1. A Guide to the Natural World David Krogh © 2011 Pearson Education, Inc. Chapter 9 Lecture Outline The Links in Life’s Chain: Genetics and Cell Division Biology Fifth Edition

2. © 2011 Pearson Education, Inc. 9.1 An Introduction to Genetics

3. © 2011 Pearson Education, Inc. An Introduction to Genetics DNA is an information-bearing molecule that plays a critical role in the reproduction, development, and everyday functioning of living things.

4. © 2011 Pearson Education, Inc. DNA DNA contains the information for the production of proteins, which carry out a wide variety of tasks in living things.

5. © 2011 Pearson Education, Inc. DNA One series of bases contains information for the production of one protein, while a different series of bases specifies a different protein. Each series of protein-specifying bases is known as a gene.

6. © 2011 Pearson Education, Inc. Genome Most of the cells in an organism contain a complete copy of that organism’s genome, meaning its collection of genetic information.

7. © 2011 Pearson Education, Inc. Genome Before cells divide, their genome must first be copied and the resulting copies apportioned evenly into what will become two daughter cells.

8. © 2011 Pearson Education, Inc. 9.2 An Introduction to Cell Division

9. © 2011 Pearson Education, Inc. Cell Division Cell division takes place because: Cells die and need to be replaced. Cells can only grow so large before they become dysfunctional. There are times in which an organism needs quantities of new cells above “replacement” level.

10. © 2011 Pearson Education, Inc. Cell Division Cell division includes: The duplication of DNA (replication) The apportioning of the copied DNA into two quantities in a parent cell (mitosis) The physical splitting of this parent cell into two daughter cells (cytokinesis)

11. © 2011 Pearson Education, Inc. Figure 9.4 cell nucleus 1. Replication DNA is duplicated. 2. Mitosis The two quantities of DNA are moved to opposite sides of the parent cell. 3. Cytokinesis The parent cell splits into two daughter cells. Cell Division

12. © 2011 Pearson Education, Inc. DNA Replication In DNA replication, the two strands of the double helix unwind, after which each single strand serves as a template for construction of a second, complementary strand of DNA.

13. © 2011 Pearson Education, Inc. DNA Replication The result is a doubling of the original quantity of DNA.

14. © 2011 Pearson Education, Inc. Figure 9.5 1. Original DNA molecule unwinds. 2. New DNA strands are synthesized from the two original strands. DNA Replication

15. © 2011 Pearson Education, Inc. 9.3 DNA in Chromosomes

16. © 2011 Pearson Education, Inc. DNA is Packaged in Chromosomes DNA comes packaged in units called chromosomes.

17. © 2011 Pearson Education, Inc. Chromosomes Chromosomes are composed of DNA and its associated proteins—a combined chemical complex called chromatin.

18. © 2011 Pearson Education, Inc.

19. Chromosomes and DNA Replication Chromosomes exist in an unduplicated state until such time as DNA replicates, prior to cell division.

20. © 2011 Pearson Education, Inc. Chromosomes and DNA Replication DNA replication results in chromosomes that are in duplicated state, meaning one chromosome composed of two identical sister chromatids.

21. © 2011 Pearson Education, Inc. (a) DNA is packaged in units called chromosomes DNA wraps around protein to make chromatin Chromatin folds up to make chromosomes duplicated chromosome cell DNA chromatin (b) DNA replication at two levels DNA replication...... has this effect at the chromosomal level. unduplicated chromosome (not actual shape) duplicated chromosome sister chromatids Figure 9.6

22. © 2011 Pearson Education, Inc. Matched Pairs Chromosomes in human beings (and many other species) come in matched pairs, with one member of each pair inherited from the mother, and the other member of each pair inherited from the father.

23. © 2011 Pearson Education, Inc. Matched Pairs Such homologous chromosomes have closely matched sets of genes on them, although many of these genes are not identical.

24. © 2011 Pearson Education, Inc. Homologous Chromosomes A given paternal chromosome may have genes that code, for example, for different hair or skin color than the counterpart genes on the homologous maternal chromosome.

25. © 2011 Pearson Education, Inc. Chromosomes Human beings have 46 chromosomes. 22 matched pairs and either a matched pair of X chromosomes (in females) or an X and a Y chromosome (in males).

26. © 2011 Pearson Education, Inc. Karyotype Figure 9.7

27. © 2011 Pearson Education, Inc. The Cell Cycle Cell division fits into the larger framework of the cell cycle, meaning a repeating pattern of growth, genetic replication, and cell division.

28. © 2011 Pearson Education, Inc. The Cell Cycle The cell cycle has two main phases: interphase and mitotic phase.

29. © 2011 Pearson Education, Inc. The Cell Cycle In interphase, the cell carries out its work, grows, and duplicates its chromosomes in preparation for division.

30. © 2011 Pearson Education, Inc. The Cell Cycle In mitotic phase, the duplicated chromosomes separate (mitosis) and the cell splits in two (cytokinesis).

31. © 2011 Pearson Education, Inc. 1. Interphase—G 1 In this gap-1 phase of the cell cycle, the cell is growing and carrying out its normal functions. 2. Interphase—S In this synthesis phase, the cell is replicating its DNA (duplicating its chromosomes) in preparation for mitosis and cytokinesis. 3. Interphase—G 2 In this gap-2 phase, DNA replication has been completed, and the cell continues with its normal functions, even as it prepares for mitosis and cytokinesis. 4. Mitosis The cell begins the process of apportioning its DNA into two opposite sides of itself. 5. Cytokinesis With mitosis nearly complete, the cell begins the process of splitting into two daughter cells. Once this is finished, each of the two cells moves back into G 1 of interphase. Cell cycle mitosis cytokinesis S G2G2 G1G1 Figure 9.9

32. © 2011 Pearson Education, Inc. 9.4 Mitosis and Cytokinesis

33. © 2011 Pearson Education, Inc. Mitosis and Cytokinesis There are four stages in mitosis: prophase, metaphase, anaphase, and telophase.

34. © 2011 Pearson Education, Inc. Mitosis The essence of the process is that duplicated chromosomes line up along an equatorial plane of the parent cell, called the metaphase plate, with the sister chromatids that make up each duplicated chromosome lying on opposite sides of the plate.

35. © 2011 Pearson Education, Inc. Mitosis Suggested Media Enhancement: Mitosis To access this animation go to folder C_Animations_and_Video_Files and open the BioFlix folder.

36. © 2011 Pearson Education, Inc. Mitosis Attached to fibers called microtubules, the sister chromatids are then pulled apart, to opposite poles of the parent cell.

37. © 2011 Pearson Education, Inc. pair of centrosomes nucleus replicated, uncondensed DNA spindle fibers (microtubules) mitotic spindle metaphase plate chromosomes (each a pair of sister chromatids joined together) End of interphase DNA has already duplicated back in S phase. Centrosome has doubled. Prophase Mitosis begins: Chromosomes take shape; the two centrosomes begin to move toward the cellular poles, sprouting microtubules as they go Metaphase Attachment and alignment: Microtubules attach to sister chromatids and align them at the metaphase plate. Mitosis and Cytokinesis Figure 9.10 (1 of 2)

38. © 2011 Pearson Education, Inc. separating chromatids spindle fibers shortening cleavage furrow Anaphase Separation: Sister chromatids are moved to opposite poles in the cell, each chromatid now becoming a full-fledged chromosome. Telophase and cytokinesis Completion of cytokinesis Exit from mitosis: Chromosomes decondense; nuclear envelopes form around the two separate complements of chromo- somes. Cleavage furrow begins to form. One cell becomes two: The cell membrane pinches together completely; membranes on either side fuse together, creating two cells. Beginning of interphase These two cells now enter the G1 phase of interphase. Figure 9.10 (2 of 2)

39. © 2011 Pearson Education, Inc. Mitosis and Cytokinesis Once cell division is complete, sister chromatids that once formed a single chromosome will reside in separate daughter cells, with each sister chromatid now functioning as a full-fledged chromosome.

40. © 2011 Pearson Education, Inc. Mitosis and Cytokinesis Cytokinesis in animal cells works through a ring of protein filaments that tightens at the middle of a dividing cell.

41. © 2011 Pearson Education, Inc. Cytokinesis in Animals Figure 9.11

42. © 2011 Pearson Education, Inc. Cytokinesis Membranes on the portions of the cell being pinched together then fuse, resulting in two daughter cells.

43. © 2011 Pearson Education, Inc. 9.5 Cell Division in Plants and Bacteria

44. © 2011 Pearson Education, Inc. Variations in Cell Division Because of their cell walls, plant cells must carry out cytokinesis differently from animal cells.

45. © 2011 Pearson Education, Inc. Plant Cell Division The plant’s solution is to grow new cell walls and plasma membranes near the metaphase plate, thus dividing the parent cell into two daughter cells.

46. © 2011 Pearson Education, Inc. Cytokinesis in Plants Figure 9.12 cell wall vesicles plasma membrane 1. Membrane-lined vesicles accumulate near the metaphase plate. The vesicles contain precursors to the cell wall. 2. Vesicles fuse together, forming a cell plate that grows toward the parent cell wall. 3. The newly formed plasma membrane and cell wall fuse with the parent plasma membrane and cell wall, forming two distinct daughter cells. two daughter cells

47. © 2011 Pearson Education, Inc. Binary Fission Prokaryotes such as bacteria employ a process called binary fission.

48. © 2011 Pearson Education, Inc. Binary Fission They double their single, circular chromosome, with the two resulting chromosomes attaching to different sites on the plasma membrane.

49. © 2011 Pearson Education, Inc. Binary Fission Then, an outgrowth of plasma membrane and cell wall, called a septum, begins growing from opposite sides of the cell, in between the two chromosomes.

50. © 2011 Pearson Education, Inc. Binary Fission When the two septum extensions join in the middle, they divide the one cell into two.

51. © 2011 Pearson Education, Inc. cell wall chromosome cell membrane parental bacterial cell two daughter cells 1. Bacterial cell starts with a single, circular chromosome attached to its plasma membrane. 2. The chromosome replicates and the daughter chromosomes attach to different sites on the plasma membrane. 3. The cell membrane and wall grow an extension between the attachment points of the two chromosomes. 4. The cell wall and membrane join together in the middle, resulting in two new cells. Binary Fission in Bacteria Figure 9.13

52. © 2011 Pearson Education, Inc. Cell Division in Bacteria Animation 9.1: Cell Division for Bacteria