cell theory general biology grade12 senior hugh

cell division and cell cycle

1. What do you think happens when your wound heals?

2. Cell Division is a fundamental biological process by which a parent cell divides to produce new cells. It is essential for growth, development, repair of damaged tissues, and reproduction in living organisms.

3. MITOSIS

4. What is mitosis? Mitosis is the process responsible for regeneration and repair. Mitosis helps in cell growth and development. Mitosis is a type of cell division that results in two identical daughter cells .

5. LET’S LOOK AT THE STAGES OF MITOSIS

6. Interphase is the longest and most active stage in the cell cycle, occurring before mitosis begins. . INTERPHASE Interphase prepares the cell for the division process. . The preparation stage in mitosis is interphase which involves the G1 phase, S phase, and G2 phase .

7. Interphase is divided into three phases: G₁ phase (Gap 1): The cell grows in size. It produces proteins and organelles. The cell performs its normal functions. S phase (Synthesis): DNA replication occurs. Each chromosome makes an exact copy of itself (forming sister chromatids). G₂ phase (Gap 2): The cell continues to grow. It prepares all the necessary materials (like spindle fibers) for mitosis. The cell checks for errors in DNA replication.

8. Prophase is the first stage of mitotic cell division after the cell had been readied during the resting stage ̶ the interphase. The following are the distinct activities of the cell. Nuclear membrane disintegrates. Centrosomes move to the opposite pole. Mitotic spindle fibers start to form. P ROPHASE

9. Metaphase begins with the formation of a bipolar spindle body in the region of nucleoplasm . It consists of numerous spindle fibers. These are fine thread-like structures formed by the organization of proteins called tubulin into microtubules. M ETAPHASE

10. The distinct processes that occur in the metaphase are as follow: Chromosomes align themselves at the M iddle of the equatorial plane. Kinetochore proteins are attached to the centromere of each chromosome. Spindle fibers are fully developed M ETAPHASE

11. Chromatids separate and move to opposite ends o f the cell. A NAPHASE This stage ens u res that each cell contains identical chromosomes a ft er splitting.

12. During anaphase, chromosomes are divided into chromatids . Further, the following occurs: Centromeres separate. Each chromatid, is linked to only one pole. Non-kinetochore spindle fibers lengthen causing the elongation of the cell. A NAPHASE

13. Two new nuclei form around each set of chromosomes. T ELOPHASE Chromosomes decondense and the cells begin to split from each other.

14. This is the last stage. Activities include: The two sets of daughter chromosomes reach the opposite poles. The chromosomes again become long and thin. A new nucleolus is organized. A nuclear envelope is formed around each set of chromosomes. A daughter nucleus is organized at each pole in the parent cell. Each daughter nucleus has the same number of chromosomes as that of the mother cell. The spindle fibers also dissolve and disappear gradually. T ELOPHASE

15. final stage of cell division where the cytoplasm of the parent cell is divided into two daughter cells . Cytokinesis

16. Mitosis for Growth and Repair Happens in body cells (like skin, bones, or muscles). Purpose: To grow, repair, or replace damaged cells. Makes 2 identical cells (same number of chromosomes as the original). Example: When you get a wound, mitosis helps create new skin cells to heal it.

17. Stages of Mitosis Prophase – The DNA coils into chromosomes. The nuclear membrane disappears. Metaphase – Chromosomes line up in the middle of the cell. Anaphase – Chromosomes are pulled apart to opposite sides. Telophase – New nuclear membranes form around the two sets of chromosomes. Cytokinesis – The cell splits into two identical daughter cells .

18. MEIOSIS

19. What is meiosis? Not all cells divide through the process of mitosis. Organisms that reproduce sexually also undergo a type of cell division called meiosis . Meiosis occurs in sex cells and is similar in process to mitosis.

20. Why is it important? Meiosis makes sure that all organisms produced via sexual reproduction contain the correct number of chromosomes - half from each parent.

21. LET’S LOOK AT THE STAGES OF MEIOSIS

22. The process of meiosis is divided into meiosis I and meiosis II which both have multiple phases. Meiosis I is a type of cell division unique to germ cells, while meiosis II is similar to mitosis.

23. MEIOSIS I

24. The DNA in the cell is copied resulting in two identical full sets of chromosomes. Outside of the nucleus are two centrosomes, each containing a part of centrioles, these structures are critical for the process of cell division. During interphase, microtubules extend from these centrosomes. INTERPHASE

25. The copied chromosomes condense into X-shaped structure that can be easily seen under a microscope. Each chromosome is composed of two sister chromatids containing identical genetic information. The chromosomes pair up so that both copies of chromosome 1 are together, both copies of chromosome 2 are together, and so on. PROPHASE 1

26. The pair of chromosomes may then exchange bits of DNA in a process called recombination or crossing over. At the end of prophase 1, the membrane around the nucleus in the cell dissolves away, releasing the chromosomes. The meiotic spindle, consisting of microtubules and other proteins, extends across the cell between centrioles. PROPHASE 1

27. The chromosome pairs line up next to each other along the center (equator) of the cell. The centrioles are now at opposite poles of the cell with the meiotic spindles extending from them. The meiotic spindle fibers attach to one chromosome of each pair. METAPHASE 1

28. The pair of chromosomes are then pulled apart by the meiotic spindle, which pulls one chromosome to one pole of the cell and the other chromosome to the opposite pole. In meiosis I, the sister chromatids stay together. This is different to what happens in mitosis and meiosis II. ANAPHASE 1

29. The chromosomes complete their move to the opposite poles of the cell. At each pole of the cell a full set of chromosomes gather together. A membrane forms around each set of chromosomes to create two new nuclei. The single cell then pinches in the middle to form two separate daughter cells each containing a full set of chromosomes within a nucleus. This process is known as cytokinesis. TELOPHASE 1 and Cytokinesis

30. MEIOSIS II

31. PROPHASE 2 Now there are two daughter cells, each with 23 chromosomes (23 pairs of chromatids) In each of the two daughter cells the chromosomes condense again into visible X-shaped structures that can be easily seen under a microscope. The membrane around the nucleus in each daughter cell dissolves away releasing the chromosomes. The centrioles duplicate. The meiotic spindle forms again.

32. In each of the two daughter cells, the chromosomes (pair of sister chromatids) line up end-to-end along the equator of the cell. The centrioles are now at opposites poles in each of the daughter cells. Meiotic spindle fibers at each pole of the cell attach to the sister chromatids. METAPHASE 2

33. ANAPHASE 2 The sister chromatids are then pulled to opposite poles due to the action of the meiotic spindle. The separated chromatids are now individual chromosomes.

34. TELOPHASE 2 The chromosomes complete their move to the opposite poles of the cell. At each pole of the cell a full set of chromosomes gather together. A membrane forms around each set of chromosomes to create two new cell nuclei.

35. TELOPHASE 2 This is the last phase of meiosis; however, cell division is not complete without another round of cytokinesis. Once cytokinesis is complete, there are four granddaughter cells, each with half a set of chromosomes (haploid).

36. PROPHASE METAPHASE ANAPHASE THE WHOLE PROCESS TELOPHASE FIRST PHASE SECOND PHASE ANAPHASE TELOPHASE METAPHASE PROPHASE

37. Quick Recap Time!

38. Mitosis for Growth and Repair Happens in body cells (like skin, bones, or muscles). Purpose: To grow, repair, or replace damaged cells. Makes 2 identical cells (same number of chromosomes as the original). Example: When you get a wound, mitosis helps create new skin cells to heal it.

39. Stages of Mitosis Prophase – The DNA coils into chromosomes. The nuclear membrane disappears. Metaphase – Chromosomes line up in the middle of the cell. Anaphase – Chromosomes are pulled apart to opposite sides. Telophase – New nuclear membranes form around the two sets of chromosomes. Cytokinesis – The cell splits into two identical daughter cells .

40. Meiosis Happens in sex cells (sperm for boys, egg for girls). Happens in body cells (like skin, bones, or muscles). Purpose: To create Gametes for reproduction. Makes 4 different cells each half the number of chromosomes. Example: When a baby is formed, it starts from a sperm and an egg made through meiosis.

41. Stages of Meiosis Meiosis I – Separates pairs of chromosomes: Prophase I – Chromosomes pair up and exchange genes ( crossing over ). Metaphase I – Pairs line up in the center. Anaphase I – Pairs are pulled apart (not the chromosomes yet!). Telophase I and Cytokinesis – Cell splits into 2 cells.

42. Stages of Meiosis Meiosis II – Like mitosis but with half the chromosomes: Prophase II – Chromosomes get ready again. Metaphase II – Chromosomes line up in the center. Anaphase II – Chromosomes are pulled apart. Telophase II and Cytokinesis – Both cells divide again → Total of 4 cells .

43. Feature Mitosis Meiosis Type of cells Body cells Sex cells # of cell divisions 1 2 Final cells 2 identical cells 4 non-identical cells Purpose Growth & repair Reproduction Chromosomes Same as original Half of the original

44. Cell- ebrate What You’ve Learned!

45. What are the two phases of the cell cycle? What metabolic activities are happening during interphase? What are the two sub phases of the mitotic or M phases? What happens during the two sub phases? What are the stages of the mitotic or M phase?

46. When Cells Go Wrong: Disorders Caused by Cell Cycle Malfunction

47. What is the Cell Cycle? Series of events in cell growth and division Phases: G1 → S → G2 → M → (Cytokinesis) Checkpoints ensure proper cell division

48. Cancer – Uncontrolled Cell Division

49. Tumors – Benign vs. Malignant Benign : Non-cancerous, localized growth Malignant : Cancerous, invasive and spreads

50. Genetic Disorders – Chromosome Errors Errors in cell division (mitosis/meiosis) Nondisjunction → wrong number of chromosomes Examples: Down Syndrome (Trisomy 21) Turner Syndrome (XO) Klinefelter Syndrome (XXY)

51. Neurodegenerative Diseases Example: Alzheimer’s, Parkinson’s Neurons wrongly try to divide Leads to brain cell death

52. Psoriasis – Overactive Cell Division Skin cells divide too fast Results in scaly, itchy patches Loss of checkpoint control

53. Why do you think cancer is so hard to treat if it starts with just a single abnormal cell? Can you name another disease linked to errors in cell division? JAM Session

54. QUIZ # 2

55. 1. Rebus Puzzle ( 10 Points) C _ _ _ _ L A N C E

56. Guide Questions: How many nuclear divisions happen in meiosis? How are the stages in meiosis similar to mitosis? What is the significance of crossing over? How many daughter cells are produced in meiosis II? 2 – points The idea is present and supported with thorough explanation. 1 – point. The idea is present but lacks explanation. ) Picture Analysis Analyze the picture below and answer the following questions below. 2 to 3 sentences only (10 – Points)