Cell Division Cell Division • Life Cycle of the Cell Life Cycle of the Cell • Mitosis Mitosis • Meiosis Meiosis
Jan 14, 2016
Cell DivisionCell Division
• Life Cycle of the CellLife Cycle of the Cell• MitosisMitosis• MeiosisMeiosis
Cell Cycle Overview VideoCell Cycle Overview Video
Cellular Cellular DivisionDivision
Cell divisionCell division is a is a process by which a process by which a cell, called the , called the parent cell, divides parent cell, divides into two or more into two or more cells, called cells, called daughter cellsdaughter cells. Cell . Cell division is usually a division is usually a small segment of a small segment of a larger larger cell cycle. .
3 major types of cell division
Prokaryotic Cells Eukaryotic Cells
Cellular DivisionCellular DivisionThe size of the cell signals time for division.The size of the cell signals time for division.
Cell Grows until it
reaches a size large enough to
start division.
Prokaryotic DivisionProkaryotic Division Ex. Bacteria Ex. Bacteria Prokaryotic Division is called Binary Prokaryotic Division is called Binary
fission, it is the division of a prokaryotic fission, it is the division of a prokaryotic cell into 2 daughter cellscell into 2 daughter cells
Consists of 3 stages:Consists of 3 stages:1. The 1 chromosome in the cell makes a copy of
itself (in a process that is similar to unzipping and then reforming each side)
2. Cell grows until it reaches twice its original size3. A cell wall forms between the 2 chromosomes
and the cell splits into 2 new cells
Identical to Original cell
Example: Example: Escherichia coli Under optimal environment conditions, a Under optimal environment conditions, a
population of E. coli cells doubles in size population of E. coli cells doubles in size every 20 minutes. Theoretically, in about every 20 minutes. Theoretically, in about one week a single E. coli cell could one week a single E. coli cell could produce a ball of bacteria the size of produce a ball of bacteria the size of Earth! Thankfully for other organisms the Earth! Thankfully for other organisms the E. coli would run out of nutrients long E. coli would run out of nutrients long before that happened.before that happened.
Eukaryotic DivisionEukaryotic Division
More complex than prokaryotic cells More complex than prokaryotic cells because of because of organellesorganelles (ex. Mitochondria, (ex. Mitochondria, endoplasmic reticulum, golgi bodies, chloroplasts, etc.)endoplasmic reticulum, golgi bodies, chloroplasts, etc.)
The life of the eukaryotic cell is The life of the eukaryotic cell is diagrammed as the cell cycle – the diagrammed as the cell cycle – the repeating sequence of growth and division repeating sequence of growth and division of eukaryotic cells (4 major phases)of eukaryotic cells (4 major phases)
Cell Life CycleCell Life Cycle
Organelles are copied
here
G1,S, & G2 all make up Interphase
Therefore, the cell is usually in interphase
Cytokinesis happens here
Cell CycleCell Cycle
AnimatedAnimated
Cell CycleCell Cycle The cell cycle is driven by a chemical control
system that both triggers and coordinates key events in the cell cycle. The cell cycle control system is regulated at certain checkpoints.
Signals from inside the cell (internal signals) and from outside the cell (external signals) are involved in turning the process of cell division off and on.
An internal signal involves the cell sensing the presence of chemicals, called enzymes, which are produced inside the cell
An external signal involves the cell sensing the presence of a chemical (such as a growth factor) which was produced in other specialized cells.
Cell CycleCell Cycle Cells can also respond to physical signals from
their environment. Cells sense when they are too closely packed and cell
division is turned off. Cells sense when they are not in contact with a
surface and cell division is turned on.
A checkpoint in the cell cycle is a critical control point where stop and go signals can regulate the cycle. The cell division mechanism in most animal cells is in the “off” position when there is no stimulus present. Specific stimuli are required to start the processes
Mitosis – Mitosis – is the process that results in two is the process that results in two nuclei with the exact same informationnuclei with the exact same information
• Interphase – pre-mitotic phase
• Prophase – 1st phase
• Metaphase – 2nd phase
• Anaphase – 3rd phase
• Telophase – 4th phase
• Cytokinesis – cell divides
PMAT:
• Chromosomes are Chromosomes are copiedcopied (# doubles) (# doubles)• Chromosomes appear as threadlike coils Chromosomes appear as threadlike coils
((chromatinchromatin) at the start, but each chromosome ) at the start, but each chromosome and its copy(and its copy(sistersister chromosome) change to sister chromosome) change to sister chromatids at end of this phasechromatids at end of this phase
• Longest phase of the cell cycle – GLongest phase of the cell cycle – G11, S, & G, S, & G22
CELL MEMBRANE
Nucleus
Cytoplasmchromatin
ChromosomesChromosomes
A A chromosomechromosome is an is an organized structure organized structure of DNA and protein of DNA and protein that is found in that is found in cells. It is a single cells. It is a single piece of coiled DNA piece of coiled DNA containing many containing many genesgenes
ChromosomesChromosomes
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
• MitosisMitosis begins (cell begins to divide) – nucleus begins (cell begins to divide) – nucleus breaks down and nucleolus disappearsbreaks down and nucleolus disappears
• CentriolesCentrioles (or poles) appear and begin to move (or poles) appear and begin to move to opposite end of the cell. to opposite end of the cell.
• Spindle fibersSpindle fibers form between the poles. form between the poles.• ChromosomesChromosomes condense & become visiblecondense & become visible
CentriolesSister chromatids
Spindle fibers
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
There are no centrioles in plant cells they can divide without them
• Chromatids Chromatids (or pairs of chromosomes) attach (or pairs of chromosomes) attach to the spindle fibers. Chromatids line up at the to the spindle fibers. Chromatids line up at the equator (center of the cell)equator (center of the cell)
Centrioles
Spindle fibers
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
• Chromatids Chromatids (or pairs of chromosomes) (or pairs of chromosomes) separate at the centromere and begin to move separate at the centromere and begin to move to opposite ends of the cell. to opposite ends of the cell.
Centrioles
Spindle fibers
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
• Spindle fibersSpindle fibers disappear disappear• Two new Two new nucleinuclei form.form. Nucleolus returns to Nucleolus returns to
the inside of each nucleusthe inside of each nucleus• Chromosomes uncoil and appear as chromatin Chromosomes uncoil and appear as chromatin
((threadsthreads rather than rather than rodsrods).).• MitosisMitosis ends.ends.
NucleiNuclei
Chromatin
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
• Cell membrane or cell plate moves inward to Cell membrane or cell plate moves inward to create two create two daughterdaughter cells – each with its own cells – each with its own nucleus nucleus with identical with identical chromosomes.chromosomes.
- animal cells - animal cells → cleavage (pinching) furrow forms → cleavage (pinching) furrow forms in the cell membrane to separate the cell.in the cell membrane to separate the cell.
- plant cells → cell wall forms to separate cell.- plant cells → cell wall forms to separate cell.
Animal Mitosis -- Review
InterphaseInterphase
ProphaseProphase
MetaphaseMetaphase
AnaphaseAnaphase
TelophaseTelophase
CytokinesisCytokinesis
Plant Mitosis -- ReviewInterphaseInterphase
ProphaseProphase
MetaphaseMetaphase
AnaphaseAnaphase
TelophaseTelophase
CytokinesisCytokinesis
Cell wall plate
http://www.cellsalive.com/mitosis.htm
Mitosis Song
MeiosisMeiosis
MeiosisMeiosis
Meiosis – the process that divides the # of Meiosis – the process that divides the # of chromosomes in cells in half (formation of chromosomes in cells in half (formation of gametes); vital to sexual reproduction gametes); vital to sexual reproduction 2 successive nuclear divisions (goes through 2 successive nuclear divisions (goes through
PMAT twice)PMAT twice) Before 1Before 1stst division, DNA is copied just like in division, DNA is copied just like in
mitosismitosis However, DNA is not copied before 2However, DNA is not copied before 2ndnd
divisiondivision
MeiosisMeiosis Broken down into 2 Broken down into 2
parts – Meiosis I and parts – Meiosis I and Meiosis IIMeiosis II
Meiosis I – homologous Meiosis I – homologous chromosomes separate chromosomes separate into 2 diploid cellsinto 2 diploid cells
Meiosis II – Each Cell Meiosis II – Each Cell Sister chromatids Sister chromatids separate into 2 haploid separate into 2 haploid cellscells
Diploid
Haploid Copied
Meiosis I
Meiosis II
Haploid
Diploid Copied
1 Diploid Cell = 4 Haploid Cells 1 Diploid Cell = 4 Haploid Cells
Difference between Animals & PlantsDifference between Animals & Plants In Animals – meiosis In Animals – meiosis
makes gametes makes gametes (reproductive cells / (reproductive cells / sex cells – sperm & sex cells – sperm & eggs)eggs)
In Plants – meiosis In Plants – meiosis makes sporesmakes spores
2 Unique Events of Meiosis:2 Unique Events of Meiosis:1.1. Crossing Over:Crossing Over:
Homologous chromosomes pair Homologous chromosomes pair up next to each otherup next to each other
Arms of chromosomes Arms of chromosomes exchange segments (same exchange segments (same sized) of DNAsized) of DNA
2.2. Skipping Replication:Skipping Replication: Only 1 replication of DNA, but 2 Only 1 replication of DNA, but 2
divisions divisions → meiosis halves → meiosis halves the number of the number of chromosomeschromosomes
Meiosis IMeiosis I
1.1. Prophase I:Prophase I:
a.a. Chromosomes condense (become thick) and Chromosomes condense (become thick) and become visible as a cluster of 4 chromatids called a become visible as a cluster of 4 chromatids called a tetradtetrad
b.b. Nuclear envelope breaks downNuclear envelope breaks down
c.c. Centrioles move to poles and begin to produce Centrioles move to poles and begin to produce spindle fibersspindle fibers
d.d. Homologous chromosomes pair upHomologous chromosomes pair up
e.e. Crossing over occursCrossing over occurs
2.2. Metaphase I:Metaphase I:
a.a. PairsPairs of homologous chromosomes attach to spindle of homologous chromosomes attach to spindle fibers at centromere and move to the equator fibers at centromere and move to the equator (center) of the cell(center) of the cell
Meiosis IMeiosis I1.1. Anaphase I:Anaphase I:
a.a. Homologous pairs separateHomologous pairs separate
b.b. Chromosomes of each pair pull apart and move to Chromosomes of each pair pull apart and move to the poles (opposite ends) of cellthe poles (opposite ends) of cell
a.a. Note: Sister chromatids of chromosome remain Note: Sister chromatids of chromosome remain attachedattached
Meiosis IMeiosis I4.4. Telophase I:Telophase I:
a.a. Chromosomes gather at each of the 2 poles and nuclear Chromosomes gather at each of the 2 poles and nuclear membrane forms around them.membrane forms around them.
b.b. Cytokinesis occurs at the end of Telophase I: Cytoplasm Cytokinesis occurs at the end of Telophase I: Cytoplasm divide, forming 2 new cells.divide, forming 2 new cells.
c.c. Each of the two daughter cells contains only one Each of the two daughter cells contains only one chromosome (consisting of two sister chromatids) from chromosome (consisting of two sister chromatids) from each parental pair.each parental pair.
d.d. Meiosis I often called reduction divisionMeiosis I often called reduction division
Skipping Replication – DNA does not copy between Skipping Replication – DNA does not copy between meiosis I and meiosis IImeiosis I and meiosis II
Prophase II Spindle fibers form in each of the daughter cells from meiosis I and attaches to the centromeres of the sister chromatidsThe chromosomes progress towards the midline of each cell.The nuclear membrane breaks down.
Metaphase II Chromosomes, made up of two sister chromatids, line up across the center of the cell.Spindle fibers from opposite poles of the cell attach to one of each pair of chromatids.
Anaphase II
The chromosomes separate so that one chromatid from each chromosome goes to each pole.
Telophase II & Cytokinesis Nuclear member forms around each set of chromosomes. The resulting daughter cells are haploid, containing one single chromosome from each pair of chromatids, either from the maternal or paternal contributor.
Meiosis IIMeiosis II
Genetic RecombinationGenetic Recombination
The formation of new combinations of The formation of new combinations of genesgenes
2 chromatids of chromosomes no longer 2 chromatids of chromosomes no longer contain identical genetic materialcontain identical genetic material
Provides a source for genetic variation, Provides a source for genetic variation, which impacts the rate of evolution in which impacts the rate of evolution in organismsorganisms
Mitosis vs MeiosisMitosis vs Meiosis
MitosisMitosis
1.1. PMAT OncePMAT Once
2.2. Ends with 2 diploid cells Ends with 2 diploid cells that are identical to that are identical to parent cellparent cell
3.3. Somatic Cells (Body Somatic Cells (Body cells) undergo this cells) undergo this cellular reproductioncellular reproduction
MeiosisMeiosis
1.1. PMAT Twice PMAT Twice
2.2. Ends with 4 haploid cells Ends with 4 haploid cells that are different from that are different from the parentthe parent
3.3. Gametes (Sex cells) Gametes (Sex cells) undergo this cellular undergo this cellular reproductionreproduction
Mitosis vs MeiosisMitosis vs Meiosis