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Chapter 9 Cellular Chapter 9 Cellular ReproductionReproduction

9.1 Cellular Growth9.1 Cellular Growth

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Cells Come in Different Cells Come in Different SizesSizes

Red Blood Cell 8 um in diameterRed Blood Cell 8 um in diameter Nerve Cell 1 m in length with very Nerve Cell 1 m in length with very

small diametersmall diameter Yolk of ostrich egg 8 cmYolk of ostrich egg 8 cm Most cells are 2-200 umMost cells are 2-200 um

1000 um = 1 mm1000 um = 1 mm

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Limits to Cell SizeLimits to Cell Size

1.1. DiffusionDiffusion

2.2. DNADNA

3.3. Surface to volume ratioSurface to volume ratio

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Diffusion Limits Cell SizeDiffusion Limits Cell Size

Within the cell nutrients must diffuse Within the cell nutrients must diffuse to all partsto all parts

Diffusion is based on random Diffusion is based on random movement of particlesmovement of particles

Diffusion is too slow for a large cellDiffusion is too slow for a large cell When cells reach maximum size they When cells reach maximum size they

die or dividedie or divide

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DNA Limits Cell SizeDNA Limits Cell Size

DNA contains all the instructions for DNA contains all the instructions for synthesizing proteins (including synthesizing proteins (including enzymes)enzymes)

Large cells would need more proteinsLarge cells would need more proteins More copies of the DNA instructions More copies of the DNA instructions

would be needed for a large cellwould be needed for a large cell Most cells contain only one set of Most cells contain only one set of

DNADNA

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Surface Area to Volume Ratio Surface Area to Volume Ratio Limits Cell SizeLimits Cell Size

As the size of a cell increases the As the size of a cell increases the volume increases faster than the volume increases faster than the surface areasurface area

If the cell size is doubled then need If the cell size is doubled then need eight times more nutrients but plasma eight times more nutrients but plasma membrane is only four times largermembrane is only four times larger

Cells divide before they become too Cells divide before they become too large to function properlylarge to function properly

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Volume Increases Faster than Volume Increases Faster than Surface AreaSurface Area

What are the surface area to volume ratios?

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The Cell CycleThe Cell Cycle

Sequence of growth and division of a Sequence of growth and division of a cellcell

Two main periodsTwo main periods– Growth also called interphaseGrowth also called interphase– Division also called mitosis and Division also called mitosis and

cytokinesiscytokinesis

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Cell Cycle

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InterphaseInterphase

NOT part of mitosis, rather the time NOT part of mitosis, rather the time between one mitosis and the nextbetween one mitosis and the next

Stages of interphaseStages of interphase– GG11 phase: rapid growth and metabolic phase: rapid growth and metabolic

activityactivity– S phase: synthesis of DNA (additional S phase: synthesis of DNA (additional

copy is made)copy is made)

– GG22 phase: centrioles and other organelles phase: centrioles and other organelles replicate; cell prepares for divisionreplicate; cell prepares for division

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Chromosomes and Chromosomes and ChromatinChromatin

Both are DNABoth are DNA Chromosomes are the condensed Chromosomes are the condensed

form of DNA that is visible as form of DNA that is visible as individual strands.individual strands.

Chromatin is the “relaxed” very thin Chromatin is the “relaxed” very thin form of DNA that is not visible as form of DNA that is not visible as individual strands.individual strands.

During interphase DNA is in the During interphase DNA is in the chromatin form.chromatin form.

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Chromosomes and Chromosomes and ChromatinChromatin

Chromatin DNA form

Chromosome DNA form

Chromatin DNA form

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Cell ReproductionCell Reproduction

Process of Process of producing new producing new cells from cells from preexisting cellspreexisting cells

Three TypesThree Types– Fission: bacteriaFission: bacteria– Meiosis: sex cellsMeiosis: sex cells– Mitosis: body cellsMitosis: body cells

Needed for growthNeeded for growth Needed for repairNeeded for repair

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Bacteria Reproduce by Bacteria Reproduce by FissionFission

Prokaryotes do not Prokaryotes do not have a nucleushave a nucleus

They divide the cell They divide the cell contents then contents then dividedivide

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Chapter 9 Cellular Chapter 9 Cellular ReproductionReproduction

9.2 Mitosis and Cytokinesis9.2 Mitosis and Cytokinesis

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Eukaryote Cell Reproduction is Eukaryote Cell Reproduction is Mitosis and CytokinesisMitosis and Cytokinesis

Mitosis is division of Mitosis is division of the nucleus producing the nucleus producing two genetically two genetically identical daughter identical daughter cells from one parent cells from one parent cellscells

Needed for growthNeeded for growth Needed for repairNeeded for repair

Cytokinesis is division Cytokinesis is division of the cell contentsof the cell contents

Usually they happen Usually they happen simultaneouslysimultaneously

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Phases of MitosisPhases of Mitosis

ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase TelophaseTelophase

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Chromosome StructureChromosome Structure

Chromosome is two sister chromatids connected by Chromosome is two sister chromatids connected by a centromerea centromere

Chromosomes are made of DNA and contain genes Chromosomes are made of DNA and contain genes (hereditary units)(hereditary units)

Chromosomes are the condensed form of chromatinChromosomes are the condensed form of chromatin

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ProphaseProphase

Chromatin coils into Chromatin coils into visible visible chromosomeschromosomes

Nuclear membrane Nuclear membrane disintegratesdisintegrates

Nucleus disappearsNucleus disappears Centrioles migrate Centrioles migrate

to opposite ends of to opposite ends of cellcell

Spindle fibers formSpindle fibers form

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ProphaseProphase

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MetaphaseMetaphase

Much shorter Much shorter amount of time amount of time than prophasethan prophase

Spindle fibers Spindle fibers attach to attach to centromerecentromere

Chromatids line up Chromatids line up at the cell’s at the cell’s equatorequator

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MetaphaseMetaphase

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AnaphaseAnaphase

Centromeres splitCentromeres split Spindle fibers Spindle fibers

shorten to pull shorten to pull chromatids to each chromatids to each end of cellend of cell

Sister chromatids Sister chromatids separateseparate

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AnaphaseAnaphase

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TelophaseTelophase

Starts when Starts when chromatids get to chromatids get to opposite polesopposite poles

Chromosome Chromosome uncoil and become uncoil and become chromatinchromatin

Spindles Spindles breakdownbreakdown

Nuclear membrane Nuclear membrane reformsreforms

Nucleus becomes Nucleus becomes visiblevisible

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TelophaseTelophase

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CytokinesisCytokinesis

Division of the Division of the cytoplasmcytoplasm

Plants form a cell Plants form a cell plate, the beginning plate, the beginning of a cell wallof a cell wall

Animals have Animals have cleavage furrow cleavage furrow where the plasma where the plasma membrane pinches membrane pinches inin

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Animal and Plant Animal and Plant CytokinesisCytokinesis

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Results of MitosisResults of Mitosis

Mitosis allows for Mitosis allows for genetic continuity genetic continuity in each generation in each generation of daughter cellsof daughter cells– Same chromosomesSame chromosomes– Same genesSame genes– Same exact DNASame exact DNA

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Levels of OrganizationLevels of Organization In unicellular organisms one organism undergoes mitosis to In unicellular organisms one organism undergoes mitosis to

make two organismsmake two organisms In multicellular organisms one cell undergoes mitosis to In multicellular organisms one cell undergoes mitosis to

make two cells that form tissuesmake two cells that form tissues– Tissues of different types functioning together form organsTissues of different types functioning together form organs– Organs functioning together form systemsOrgans functioning together form systems– Systems functioning together form organismsSystems functioning together form organisms

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Chapter 9 Cellular Chapter 9 Cellular ReproductionReproduction

9.3 Cell Cycle Regulation9.3 Cell Cycle Regulation

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Length of Cell CycleLength of Cell Cycle

Each cell type has a specific growth Each cell type has a specific growth and reproduction time tableand reproduction time table– Frog embryo cell cycle of less than one Frog embryo cell cycle of less than one

hourhour– Cells lining your intestine 24-48 hoursCells lining your intestine 24-48 hours– Mature nerve cells do not divideMature nerve cells do not divide

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Normal Control of the Cell Normal Control of the Cell CycleCycle

Much that science does not fully Much that science does not fully understandunderstand

Enzymes control the cell cycleEnzymes control the cell cycle– Many enzymes needed Many enzymes needed – Most enzymes are used at just one point Most enzymes are used at just one point

in the cyclein the cycle– Loss of a functional enzyme can cause Loss of a functional enzyme can cause

the cell cycle to be “out of control”the cell cycle to be “out of control”

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Normal Control of the Cell Normal Control of the Cell CycleCycle

Signaling molecules Signaling molecules made of a cyclin made of a cyclin bound to a CDK kick bound to a CDK kick off the cell cycle and off the cell cycle and drive it through drive it through mitosis.mitosis.

Checkpoints monitor Checkpoints monitor the cell cycle for the cell cycle for errors and can stop errors and can stop the cycle if an error the cycle if an error occursoccurs

CDK are enzymes, cyclins are proteins

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Genes and ProteinsGenes and Proteins

Genes located on DNA are Genes located on DNA are responsible for giving direction about responsible for giving direction about what proteins (enzymes) to producewhat proteins (enzymes) to produce

A defective gene would produce a A defective gene would produce a faculty enzyme that would not faculty enzyme that would not function correctlyfunction correctly

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Key Time for Control of the Cell Key Time for Control of the Cell CycleCycle

Key control of the Key control of the cell cycle is just cell cycle is just prior to S phase prior to S phase during interphaseduring interphase

If new DNA is If new DNA is synthesized then synthesized then the cell will the cell will continue on with continue on with mitosismitosis

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CancerCancer

A cell “out of control” of the cell A cell “out of control” of the cell cyclecycle

Mistake in the Cell CycleMistake in the Cell Cycle Too fast rate of mitosisToo fast rate of mitosis Result of changes in one or more Result of changes in one or more

genes that produce enzymes that are genes that produce enzymes that are involved in controlling the cell cycle involved in controlling the cell cycle

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Cancer CellsCancer Cells

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Cancer CellsCancer Cells

Cancer cells form Cancer cells form tumorstumors

Tumors are masses of Tumors are masses of cells that interfere cells that interfere with normal with normal functioningfunctioning

Metastasis: cancer Metastasis: cancer cells break off the cells break off the tumor and travel to tumor and travel to other locations to form other locations to form tumorstumors

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Causes of CancerCauses of Cancer

Both genetic and environmentalBoth genetic and environmental When people move from one country When people move from one country

to another their rate of cancer is that to another their rate of cancer is that of the country they are now livingof the country they are now living

Example: Rate of breast cancer is Example: Rate of breast cancer is high in US and low in Japan; when high in US and low in Japan; when people move from Japan to US their people move from Japan to US their rate of breast cancer increasesrate of breast cancer increases

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Environmental Causes of Environmental Causes of CancerCancer

UV Light

Diet

Smoking

Air Pollution

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Environmental Causes of Environmental Causes of CancerCancer

Viruses

Cervical CancerWater Pollution

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Cancer PreventionCancer Prevention

Clear link between healthy lifestyles Clear link between healthy lifestyles and incidence of cancerand incidence of cancer

Low fat, high fiber diet reduces riskLow fat, high fiber diet reduces risk Daily exercise reduces riskDaily exercise reduces risk No tobacco in any form reduces riskNo tobacco in any form reduces risk

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ApoptosisApoptosis Programmed cell deathProgrammed cell death All animal cells have a “death program”All animal cells have a “death program” Fetal human tail cells have undergone Fetal human tail cells have undergone

apoptosis; programmed cell death at apoptosis; programmed cell death at the appropriate time the appropriate time

Plant leaves undergo apoptosis in Plant leaves undergo apoptosis in autumn when the leaves are fallingautumn when the leaves are falling

Apoptosis can help protect organisms Apoptosis can help protect organisms from developing cancerous growths.from developing cancerous growths.

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Stem CellsStem Cells

Stem cells are Stem cells are unspecialized cells unspecialized cells that can develop that can develop into specialized into specialized cells under the cells under the right conditionsright conditions

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Embryonic Stem CellsEmbryonic Stem Cells

After a sperm fertilizes an egg the After a sperm fertilizes an egg the cell divides until there is 100-150 cell divides until there is 100-150 cellscells

Each of these cells can develop into a Each of these cells can develop into a wide variety of specialized cellswide variety of specialized cells

Much controversy exists due to the Much controversy exists due to the ethical concerns about the source of ethical concerns about the source of these embryonic stem cellsthese embryonic stem cells

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Adult Stem CellsAdult Stem Cells

Present in adults (and newborns) to Present in adults (and newborns) to produce the same type of cellproduce the same type of cell

Not pluripotent (can’t become any Not pluripotent (can’t become any cell type)cell type)

In 2000 adult stem cells ere used to In 2000 adult stem cells ere used to restore lost brain tissue in micerestore lost brain tissue in mice

Less controversy exists to the use of Less controversy exists to the use of adult stem cellsadult stem cells