Cell Growth and Division

1. Cell Growth and Division Chapter 10 P 272- 301 Chap 10: Cell Growth and Division 2009

2. Cell Division About 2 trillion cells- about 25 million cells per second- are produced by an adult human body every day. All cells come from the division of preexisting cells. (cell theory) Cell division or reproduction is the process by which cells produce offspring cells. Cell division differs in prokaryotes and eukaryotes. Cell reproduction in both prok and euk produce the same result – two cells from one!!

3. Review What are the three parts to the cell theory? • All living organisms are composed of one or more cells. • Cells are the basic units of structure and function in an organism. • Cells come only from the reproduction of existing cells. Four things common is all cells: cell membrane, cytoplasm, DNA, ribosomes

4. How does a cell produce a new cell? 10.1- Why do cells Divide? 10.2- How do cells Divide? 10.3- How does a cell control the process of cell division? 10.4- How does a single undifferentiated cell lead to a complex multicellular organism? Chap 10: Cell Growth and Division 2009

5. Voc Terms 10.1- 10.2 • Cell Division • Asexual reproduction • Sexual reproduction • Chromosomes • Chromatin • Cell cycle • Interphase • Mitosis • Cytokinesis • Prophase • Centromere • Chromatid • Centriole • Metaphase • Anaphase • telophase Chap 10: Cell Growth and Division 2009

6. THINK ABOUT IT –Limits to Cell Size • When a living thing grows, what happens to its cells? • What is there about growth that requires cells to divide and reproduce themselves? What are some of the difficulties a cell faces as it increases in size? The larger a cell becomes, the more demands the cell places on its DNA. In addition, a larger cell is less efficient in moving nutrients and waste materials across its cell membrane. Chap 10: Cell Growth and Division 2009

7. Information “Overload” • Living cells store critical information in DNA. • As a cell grows, that information is used to build the molecules needed for cell growth. • As size increases, the demands on that information grow as well. If a cell were to grow without limit, an “information crisis” would occur. Chap 10: Cell Growth and Division 2009

8. Information “Overload” • Compare a cell to a growing town. The town library has a limited number of books. As the town grows, these limited number of books are in greater demand, which limits access. • A growing cell makes greater demands on its genetic “library.” If the cell gets too big, the DNA would not be able to serve the needs of the growing cell. Chap 10: Cell Growth and Division 2009

9. Exchanging Materials • Food, oxygen, and water enter a cell through the cell membrane. Waste products leave in the same way. • The rate at which this exchange takes place depends on the surface area of a cell. • The rate at which food and oxygen are used up and waste products are produced depends on the cell’s volume. • The ratio of surface area to volume is key to understanding why cells must divide as they grow. Chap 10: Cell Growth and Division 2009

10. Ratio of Surface Area to Volume • Imagine a cell shaped like a cube. As the length of the sides of a cube increases, its volume increases faster than its surface area, decreasing the ratio of surface area to volume. • If a cell gets too large, the surface area of the cell is not large enough to get enough oxygen and nutrients in and waste out. Chap 10: Cell Growth and Division 2009

11. Traffic Problems • To use the town analogy again, as the town grows, more and more traffic clogs the main street. It becomes difficult to get information across town and goods in and out. • Similarly, a cell that continues to grow would experience “traffic” problems. If the cell got too large, it would be more difficult to get oxygen and nutrients in and waste out. Chap 10: Cell Growth and Division 2009

12. Division of the Cell • Before a cell grows too large, it divides into two new “daughter” cells in a process called cell division. • Before cell division, the cell copies all of its DNA. • It then divides into two “daughter” cells. Each daughter cell receives a complete set of DNA. • Cell division reduces cell volume. It also results in an increased ratio of surface area to volume, for each daughter cell. Chap 10: Cell Growth and Division 2009

13. Cell Division and Reproduction How do asexual and sexual reproduction compare? • The production of genetically identical offspring from a single parent is known as asexual reproduction. • Offspring produced by sexual reproduction inherit some of their genetic information from each parent. Chap 10: Cell Growth and Division 2009

14. Asexual Reproduction • In multicellular organisms, cell division leads to growth. It also enables an organism to repair and maintain its body. • In single-celled organisms, cell division is a form of reproduction. Chap 10: Cell Growth and Division 2009

15. Asexual Reproduction • Asexual reproduction is reproduction that involves a single parent producing an offspring. The offspring produced are, in most cases, genetically identical to the single cell that produced them. • Asexual reproduction is a simple, efficient, and effective way for an organism to produce a large number of offspring. • Both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can reproduce asexually. • -Bacteria cells reproduce by binary fission Chap 10: Cell Growth and Division 2009

16. Sexual Reproduction - In sexual reproduction, offspring are produced by the fusion of two sex cells – one from each of two parents. These fuse into a single cell before the offspring can grow. • The offspring produced inherit some genetic information from both parents. • Most animals and plants, and many single-celled organisms, reproduce sexually. Chap 10: Cell Growth and Division 2009

17. Cell Division -Eukaryotes Two main types of division: • Mitosis- results in new cells with genetic material that is identical to the genetic material of original cell During: growth, development, repair, asexual reproduction (production of offspring from one parent) 2. Meiosis- occurs during the formation of gametes (reproductive cells, 1n), reduces the chromosome number by ½ in new cells, often combine to make 2n cells

18. Comparing Sexual and Asexual Reproduction Chap 10: Cell Growth and Division 2009

19. 8.2- THINK ABOUT IT • What role does cell division play in your life? • Does cell division stop when you are finished growing? What is the role of chromosomes in cell division? • Chromosomes make it possible to separate DNA precisely during cell division Chap 10: Cell Growth and Division 2009

20. Chromosomes • The genetic information that is passed on from one generation of cells to the next is carried by chromosomes. • Every cell must copy its genetic information before cell division begins. • Each daughter cell gets its own copy of that genetic information. • Cells of every organism have a specific number of chromosomes. Chap 10: Cell Growth and Division 2009

21. Prokaryotic Chromosomes • Prokaryotic cells lack nuclei. Instead, their DNA molecules are found in the cytoplasm. • Most prokaryotes contain a single, circular DNA molecule, or chromosome, that contains most of the cell’s genetic information. Chap 10: Cell Growth and Division 2009

22. Eukaryotic Chromosomes • In eukaryotic cells, chromosomes are located in the nucleus, and are made up of chromatin. Chap 10: Cell Growth and Division 2009

23. Chromatin is composed of DNA and histone proteins. Chap 10: Cell Growth and Division 2009

24. DNA coils around histone proteins to form nucleosomes. Chap 10: Cell Growth and Division 2009

25. The nucleosomes interact with one another to form coils and supercoils that make up chromosomes. Chap 10: Cell Growth and Division 2009

27. Chromosomes structure cont: • Chromosomes contain 2 identical halves each half of the chromosome is called a chromatid • Chromatids form when the DNA makes a copy of itself before cell division • When the cell divides each ½ gets a copy • Chromatids are attached by the centromere • When DNA is not tightly packed it is call chromatin • Prokaryotes DNA is simple, circular, one chromosome, very compact to fit in the cell

29. Chromosomes Numbers • Each species has a set number of chromosomes Must know terms: • Sex chromosomes: are chromosomes that determine the sex of an organism, they may also carry genes for other characteristics (X, Y) (2 humans) • Autosomes- all non sex chromosomes (44 of humans )

30. Chromosomes Numbers cont: 3. Homologous chromosomes- they are chromosomes that are the same sex and shape and carry genes from the same traits 4. Karyotype- photomicrograph of chromosomes in a normal dividing cell found in human cells (46 chromosomes) 22 homologous pairs of autosomes 2 sex chromosomes

31. Karyotype

32. Diploid (2n) and haploid (n) • If a cell is said to have 2 sets of chromosomes it is said it is diploid • They have two sex chromosomes in animals including animals • Except for reproductive cells like sperm and eggs or generally called gametes Ex the 2n or diploid or number of chromosomes is 46 and 22 pairs If it is haploid it contains only one set of chromosomes for example only has one set of the autosomes and sex chromosomes 23 total

34. The Cell Cycle What are the main events of the cell cycle? • During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells. Chap 10: Cell Growth and Division 2009

35. The Prokaryotic Cell Cycle • The prokaryotic cell cycle is a regular pattern of growth, DNA replication, and cell division. • Most prokaryotic cells begin to replicate, or copy, their DNA once they have grown to a certain size. • When DNA replication is complete, the cells divide through a process known as binary fission. Chap 10: Cell Growth and Division 2009

36. Cell division in prokaryotes • Have no true nuclei or membrane-bound organelles • DNA is not coiled around proteins- it is circular attached to the inner surface of the plasma membrane like a rope attached to the inner wall of a tent • Process of cell division is Binary fission

37. Binary fission Is the division of a prok into two offspring cells 1. DNA is copied  get two identical chromosomes 2. A new cell membrane then begins to develop between the two DNA copies 3. Cell grows till its 2x the original size 4. Cells split containing identical chromosomes

38. Binary fission

39. The Eukaryotic Cell Cycle • The eukaryotic cell cycle consists of four phases: G1, S, G2, and M. • Interphase is the time between cell divisions. It is a period of growth that consists of the G1, S, and G2 phases. The M phase is the period of cell division. Chap 10: Cell Growth and Division 2009

40. G1 Phase: Cell Growth • In the G1 phase, cells increase in size and synthesize new proteins and organelles. Chap 10: Cell Growth and Division 2009

41. S Phase: DNA Replication • In the S (or synthesis) phase, new DNA is synthesized when the chromosomes are replicated. Chap 10: Cell Growth and Division 2009

42. G2 Phase: Preparing for Cell Division • In the G2 phase, many of the organelles and molecules required for cell division are produced. Chap 10: Cell Growth and Division 2009

43. M Phase: Cell Division • In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis. • Mitosis is the division of the cell nucleus. • Cytokinesis is the division of the cytoplasm. • Or a G0: stage in which the cell is mature and no longer dividing Chap 10: Cell Growth and Division 2009

45. What events occur during each of the four phases of mitosis? • Division of the nucleus • Occurs during cell division • Continuous process that allows for the organized distribution of cell’s copied DNA to offspring cells • Divided into four phases PMAT 1. prophase 2. metaphase 3. Anaphase 4. telophase Chap 10: Cell Growth and Division 2009

46. Important Cell Structures Involved in Mitosis • Chromatid – each strand of a duplicated chromosome • Centromere – the area where each pair of chromatids is joined • Centrioles – tiny structures located in the cytoplasm of animal cells that help organize the spindle • Spindle – a fanlike microtubule structure that helps separate the chromatids Chap 10: Cell Growth and Division 2009

47. Prophase • During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible. Chap 10: Cell Growth and Division 2009

48. Prophase • During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible. • The centrioles move to opposite sides of nucleus and help organize the spindle. Chap 10: Cell Growth and Division 2009

49. Prophase • During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible. • The centrioles move to opposite sides of nucleus and help organize the spindle. • The spindle forms and DNA strands attach at a point called their centromere. Chap 10: Cell Growth and Division 2009

50. Prophase • During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible. • The centrioles move to opposite sides of nucleus and help organize the spindle. • The spindle forms and DNA strands attach at a point called their centromere. • The nucleolus disappears and nuclear envelope breaks down. Chap 10: Cell Growth and Division 2009