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