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Transcript
How to Make a Sea Star • 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 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION • 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 8.1 Like begets like, more or less • Some organisms make exact or identical copies of themselves, asexual reproduction Figure 8.1A 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 8.2 Cells arise only from preexisting cells • 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 8.3 Prokaryotes reproduce by binary fission • 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 Prokaryotic chromosomes Figure 8.3B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Binary fission of a prokaryotic cell Plasma membrane Prokaryotic chromosome Cell wall Duplication of chromosome and separation of copies Continued growth of the cell and movement of copies Division into two cells Figure 8.3A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings THE EUKARYOTIC CELL CYCLE AND MITOSIS 8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division • 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 Figure 8.4A 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Before a cell starts dividing, the chromosomes are duplicated – This process produces sister chromatids Sister chromatids Centromere Figure 8.4B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • When the cell divides, the sister chromatids separate Chromosome duplication – Two daughter cells are produced – Each has a complete and identical set of chromosomes Sister chromatids Centromere Chromosome distribution to daughter cells Figure 8.4C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 8.5 The cell cycle multiplies cells • The cell cycle consists of two major phases: – Interphase, where chromosomes duplicate and cell parts are made – The mitotic phase, when cell division occurs Figure 8.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 8.6 Cell division is a continuum of dynamic changes • Eukaryotic cell division consists of two stages: – Mitosis – Cytokinesis 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings INTERPHASE PROPHASE Centrosomes (with centriole pairs) Early mitotic spindle Centrosome Chromatin Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Figure 8.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Fragments of nuclear envelope Centrosome Kinetochore Spindle microtubules • 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings METAPHASE ANAPHASE Cleavage furrow Metaphase plate Spindle TELOPHASE AND CYTOKINESIS Daughter chromosomes Figure 8.6 (continued) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Nuclear envelope forming Nucleolus forming 8.7 Cytokinesis differs for plant and animal cells • In animals, cytokinesis occurs by cleavage Cleavage furrow – This process pinches the cell apart Cleavage furrow Figure 8.7A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Contracting ring of microfilaments Daughter cells • In plants, a membranous cell plate splits the cell in two Cell plate forming Wall of parent cell Cell wall Figure 8.7B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Vesicles containing cell wall material Daughter nucleus New cell wall Cell plate Daughter cells 8.8 Anchorage, cell density, and chemical growth factors affect cell division • 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 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. 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). Figure 8.8A 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 •These checkpoints are controlled by specific proteins inside cells and growth factor signaling from outside the cell. G1 checkpoint Control system M checkpoint Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings G2 checkpoint • 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 Growth factor Plasma membrane Receptor protein Relay proteins Signal transduction pathway Figure 8.8B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.8B G1 checkpoint Cell cycle control system 8.10 Connection: Growing out of control, cancer cells produce malignant tumors • 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 8.11 Review of the functions of mitosis: Growth, cell replacement, and asexual reproduction • When the cell cycle operates normally, mitotic cell division functions in: – Growth (seen here in an onion root) Figure 8.11A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Cell replacement (seen here in skin) Dead cells Epidermis, the outer layer of the skin Dividing cells Dermis Figure 8.11B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Asexual reproduction (seen here in a hydra) Figure 8.11C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings