CELL REPRODUCTIO

NChapter 8

Video: Cell Division (19)

“CELLS ARE COMING FROM OTHER CELLS”

(Virchow, Cell Theory)

CELL DIVISION: It is the process by which new cells are produced from one cell and they are identical to the original one.

(In this moment as you are reading this, millions of your cells are growing, dividing and dying)

All living things have CHROMOSOMES.CHROMOSOMES: Structures made of

DNA that contain the genetic material. There are 46 in each human body cell. They are in the Nucleus (or cytoplasm).

DNA must be copied in cell reproduction.

Most of the cell’s lifetime, chromosomes are in the shape of CHROMATIN (long strands of DNA wrapped without order around Proteins, in the nucleus)

Before the cell divides, the CHROMATIN is organized in the shape of CHROMOSOMES.

Each chromosome is made of 2 SISTER CHROMATIDS.

CELL CYCLE

G1 + S + G2= INTERPHASE (Preparation for Mitosis)

INTERPHASEThe cell spends most of the time in this The cell spends most of the time in this

phasephaseG1: Cells grow in sizeS: DNA is copiedG2: The cell gets ready for division

(Mitosis)They have CHROMATINThey have CHROMATINThey have 2 CENTRIOLESThey have 2 CENTRIOLESThey have NUCLEAR ENVELOPEThey have NUCLEAR ENVELOPE

MITOSISMitosis has 4 Mitosis has 4 phases:phases:

PROPHASEMETAPHASEANAPHASETELOPHASE

Video: Biologix: Cell Cycle Mitosis and Cytoplasmic Division (29)

PROPHASE• First and longest phase of MitosisFirst and longest phase of Mitosis

• The chromatin is organized into visible The chromatin is organized into visible chromosomeschromosomes

• Nuclear envelope and nucleolus Nuclear envelope and nucleolus disappeareddisappeared

• In animal cells, the CENTRIOLES migrate to In animal cells, the CENTRIOLES migrate to the opposite ends of the cell and the the opposite ends of the cell and the SPINDLE FIBERS begin to formSPINDLE FIBERS begin to form

• In plant cells, the SPINDLES FIBERS form In plant cells, the SPINDLES FIBERS form without centrioles.without centrioles.

METAPHASE• Short phaseShort phase

• The chromosomes lined up in the The chromosomes lined up in the middle of the SPINDLE FIBERS by middle of the SPINDLE FIBERS by their CENTROMERES.their CENTROMERES.

ANAPHASE• Complete separation of homologous Complete separation of homologous

chromosomes.chromosomes.

• The chromosomes are pulled apart The chromosomes are pulled apart by the SPINDLE FIBERS.by the SPINDLE FIBERS.

• The chromosomes The chromosomes

separate completely to the separate completely to the

opposite sides of the cell.opposite sides of the cell.

TELOPHASE• Final phase of MitosisFinal phase of Mitosis

• The chromosomes unwind again The chromosomes unwind again (CHROMATIN)(CHROMATIN)

• The SPINDLE FIBERS begin to break The SPINDLE FIBERS begin to break downdown

• Nucleolus reappearsNucleolus reappears

• New NUCLEAR ENVELOPE reappearsNew NUCLEAR ENVELOPE reappears

• New CELL MEMBRANE forms around the New CELL MEMBRANE forms around the new cellsnew cells

CYTOKINESIS• Division of the cytoplasm after MITOSIS.Division of the cytoplasm after MITOSIS.

Animal cells (contractileAnimal cells (contractileRing that divides the Ring that divides the cytoplasm)cytoplasm)

Plant cells (form a Plant cells (form a CELL PLATE betweenCELL PLATE betweenThe cells) The cells)

RESULT OF MITOSISFrom ONE original cell

2 DAUGHTER CELLS result that are identical to the parent cell.

MEIOSIS

WHY MEIOSIS?

Process of cell division in which one cell produces 4 daughter cells with HALF the chromosomes than the original one.

The daughter cells are called The daughter cells are called GAMETES (eggs, sperm)

TESTICULESTESTICULES

SPERMSPERM

OVARIESOVARIES ZYGOTE Mitosis ZYGOTE Mitosis

EGGSEGGS

•Human body cells have 46 chromosomes.

•They are in pairs that contain information for the same traits: HOMOLOGOUS CHROMOSOMES.

•Cells with 2 sets of chromosomes are called DIPLOID (2n)

•Human sex cells (sperm and eggs) have 23 chromosomes. They do not have homologous chromosomes. HAPLOID (n)

Before Meiosis…Before Meiosis…

INTERPHASE• DNA and CENTRIOLES duplicateDNA and CENTRIOLES duplicate

• Cells grow to its maximum sizeCells grow to its maximum size

• Chromatin changes into Chromatin changes into HOMOLOGOUS CHROMOSOMESHOMOLOGOUS CHROMOSOMES

MEIOSISMEIOSIS I (1 cell 2 cells with the (1 cell 2 cells with the

same number of the chromosomes of the same number of the chromosomes of the parent cell)parent cell)

PROPHASE I• Chromatin forms homologous Chromatin forms homologous

chromosomeschromosomes• Nucleolus and nuclear envelope disappearNucleolus and nuclear envelope disappear• Spindle fibers are formed from the Spindle fibers are formed from the

centriolescentrioles• CROSSING OVER takes placeCROSSING OVER takes place

CROSSING OVER: Exchange of : Exchange of genetic information between pairs of genetic information between pairs of homologous chromosomes.homologous chromosomes.

METAPHASE I• The homologous chromosomes line The homologous chromosomes line

up in the middle of the cell by the up in the middle of the cell by the

spindle fibers.spindle fibers.

ANAPHASE I• The homologous chromosomes The homologous chromosomes

separate from each other.separate from each other.

TELOPHASE I• Nuclear envelope and nucleolus Nuclear envelope and nucleolus

reappearreappear• 2 cells begin to form2 cells begin to form• Spindle fibers begin to Spindle fibers begin to disappeardisappear

CYTOKINESIS I• Cytoplasm divides forming 2 new cells Cytoplasm divides forming 2 new cells

with the same number of with the same number of chromosomes as the original cell.chromosomes as the original cell.

MEIOSIS II (2 cell 4 cells with (2 cell 4 cells with half of the chromosomes of the half of the chromosomes of the parent cell)parent cell)

PROPHASE II• Sister chromatids are togetherSister chromatids are together

• Nucleolus and nuclear envelope Nucleolus and nuclear envelope disappeardisappear

• Spindle fibers are formed from the Spindle fibers are formed from the centriolescentrioles

METAPHASE II• The sister chromatids line up inThe sister chromatids line up in

the middle of the cell by the middle of the cell by

spindle fibers.spindle fibers.

ANAPHASE II• The sister chromatids The sister chromatids

separate from each other.separate from each other.

TELOPHASE II• Nuclear envelope and nucleolus Nuclear envelope and nucleolus

reappearreappear

• 4 cells begin to form4 cells begin to form

• Spindle fibers begin to disappearSpindle fibers begin to disappear

CYTOKINESIS II• Cytoplasm divides forming Cytoplasm divides forming

4 new cells with half of 4 new cells with half of

the chromosomes of the the chromosomes of the

original one.original one.

•MITOSIS: CHROMOSOMES

•MEIOSIS I: HOMOLOGOUS CHROMOSOMES

•MEIOSIS II: SISTER CHROMATIDS

MITOSIS

MEIOSIS

NUMBER OF CELLS AT THE END

2 4

NUMBER OF CHROMOSOME

S AT THE END

The same amount than the

parent cell

Half of the chromosomes of the parent cell

TYPE OF CELLS

Any body cell

Only sex cells

CANCERIf the cell cycle goes out of control. If the cell cycle goes out of control. Normal cells with damaged genes.Normal cells with damaged genes.

CANCERCANCER

Cancer cells keep dividing and form Cancer cells keep dividing and form clumps called clumps called TUMORSTUMORS..

A BENIGN TUMOR is harmless because the cells stay together and can be removed

A A MALIGNANT TUMOR MALIGNANT TUMOR can be lethal can be lethal and has cancer cells that break away and has cancer cells that break away from the tumor and travel to other from the tumor and travel to other parts of the body (parts of the body (METASTASIS))

CAUSES OF CANCER:CAUSES OF CANCER:• GeneticsGenetics

• External factors: External factors: SunlightSunlight

Smoke/Drugs/Smoke/Drugs/AlcoholAlcohol

PollutionPollution

X-RaysX-Rays

Bad nutrition Bad nutrition (obesity)(obesity)

StressStress

CANCER CANCER FACTSFACTS

• Cancer may affect people at any age.Cancer may affect people at any age.

• Cancer causes about 13% of all deaths in Cancer causes about 13% of all deaths in the world.the world.

•Cancer can affect all animals.

• Most cancers can be treated and some Most cancers can be treated and some cured using radiotherapy, chemotherapy or cured using radiotherapy, chemotherapy or surgery.surgery.

• Video: Life Science: Cells (20)Video: Life Science: Cells (20)

• WS: Mitosis & MeiosisWS: Mitosis & Meiosis