Cell Growth and Reproduction

1. Cell Growth and Reproduction Cell Size Limitations Cell Reproduction Cell Cycle Mitosis

2. Cell Size Limitations • Just like us, cells come in a variety of sizes! • What determines a cell’s size? • DNA • Diffusion • Surface Area – to – Volume Ratio

3. Cell Size Limitations DNA • DNA provides the blueprints or instructions for protein synthesis. • Cells cannot survive unless there is enough DNA to support the protein needs of the cell.

4. Cell Size Limitations Diffusion • Nutrients and wastes are moved around a cell using diffusion. • Usually diffusion is fast and efficient over short distances, but when a cell gets too big it becomes slow and inefficient! • Cells can’t be too big because they would die before nutrients reached the organelles that need them!

5. Cell Size Limitations Surface Area –to-Volume Ratio • As a cell’s size increases, its volume increases faster than its surface area. • If a cell size is doubled, the cell would require 8 times more nutrients and would have 8 times more waste! • The surface area would only have increased by 4 and therefore the plasma membrane would not have enough surface area to let in the nutrients and let out the wastes. • The cell would either starve to death or become poisoned by its own waste! • Usually, cells divide before they get too big to control this factor.

6. Cell Reproduction • The cell theory states that “all cells come from pre-existing cells.” • Cell division is the process by which this happens! • Cell division results in two cells that are identical to the original parent cell. • All organisms grow and change; worn out tissues are repaired or replaced by newly produced cells!

7. The Cell Cycle • The cell cycle is the sequence of growth and division of a cell. • It starts with 2 general periods: • Period of Growth • The majority of a cell’s life is spent in growth! • This phase is known as INTERPHASE! • During INTERPHASE, a cell grows in size and carries on metabolism. • Chromosomes are duplicated in preparation for division • Interphase is like the training before a big race! • Period of Division • This phase is known as MITOSIS! • In MITOSIS, two daughter cells are formed each containing a complete set of chromosomes.

8. INTERPHASE • 3 stages • G1 – Cell grows rapidly and protein production is high • S – Cell copies its chromosomes and DNA synthesis occurs • G2 – Short growth period in which mitochondria and other organelles are made and parts needed for cell division (centrioles) are manufactured

9. INTERPHASE

10. MITOSIS: Many phases of Division • PROPHASE – longest phase of mitosis • Chromatin (DNA strands) coil up into visible chromosomes • They look kind of hairy! • Each chromosome is made of two identical halves called SISTER CHROMATIDS • These halves are held together by a CENTROMERE

11. PROPHASE

12. PROPHASE CONTINUED… • As prophase continues, the nucleus begins to disappear as the nuclear envelope and the nucleolus disintegrate. • At this time, the CENTRIOLES begin to migrate to opposite poles of the cell • The SPINDLE begins to form between the centrioles.

13. PROPHASE CONTINUED… CENTRIOLES SPINDLE FIBERS

14. METAPHASE • METAPHASE-short second phase of mitosis • The doubled chromosomes become attracted to the spindle fibers by their centromeres • The chromosomes begin to line up on the midline or equator of the spindle

15. METAPHASE

16. ANAPHASE 3) ANAPHASE – Third phase of mitosis • Sister chromatids begin to separate • Centromeres split apart and the chromatids are pulled apart

17. TELOPHASE 4) TELOPHASE – Fourth phase of mitosis • Chromatids are pulled to opposite poles of the cell • Nucleolus reappears and new nuclear envelope forms around each new set of chromosomes • New double membrane begins to form between two new nuclei

18. TELOPHASE

19. CYTOKINESIS • The cell’s cytoplasm finally divides and the cell starts to pinch along the equator of the cell forming two new cells!

20. MITOSIS

21. MITOSIS