1. 1 Section A: The Key Roles of Cell Division CHAPTER 12 THE CELL CYCLE

2. 2 The continuity of life from one cell to another is based on the reproduction of cells via cell division.The continuity of life from one cell to another is based on the reproduction of cells via cell division. The division of a unicellular وحيد الخلية organism (e.g. Amoeba) reproduces an entire organism, increasing the population.The division of a unicellular وحيد الخلية organism (e.g. Amoeba) reproduces an entire organism, increasing the population. Introduction Fig. 12.1, Page 216 Figs. 12.1, Page 216 Division is differ among cells:. - Skin cells divide frequently. - Liver cells divide when needed (damage repair). - Nerve cells and muscle cells do not divide at all.

3. 3 –Every eukaryotic species نوع من حقيقيات النواة has a characteristic رقم مميز number of chromosomes in the nucleus. –Human somatic cells (body cells) have 46 chromosomes. –Human gametes (sperm or eggs) have 23 chromosomes, half the number in a somatic cell. –Human gametes أمشاج (sperm or eggs) have 23 chromosomes, half the number in a somatic cell الخلية الجسدية. Each eukaryotic chromosome consists يتكون من of a longطويل, linearخيطي DNA molecule.Each eukaryotic chromosome consists يتكون من of a longطويل, linearخيطي DNA molecule. Cell division الانقسام الخلوي distributes يوزع chromosomes to daughter cellsالخلايا البنوية Fig. 12.2, Page 216

4. 4Chromatid Chromatin + DNA Sister chromatid Chromosome Chromosome الصبغCentromere القطعة المركزية Homologous Chromosome

5. 5 Genes: The units that specify an organism’s inherited characters. Chromatin: A DNA-protein complex which is organized into a long thin fiber Chromosome: The package that formed from a condensed, coiled and folded chromatin. Chromatids: Chromatids: Two sister arms (chromatids) formed from each duplicated chromosome. They contain identical copies of the chromosome’s DNA Centromere: The narrow region at which the chromosomal strands are connect togreher. Mitosis: Is the division process which forms two daughter nuclei Cytokinesis: الإنشطار الخلوى Is the division stage of the cytoplasm which usually follow the mitosis. Definitions Meiosis: A division process that occurs In the gonads المناسل, and yields four daughter cells, each with half the chromosomes of the parent.

6. 6 Section B1: The Mitotic Cell Cycleدورة الخلية Fig. 12.4, Page 217 The mitotic (M) phase مرحلةof the cell cycle alternates تتبادل with the much longer interphase المرحلة البينية.The mitotic (M) phase مرحلةof the cell cycle alternates تتبادل with the much longer interphase المرحلة البينية. –The M phase includes mitosis and cytokinesis الإنشطار الخلوى. –Interphase accounts for 90% of the cell cycle. A.Interphase has three subphases: 1.The G 1 phase (“first gap”): the cell grows تنمو. 2.The S phase (“synthesis”): the chromosomes are copied استنساخ الكروموسومات. 3.The G 2 phase (“second gap”): the cell completes preparationsالاستعداد for cell division. B.Division phase ( M ). The cell starts the division process. The resulting daughter cells may then repeatتعيد the cycle again.The resulting daughter cells may then repeatتعيد the cycle again.

7. 7 A.Mitosis: is usually include five sub-phases مراحل فرعية :  Prophase,  Prophase, التمهيدية  Prometaphase,  Prometaphase, قبل الإستوائية  Metaphase,  Metaphase, الإستوائية  Anaphase, الإنفصالية  Telophase.  Telophase. الإنتهائية By late interphase (G2), the chromosomes have been duplicated تضاعفتBy late interphase (G2), the chromosomes have been duplicated تضاعفت Fig. 12.5a, 218

8. 8 1)Prophase, the chromosomes are coiled, with sister chromatids joinedترتبط together, The nucleoli النوياتdisappearتختفي 1)Prophase, التمهيدية the chromosomes are coiled, with sister chromatids joinedترتبط together, The nucleoli النوياتdisappearتختفي 2)Prometaphase, the nuclear envelope fragments يتجزأand microtubules from one poleقطب attachترتبط to one of two kinetochores (special regions of the centromere) while microtubules from the other pole attach to the other kinetochore. 2)Prometaphase, قبل الإستوائية the nuclear envelope fragments يتجزأand microtubules from one poleقطب attachترتبط to one of two kinetochores (special regions of the centromere) while microtubules from the other pole attach to the other kinetochore. 3)Metaphase, the spindle fibers push the sister chromatids 3)Metaphase, الإستوائية the spindle fibers push the sister chromatids Fig. 12.5b, C & D, Page 218-219

9. 9 Anaphase, الإنفصالية the centromeres divideتنقسم, result in separating the sister chromatids.Anaphase, الإنفصالية the centromeres divideتنقسم, result in separating the sister chromatids. Telophase, الإنتهائية the cell continuesتستمر to elongateتستطيل and finally اخيراً the two cells separate.تنفصلTelophase, الإنتهائية the cell continuesتستمر to elongateتستطيل and finally اخيراً the two cells separate.تنفصل 1)Two nuclei begin to form, surrounded by the fragments of the parent’s nuclear envelope غلاف النواة الابوي. 2)Cytokinesis انشطار السيتوبلازم, begins as the division of the cytoplasm occurs. Fig. 12.5e & f, Page 219

10. 10 Fig. 12.5 left

11. 11 Fig. 12.5 right

12. 12 Cytokinesis (division of the cytoplasm)Cytokinesis (division of the cytoplasm) B. The cytokinesis: الإنشطار الخلوى divides the cytoplasm: Fig. 12.8, Page 222

13. 13 Cell Cycle Interphase Prophase التمهيدية Prometaphase قبل الإستوائية Metaphase الإستوائية Anaphase الإنفصالية Telophase الإنتهائية G1SG2 Division process MitosisCytokinesis