra, and many trees, plants, and fungi.

9. Copyright © 2009 Pearson Education Inc. Cell division in Paramecium Dividing bacteria Hydra reproduces asexually by budding A grove of aspens often consists of genetically identical trees produced by asexual reproduction The trees in this grove have already lost their leaves The trees in this grove are still green The trees in this grove have begun to change color bud (b) (a) (c)(d) Fig. 8-2

10. Copyright © 2009 Pearson Education Inc. 8.2 What Occurs During The Prokaryotic Cell Cycle?  The prokaryotic cell cycle consists of a long period of growth, during which the cell duplicates its DNA. Fig. 8-3a The prokaryotic cell cycle cell division by binary fission cell growth and DNA replication (a)

11. Copyright © 2009 Pearson Education Inc. 8.2 What Occurs During The Prokaryotic Cell Cycle?  Cell division in prokaryotes occurs by binary fission, which means “splitting in two.”  The prokaryotic chromosome is attached at one point to the plasma membrane of the cell. Fig. 8-3b(1) cell wall plasma membrane circular DNA attachment site The circular DNA double helix is attached to the plasma membrane at one point.

12. Copyright © 2009 Pearson Education Inc. 8.2 What Occurs During The Prokaryotic Cell Cycle?  During the growth phase of the cell cycle, the DNA is replicated, producing two identical chromosomes that become attached to the plasma membrane at two separate points.  As the cell grows, new plasma membrane is added between the attachment points of the chromosomes, pushing them apart. Fig. 8-3b(2)(3) The DNA replicates and the two DNA double helices attach to the plasma membrane at nearby points. New plasma membrane is added between the attachment points, pushing them further apart.

13. Copyright © 2009 Pearson Education Inc. 8.2 What Occurs During The Prokaryotic Cell Cycle?  Once the cell has doubled in size, the plasma membrane in the middle of the cell grows inward between the two DNA attachment sites. Fig. 8-3b(4) The plasma membrane grows inward at the middle of the cell.

14. Copyright © 2009 Pearson Education Inc. 8.2 What Occurs During The Prokaryotic Cell Cycle? Fig. 8-3b(5) The parent cell divides into two daughter cells.  Fusion of the plasma membrane along the equator of the cell completes binary fission, producing two daughter cells, each with its own chromosomes  The two daughter cells are genetically identical to each other and to the parent cell

15. Copyright © 2009 Pearson Education Inc. 8.3 How Is The DNA In Eukaryotic Cells Organized?  Unlike prokaryotic chromosomes, eukaryotic chromosomes are separated from the cytoplasm by a membrane-bound nucleus.  Eukaryotic cells always have multiple chromosomes.  Eukaryotic chromosomes contain more DNA than prokaryotic chromosomes.  The eukaryotic chromosome consists of DNA bound to __________.

16. Copyright © 2009 Pearson Education Inc. 8.3 How Is The DNA In Eukaryotic Cells Organized?  Prior to cell division, the DNA within each chromosome is replicated. The duplicated chromosomes then consist of two DNA double helixes and associated proteins that are attached to each other at the centromere.  During cell division, proteins fold up the DNA into compact structures that are 10 times shorter than during the rest of the cell cycle. Fig. 8-4

17. Copyright © 2009 Pearson Education Inc. 8.3 How Is The DNA In Eukaryotic Cells Organized? Each of the duplicated chromosomes attached at the centromere is called a sister ___________. During mitotic cell division, the sister chromatids separate and each becomes a separate chromosome that is delivered to one of the two resulting daughter cells.

18. Copyright © 2009 Pearson Education Inc. sister chromatids centromeregenes duplicated chromosome (2 DNA double helices) A replicated chromosome consists of two sister chromatids Sister chromatids separate during cell division (a) (b) independent daughter chromosomes, each with one identical DNA double helix 8.3 How Is the DNA In Eukaryotic Cells Organized? Fig. 8-5

19. Copyright © 2009 Pearson Education Inc. 8.3 How Is The DNA In Eukaryotic Cells Organized?  Eukaryotic chromosomes usually occur in pairs. An entire set of stained chromosomes from a single cell is called a _____________. Fig. 8-6 sex chromosomes

20. Copyright © 2009 Pearson Education Inc. 8.3 How Is The DNA In Eukaryotic Cells Organized?  The nonreproductive cells of many organisms have chromosomes in pairs, with both members of the pair being the same length. The chromosomes are the same length and have the same staining properties because they have the same genes arranged in the same order.  Chromosomes with the same genes are called homologous chromosomes, or _____________.  Cells with pairs of homologous chromosomes are called _________.  Homologous chromosomes are usually not identical.

21. Copyright © 2009 Pearson Education Inc. 8.3 How Is The DNA In Eukaryotic Cells Organized?  A typical human cell has ____ pairs of chromosomes.  22 of these pairs have a similar appearance and are called _________.  Human cells also have a pair of ____ chromosomes, which differ from each other in appearance and in genetic composition. Females have two ___ chromosomes. Males have one ___ and one ___ chromosome.

22. Copyright © 2009 Pearson Education Inc. 8.3 How Is The DNA In Eukaryotic Cells Organized?  Not all cells have paired chromosomes.  The ovaries and testes undergo a special kind of cell division, called meiotic cell division, to produce gametes (________ and _________). Gametes contain only one member of each pair of autosomes, plus one of the two sex chromosomes. Cells with half the number of each type of chromosome are called __________ cells. Fusion of two haploid cells at ______________ produces a diploid cell with the full complement of chromosomes.

23. Copyright © 2009 Pearson Education Inc. 8.3 How Is The DNA In Eukaryotic Cells Organized?  The number of different types of chromosomes in a species is called the haploid number and is designated n. In humans, n = 23.  Diploid cells contain 2n chromosomes. Humans body cells contain 2n = 46 (2 x 23) chromosomes.

24. Copyright © 2009 Pearson Education Inc. 8.4 What Occurs During The Eukaryotic Cell Cycle?  The eukaryotic cell cycle is divided into two major phases: interphase and cell division. During interphase, the cell acquires nutrients from its environment, grows, and duplicates its chromosomes. During cell division, one copy of each chromosome and half of the cytoplasm are parceled out into each of two daughter cells.

25. Copyright © 2009 Pearson Education Inc. cell growth synthesis of DNA; chromosomes are duplicated cell growth and differentiation telophase and cytokinesis anaphase metaphase prophase mitotic cell division interphase 8.4 What Occurs During The Eukaryotic Cell Cycle?  The eukaryotic cell cycle Fig. 8-7

26. Copyright © 2009 Pearson Education Inc. 8.4 What Occurs During The Eukaryotic Cell Cycle?  There are two types of division in eukaryotic cells: mitotic cell division and meiotic cell division. ___________ cell division may be thought of as ordinary cell division, such as occurs during development from a fertilized egg, during asexual reproduction, and in skin, liver, and the digestive tract every day. ___________ cell division is a specialized type of cell division required for sexual reproduction.

27. Copyright © 2009 Pearson Education Inc. 8.4 What Occurs During The Eukaryotic Cell Cycle?  Mitotic cell division Mitotic cell division consists of nuclear division (called mitosis) followed by cytoplasmic division (called cytokinesis) and the formation of two daughter cells.  Meiotic cell division: Is a prerequisite for sexual reproduction in all eukaryotic organisms. Meiotic cell division involves a specialized nuclear division called meiosis. It involves two rounds of cytokinesis, producing four daughter cells that can become gametes.

28. Copyright © 2009 Pearson Education Inc. 8.4 What Occurs During The Eukaryotic Cell Cycle?  The life cycle of eukaryotic organisms include both mitotic and meiotic cell division. A new generation begins with the fusion of two gametes. Through mitosis and differentiation, the fertilized egg grows and develops a multicellular body. Meiotic cell division generates new gametes that may unite with other gametes to produce the next generation.

29. Copyright © 2009 Pearson Education Inc. haploid diploid meiotic cell division in testes meiotic cell division in ovaries adults egg fertilized egg fusion of gametes sperm embryo baby mitotic cell division, differentiation, and growth 8.4 What Occurs During The Eukaryotic Cell Cycle?  Mitotic and meiotic cell division in the human life cycle Fig. 8-8