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Principals of General Zoology (Zoo-103)Principals of General Zoology (Zoo-103)Principals of General Zoology (Zoo-103)Principals of General Zoology (Zoo-103)

Zoology Department, 1431-1432HZoology Department, 1431-1432H

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

• This division process occurs as part of the This division process occurs as part of the cell cyclecell cycle ( (the life of a cell from its origin in the the life of a cell from its origin in the division of a parent cell until its own division into division of a parent cell until its own division into twotwo).).

• The division of a unicellular The division of a unicellular الخلية الخلية وحيد وحيدorganism (organism (e.g. Amoebae.g. Amoeba) reproduces an entire ) reproduces an entire organism, increasing the population.organism, increasing the population.

• Cell division is also central to the Cell division is also central to the development of a multicellular development of a multicellular الخلية الخلية عديد عديدorganism that begins as a organism that begins as a fertilized egg or fertilized egg or zygotezygote..

IntroductionIntroduction

Fig. 12.1, Page 216

Figs. 12.1, Page 216Figs. 12.1, Page 216

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Division is differ among cells:.Division is differ among cells:.

- Skin cells divide frequently.Skin cells divide frequently.

- Liver cells divide when needed (damage repair).Liver cells divide when needed (damage repair).

- Nerve cells and muscle cells do not divide at all.Nerve cells and muscle cells do not divide at all.

Cell division distributes the genetic material (DNA) to two Cell division distributes the genetic material (DNA) to two daughter cells.daughter cells.

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• A cell’s genetic information (A cell’s genetic information (genome genome الـ ينىچالبنك ) is packaged as DNA.) is packaged as DNA.• In prokaryotes, the genome is often a single long DNA molecule.In prokaryotes, the genome is often a single long DNA molecule.

– In eukaryotes, the genome consists of several DNA moleculesIn eukaryotes, the genome consists of several DNA molecules..

• A human cell must duplicate about 3 m of DNA and separate the two A human cell must duplicate about 3 m of DNA and separate the two copies such that each daughter cell ends up with a complete copies such that each daughter cell ends up with a complete genome.genome.

• DNA molecules are packaged into chromosomes.DNA molecules are packaged into chromosomes. – Every eukaryotic species has a characteristic Every eukaryotic species has a characteristic

number of chromosomes in the nucleus.number of chromosomes in the nucleus.

– Human somatic cells (Human somatic cells (body cellsbody cells) have ) have 46 chromosomes46 chromosomes..

– Human gametes Human gametes أمشاج (sperm or eggs) have (sperm or eggs) have 23 chromosomes23 chromosomes, half the number in , half the number in a somatic cell a somatic cell الجسدية ..الخلية

• Each eukaryotic chromosome consists Each eukaryotic chromosome consists of a long, linear DNA molecule. of a long, linear DNA molecule.

Cell division distributes identical sets of chromosomes to Cell division distributes identical sets of chromosomes to daughter cellsdaughter cells

Fig. 12.2, Page 216

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• Each chromosome has hundreds or thousands of genes (Each chromosome has hundreds or thousands of genes (the units that the units that specify an organism’s inherited characters specify an organism’s inherited characters الوراثية الوراثية الصفات .(.(الصفات

• This DNA-protein complex (This DNA-protein complex (chromatinchromatin) is organized into a long thin fiber.) is organized into a long thin fiber.• After the DNA duplication, chromatin After the DNA duplication, chromatin

condensescondenses form (form (chromosomechromosome). ).

• Each duplicated chromosome consists Each duplicated chromosome consists of two sister of two sister chromatidschromatids which contain which contain identical copies of the chromosome’s identical copies of the chromosome’s DNA.DNA.

• The narrow region where the The narrow region where the chromosomal strands connect is the chromosomal strands connect is the called called centromerecentromere..

• Later, the sister chromatids are pulled Later, the sister chromatids are pulled apart and repackaged into two new apart and repackaged into two new nuclei at opposite ends of the parent nuclei at opposite ends of the parent cell during cell division.cell during cell division.

• The process of the formation of the two The process of the formation of the two daughter nuclei called (daughter nuclei called (mitosismitosis) and is ) and is usually followed by division of the usually followed by division of the cytoplasm (cytoplasm (cytokinesis cytokinesis الخلوىالخلوى اإلنشطاراإلنشطار ).). It occurs in somatic cells It occurs in somatic cells الجسدية الجسدية الخاليا الخاليا

Fig. 12.3, Page 217Fig. 12.3, Page 217

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ChromatidChromatidChromatin Chromatin

+ DNA+ DNA

Sister chromatidSister chromatid

Chromosome Chromosome الصبغ

CentromereCentromere

Homologous Homologous ChromosomeChromosome

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The Mitotic Cell Cycle (division)The Mitotic Cell Cycle (division)

Fig. 12.4, Page 217

• The mitotic (The mitotic (MM) phase of the cell cycle alternates ) phase of the cell cycle alternates تتبادلتتبادل with the with the much longer much longer interphase interphase البينية البينية المرحلة ..المرحلة

– The The MM phase includes phase includes mitosismitosis and and cytokinesiscytokinesis الخلوىالخلوى اإلنشطاراإلنشطار ..

– Interphase accounts for Interphase accounts for 90%90% of the of the cell cycle.cell cycle.

• During interphase the cell prepares for During interphase the cell prepares for division by producing cytoplasmic division by producing cytoplasmic organelles and copying its chromosomes.organelles and copying its chromosomes.

A.A. InterphaseInterphase has three subphases: has three subphases:

1.1. The The GG11 phase (“ phase (“first gapfirst gap”): ”):

the cell grows. the cell grows.

2.2. The The SS phase (“ phase (“synthesissynthesis”): the chromosomes are copied. ”): the chromosomes are copied.

3.3. The The GG22 phase (“phase (“second gapsecond gap”): the cell completes preparations for ”): the cell completes preparations for

cell division.cell division.

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

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

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

• By late interphase (By late interphase (G2G2), the ), the chromosomes have been chromosomes have been duplicated duplicated تضاعفتتضاعفت but are but are loosely packed.loosely packed.

• The centrosomes have been The centrosomes have been duplicated and begin to duplicated and begin to organize microtubules into organize microtubules into an aster (“star”).an aster (“star”).

Fig. 12.5a, 218Fig. 12.5a, 218

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1)1) ProphaseProphase, , التمهيدية the chromosomes are the chromosomes are tightly coiled, with sister chromatids joined tightly coiled, with sister chromatids joined together, The nucleoli disappear. The together, The nucleoli disappear. The mitotic mitotic spindle begins to formspindle begins to form and appears to push and appears to push the centrosomes away from each other the centrosomes away from each other towards opposite ends (poles) of the cell.towards opposite ends (poles) of the cell.

2)2) PrometaphasePrometaphase, , اإلستوائية the nuclear the nuclear قبلenvelope fragments and microtubules from envelope fragments and microtubules from one pole attach to one of two one pole attach to one of two kinetochoreskinetochores (special regions of the centromere) while (special regions of the centromere) while microtubules from the other pole attach to microtubules from the other pole attach to the other kinetochore.the other kinetochore.

3)3) MetaphaseMetaphase,, اإلستوائية tthe spindle fibers push he spindle fibers push the sister chromatids until they are all the sister chromatids until they are all arranged at the imaginary plane equidistant arranged at the imaginary plane equidistant between the poles, defining metaphase.between the poles, defining metaphase.

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

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• AnaphaseAnaphase, , اإلنفصاليةاإلنفصالية the centromeres the centromeres divide, result in separating the sister divide, result in separating the sister chromatids. Each is then pulled toward chromatids. Each is then pulled toward the pole to which it is attached by the pole to which it is attached by spindle fibers. By the end, the two spindle fibers. By the end, the two poles have equivalent collections of poles have equivalent collections of chromosomes.chromosomes.

• Telophase,Telophase, اإلنتهائيةاإلنتهائية the cell continues to the cell continues to elongate as free spindle fibers from elongate as free spindle fibers from each centrosome push off each other.each centrosome push off each other.

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

2)2) Chromatin becomes less tightly coiled.Chromatin becomes less tightly coiled.

3)3) CytokinesisCytokinesis, begins as the division of , begins as the division of the cytoplasm occurs.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 (Cytokinesis (division of the division of the cytoplasmcytoplasm) typically follows ) typically follows mitosis.mitosis.

• Contraction Contraction إنقباضإنقباض of the cell of the cell pinches the cell into two new cellspinches the cell into two new cells

B. The cytokinesis:B. The cytokinesis: الخلوىالخلوى اإلنشطاراإلنشطار divides the cytoplasm:divides the cytoplasm:

Fig. 12.8, Page 222

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Cell CycleCell Cycle

InterphaseInterphase

ProphaseProphase التمهيديةالتمهيدية

Prometaphase Prometaphase اإلستوائية اإلستوائية قبل قبل

Metaphase Metaphase اإلستوائيةاإلستوائية

Anaphase Anaphase اإلنفصاليةاإلنفصالية

TelophaseTelophase اإلنتهائيةاإلنتهائية

G1G1 SS G2G2

Division processDivision process

Mitosis CytokinesisCytokinesis

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GenesGenes:: The units that specify an organism’s inherited charactersThe units that specify an organism’s inherited characters..

ChromatinChromatin:: A DNA-protein complex which is organized into a longA DNA-protein complex which is organized into a long thin fiber thin fiber

ChromosomeChromosome:: The The packagepackage that formed from a that formed from a condensed,condensed, coiledcoiled and folded and folded chromatinchromatin..

ChromatidsChromatids:: Two sister arms (chromatids) formed from each duplicated chromosome. They contain identical copies of the chromosome’s DNA

CentromereCentromere:: The narrow region at which the chromosomal strandsThe narrow region at which the chromosomal strands are connect togreher. are connect togreher.

MitosisMitosis:: Is tIs the division process which forms two daughter nucleihe division process which forms two daughter nuclei

CytokinesisCytokinesis:: الخلوىالخلوى اإلنشطاراإلنشطار IIs the division stage of the s the division stage of the cytoplasmcytoplasm which which usually follow the usually follow the mitosis mitosis..

DefinitionsDefinitions

MeiosisMeiosis:: A division process that occurs A division process that occurs In the gonads In the gonads المناسلالمناسل, and , and yieldsyields four daughter cellsfour daughter cells, each with , each with half the chromosomeshalf the chromosomes of the parent. of the parent.