Cell Cycle and MitosisCell Cycle and Mitosis

Cell DivisionCell Division

The process by which a cell divides into two The process by which a cell divides into two new “daughter” cells.new “daughter” cells. Daughter cells are the NEW cells Daughter cells are the NEW cells the product of the product of

cell division.cell division.

Cell DivisionCell Division

Before cell division occurs, the cell Before cell division occurs, the cell replicates (copies) all of its DNA.replicates (copies) all of its DNA. This solves the problem of information This solves the problem of information

overloadoverload Each cell gets one complete copy of genetic Each cell gets one complete copy of genetic

informationinformation

Cell DivisionCell Division

Cell division also solves the problem of Cell division also solves the problem of increasing size by reducing cell volume.increasing size by reducing cell volume. Cell division results in an increase in the Cell division results in an increase in the

ratio of surface area to volume.ratio of surface area to volume. This allows for the efficient exchange of This allows for the efficient exchange of

materials within a cell.materials within a cell.

Cell Division and ReproductionCell Division and Reproduction

Asexual Reproduction – the production of Asexual Reproduction – the production of genetically identical offspring from a single genetically identical offspring from a single parent.parent.

Sexual Reproduction – fusion of two cellsSexual Reproduction – fusion of two cells The offspring produced by sexual reproduction The offspring produced by sexual reproduction

inherit some of their genetic information from each inherit some of their genetic information from each parent.parent.

Asexual ReproductionAsexual Reproduction

Occurs in many single-celled organisms.Occurs in many single-celled organisms. Ex, bacteriumEx, bacterium Cell divisionCell division

Also occurs in multi-cellular organismsAlso occurs in multi-cellular organisms Budding – small bud growing off hydra plant will Budding – small bud growing off hydra plant will

eventually break off and become a new planteventually break off and become a new plant

Advantages of Asexual Advantages of Asexual ReproductionReproduction

Asexual reproduction is very fast.Asexual reproduction is very fast. If conditions are right, quick reproduction can be a If conditions are right, quick reproduction can be a

very good thing.very good thing. If conditions remain the same, genetically identical If conditions remain the same, genetically identical

offspring is a good thing too.offspring is a good thing too.

Disadvantages of Asexual Disadvantages of Asexual ReproductionReproduction

A lack of genetic diversity is a disadvantage A lack of genetic diversity is a disadvantage when conditions change in ways that do not fit when conditions change in ways that do not fit the characteristics of an organism.the characteristics of an organism.

Sexual ReproductionSexual Reproduction

Many animals and plants reproduce sexuallyMany animals and plants reproduce sexually Many single-celled organisms also reproduce Many single-celled organisms also reproduce

sexuallysexually Offspring are produced by the fusion of Offspring are produced by the fusion of

special reproductive cells formed by each of special reproductive cells formed by each of two parents.two parents.

Advantages of Sexual ReproductionAdvantages of Sexual Reproduction

Provides genetic diversityProvides genetic diversity In a changing environment, genetic diversity In a changing environment, genetic diversity

provides the right combination of characteristics provides the right combination of characteristics needed to survive.needed to survive.

Disadvantages of Sexual Disadvantages of Sexual ReproductionReproduction

Process of finding a mate and raising offspring Process of finding a mate and raising offspring requires time.requires time.

Chromosomes and the Cell CycleChromosomes and the Cell Cycle

ChromosomeChromosome Threadlike structure within the nucleus that Threadlike structure within the nucleus that

contains genetic information contains genetic information Bundle of DNABundle of DNA Replicated at the beginning of the cell cycleReplicated at the beginning of the cell cycle Passed on from parent cell to daughter cellPassed on from parent cell to daughter cell

Prokaryotic ChromosomesProkaryotic Chromosomes

Prokaryotes lack nucleiProkaryotes lack nuclei Most prokaryotes contain a single, circular Most prokaryotes contain a single, circular

DNA chromosome that contains all, or nearly DNA chromosome that contains all, or nearly all, of the cell’s genetic information.all, of the cell’s genetic information.

Eukaryotic ChromosomesEukaryotic Chromosomes

Eukaryotic cells usually have more DNA than Eukaryotic cells usually have more DNA than prokaryotes.prokaryotes.

Eukaryotes contain multiple chromosomes.Eukaryotes contain multiple chromosomes. Fruit flies have 8 chromosomes per cell.Fruit flies have 8 chromosomes per cell. Humans have 46 chromosomes per cell.Humans have 46 chromosomes per cell.

Eukaryotic ChromosomesEukaryotic Chromosomes

Chromosomes make it possible to separate Chromosomes make it possible to separate DNA precisely during cell division.DNA precisely during cell division.

Chromosomes form a close association with Chromosomes form a close association with histones (type of protein).histones (type of protein).

This complex of chromosomes and proteins is This complex of chromosomes and proteins is known as chromatin.known as chromatin.

ChromatinChromatin

Cell CycleCell Cycle

During the cell cycle, a cell grows, prepares During the cell cycle, a cell grows, prepares for division, and divides to form two daughter for division, and divides to form two daughter cells.cells.

Prokaryotic Cell CycleProkaryotic Cell Cycle

The process of cell division in prokaryotes is a The process of cell division in prokaryotes is a form of asexual reproduction.form of asexual reproduction.

This process is known as binary fission.This process is known as binary fission.

Eukaryote Cell CycleEukaryote Cell Cycle

Consists of 4 phasesConsists of 4 phases G1 phaseG1 phase S phaseS phase G2 phase G2 phase M phaseM phase

InterphaseInterphase

Period of cell cycle between cell divisions.Period of cell cycle between cell divisions. Divided into 3 phases:Divided into 3 phases:

G1 phaseG1 phase S phaseS phase G2 phaseG2 phase

G1 PhaseG1 Phase

Cells do most of their growing during G1 Cells do most of their growing during G1 phase.phase.

Cells increase in size during this phase.Cells increase in size during this phase. Cells synthesize new proteins and organelles Cells synthesize new proteins and organelles

during this phase.during this phase.

S PhaseS Phase

S stands for synthesis (to make).S stands for synthesis (to make). During this phase, new DNA is synthesized During this phase, new DNA is synthesized

(made) when the chromosomes are replicated (made) when the chromosomes are replicated (doubled). (doubled).

The cell at the end of this phase contains twice The cell at the end of this phase contains twice as much DNA as it did at the beginning.as much DNA as it did at the beginning.

G2 PhaseG2 Phase

During this phase, many of the organelles and During this phase, many of the organelles and molecules required for cell division are molecules required for cell division are produced.produced. Chromatid – one of two identical “sister” parts of a Chromatid – one of two identical “sister” parts of a

duplicated chromosomeduplicated chromosome Centromere – region of a chromosome where the Centromere – region of a chromosome where the

two sister chromatids attachtwo sister chromatids attach Centriole – structure in an animal cell that helps to Centriole – structure in an animal cell that helps to

organize cell divisionorganize cell division

M PhaseM Phase

Two new daughter cells are produced during Two new daughter cells are produced during this phase.this phase.

M comes from the word mitosis.M comes from the word mitosis. This phase has two stages –This phase has two stages –

MitosisMitosis CytokinesisCytokinesis

In many cells, this process may overlap.In many cells, this process may overlap.

MitosisMitosis

Consists of 4 stages –Consists of 4 stages – ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase TelophaseTelophase

ProphaseProphase

During prophase, the genetic material inside During prophase, the genetic material inside the nucleus condenses and the duplicated the nucleus condenses and the duplicated chromosomes become visible. chromosomes become visible.

Outside the nucleus, a spindle starts to form.Outside the nucleus, a spindle starts to form. Cell starts to build spindlesCell starts to build spindles

Spindles – fanlike system of microtubules that will Spindles – fanlike system of microtubules that will help to separate the duplicated chromosomes.help to separate the duplicated chromosomes.

Spindle fibers extend from tiny paired structures Spindle fibers extend from tiny paired structures called centriolescalled centrioles

Prophase and CentriolesProphase and Centrioles

Centrioles are only found in animal cells.Centrioles are only found in animal cells. During prophase centrioles start to move During prophase centrioles start to move

toward opposite ends (poles) of the cell.toward opposite ends (poles) of the cell. As prophase ends, the chromosomes coil more As prophase ends, the chromosomes coil more

tightly, the nucleolus disappears, and the tightly, the nucleolus disappears, and the nuclear envelope breaks down.nuclear envelope breaks down.

ProphaseProphase

MetaphaseMetaphase

During metaphase, the centromeres of the During metaphase, the centromeres of the duplicated chromosomes line up across the duplicated chromosomes line up across the center of the cell.center of the cell.

Spindle fibers connect the centromere of each Spindle fibers connect the centromere of each chromosome to the two poles of the spindle.chromosome to the two poles of the spindle.

MetaphaseMetaphase

AnaphaseAnaphase

During anaphase, the chromosomes separate During anaphase, the chromosomes separate and move along spindle fibers.and move along spindle fibers.

Once anaphase begins, each sister chromatid is Once anaphase begins, each sister chromatid is now considered an individual chromosome.now considered an individual chromosome.

Anaphase comes to an end when this Anaphase comes to an end when this movement stops and the chromosomes are movement stops and the chromosomes are completely separated into two groups.completely separated into two groups.

AnaphaseAnaphase

TelophaseTelophase

During telophase, the chromosomes, which During telophase, the chromosomes, which were distinct and condensed, begin to spread were distinct and condensed, begin to spread out in into a tangle of chromatin.out in into a tangle of chromatin.

A nuclear envelope reforms around each A nuclear envelope reforms around each cluster of chromosomes.cluster of chromosomes.

The spindle begins to break apart.The spindle begins to break apart. A nucleolus becomes visible in each daughter A nucleolus becomes visible in each daughter

nucleus.nucleus.

TelophaseTelophase

CytokinesisCytokinesis

Cytokinesis completes the process of cell Cytokinesis completes the process of cell division – it splits one cell into two.division – it splits one cell into two.

This process is different in animal cells and in This process is different in animal cells and in plant cells.plant cells.

Cytokinesis in animal cellsCytokinesis in animal cells

The cell membrane is drawn inward until the The cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts.cytoplasm is pinched into two nearly equal parts.

Cytokinesis in plant cellsCytokinesis in plant cells

The cell membrane is not flexible enough to The cell membrane is not flexible enough to pinch because of the rigid cell wall.pinch because of the rigid cell wall.

A structure known as the cell plate forms A structure known as the cell plate forms halfway between the divided nuclei.halfway between the divided nuclei.

The cell plate gradually develops into cell The cell plate gradually develops into cell membranes that separate the two daughter membranes that separate the two daughter cells.cells.

A cell wall then forms in between the two new A cell wall then forms in between the two new membranes.membranes.

Cytokinesis in plant cellsCytokinesis in plant cells