Cell Growth & Reproduction

1. Cell Growth & Reproduction Section 8.2 Chapter 8 Pages 203 - 210

2. Cell Reproduction All cells come from preexisting cells. Cell division is the way that new cells are produced from one cell.

3. Cell Reproduction Cell division gives you two cells that are identical to the original or parent cell.

4. Cell Reproduction Cells are constantly getting old, dying and being replaced. New cells are needed for growth.

5. The Discovery of Chromosomes Early biologists observed that stringy structures appeared in the nucleus just before cell division. They also noticed that these structures seemed to vanish soon after cell division. These stringy structures are chromosomes.

6. The Discovery of Chromosomes Chromosomes contain DNA.

7. The Discovery of Chromosomes Chromosomes carry the genetic information that is copied from one generation to the next. It is important that this information is accurately passed along during cell division.

8. When most of you think of chromosomes, this is probably the image you have in your head.

9. Electron scanning microscope’s photo of chromosomes

10. Karotype Humans have 23 pairs of chromosomes This is a male… the sex chromosomes are an XY pair

11. The structure of eukaryotic chromosomes For most of a cells lifetime, chromosomes exist as chromatin. Chromatin are long strands of DNA wrapped around proteins.

12. The structure of eukaryotic chromosomes Under an electron microscope, chromatin looks like a string of beads.

13. The structure of eukaryotic chromosomes Before a cell can divide, the long strand of chromatin needs to be organized… kind of like when we wrap up a cord to store it. In this wrapped up coil, the chromatin is very tightly packed.

17. Chromosome Structure The chromosomes of eukaryotic cells change shape depending on which phases of the cell cycle they are in.

18. Chromosome Structure A metaphase chromosome is a compact arrangement of DNA. Chromosomes during interphase are long and tangled.

20. The Cell Cycle What kind of cycles can you think of? Seasons, tides, day and night…

21. Cells have cycles too. The cell cycle is the sequence of growth & division.

22. There are two periods in the cell cycle. One period is for growth, the other is for division.

23. Interphase Interphase is the growth period. Most of the cells life is spent in interphase.

24. Interphase • During interphase a cell: • grows in size • carries on metabolic functions • duplicates chromosomes for division

25. Mitosis is the period of division.

26. Mitosis During mitosis, two daughter cells are formed from one parent cell. Each daughter cell has a complete set of chromosomes. After mitosis, the cytoplasm divides to separate the two daughter cells.

27. The Cell Cycle S phase G1 phase G2 phase M phase

28. Interphase is the busiest time of the cell cycle.

29. Interphase is divided into three parts: • G1 The cell grows and protein production is high. • S The cell copies its chromosomes. This is the only time during the cell cycle that DNA synthesis occurs. • G2 The cell then enters another growth period where mitochondria and other organelles are manufactured and other parts needed for cell division are produced.

30. Interphase now ends and mitosis begins!

31. The Phases of Mitosis Cells undergo mitosis when they reach maximum cell size. Remember, a cell can only grow so large until the surface area of the cell membrane becomes too small in proportion to its volume. The cell membrane transports nutrients andwaste into and out of the cell.

32. Although cell division is a continuous process, it can be broken up into four phases. The 4 phases of mitosis are: prophase metaphase anaphase telophase

33. How long does the cell cycle take? • Each turn of the cell cycle is a generation. • Generation time varies greatly depending on the species and type of cell. • The minimum time needed is about 10 minutes. • It takes about 2 hours for sea urchin cells to divide. • Most growing plant and animal cells need 8 – 10 hours to divide.

34. How long does the cell cycle take? • The generation time for a bean seed is 19 hours • The G1 phase lasts about 5 hours • The S phase lasts about 7 hours • The G2 phase lasts about 5 hours • The M phase lasts about 2 hours

35. How long does the cell cycle take? • The generation time for some mouse cells is about 22 hours • The G1 phase lasts about 9 hours • The S phase lasts about 10 hours • The G2 phase lasts about 2 hours • The M phase lasts about 1 hour

36. How long does the cell cycle take? • Many mature cells like nerve cells and red blood cells, never divide. • They are said to be in the G0 phase which is a lot like the G1 phase.

37. Mitosis Notes Cell Division occurs in a series of stages, or phases.

39. 1st phase: Interphase • (Not mitosis… but part of the cell cycle!) • Chromosomes are copied (# doubles) • Chromosomes appears as threadlike coils (chromatin) at the start, but each chromosome and its copy (sisterchromosome) change to sister chromatids at the end of this phase

40. 2 Interphase

41. 2nd phase: Prophase • Mitosisbegins (cell begins to divide) • Centrioles (or poles appear and begin to move to opposite ends of cell • Spindle fibers form between the poles

42. 4 Prophase

43. Prophase Spindle fibers Disappearing nuclear envelope Doubled chromosome

44. Prophase: the first phase of mitosis • longest phase of mitosis. • The long stringy chromatin coils up into visible chromosomes. • Each chromosome is made of two halves.

45. Prophase: the first phase of mitosis The two halves of the doubled structure are called sister chromatids. Sister chromosomes are an exact copy of each other. Sister chromosomes are made when DNA is copied during interphase. Sister chromatids are held together with a structure called a centromere.

46. 2 sister chromatids held together with a centromere telomeres centromere 2 sister chromatids

47. Centromeres play a role in chromosome movement during mitosis. The position of the centromere also helps scientists identify the chromosomes.

48. As prophase continues, the nucleus disappears as the nuclear envelop and the nucleolus disintegrate. In animal cells, pairs of structures called centrioles migrate to opposite ends of the cell.

49. Centrioles are small, dark, cylindrical structures that are made of small tubes. Centrioles play a role in chromatid separation.

50. As the pairs of centrioles move to the opposite ends, another structure called spindles, form between them. The spindle fibers make a cage like structure made of microtubules.