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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The life cycle of a multicellular organism includes –development –reproduction.

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Presentation on theme: "Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The life cycle of a multicellular organism includes –development –reproduction."— Presentation transcript:

1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The life cycle of a multicellular organism includes –development –reproduction This sea star embryo (morula) shows one stage in the development of a fertilized egg (fusion of egg and sperm) –The cluster of cells will continue to divide as development proceeds by a series of cell division How to Make a Sea Star

2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Some organisms can also reproduce asexually –This sea star is regenerating a lost arm –Regeneration results from repeated cell divisions

3 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cell division is at the heart of the reproduction of cells and organisms Organisms can reproduce sexually or asexually Asexual reproduction- no variety Sexula reproduction Variety CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION

4 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Some organisms make exact or identical copies of themselves, asexual reproduction 8.1 Like begets like, more or less Figure 8.1A

5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Other organisms make similar but not identical copies of themselves in a more complex process, sexual reproduction Figure 8.1B

6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings All cells come from cells Cellular reproduction is called cell division –Cell division allows an embryo to develop into an adult –It also ensures the continuity of life from one generation to the next 8.2 Cells arise only from preexisting cells

7 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Prokaryotic cells divide asexually –These cells possess a single chromosome (packaged DNA during cell division) containing genes –The chromosome is replicated –The cell then divides into two cells, a process called binary fission 8.3 Prokaryotes reproduce by binary fission Figure 8.3B Prokaryotic chromosomes

8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.3A Binary fission of a prokaryotic cell Prokaryotic chromosome Plasma membrane Cell wall Duplication of chromosome and separation of copies Continued growth of the cell and movement of copies Division into two cells

9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A eukaryotic cell has many more genes than a prokaryotic cell –The genes are grouped into multiple chromosomes, found in the nucleus –The chromosomes of this plant cell are stained dark purple 8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division THE EUKARYOTIC CELL CYCLE AND MITOSIS Figure 8.4A

10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chromosomes contain a very long DNA molecule with thousands of genes –Individual chromosomes are only visible during cell division

11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Before a cell starts dividing, the chromosomes are duplicated –This process produces sister chromatids Centromere Sister chromatids Figure 8.4B

12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings When the cell divides, the sister chromatids separate –Two daughter cells are produced –Each has a complete and identical set of chromosomes Centromere Sister chromatids Figure 8.4C Chromosome duplication Chromosome distribution to daughter cells

13 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The cell cycle consists of two major phases: –Interphase, where chromosomes duplicate and cell parts are made –The mitotic phase, when cell division occurs 8.5 The cell cycle multiplies cells Figure 8.5

14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Eukaryotic cell division consists of two stages: –Mitosis –Cytokinesis 8.6 Cell division is a continuum of dynamic changes

15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In mitosis, the duplicated chromosomes are distributed into two daughter nuclei –After the chromosomes coil up, a mitotic spindle (microtubules) moves them to the middle of the cell

16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings INTERPHASEPROPHASE Centrosomes (with centriole pairs) Chromatin NucleolusNuclear envelope Plasma membrane Early mitotic spindle Centrosome Chromosome, consisting of two sister chromatids Fragments of nuclear envelope Kinetochore Spindle microtubules Figure 8.6

17 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The sister chromatids then separate and move to opposite poles of the cell –The process of cytokinesis divides the cell into two genetically identical cells

18 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings METAPHASETELOPHASE AND CYTOKINESIS Metaphase plate SpindleDaughter chromosomes Cleavage furrow Nucleolus forming Nuclear envelope forming ANAPHASE Figure 8.6 (continued)

19 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In animals, cytokinesis occurs by cleavage –This process pinches the cell apart 8.7 Cytokinesis differs for plant and animal cells Figure 8.7A Cleavage furrow Contracting ring of microfilaments Daughter cells

20 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In plants, a membranous cell plate splits the cell in two Vesicles containing cell wall material Cell plate forming Figure 8.7B Cell plateDaughter cells Wall of parent cell Daughter nucleus Cell wallNew cell wall

21 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Most animal cells divide only when stimulated, and others not at all In laboratory cultures, most normal cells divide only when attached to a surface –They are anchorage dependent 8.8 Anchorage, cell density, and chemical growth factors affect cell division

22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cells continue dividing until they touch one another –This is called density-dependent inhibition Cells anchor to dish surface and divide. Figure 8.8A When cells have formed a complete single layer, they stop dividing (density-dependent inhibition). If some cells are scraped away, the remaining cells divide to fill the dish with a single layer and then stop (density-dependent inhibition).

23 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cell Cycle control The cell cycle has critical checkpoint which determine whether the cycle will continue, pause or stop. Signals affecting critical checkpoints determine whether the cell will go through a complete cycle and divide G 1 checkpoint M checkpoint G 2 checkpoint Control system These checkpoints are controlled by specific proteins inside cells and growth factor signaling from outside the cell.

24 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Growth factors are proteins secreted by cells that stimulate other cells to divide They act by binding to the cell surface receptor and activate signalling mechanisms inside the cell to regulate proteins affecting the cell cycle control checkpoints Figure 8.8B Growth factor Figure 8.8B Cell cycle control system Plasma membrane Receptor protein Signal transduction pathway G 1 checkpoint Relay proteins

25 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cancer cells have abnormal cell cycles –They divide excessively and can form abnormal masses called tumors Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division 8.10 Connection: Growing out of control, cancer cells produce malignant tumors

26 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings When the cell cycle operates normally, mitotic cell division functions in: –Growth (seen here in an onion root) 8.11 Review of the functions of mitosis: Growth, cell replacement, and asexual reproduction Figure 8.11A

27 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cell replacement (seen here in skin) Dead cells Figure 8.11B Dividing cells Epidermis, the outer layer of the skin Dermis

28 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Asexual reproduction (seen here in a hydra) Figure 8.11C


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