Chapter 8-Cellular Transport & the Cell Cycle

1. Chapter 8-Cellular Transport & the Cell Cycle Section 8.2-Cell Growth & Reproduction (Mitosis)

2. Cell Size Limitations • Cells that make up multicellular org can come in many sizes & shapes • Cell w/largest diameter= yolk of an ostrich egg = 8 cm • Most living cells range = 2-200uM(10-6) in diameter • Factors that limit cell size: (1) Rate of diffusion (2) Amount of DNA w/in a cell (3) Surface area to volume ratio

3. Diffusion limits cell size • Diffusion: • Fast & efficient over short distances • Slow & inefficient over long distances • Due to slow rate of diffusion to move materials w/in the cell organisms can’t be one giant size

4. DNA Limits cell size • Cell is limited as to how quickly they can copied blueprints to make more protein • Cell can’t survive if not enough DNA to support protein needs of cell • In many lrg cells-more than one nucleus is present  so than cell activities are carried out quickly & efficiently

5. Surface area to volume ratio • Cell Size limiting Factor-surface area to volume ratio • As cell size increases its volume increases faster than its surface area • Refer to Figure 8.9-pg.202 • If cell size doubles-cell requires : • Volume-8X more nutrients & would have 8X more waste to excrete • Surface Area- only increases 4X

6. Surface area to volume ratio • This means that if a cell were to double in size: • The cell membrane would not have enough surface area to: • Have oxygen diffuse into & out of the cell • Have nutrients diffuse into the cell • Have waste diffuse out of the cell • This would mean that the cell would either: • Starve to death • Poisoned by the buildup of waste products in the cell • Cell have method of maintaining optimum cell size b/c size change have negative effects • Cells divide b/f they become too large to fxn properly

7. Cell Reproduction • Cell division-def-pg.203-the process by which new cells are produced from once cell. Results in 2 identical cells coming from one parent (original parent cell) • All organisms grow & change which means that cells must divide • Cell divide: • To replace worn-out tissue • To repair tissues that are injured

8. The discovery of chromosomes • Early biologist observed that just before cell division: • Several short stringy structures would appear in the nucleus • Structures then vanished soon after cell division • Structures were identified as chromosomes • Chromosomes-def-pg.203- structures which contain DNA and become darkly colored when stained

9. The structure of eukaryotic chromosomes • Chromosomes for most of the cell’s life exist as chromatin • Chromatin-def-pg.204- long strands of DNA wrapped around proteins called histones • Chromatins look like beads on a string under an electron microscope • Nucleosomes-def-pg.204­a group of histones with DNA wrapped around it which look like a bead on a string. • As nucleus begins division the chromosomes take on a different structure-chromatin becomes tightly packed

10. The Cell Cycle-Chromosome structure • Cell Cycle-def-pg.204-the sequence of growth and division of a cell • Cell goes through 2 general periods: • Period of growth • Period of division • Majority of a cell’s life is spent in interphase (the period of growth) • Interphase-def-pg.204-cell growth phase where a cell increases in size, carries on metabolism, and duplicated chromosomes prior to division • Mitosis-def-pg204-the cell’s period of nuclear division in which 2 daughter cells are formed, each containing a complete set of chromosomes

11. Interphase: A busy time • Interphase: A busy time • The busiest phase of the cell cycle-divided into 3 parts: • Gap 1(G1 phase)-cell grows & protein production high • Synthesis (S phase)-cell copies its chromosomes-this is the only time the cell copies its chromosomes • Gap 2(G2 Phase)-cell enters another shorter growth period, where mitochondria & other organelles are manufactured & other cell parts needed for cell division are assembled

12. The Phases of Mitosis • Cell undergo mitosis when they get to a cell size where: • The nucleus can provide blueprints for proteins • The cell membrane can efficiently transport nutrients & waste out of the cell • Mitosis has 4 distinct phases: • Prophase • Metaphase • Anaphase • Telophase

13. Mitosis Stage 4: Telophase Stage 5: Cytokinesis Frayer Model-Mitosis Stage 1:Prophase • Stage 2: Metaphase Stage 3: Anaphase

14. Prophase: 1st phase of mitosis • 1st & longest phase of mitosis • During prophase all of the following happens: • Chromatin condenses and are now visible chromosomes • Nucleus disappears • Nuclear envelope & nucleolus disintegrate

15. Prophase: 1st phase of mitosis 4. Centrioles migrate to opposite ends of the cell • Centrioles-def-pg.208-small dark, cylindrical structures that are made of microtubules & are located just outstide the nucleus • Centrioles play a role in chromatid separation 5. Spindle forms • Spindle-def-pg.208-a football-shaped, cagelike structure consisting of thin fibers made of microtubules • No spindles are found in plant cells • Spindles play a role in chromatid separation

16. Parts of the Chromosomes • Parts of the chromosome: • Duplicated chromosomes are made up of 2 halves called the sister chromatid • Sister chromatid contain DNA that are exact copies of each other and are formed during the synthesis portion of interphase • Sister chromatid are held together by centromere • Centromeres play a role chromosome movement during mitosis • Centromere locations help to identify chromosomes

17. Metaphase: 2nd stage of mitosis • Short 2nd phase of mitosis • During metaphase all of the following happens: • Doubled chromosomes become attached to spindle fibers at their centromere, each centromere is attached to one spindle fiber • Chromosomes are pulled by their centromeres to line up along the equator or metaphase plate of the cell

18. Anaphase:3rd phase of mitosis • During anaphase all of the following happens: • Separation of sister chromatids happens at the beginning of anaphase • Centromeres split apart & chromatid pairs from each chromosome separate from each other • Chromatids-pulled apart by shortening of microtubules in spindle fibers

19. Telophase: 4th phase of mitosis • Final phase of mitosis • During telophase all of the following happens: • Begins with chromatids reaching opposite poles of cell • Reverse of prophase happens to make 2 new cells: • Chromosomes unwind-to direct metabolic activity • Spindle breaks down • Nucleolus reappears • New nuclear envelope forms around each set of chromosomes • New double membrane forms between 2 new nuclei

20. Cytokinesis • Cytokinesis-def-pg209-the process by which a cell’s cytoplasm divides • Different between plants & animals • Plant cells don’t pinch membrane in middle-b/c of cell wall • How plant goes through cytokinesis: • A cell plate is laid down across the cell’s equator • Cell membrane forms around each cell • New cell walls form on either side of the cell plate until separation is complete

21. The Results of Mitosis • After mitosis 1 parent cell  becomes 2 identical daughter cells • Unicellular organisms  b/come multiplied • Multicellular organisms  b/come more cells within one organism • Tissue-def-pg210- group of cells that work together to perform a specific fxn • Organ-def-pg.210- tissues organized in various combos that perform more complex roles w/in organism • Organ system-def-pg210-multiple organs working together to form a system