cell division
TRANSCRIPT
Why do cells need to Why do cells need to divide?divide?
o Depends on organismDepends on organismo Unicellular organisms, like Unicellular organisms, like
bacteria, divide to reproduce.bacteria, divide to reproduce.
Unicellular Cell DivisionUnicellular Cell Division
o ““Binary Binary FissionFission””
o Result = 2 Result = 2 identical cellsidentical cells
o What has to What has to happen?happen?
Reasons Multicellular Reasons Multicellular Organisms Need Cell Organisms Need Cell
DivisionDivision1) Growth (mitosis)1) Growth (mitosis)
2) Repair/replacement of cells (mitosis)2) Repair/replacement of cells (mitosis)oSome cells die quickly (skin cells).Some cells die quickly (skin cells).oSome cells never get replaced (nerve Some cells never get replaced (nerve cells).cells).
3) Create reproductive cells (meiosis)3) Create reproductive cells (meiosis)
2 Types of Cells2 Types of Cells
o ““Body cells” (Body cells” (somaticsomatic) vs. ) vs. reproductive cells (reproductive cells (gametesgametes).).
o Examples of somatic cellsExamples of somatic cells: skin cell, : skin cell, liver cell, brain cell, red blood cell…liver cell, brain cell, red blood cell…
o Examples of gametesExamples of gametes: egg cell or : egg cell or sperm cellsperm cell
How much DNA is in our How much DNA is in our cells?cells?
o DNADNAchromosomeschromosomeso How many How many chromosomes in a human chromosomes in a human
somatic cell?somatic cell? 46 chromosomes or 23 homologous pairs46 chromosomes or 23 homologous pairso WhatWhat is the is the originorigin of these pairs? of these pairs? mom and dadmom and dado Homologous pairHomologous pair- chromosomes that - chromosomes that
carry the carry the samesame genes geneso These cells are These cells are diploiddiploid. . o The diploid number in humans is The diploid number in humans is 4646. .
How much DNA is in our How much DNA is in our cells?cells?
o How many chromosomes are in a How many chromosomes are in a gamete (reproductive cell)? gamete (reproductive cell)?
-23 chromosomes-23 chromosomeso Process of cell division (meiosis) Process of cell division (meiosis)
divides homologous pairs. Allows divides homologous pairs. Allows parent to pass on one chromosomes parent to pass on one chromosomes from each homologous pair.from each homologous pair.
o These cells are These cells are haploidhaploid..o The haploid number in humans is 23.The haploid number in humans is 23.
The Story of Life:The Story of Life:
o Organisms get one copy of a trait Organisms get one copy of a trait (chromosome) from mom, the other from (chromosome) from mom, the other from dad.dad.
o Passed from parents to kids in Passed from parents to kids in chromosomes of reproductive cells.chromosomes of reproductive cells.
The Story of Life:The Story of Life:
o Gametes- Gametes- reproductive cellsreproductive cells
o Two gametes join Two gametes join (fertilization)(fertilization)
o Egg (23) + Sperm Egg (23) + Sperm (23) = You (46) –(23) = You (46) –Zygote Zygote
o If egg (46) + If egg (46) + Sperm (46) = NO Sperm (46) = NO you (92)you (92)
If all body cells contain the If all body cells contain the same DNA, why are they so same DNA, why are they so
different?different?
o Different cells make different Different cells make different proteins. proteins.
o Different “active segments” of Different “active segments” of DNA.DNA.
o During early stages of development, During early stages of development, cells become “specialized.”cells become “specialized.”
Cell DifferentiationCell Differentiationo The first few cells that develop from the The first few cells that develop from the
zygote are called “stem cells.”zygote are called “stem cells.”o Stem cells-Stem cells- undifferentiated (generic) undifferentiated (generic)
cells that become specialized cells…cells that become specialized cells…
The Cell CycleThe Cell Cycle
o Different cells have different “life Different cells have different “life spans.”spans.”
o This depends on the type of cell and This depends on the type of cell and the DNA that is “active.”the DNA that is “active.”
o Each cell goes through a series of Each cell goes through a series of phases through out its life.phases through out its life.
The Cell CycleThe Cell Cycle
o There are 2 major parts in the life of There are 2 major parts in the life of a cell.a cell.
1.1. GG11 Phase Phase
S PhaseS Phase INTERPHASEINTERPHASE
GG22 Phase Phase
2. Division (Mitosis and Cytokinesis)2. Division (Mitosis and Cytokinesis)
The Cell CycleThe Cell Cycle
Step #1 “G1 Phase”Step #1 “G1 Phase”o First growth phase.First growth phase.o 46 chromosomes present (two #7’s).46 chromosomes present (two #7’s).o Newly formed cells that go through Newly formed cells that go through
intense growth.intense growth.
Step 2 “S Phase”Step 2 “S Phase”o ““S” = SynthesisS” = Synthesiso All chromosomes copied during All chromosomes copied during o (DNA replication)(DNA replication)o 92 chromatids present (four #7’s).92 chromatids present (four #7’s).
Duplicated chromosome
Sister chromatids
Chromosome
Step #3 “G2 Phase”Step #3 “G2 Phase”
o Second growth phase.Second growth phase.o Cell grows some more.Cell grows some more.o Organelles copied.Organelles copied.o Still 92 chromatids present (four Still 92 chromatids present (four
#7’s).#7’s).
Interphase SummaryInterphase Summaryo G1, S, G2 all part interphase.G1, S, G2 all part interphase.o Cell spends most of its life here- Cell spends most of its life here-
growing/preparing to divide.growing/preparing to divide.o If cell enters “S,” then must If cell enters “S,” then must
continue the cycle and divides.continue the cycle and divides.
Interphase DiagramInterphase Diagram
o Chromosomes Chromosomes
NOT visible- NOT visible-
““chromatin”chromatin”
Step #4 “M Phase”Step #4 “M Phase”
o Mitosis = “nuclear division”Mitosis = “nuclear division”o Creates 2 nuclei with equal amounts Creates 2 nuclei with equal amounts
DNA in one cellDNA in one cello Four phases: prophase, metaphase, Four phases: prophase, metaphase,
anaphase, telophase.anaphase, telophase.
ProphaseProphase
o Nuclear envelope/Nuclear envelope/
nucleolus nucleolus
disappear.disappear.o ChromosomesChromosomes
visible.visible.o Centrioles/Centrioles/
spindle fibers spindle fibers
appearappearo Still 92 chromatids present (four #7’s)Still 92 chromatids present (four #7’s)
MetaphaseMetaphase
o Chromosomes middleChromosomes middleo Spindle fibers Spindle fibers
attach centerattach center
(centromere) each(centromere) each
chromosome.chromosome.o Still 92 chromatids (four #7’s)Still 92 chromatids (four #7’s)
AnaphaseAnaphase
o Spindle fibers Spindle fibers
pull apart pull apart
identical chromatidsidentical chromatids
(separates chromosome(separates chromosome
pairs)pairs)o Still 92 chromatids Still 92 chromatids
(four #7’s) (four #7’s)
TelophaseTelophaseo Each side Each side
full setfull setchromosomes (DNA).chromosomes (DNA).
o Nuclear envelope Nuclear envelope reforms.reforms.
o Spindle fibers Spindle fibers disappear.disappear.
o Nucleolus Nucleolus reappears.reappears.
o 46 chromosomes per 46 chromosomes per nucleus (two #7’s per nucleus)nucleus (two #7’s per nucleus)
CytokinesisCytokinesis
o Division cytoplasm- Division cytoplasm- creates 2 new cellscreates 2 new cells
Interphase vs. MitosisInterphase vs. Mitosis
Mitosis StagesMitosis Stages
Regulating the Cell CycleRegulating the Cell Cycle
o Not all cells move through the cell cycle Not all cells move through the cell cycle at the same rate.at the same rate.
o Examples: skin cell 2-3 daysesophagus 2-3 days large intestine 6 daysRBC 120 dayscardiac muscle no divisionbrain/nerve cell no division
Controls on Cell DivisionControls on Cell Division
o CyclinsCyclins – proteins that regulate different – proteins that regulate different phases of cell cyclephases of cell cycle
o 2 Types of Cyclins-2 Types of Cyclins-
1) Internal regulators1) Internal regulators
2) External regulators2) External regulators
Internal RegulatorsInternal Regulators
o Respond to events “inside” cellRespond to events “inside” cello Control each step of cell cycleControl each step of cell cycleo Prevent things from happening until Prevent things from happening until
certain events happen in the cellcertain events happen in the cello Ex) Cell will not be allowed to enter Ex) Cell will not be allowed to enter
“M phase” until all chromosomes “M phase” until all chromosomes have been copied.have been copied.
External RegulatorsExternal Regulators
o Respond to events “outside” the cellRespond to events “outside” the cello Directs cell to speed up or slow down Directs cell to speed up or slow down
cell cycle based on what is cell cycle based on what is happening outside the cell.happening outside the cell.
o Ex) wound healing or growth of Ex) wound healing or growth of embryo developmentembryo development
Controls on Cell DivisionControls on Cell Division
o Cells are “cohesive”Cells are “cohesive”o If cells are removed, they will “fill in If cells are removed, they will “fill in
the gaps.”the gaps.”o Once all cells come in contact with Once all cells come in contact with
each other, cell division stops.each other, cell division stops.o ““Contact InhibitionContact Inhibition””o Happens in body when cells are Happens in body when cells are
injured injured
o Sometimes cells lose ability to Sometimes cells lose ability to regulate cell cycles.regulate cell cycles.
o CancerCancero Cancer cells do not respond to Cancer cells do not respond to
internal/external regulatorsinternal/external regulatorso Results:Results:
1) uncontrolled cell division1) uncontrolled cell division
2) loss of cell cohesion2) loss of cell cohesion
Abnormal Cell DivisionAbnormal Cell Division
Abnormal Cell DivisionAbnormal Cell Divisiono Cells grow at an abnormal rate because Cells grow at an abnormal rate because
the DNA was mutated. the DNA was mutated. o This can cause This can cause tumorstumors..o BenignBenign tumor- abnormal cells remain at tumor- abnormal cells remain at
original siteoriginal siteo MalignantMalignant tumors- abnormal cells tumors- abnormal cells
become invasive to surrounding tissues become invasive to surrounding tissues due to loss of “cohesiveness”due to loss of “cohesiveness”
o MetastasisMetastasis- cancer cells spread to new - cancer cells spread to new areas through blood/lymph vessels and areas through blood/lymph vessels and new tumors formnew tumors form
How are reproductive cells How are reproductive cells formed?formed?
o Meiosis is nuclear division that produces Meiosis is nuclear division that produces haploid gametes.haploid gametes.
o Chromosomes - no longer in pairs.Chromosomes - no longer in pairs.o Each parent passes on one chromosome Each parent passes on one chromosome
from each homologous pair in the gamete.from each homologous pair in the gamete.o Reproductive cells contain half the number Reproductive cells contain half the number
of chromosomes that a somatic cell of chromosomes that a somatic cell contains.contains.
o 46462323
How is Mitosis different from How is Mitosis different from Meiosis?Meiosis?
MITOSISMITOSIS MEIOSISMEIOSIS
Chromosome # Chromosome #
stays samestays sameChromosome # Chromosome #
reduced halfreduced half
2 new cells produced2 new cells produced 4 new cells produced4 new cells produced
Somatic cellsSomatic cells GametesGametes
Identical Identical VariationVariation
What are reproductive cells?What are reproductive cells?
o In males reproductive cells originate from cells called spermatogonium.
o In females reproductive cells (egg cells) originate from cells called oogonium.
46
46 46
23 23 23 23
Spermatogonium
Sperm
23 23 23
46
46 46
23
Oogonium
Polar Body
Egg
Meiosis in Humans Meiosis in Humans
o How is meiosis different in males and How is meiosis different in males and females?females?