Cells divide through the process of mitosis in order to repair and replace old or damaged cells, to grow, and to develop multicellular organisms. Mitosis consists of prophase, metaphase, anaphase and telophase where the genetic material and cytoplasm are divided to form two identical daughter cells. The cell cycle, which is the life of a cell, includes interphase where the cell grows and duplicates its DNA in preparation for division, and M-phase where mitosis and cytokinesis occur. The cell cycle is tightly regulated by internal factors such as cyclins and cyclin-dependent kinases and external growth factors to ensure cells only divide when necessary.

1. Mitosis Why do cells need to divide?

3. Recap… Cell theory… Cells are the basic structural unit of life Cells are the functional units of life Cells come from pre-existing cells

4. Overview Why do cells need to divide? Repair, growth, development Types of reproduction Sexual Genetically different 2 parents Takes time to develop, better chance of survival asexual Genetically identical One parent Many offspring very quickly

5. DNA Blueprint of life, nucleic acid Chromatin Granular genetic material, spread out in nucleus of non-dividing cells Chromosomes Condensed genetic material, in dividing cells Sister chromatids Identical copies of Chromosomes joined by a centromere (“centro-” middle)

8. Humans 46 chromosomes 46 sister chromatids One from your mom, one from your dad

9. Cell Cycle: Life of a Cell

10. Cell Cycle Interphase 90 % of cell’s life, non dividing G1 phase Grows, makes organelles S phase DNA Synthesis…DNA replicates G2 phase Cell prepares to divide, makes sure it has all important organelles for division M phase When the cytoplasm and nucleus of the cell divides

11. Cell Cycle There are check points in G1, S, and G2 Make sure cell is ready to move onto the next phase (has all necessary organelles, copied DNA, etc.) Once the cell has past the G1 checkpoint, it will complete the cell cycle Some cells stay in the G1 phase all their life (muscle cell, brain cells)

12. Regulators of Cell Cycle Cyclins Protein that regulates the timing of the cell cycle in eukaryotic cells Levels of cyclins rise and fall throughout the cell cycle Cyclin-dependent Kinases (cdks) Enzymes that are activated when they bind with cyclin and they make the cell cycle continue

14. Regulators Internal Factors within the cell that control cell cycle Cyclin and CDKs Allow cell cycle to proceed only when certain processes have occurred Replication of chromosomes Chromosome Attachment to spindle before anaphase External Factors Outside the cell Growth factorsmolecules that bind to cell surface that signal cell to divide Similar cells have molecules that have opposite effect so that when it becomes to crowded, cells stop dividing

19. M-phase Consists of mitosis and cytokinesis Mitosis Process by which the nucleus of a cell divides One parent cell makes two identical daughter cells This is how organisms repair tissue and grow and develop Cytokinesis-division of the cytoplasm

20. Depending on cell type… Mitosis can take a few minutes or a few days Muscle cells (non-dividing) Nerve cells (non-dividing) Skin cells (divide all the time) Digestive Tract cells (divide all the time)

21. Life Span of Some Human Cells

22. Easy way to remember M-Phase PMAT Pilates Make Annie Toned Practice Makes Athletes Train Prophase Metaphase Anaphase Telophase

23. Prophase 50-60% of time Chromosomes become visible Centrioles develop in cytoplasm near nuclear envelope Centrioles separate and migrate to opposite ends of nuc. Env. Centrosome Region where Centrioles are found Organize the “spindle” Fan like microtubule structure that helps separate chromosomes Plants do NOT have Centrioles

26. End of prophase Chromosomes coil together tightly Nucleolus disappears Nuclear envelope breaks down

27. Metaphase Few minutes Chromosomes line up in middle (M in metaphase MIDDLE) Microtubules connect centromere of each chromosome to the 2 poles of spindle

31. Anaphase Centromeres joining sister chromatids separate and become individual chromosomes They are dragged by fibers to opposite poles Ends when chromosomes stop moving

35. Telophase Opposite of prophase Condensed chromosomes disperse into tangle of material Nuclear envelope reforms Spindle breaks apart Nucleolus becomes visible At the end 2 identical nuclei in one cell

39. Cytokinesis Happens at the same time as Telophase Division of cytoplasm Animal Cells Cell membrane drawn inward until it pinches off and forms 2 id daughter cells Plant Cells Cell plate forms between nuclei Cell Plate develops into separate membrane Cell wall appears

45. Regulators of Cell Cycle Cyclins Protein that regulates the timing of the cell cycle in eukaryotic cells Levels of cyclins rise and fall throughout the cell cycle Cyclin-dependent Kinases (cdks) Enzymes that are activated when they bind with cyclin and they make the cell cycle continue

46. Regulators Internal Factors within the cell that control cell cycle Cyclin and CDKs Allow cell cycle to proceed only when certain processes have occurred Replication of chromosomes Chromosome Attachment to spindle before anaphase External Factors Outside the cell Growth factorsmolecules that bind to cell surface that signal cell to divide Similar cells have molecules that have opposite effect so that when it becomes to crowded, cells stop dividing