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Section A: The Key Roles of Cell DivisionSection A: The Key Roles of Cell Division

CHAPTER 12THE CELL CYCLE

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• The continuity of life from one cell to another is based on the reproduction of cells via cell division.

• The division of a unicellular الخلية .organism (e.g وحيدAmoeba) 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.

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– Every eukaryotic species النواة حقيقيات من has a نوعcharacteristic مميز number of chromosomes in رقمthe nucleus.

– Human somatic cells (body cells) have 46 chromosomes.

– Human gametes أمشاج (sperm or eggs) have 23 chromosomes, half the number in a somatic cell الجسدية .الخلية

• Each eukaryotic chromosome consists من خيطيlinear , طويلof a long يتكون

DNA molecule.

Cell division الخلوي يوزع distributes االنقسامchromosomes to daughter cells البنوية الخاليا

Fig. 12.2, Page 216

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ChromatidChromatin

+ DNA

Sister chromatid

Chromosome الصبغ

Centromereالمركزية القطعة

Homologous Chromosome

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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: 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: الخلوى اإلنشطار 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.

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Section B1: The Mitotic Cell Cycle الخلية دورة

Fig. 12.4, Page 217

• The mitotic (M) phase مرحلةof the cell cycle alternates تتبادل with the much longer interphase البينية .المرحلة

– The M phase includes mitosis and cytokinesis الخلوى اإلنشطار .

– Interphase accounts for 90% of the cell cycle.

A. Interphase has three subphases:

1. The G1 phase (“first gap”):

the cell grows تنمو.

2. The S phase (“synthesis”): the chromosomes are copied استنساخ .الكروموسومات

3. The G2 phase (“second gap”): the cell completes preparationsاالستعداد

for cell division.

B. Division phase (M). The cell starts the division process.

• The resulting daughter cells may then repeatتعيد the cycle again.

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A. Mitosis: is usually include five sub-phases فرعية :مراحل Prophase, التمهيدية Prometaphase, اإلستوائية قبل Metaphase, اإلستوائية Anaphase, اإلنفصالية Telophase. اإلنتهائية

• By late interphase (G2), the chromosomes have been duplicated تضاعفت

Fig. 12.5a, 218

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1) Prophase, التمهيدية the chromosomes are coiled, with sister chromatids joinedترتبط together, The nucleoli تختفيdisappearالنويات

2) Prometaphase, اإلستوائية the قبلnuclear 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, اإلستوائية the spindle fibers push the sister chromatids

Fig. 12.5b, C & D, Page 218-219

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• Anaphase, اإلنفصالية the centromeres divideتنقسم , result in separating the sister chromatids.

• Telophase, اإلنتهائية the cell continuesتستمر to elongateتستطيل and finally 5 the two cells اخيراseparate.تنفصل

1) Two nuclei begin to form, surrounded by the fragments of the parent’s nuclear envelope غالف

االبوي .النواة2) Cytokinesis السيتوبالزم , انشطار

begins as the division of the cytoplasm occurs.

Fig. 12.5e & f, Page 219

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Fig. 12.5 left

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Fig. 12.5 right

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• Cytokinesis (division of the cytoplasm)

B. The cytokinesis: الخلوى اإلنشطار divides the cytoplasm:

Fig. 12.8, Page 222

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Cell Cycle

Interphase

Prophase التمهيدية

Prometaphase اإلستوائية قبل

Metaphase اإلستوائية

Anaphase اإلنفصالية

Telophase اإلنتهائية

G1 S G2

Division process

Mitosis Cytokinesis