Cell cycle
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The document discusses the cell cycle, including its key phases and control mechanisms. It begins with an overview of the cell cycle phases: interphase (G1, S, G2) and mitosis (prophase, metaphase, anaphase, telophase, cytokinesis). It then covers intracellular control, noting positive roles of cyclins and CDKs, and negative roles of Rb and p53 tumor suppressors. Finally, it discusses extracellular control by mitogens, growth factors, and survival factors that regulate cell division, growth, and apoptosis.
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Cell cycle
- 1. • OVERVIEW OF THE CELL CYCLE • INTRACELLULAR CONTROL OF THE CELL CYCLE • EXTRACELLULAR CONTROL OF CELL DIVISION AND CELL GROWTH fatimaArivera
- 2. FLOW OF DISCUSSION 1.Overview of the cell cycle a. G1phase b. S phase Interphase c. G2 phase d. Mitosis phase * prophase, metaphase, anaphase, telophase, * cytokinesis Meiosis 2.Intracellular Control of the Cell Cycle a. Positive: Cyclin- dependent kinase & Cyclins b. Negative: Rb & p53 3. Extracellular Control of the Cell Cycle a. Mitogens b. Growth factors c. Survival factors fatimaArivera
- 3. OVERVIEW: THE KEY ROLES OF CELL DIVISION The ability of organisms to reproduce best distinguishes living things from non-living matter. The continuity of life is based upon the reproduction of cells, or cell division. Cell division is integral part of cell cycle.
- 4. OVERVIEW OF THE CELL CYCLE fatimaArivera
- 5. INTERPHASE Interphase includes: • G1 Phase: • S Phase: • G2 Phase: fatimaArivera
- 6. INTERPHASE: G1 PHASE • Recovery from previous division • Cell doubles its organelles • Cell grows in size • Accumulates raw materials for DNA synthesis (DNA replication) fatimaArivera
- 7. INTERPHASE: S PHASE • DNA replication • Proteins associated with DNA are synthesized fatimaArivera
- 8. INTERPHASE: G2 PHASE • Between DNA replication and onset of mitosis • Cell synthesizes proteins necessary for division fatimaArivera
- 9. CELL CYCLE: MITOSIS PHASE Mitosis phase includes: • Mitosis (karyokinesis) • Nuclear division • Daughter chromosomes distributed to two daughter nuclei • Cytokinesis • Cytoplasm division • Results in two genetically identical daughter cells fatimaArivera
- 10. CELL CYCLE: MITOSIS PHASE fatimaArivera
- 11. SIGNIFICANCE OF MITOSIS • Permits growth and repair. • In plants it retains the ability to divide throughout the life of the plant • In mammals, mitosis is necessary: • Fertilized egg becomes an embryo • Embryo becomes a fetus • Allows a cut to heal or a broken bone to mend fatimaArivera
- 12. MITOSIS PHASE: PROPHASE What’s happening? • Chromatin condenses. • Centrosomes separate, moving to opposite ends of the nucleus • The centrosomes start to form a framework used to separate the two sister chromatids called the mitotic spindle, that is made of microtubules • Nucleolus disappears • Nuclear envelope disintegrates What the cell looks like? fatimaArivera
- 13. MITOSIS PHASE: PROMETAPHASE What’s happening? • Nuclear envelope fragments • Chromosomes become more condensed • A kinetochore is formed at the centromere, the point where the sister chromatids are attached • Microtubules attach at the kinetochores What the cell looks like? fatimaArivera
- 14. MITOSIS PHASE: METAPHASE What’s happening? • Chromosomes align on an axis called the metaphase plate • Note: the spindle consists of microtubules, one attached to each chromosome What the cell looks like? fatimaArivera
- 15. MITOSIS PHASE: ANAPHASE What’s happening? • Each centromere splits making two chromatids free • Each chromatid moves toward a pole • Cell begins to elongate, caused by microtubules not associated with the kinetochore What the cell looks like? fatimaArivera
- 16. MITOSIS PHASE: TELOPHASE What’s happening? • Formation of nuclear membrane and nucleolus • Short and thick chromosomes begin to elongate to form long and thin chromatin • Formation of the cleavage furrow - a shallow groove in the cell near the old metaphase plate • Cytokinesis = division of the cytoplasm What the cell looks like? fatimaArivera
- 17. RESULTS OF MITOSIS fatimaArivera • Two daughter nuclei • Each with same chromosome number as parent cell ( 2n) • Genetically identical to each other and the parent cell
- 18. MEIOSIS • Formation of Gametes (Eggs & Sperm) • Called Reduction- division • Preceded by interphase which includes chromosome replication • Two meiotic divisions • Meiosis I and Meiosis II • Original cell is diploid (2n) • Four daughter cells produced that are haploid (n) fatimaArivera
- 19. SIGNIFICANCE OF MEIOSIS • Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote fatimaArivera
- 20. SIGNIFICANCE OF MEIOSIS • Meiosis must reduce the chromosome number by half • Fertilization then restores the 2n number from mom from dad child meiosis reduces genetic content Too much! The right number!fatimaArivera
- 21. MEIOSIS I: PROPHASE I Prophase I is further subdivided into periods known as •Leptotena •Zygotena •Pachytena •Diplotena •Diakinesis fatimaArivera
- 22. A physical exchange of chromosome pieces PROPHASE I fatimaArivera
- 23. METAPHASE I Homologous pairs of chromosomes align along the equator of the cell fatimaArivera
- 24. ANAPHASE I Homologs separate and move to opposite poles. Sister chromatids remain attached at their centromeres. fatimaArivera
- 25. TELOPHASE I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two. fatimaArivera
- 26. MEIOSIS II: PROPHASE II Nuclear envelope fragments. Spindle forms. fatimaArivera
- 27. MEIOSIS II: METAPHASE II Chromosomes align along equator of cell. fatimaArivera
- 28. MEIOSIS II: ANAPHASE II Sister chromatids separate and move to opposite poles. Equator Pole fatimaArivera
- 29. MEIOSIS II: TELOPHASE II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two. fatimaArivera
- 30. RESULTS OF MEIOSIS • Four haploid cells with one copy of each chromosome fatimaArivera
- 31. SUMMARY OF MEIOSIS I fatimaArivera Nucleus Spindle fibers Nuclear envelope EARLY PROPHASE I LATE PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I & CYTOKINESIS
- 32. SUMMARY OF MEIOSIS II Prophase II Metaphase II Anaphase II Telophase II 4 I Undentical haploid cellsfatimaArivera
- 33. Mitosis Meiosis Number of divisions 1 2 Number of daughter cells 2 4 Genetically identical? Yes No Chromosome # Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction COMPARISON OF DIVISIONS fatimaArivera
- 34. ANIMATION
- 35. FLOW OF DISCUSSION 1.Overview of the cell cycle a. G1phase b. S phase Interphase c. G2 phase d. Mitosis phase * prophase, metaphase, anaphase, telophase, * cytokinesis Meiosis 2.Intracellular Control of the Cell Cycle a. Positive: Cyclin- dependent kinase & Cyclins b. Negative: Rb & p53 3. Extracellular Control of the Cell Cycle a. Mitogens b. Growth factors c. Survival factors fatimaArivera
- 36. Intracellular control of the cell cycle The cell cycle is controlled by regulator molecules that either: promote the process (positive) stop it from progressing (negative) fatimaArivera
- 37. Positive: Cdks & Cyclins Cyclins ◦ The regulatory subunits of the protein kinases that control the cell cycle Cyclin-Dependent Kinases (Cdks) ◦ The catalytic subunits of the protein kinases ◦ Must be associated with a cyclin in order to be activated fatimaArivera
- 38. fatimaArivera
- 39. Negative: Rb & p53 Tumor suppressor genes Tumor suppressor gene codes for a signaling protein in an inhibitory pathway. If a tumor suppressor gene mutates, the end result can be active cell division. fatimaArivera
- 40. Negative: Rb & p53 ◦ Retinoblastoma protein(Rb) ◦ prevents cell moving into S phase by binding to a transcription factor ◦ When Rb is phosphorylated it cannot bind so cell can move into S phase ◦ p53 ◦ prevents damaged from dividing (by inhibiting Rb pathway) fatimaArivera
- 41. Retinoblastoma protein (Rb) fatimaArivera Rb halts the cell cycle by binding E2F. Rb releases its hold on E2F in response to cell growth to advance the cell cycle. • group of tumor-suppressor proteins
- 42. p53 p53 protein halts cell division if it detects damaged DNA options: stimulates repair enzymes to fix DNA forces cell into G0 resting stage keeps cell in G1 arrest causes apoptosis of damaged cell ALL cancers have to shut down p53 activity Cancer is essentially a failure of cell division control fatimaArivera p53 is the Cell Cycle Enforcer
- 43. fatimaArivera
- 44. Major molecule players in the cell cycle control fatimaArivera Cyclin-dependent kinases (Cdks) Cyclins Cdk-cyclin complex P regulatory proteinsphosphorylates cellular proteins triggers passage through different stages of cell cycle
- 45. Generic cell cycle checkpoints fatimaArivera Is environment favorable? Is environment favorable? Are all DNA replicated?Are all chromosomes attached to the spindle?
- 46. G1 S G2 M G1 CheckpointG2 CheckpointM Checkpoint G1 Cdk G1 Cyclin P Active G1 Cdk-Cyclin • Growth factors • Nutritional state of cell • Size of cell Degraded G1 Cyclin Mitotic Cdk Mitotic Cyclin P Active Mitotic Cdk-Cyclin (MPF) • Replication completed • DNA integrity APC Chromosomes attached at metaphase plate Degraded Mitotic Cyclin Control of the Cell Cycle
- 47. FLOW OF DISCUSSION 1.Overview of the cell cycle a. G1phase b. S phase Interphase c. G2 phase d. Mitosis phase * prophase, metaphase, anaphase, telophase, * cytokinesis Meiosis 2.Intracellular Control of the Cell Cycle a. Positive: Cyclin- dependent kinase & Cyclins b. Negative: Rb & p53 3. Extracellular Control of the Cell Cycle a. Mitogens b. Growth factors c. Survival factors fatimaArivera
- 48. EXTRACELLULAR CONTROL OF THE CELL DIVISION AND CELL GROWTH • What regulates cell size and cell number? • Regulated by extracellular signals Mitogens stimulate cell division (PDGF) • Growth factors • stimulate cell growth • Survival Factors • inhibit apoptosis fatimaArivera
- 49. MITOGEN: PLATELET DERIVED GROWTH FACTOR PDGF is released by platelets in at the site of a wound
- 50. fatimaArivera
- 51. GROWTH FACTORS fatimaArivera • A signal transduction through phosphatidyl inositol pathway • Kinase cascade leads to increased translation • Some factors stimulate both growth and cell cycle progression
- 52. ` fatimaArivera
- 53. fatimaArivera
- 54. protein signals released by body cells that stimulate other cells to divide density-dependent inhibition crowded cells stop dividing each cell binds a bit of growth factor not enough activator left to trigger division in any one cell anchorage dependence to divide cells must be attached to a substrate “touch sensor” receptors GROWTH FACTORS
- 55. NORMAL CELLS NEED BOTH MITOGENS AND “ANCHORAGE”- TO ENTER A NEW CELL CYCLE
- 56. NERVE GROWTH FACTORS CAN INFLUENCE BOTH RATE AND DIRECTION OF GROWTH
- 57. SURVIVAL FACTOR: MYOSTATIN • Myostatins are inhibitory factors that inhibit the proliferation of myoblast that fuse to form skeletal muscle cells. • Myostatin Mutants decrease apoptosis in muscle tissue