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Cell cycle
The document summarizes key aspects of the cell cycle, including its main phases (interphase consisting of G1, S, G2 phases and the mitosis phase) and their characteristics. It also discusses meiosis, its two divisions, and its significance in forming gametes. Control of the cell cycle involves positive regulators like cyclins and CDKs that promote the cycle and negative regulators like Rb and p53 tumor suppressor proteins that inhibit the cycle progression under certain conditions. Checkpoints exist at different phases to ensure replication and chromosome separation are completed before progression.
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Cell cycle
- 1. Cell Cycle By Mrs SanchitaChoubey (M.Sc., PGDCR, Pursuing Ph. D) Assistant Professor of Microbiology Dr. D Y Patil Arts Commerce and Science College Pimpri, Pune
- 2. OVERVIEW OF THECELL CYCLE fatimaArivera
- 3. INTERPHASE Interphase includes: • G1Phase: • S Phase: • G2 Phase:
- 4. INTERPHASE: G1 PHASE fatimaArivera •Recovery from previous division • Cell doubles its organelles • Cell grows in size • Accumulates raw materials for DNAsynthesis (DNA replication)
- 5. INTERPHASE: S PHASE fatimaArivera •DNA replication • Proteins associated with DNA are synthesized
- 6. INTERPHASE: G2 PHASE fatimaArivera •Between DNA replication and onset of mitosis • Cell synthesizes proteins necessary for division
- 7. CELL CYCLE: MITOSISPHASE fatimaArivera Mitosis phase includes: • Mitosis (karyokinesis) • Nuclear division • Daughter chromosomes distributed to two daughter nuclei • Cytokinesis • Cytoplasm division • Results in two genetically identical daughter cells
- 8. CELL CYCLE: MITOSISPHASE fatimaArivera
- 9. SIGNIFICANCE OF MITOSIS fatimaArivera •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
- 10. • 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 MITOSIS PHASE: PROPHASE What’s happening? What the cell looks like? fatimaArivera
- 11. MITOSIS PHASE: PROMETAPHASE fatimaArivera What’shappening? What the cell looks like? • 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
- 12. MITOSIS PHASE: METAPHASE fatimaArivera What’shappening? What the cell looks like? • Chromosomes align on an axis called the metaphase plate • Note: the spindle consists of microtubules, one attached to each chromosome
- 13. MITOSIS PHASE:ANAPHASE fatimaArivera What’s happening?What the cell looks like? • 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
- 14. MITOSIS PHASE: TELOPHASE fatimaArivera What’shappening? What the cell looks like? • 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
- 15. 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
- 16. MEIOSIS fatimaArivera • Formation ofGametes (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)
- 17. SIGNIFICANCE OF MEIOSIS fatimaArivera •Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote
- 18. MEIOSIS I: PROPHASEI fatimaArivera Prophase I is further subdivided into periods known as •Leptotena •Zygotena •Pachytena •Diplotena •Diakinesis
- 19. A physical exchangeof chromosome pieces PROPHASE I fatimaArivera
- 20. METAPHASE I fatimaArivera Homologous pairs ofchromosomes align along the equator of the cell
- 21. ANAPHASE I fatimaArivera Homologs separateand move to opposite poles. Sister chromatids remain attached at their centromeres.
- 22. TELOPHASE I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two. fatimaArivera
- 23. MEIOSIS II: PROPHASEII fatimaArivera Nuclear envelope fragments. Spindle forms.
- 24. MEIOSIS II: METAPHASEII fatimaArivera Chromosomes align along equator of cell.
- 25. MEIOSIS II: ANAPHASEII Sister chromatids separate and move to opposite poles. fatimaArivera Equator Pole
- 26. MEIOSIS II: TELOPHASEII fatimaArivera Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two.
- 27. RESULTS OF MEIOSIS fatimaArivera •Four haploid cells with one copy of each chromosome
- 28. SUMMARY OF MEIOSISI fatimaArivera Nucleus Spindle fibers Nuclear envelope EARLY PROPHASE I LATE PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I & CYTOKINESIS
- 29. SUMMARY OF MEIOSISII Prophase II Metaphase II Anaphase II Telophase II 4 I Undentical haploid cells fatimaArivera
- 30. Intracellular control ofthe cell cycle fatimaArivera The cell cycle is controlled by regulator molecules that either: promote the process (positive) stop it from progressing (negative)
- 31. Positive: Cdks &Cyclins fatimaArivera 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
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- 33. Negative: Rb &p53 fatimaArivera 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.
- 34. Negative: Rb &p53 fatimaArivera ◦ 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)
- 35. p53 p53 proteinhalts 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 p53 is the Cell Cycle Enforcer fatimaArivera
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- 37. Generic cell cyclecheckpoints Is environment favorable? Is environment favorable? Are all DNA replicated? Are all chromosomes attached to the spindle? fatimaArivera
- 38. G1 S G2 M G1 Checkpoint G2 Checkpoint MCheckpoint 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 ActiveMitotic Cdk-Cyclin (MPF) • Replication completed • DNA integrity APC Chromosomes attached at metaphase plate Degraded Mitotic Cyclin Control of the Cell Cycle
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