Chapter 10Chapter 10

Cell Growth and DivisionCell Growth and Division

Think about it…Think about it…

How would you describe the process by How would you describe the process by which a multicellular organism increases which a multicellular organism increases its size? its size?

Why do cells stay small?Why do cells stay small?

Liver cell completes cell division – Magnification 11,500x

Limits to Cell GrowthLimits to Cell Growth

Two reasons why cells can’t grow Two reasons why cells can’t grow indefinitely and must divide:indefinitely and must divide: DNA overloadDNA overload Exchange of materials Exchange of materials

DNA OverloadDNA Overload

When the cell is small, the information When the cell is small, the information stored in that DNA is able to meet all of stored in that DNA is able to meet all of the cell’s needsthe cell’s needs

If the cell grows too large, the DNA If the cell grows too large, the DNA cannot produce enough proteins to cannot produce enough proteins to supply the cellsupply the cell

Exchanging MaterialsExchanging Materials The rate at which The rate at which

food, oxygen, water, food, oxygen, water, and wastes are and wastes are moved in and out of moved in and out of the cell is dependent the cell is dependent on the surface area on the surface area of the cell.of the cell.

Surface area – the cell membrane

Exchanging Materials Exchanging Materials

The rate at which The rate at which food, oxygen and food, oxygen and water are used and water are used and waste is produced waste is produced depends on the cell’s depends on the cell’s volume.volume.

Exchanging Materials Exchanging Materials

Ratio of Surface Area to Volume  Ratio of Surface Area to Volume   As the length of a cell increases, its volume As the length of a cell increases, its volume

increases faster than the surface area.increases faster than the surface area. The decrease in the cell’s ratio of surface The decrease in the cell’s ratio of surface

area to volume makes it more difficult for the area to volume makes it more difficult for the cell to move needed materials in and waste cell to move needed materials in and waste products out quickly enough for the cell to products out quickly enough for the cell to survive.survive.

The surface area must be must allow sufficient exchange to support the contents of the cell!

Calculate the following of a cubic cell Calculate the following of a cubic cell measuring 4cm on each side:measuring 4cm on each side:

Surface Area

Volume

Ratio of Surface Area to Volume:

Division of the CellDivision of the Cell

Before it becomes too large, a growing Before it becomes too large, a growing cell divides forming two ‘daughter’ cells cell divides forming two ‘daughter’ cells called called cell divisioncell division

BeforeBefore cell division occurs, the cell cell division occurs, the cell replicates all of its DNAreplicates all of its DNA Each daughter cell gets one complete set of Each daughter cell gets one complete set of

genetic infogenetic info

10.2 Cell Division10.2 Cell Division

In eukaryotic cells, cell division In eukaryotic cells, cell division occurs in two main stages:occurs in two main stages:

1.1. Mitosis – division of the cell nucleusMitosis – division of the cell nucleus

2.2. Cytokinesis – division of cell Cytokinesis – division of cell cytoplasmcytoplasm

ChromosomesChromosomes

Genetic information is passed from one Genetic information is passed from one generation to the next on generation to the next on chromosomes chromosomes (made of DNA).(made of DNA).

Chromosomes are not visible in most cells Chromosomes are not visible in most cells except during cell division (other times the except during cell division (other times the DNA is in the DNA is in the chromatinchromatin state) state)

Before cell division, the DNA condenses into Before cell division, the DNA condenses into compact structures, chromosomescompact structures, chromosomes

Each chromosome is duplicated, or copied.Each chromosome is duplicated, or copied.

ChromosomesChromosomes Once copied, each Once copied, each

chromosome consists chromosome consists of two identical of two identical “sister” “sister” chromatids.chromatids.

Chromatids are Chromatids are attached at the attached at the centromerecentromere

When the cell divides, When the cell divides, the sister chromatids the sister chromatids separate and each new separate and each new cell receives onecell receives one

Centromere

Sister chromatids

The Cell CycleThe Cell Cycle

The The cell cyclecell cycle is the series of events that cells is the series of events that cells go through as they go through as they growgrow and and dividedivide..

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

begins the cycle againbegins the cycle again

InterphaseInterphase is the period of growth that occurs is the period of growth that occurs betweenbetween cell divisions. cell divisions.

The Cell CycleThe Cell Cycle The cell cycle The cell cycle

consists of four consists of four phases:phases: GG11 (First Gap (First Gap

Phase)Phase) S PhaseS Phase GG22 (Second Gap (Second Gap

Phase)Phase) M PhaseM Phase

Events of the Cell CycleEvents of the Cell Cycle

During GDuring G11, the cell, the cell increases in sizeincreases in size synthesizes new synthesizes new

proteins and proteins and organellesorganelles

Events of the Cell CycleEvents of the Cell Cycle During the S phase,During the S phase,

chromosomes are chromosomes are replicatedreplicated

DNA synthesis takes DNA synthesis takes placeplace

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

Events of the Cell CycleEvents of the Cell Cycle

The GThe G22 Phase (Second Gap Phase) Phase (Second Gap Phase) organelles and molecules required for cell division are producedorganelles and molecules required for cell division are produced Once GOnce G22 is complete, the cell is ready to start the M phase—Mitosis is complete, the cell is ready to start the M phase—Mitosis

Cell Cycle

Events of the Cell CycleEvents of the Cell Cycle

MitosisMitosis

Biologists divide the events of Biologists divide the events of mitosis into four phases:mitosis into four phases: ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase TelophaseTelophase

MitosisMitosis

Section 10-2ProphaseSpindle

forming

Chromosomes (paired

chromatids)Centromere

MitosisMitosisProphaseProphase

MitosisMitosis ProphaseProphase

Prophase is the first and Prophase is the first and longest phase of mitosis.longest phase of mitosis.

The The centriolescentrioles separate separate and take up positions on and take up positions on opposite sides of the opposite sides of the nucleus.nucleus.

The spindle, a microtubule The spindle, a microtubule structure, forms between structure, forms between the centriolesthe centrioles

The nuclear envelope The nuclear envelope breaks down.breaks down.

Spindle forming

CentromereChromosomes(paired chromatids)

Centriole

Centriole

Spindle

MitosisMitosis

Click to Continue

Metaphase

MetaphaseMetaphase

MitosisMitosis MetaphaseMetaphase

The second phase The second phase The chromosomes The chromosomes line up across the line up across the center of the cell.center of the cell.

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

Centriole

Spindle

Individual chromosomes

Anaphase

MitosisMitosis AnaphaseAnaphase

MitosisMitosis AnaphaseAnaphase

The third phase of The third phase of mitosis.mitosis.

The sister chromatids The sister chromatids separate into separate into individual individual chromosomes. chromosomes.

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

Individualchromosomes

Nuclear envelope reforming

Telophase

MitosisMitosis TelophaseTelophase

MitosisMitosis TelophaseTelophase

Telophase is the fourth Telophase is the fourth and final phase of mitosis.and final phase of mitosis.

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

A new nuclear envelope A new nuclear envelope forms around each cluster forms around each cluster of chromosomes.of chromosomes.

Spindle breaks apart and Spindle breaks apart and the nucleolus reappears.the nucleolus reappears.

CytokinesisCytokinesis

Cytokinesis

CytokinesisCytokinesis

CytokinesisCytokinesis Not a phase of mitosisNot a phase of mitosis During cytokinesis, the During cytokinesis, the

cell membrane pinches cell membrane pinches in and the cytoplasm is in and the cytoplasm is split between the two split between the two cells.cells.

Each daughter cell has Each daughter cell has an identical set of an identical set of duplicate chromosomesduplicate chromosomes

Cytokinesis in PlantsCytokinesis in Plants In plants, a structure known as the cell plate In plants, a structure known as the cell plate

forms midway between the divided nuclei.forms midway between the divided nuclei.

Cell wallCell plate

Cytokinesis in PlantsCytokinesis in Plants

The cell plate gradually develops into a The cell plate gradually develops into a separating membrane.separating membrane.

A cell wall then begins to appear in the A cell wall then begins to appear in the cell plate.cell plate.

Cells in MitosisCells in Mitosis

http://www.uoguelph.ca/zoology/devobio/210labs/mitosis1.htmlhttp://www.uoguelph.ca/zoology/devobio/210labs/mitosis1.html

http://web.mac.com/mrgaskell/iWeb/Science%20Extras/Mitosishttp://web.mac.com/mrgaskell/iWeb/Science%20Extras/Mitosis%20Slides.html%20Slides.html

Things to look:Things to look:Shape of CellShape of CellChromosomesChromosomesPresence of a nucleusPresence of a nucleusWhere the chromosomes are in the cellWhere the chromosomes are in the cellIf there is a division forming between cellsIf there is a division forming between cells

Mitosis AnimationsMitosis Animations

http://www.johnkyrk.com/mitosis.html http://www.johnkyrk.com/mitosis.html http://www.youtube.com/watch?v=VlN7K1-http://www.youtube.com/watch?v=VlN7K1-

9QB0 9QB0 http://outreach.mcb.harvard.edu/animations/http://outreach.mcb.harvard.edu/animations/

biochem.swfbiochem.swf http://www.hybridmedicalanimation.com/http://www.hybridmedicalanimation.com/

anim_mitosis.html anim_mitosis.html http://www.biology.arizona.edu/Cell_bio/http://www.biology.arizona.edu/Cell_bio/

tutorials/cell_cycle/cells3.html tutorials/cell_cycle/cells3.html

Controls on Cell DivisionControls on Cell Division

Normal cells will reproduce until they Normal cells will reproduce until they come into contact with other cells.come into contact with other cells.

When cells come into contact with other When cells come into contact with other cells, they respond by not growing.cells, they respond by not growing.

This shows that cell growth and division This shows that cell growth and division can be turned on and off.can be turned on and off.

Cell Cycle RegulatorsCell Cycle Regulators

The cell cycle is regulated by a specific The cell cycle is regulated by a specific protein called protein called cyclincyclin

The amount of this protein in the cell The amount of this protein in the cell rises and falls in time with the cell cyclerises and falls in time with the cell cycle

Internal Regulators Internal Regulators 

Proteins that respond to events inside the Proteins that respond to events inside the cell are called internal regulators.cell are called internal regulators.

Internal regulators allow the cell cycle to Internal regulators allow the cell cycle to proceed only when certain processes proceed only when certain processes have happened inside the cell.have happened inside the cell.

External Regulators External Regulators 

Proteins that respond to events outside Proteins that respond to events outside the cell are called external regulators.the cell are called external regulators.

External regulators direct cells to speed External regulators direct cells to speed up or slow down the cell cycle.up or slow down the cell cycle.

Uncontrolled Cell GrowthUncontrolled Cell Growth Cancer is a disorder when cells lose the ability Cancer is a disorder when cells lose the ability

to control growth.to control growth. Cancer cells do not respond to the signals that Cancer cells do not respond to the signals that

regulate the growth of most cells. regulate the growth of most cells. Cancer cells divide uncontrollably and form Cancer cells divide uncontrollably and form

masses of cells called masses of cells called tumorstumors that can damage that can damage the surrounding tissues. the surrounding tissues.

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

http://science.education.nih.gov/http://science.education.nih.gov/supplements/nih1/cancer/activities/supplements/nih1/cancer/activities/activity2_animations.htmactivity2_animations.htm