2. What Limits a Cell’s Size? 1. DNA content if cell is too large, DNA can’t control all of it 2. Diffusion Is efficient only over short distances – big cells move materials too slowly

3. What Limits a Cell’s Size? 3. Surface Area – to – Volume Ratio As a cell grows, its cytoplasm increases faster than its cell membrane Divide or Die

4. Prokaryotic Cell Division Bacteria have one chromosome made of one circular piece of DNA Bacteria use binary fission to create new cells This is asexual reproduction

5. Eukaryotic Cell Division Chromosomes Are found in the nucleus Contain DNA and protein Are in linear strands

6. Eukaryotic Cell Division Each species has a specific number Ex. Humans = 46 Are only visible during cell division Are usually found as thin, uncoiled chromatin

7. Cell Cycle 1. Interphase (longest stage of cell cycle) G 1 – initial growth to normal size S – synthesis of DNA (replication) G 2 – growth to 2x the normal size

8. Cell Cycle 2. M phase Mitosis – nuclear division Cytokinesis – cytoplasmic division

9. Stages of Cell Cycle Interphase Chromosomes duplicate Cell grows 2x its normal size In animal cells, centrioles duplicate

10. Stages of Cell Cycle - Mitosis 1. Prophase Chromatin coils into visible chromosomes Each chromosome is made of 2 sister chromatids that are held together by a centromere

11. Stages of Cell Cycle - Mitosis Nuclear envelope starts to disappear Spindle fibers start to form Centrioles move to opposite ends of cell

12. Stages of Cell Cycle - Mitosis 2. Metaphase Chromosomes line up at equator of cell

13. Stages of Cell Cycle - Mitosis 3. Anaphase Centromeres split apart Sister chromatids are pulled to opposite ends of the cell

14. Stages of Cell Cycle - Mitosis 4. Telophase Cell has 2 complete sets of chromosomes Spindle disappears Nuclear envelope reappears Chromosomes uncoil back into chromatin

15. Stages of Cell Cycle Cytokinesis Animal Cells Cleavage furrow forms at middle of cell Cytoplasm underneath pinches in forming 2 new daughter cells

16. Stages of Cell Cycle Cytokinesis Plant Cells Vesicles form a cell plate at equator Cell plate grows into the existing cell wall forming 2 new cells

19. Cell Cycle Control Most cells start dividing when they are not surrounded by other cells Cells will stop dividing once they are touching other cells  contact inhibition

20. Cell Cycle Control Cancer cells ignore contact inhibition and continue to divide This creates a mass of cells called a tumor

21. Benign tumors stay in one place Malignant tumors spread to other parts of the body (metastasis)