16-cell cycle and mitosis part 1
TRANSCRIPT
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Chapter 12
The Cell Cycle
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Cell Division
http://www.youtube.com/watch?v=rgLJrvoX_qo
http://www.youtube.com/watch?v=DD3IQknCEdc
Interphase Prophase Prometaphase
Metaphase Anaphase Telophase Cytokinesis
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Cell Division
Cell Division – creation of new cells (daughter cells)
by division of pre-existing cell (parent cell)
Why do cells divide?
Do cells divide continuously?
Parent Cell
Daughter Cells
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Why do cells divide?
Cell Division – creation of new cells (daughter cells)
by division of pre-existing cell (parent cell)
Purposes:
Growth of multicellular organisms
Repair of damaged tissues and
renewal of old cells
Reproduction – production of offspring
Asexual – utilizes mitosis
Sexual – utilizes meiosis
Parent Cell
Daughter Cells
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Do Cells Divide Continuously?
Cell Division Stage – M (mitotic) Stage
Division of the nucleus (division of genetic material)
Mitosis – used for asexual reproduction, growth and repair
Meiosis – used for sexual reproduction
Division of the cytoplasm – Cytokinesis
Preparation Stage – Interphase
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Interphase: Preparing for Cell
Division
G1 of Interphase (gap 1) - Interval of Growth
Number of organelles doubles
Materials (such as proteins) needed for DNA synthesis are
produced Stage at which normal cell functions occur
S of Interphase (synthesis) - DNA Replication
Chromosomes (DNA and proteins) are duplicated
G2 of Interphase (gap 2) - Preparation for Division
Proteins needed for cell division (such as tubulin) aresynthesized
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The Cell Cycle
What is G0 ?
Stage occupied by cells that are arrested (not dividing)
Cells can perform normal functions in this stage
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Mitosis & MeiosisKeeping it all straight!
The lifecycle of sexually reproducing organisms requires
two kinds of nuclear division – mitosis and meiosis
MEIOSIS
(2n n)
Egg Sperm
Gameteshaploid (n)
Fertilized eggdiploid (2n)
Cell divisionsresponsible for growth(addition of somatic cells)
In animals, meiosis occurs priorto production of eggs and sperm
Adultdiploid (2n)
The key to keeping
it all straight…
knowing the
terminology !
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Genetic Material Terminology
Chromosome – single, long molecule of DNA and its
associated proteins (linear in eukaryotes); this DNA-
protein complex is called chromatin
Non-Dividing Cells (Interphase): diffuse, threadlike DNA
Dividing Cells (M phase): chromosomes are in duplicated
and condensed form
NOTE: Table 12.1 in your text is very helpful!
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Chromatin
DNA
histonecore
DNA
Non-Dividing
Dividing
Length of DNA in one human cell = ~2 m!
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Genetic Material Terminology
Each chromosome contains a particular set of genes
Gene – a section of DNA that carries instructions for
building a protein (influences hereditary traits)Example: flower color gene
Allele – different versions of the same gene
Example: “white” allele and “purple” allele
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Genetic Material Terminology
The human genome* contains
46 chromosomes
Different species have different
numbers of chromosomes
*genome - complete set of genetic information
karyotype of human cell
SpeciesChromosome Number
(Diploid)
Human 46
Kangaroo 12
Shrimp 254
Mosquito 6
Algae 148
Pea 14
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Genetic Material Terminology
The chromosomes are
arranged in pairs called
homologouschromosomes
karyotype of human cell
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Genetic Material Terminology
Homologous Chromosomes – pair of same “kind” of
chromosomes – similar in size, shape, and gene
content (Note: alleles may differ)
one chromosome is inherited from mother
one chromosome is inherited from father
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Genetic Material Terminology
Each chromosome may exist in…
An unduplicated form (prior to DNA replication in S phase or
after cell division), or…
A duplicated form (following S phase)
Each copy is called a chromatid
one chromosome (unduplicated)
one chromosome (duplicated)
chromatid
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Genetic Material Terminology
Sister chromatids – the two chromatids
of a duplicated chromosome
Contain identical genetic information
Associated with one another along
entire length
Centromere – specialized region at which sister
chromatids are joined
Kinetochore – protein complexes on either side
of centromere; site at which spindle fibers attach
(more later…)
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Homologous Chromosomes v.
Sister Chromatids
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Ploidy
Ploidy – number of sets of chromosomes in a cell
Cells that have two chromosomes of each “kind” (i.e. have
homologous pairs of chromosomes) are called diploid (2n)
Example: somatic (body) cells
Cells that have one chromosome of each “kind” are called
haploid (n)Example: gametes (sperm and egg)
What is the value of n for humans?
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Human Lifecycle:Diploid & Haploid Stages
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DNA Replication in S Phase
How many
chromosomes are in
each cell?Count the centromeres!
4 replicatedchromosomes
4 unreplicatedchromosomes
Are these cells haploidor diploid?
How do you know?
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Lifecycle of Sexually Reproducing Organisms:
Requires Mitosis and Meiosis
MEIOSIS(2n n)
Amount o f
hereditary m aterial
is reduced by half
Egg Sperm
Gameteshaploid (n)
Normal amount of
hereditary m aterial
is restored Fertilized eggdiploid (2n)
Cell divisionsresponsible for growth(addition of somatic cells)
In animals, meiosis occurs priorto production of eggs and sperm
Adultdiploid (2n)
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Mitosis & Meiosis
Mitosis - used for growth, repair, & asexual
reproduction
duplication division
2n 2n
Meiosis - used for sexual reproduction reduction division
2n n
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Mitosis: Features
Occurs in somatic (body) cells -
involved in growth and repair
Produces 2 daughter nuclei
Daughter nuclei are diploid (like
parent nucleus)
Daughter cells are clones
(genetically identical) of parent
cell and each other
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Mitosis: Overview
G1 S PHASE AND G2 MITOSIS
Sisterchromatids
Parent cell:4 replicatedchromosomes
Replicatedchromosomescondense at thestart of mitosis.
Parent cell:4 unreplicatedchromosomes
Chromosom es are shown par t ia lly
condensed to make them vis ible
During mitosis, sisterchromatids separate.
Two daughter cells areformed by cytokinesis.
Daughter cells:contain thesamecomplement ofchromosomes asthe parent cell.
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Mitosis
Mitosis is a continuous process, but it is typically
broken into steps for descriptive purposes
Prophase Prometaphase
Metaphase
Anaphase
Telophase
Remember: prior to the start of mitosis, the
chromosomes are replicated (in S phase)
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Prophase
Chromatin condenses
Nuclear envelope begins to break down
Nucleolus disappears
Centrosomes move to opposite poles
Mitotic Spindle begins to form
ProphaseEarly Prophase
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Mitotic Spindle
Mitotic Spindle - system of microtubules; orients chromosomes
and provides mechanical force used to separate chromosomes into
daughter cells
Forms between two centrosomes (microtubule organizingcenters)
Each contains a pair of centrioles and radiating asters
(microtubule bundles)
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Mitotic Spindle
Types of Spindle Fibers:
Kinetochore (centromeric) spindle fibers
attach to kinetochores on the surface of centromeres pull chromosomes
Polar spindle fibers
spindle fibers that extend beyond midpoint of cell
push cell poles apart
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Prometaphase
Nuclear envelope completely broken down
Kinetochores appear on each side of centromeres
Kinetochore microtubules contact chromosomes
Push-pull forces of the spindle apparatus - begin to align
chromosomes at center of cell
Prometaphase
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Metaphase
Mitotic spindle is fully formed
All chromosomes are lined up at the metaphase plate
(spindle equator) at the end of metaphase
Metaphase
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Anaphase
Centromeres divide
Sister chromatids separate
Daughter chromosomes pulled (along kinetochore spindle
fibers)/pushed (by polar spindle fibers) to opposite poles of cell
Finished when equivalent (and complete) collections of chromosomes arelocated at the two poles of the cell
Anaphase
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Chromosome Movement
Motor proteins (dynein and others) on kinetochores
“walk” the chromosomes down microtubules (kinetochore
spindle fibers)
Microtubules shorten from kinetochore endMicrotubules
Fiberscontaining
motorproteins
Kinetochoreplates
Tubulinsubunits
–
+
+
Chromosome
Chromosomemovement
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Telophase
(basically the reverse of prophase)
Mitotic spindle disassembles
Nuclear envelope reassembles around daughternuclei
Chromosomes decondense
Nucleolus reappears
Finished when two daughter nuclei have formed - each areclones of one another and of the parent cell
Telophase
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Cell Division and the Cell Cycle
Preparation Phase – Interphase
Cell Division Phase – M (mitotic) Phase
Division of the nucleus (division of genetic material)
Mitosis – used for asexual reproduction, growth and repair
Meiosis – used for sexual reproduction
Division of the cytoplasm – Cytokinesis
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Cytokinesis
Cytokinesis
mechanism that splits
cytoplasm into daughtercells
usually occurs
immediately followingmitosis
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Cytokinesis in Animal Cells
Formation of a cleavage furrow - due to band of actin
filaments working in association with myosin beneath
plasma membrane
Cytoplasm is pinched in two
Mitosis is over, and
the spindle is nowdisassembling.
Band of actin filaments
(contractile ring) at the formerspindle equator contracts.
The contractions
continue and cutthe cell in two.
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Cytokinesis in Animal Cells
Formation of a cleavage furrow - due to band of actin
filaments working in association with myosin beneath
plasma membrane
Cytoplasm is pinched in two
Myosin
“Head” region
Actin
When myosin’s “head” attaches to actin and moves,
the actin filament slides
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Cytokinesis in Plant Cells
Formation of a cell plate
Vesicles filled with wall-building material fuse along cellequator
Cell plate thickens to become a crosswall - divides the
parent cell into two daughter cells
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Cytokinesis in Plant Cells
cell wall
formerspindleequator
cell plate
vesiclesconverging
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Mitosis and Cytokinesis
Interphase Prophase Prometaphase
Metaphase Anaphase Telophase Cytokinesis
http://highered.mcgraw-hill.com/olc/dl/120073/bio14.swf
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Mitosis and Cytokinesis
Animal Cell:http://www.youtube.com/watch?v=DD3IQknCEdc&feature=related
Plant Cell:http://www.youtube.com/watch?v=aDAw2Zg4IgE&feature=related
Prokaryotic Cell Division: Binary
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Prokaryotic Cell Division: Binary
Fission
Prokaryotic cell
division is
often very fast!
Some
antibiotic
s inhibit
cell wall
synthesis