10-2 cell division copyright pearson prentice hall

10-2 Cell Division

Copyright Pearson Prentice Hall

Cell Division

In eukaryotes, cell division occurs in two major stages.The first stage, division of the cell nucleus, is called

mitosis.The second stage, division of the cell cytoplasm, is called

cytokinesis.


ChromosomesChromosomesGenetic information is passed from one generation to

the next on chromosomes.Before cell division, each chromosome is duplicated,

or copied.

Chromosomes


Chromosomes

Each chromosome consists of two identical “sister” chromatids.Each pair of chromatids is attached at an area called the centromere.


Sister chromatids

Centromere

Chromosomes

When the cell divides, the chromatids separate.Each new cell gets one chromatid.


The Cell Cycle

Cell CycleThe cell cycle is the series of events that cells go through

as they grow and divide.Interphase is the period of growth that occurs between

cell divisions.


The Cell Cycle

During the cell cycle:• a cell grows• prepares for division• divides to form two daughter cells, each of which

begins the cycle again


The cell cycle consists of four phases:– G1 (First Gap Phase)

– S Phase– G2 (Second Gap Phase)

– M Phase


Events of the Cell Cycle

Events of the Cell CycleDuring G1, the cell

– increases in size– synthesizes new proteins and organelles



During the S phase,• chromosomes are replicated• DNA synthesis takes place

Once a cell enters the S phase, it usually completes the rest of the cell cycle.



The G2 Phase (Second Gap Phase) • organelles and molecules required for cell division are

produced• Once G2 is complete, the cell is ready to start the M

phase—Mitosis




Cell Cycle

Mitosis

MitosisBiologists divide the events of mitosis into four phases: (PMAT)

• Prophase• Metaphase• Anaphase• Telophase


Mitosis


Mitosis

Mitosis


Section 10-2ProphaseSpindle

forming

Chromosomes (paired

chromatids)Centromere

Click to Continue

Prophase

Mitosis

ProphaseProphase is the first and

longest phase of mitosis.The centrioles separate

and take up positions on opposite sides of the nucleus.


Spindle forming

CentromereChromosomes(paired chromatids)

Mitosis

The centrioles lie in a region called the centrosome.

The centrosome helps to organize the spindle, a fanlike microtubule structure that helps separate the chromosomes.


Spindle forming


Mitosis

Chromatin condenses into chromosomes.

The centrioles separate and a spindle begins to form.

The nuclear envelope breaks down.


Spindle forming


Mitosis


Centriole

Centriole

Spindle

Click to Continue

Metaphase

Metaphase

Mitosis

MetaphaseThe second phase of

mitosis is metaphase.The chromosomes line up

across the center of the cell.

Microtubules connect the centromere of each chromosome to the poles of the spindle.


Centriole

Spindle

Mitosis

Anaphase


Individual chromosomes

Anaphase

Mitosis

AnaphaseAnaphase is the third phase

of mitosis.The sister chromatids

separate into individual chromosomes.

The chromosomes continue to move until they have separated into two groups.


Individualchromosomes

Mitosis

Telophase


Nuclear envelope reforming

Telophase

Mitosis

TelophaseTelophase is the fourth

and final phase of mitosis.

Chromosomes gather at opposite ends of the cell and lose their distinct shape.


Mitosis

A new nuclear envelope forms around each cluster of chromosomes.


Cytokinesis


Cytokinesis

Cytokinesis

Cytokinesis

During cytokinesis, the cytoplasm pinches in half.

Each daughter cell has an identical set of duplicate chromosomes


Cytokinesis in Plants


In plants, a structure known as the cell plate forms midway between the divided nuclei.

Cell wallCell plate

The series of events that cells go through as they grow and divide is called

• the cell cycle.• mitosis.• interphase.• cytokinesis.


The phase of mitosis during which the chromosomes line up across the center of the cell is

• prophase.• metaphase.• anaphase.• telophase.


Cytokinesis usually occurs • at the same time as telophase.• after telophase.• during interphase.• during anaphase


DNA replication takes place during the• S phase of the cell cycle.• G1 phase of the cell cycle.

• G2 phase of the cell cycle.

• M phase of the cell cycle.


During mitosis, “sister” chromatids separate from one another during

• telophase.• interphase.• anaphase.• metaphase.


10-3 Regulating the Cell Cycle


Controls on Cell Division

Controls on Cell DivisionExperiments show that normal cells will reproduce until

they come into contact with other cells.When cells come into contact with other cells, they respond

by not growing.This demonstrates that controls on cell growth and division

can be turned on and off.


Controls on Cell Division

Contact Inhibition


Cell Cycle Regulators

How is the cell cycle regulated?



Cell Cycle RegulatorsThe cell cycle is regulated by a specific protein.The amount of this protein in the cell rises and falls in time with the cell cycle. Scientists called this protein cyclin because it seemed to regulate the cell cycle. Cyclins regulate the timing of the cell cycle in eukaryotic cells.




A sample of cytoplasmis removed from a cellin mitosis.

The sample is injectedinto a second cell inG2 of interphase.

As result, the secondcell enters mitosis.

Cyclins were discovered during a similar experiment to this one.

Internal Regulators Internal regulators allow the cell cycle to proceed only

when certain processes have happened inside the cell.

Example: p53 Gene that regulates the passage into mitosis




External Regulators Proteins that respond to events outside the cell are called

external regulators.External regulators direct cells to speed up or slow down

the cell cycle.


Uncontrolled Cell Growth

Uncontrolled Cell GrowthCancer is a disorder in which some of the body's own cells lose the ability to control growth.How are cancer cells different from other cells?



Cancer cells do not respond to the signals that regulate the growth of most cells.



Cancer cells divide uncontrollably and form masses of cells called tumors that can damage the surrounding tissues.

Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities and causing serious medical problems or even death.


The cell cycle is believed to be controlled by proteins called

• spindles.• cyclins.• regulators.• centrosomes.


Proteins that respond to events inside the cell are called

• internal regulators.• external regulators.• cyclins.• growth factors.


10-3

Once a multicellular organism reaches adult size, the cells in its body

• stop dividing.• grow and divide at different rates, depending on the

type.• have the same life span between cell divisions.• undergo cell division randomly.


10-3

One effect of an internal regulator is that a cell will not begin mitosis until

• it becomes too large.• the cell’s growth is stimulated.• it is in physical contact with other cells.• all its chromosomes have been replicated.


One factor common to almost all cancer cells is• a lack of cyclin.• a defect in gene p53.• exposure to tobacco smoke.• exposure to radiation.


10-2 cell division copyright pearson prentice hall

Documents

cell cycle cell

new cell

cell divides

cell nucleus

cell cytoplasm

cell divisions

prophase slide

events of mitosis