The Cell CycleThe Cell Cycle

Mitosis and InterphaseMitosis and Interphase

Cells Make Cells…..Why?Cells Make Cells…..Why?

GrowGrow RepairRepair Regenerate or ReplaceRegenerate or Replace

So wouldn’t it be easier to just be ONE cell?

Hhmm…let’s check out the Hhmm…let’s check out the surface area to volume ratio….surface area to volume ratio….

As the cell increases in size, could it As the cell increases in size, could it move substances in and out of the move substances in and out of the cell fast enough?cell fast enough?

Therefore, cells are…Therefore, cells are…

SMALL!! HAVE UNIQUE HAVE UNIQUE SHAPES TO SHAPES TO INCREASE INCREASE SURFACE AREASURFACE AREA

Prokaryotic Cell DivisionProkaryotic Cell Division

Bacterial cells reproduce Bacterial cells reproduce by Binary Fissionby Binary Fission

Much simpler process Much simpler process than in eukaryotic than in eukaryotic organisms (why?)organisms (why?)

Begins with DNA replication Begins with DNA replication (why?); each copy moves to (why?); each copy moves to opposite sides of cellopposite sides of cell

Followed by elongation of cell, Followed by elongation of cell, and formation of a septum and formation of a septum (separation) between the two (separation) between the two halves, forming two new cellshalves, forming two new cells

Prokaryotic Cell Division

Prokaryotic Cell DivisionProkaryotic Cell Division

Results in two cells that are Results in two cells that are identical (clones) of original identical (clones) of original cellscells

Eukaryotic Cell DivisionEukaryotic Cell DivisionTwo formsTwo forms

Mitosis Mitosis grow, replace dead or worn grow, replace dead or worn out cells, or to repair woundsout cells, or to repair wounds

Asexual reproduction in fungi, Asexual reproduction in fungi, protists, some plants/animalsprotists, some plants/animals

MeiosisMeiosisSexual reproductionSexual reproduction

DNA and Cell DivisionDNA and Cell Division During cell division, the During cell division, the

genetic material DNA, needs genetic material DNA, needs to be copied and divided to be copied and divided between the two new cellsbetween the two new cells

DNA in cells is divided into DNA in cells is divided into long chains called long chains called chromosomeschromosomes

All living things..All living things..

....begin life as a begin life as a single fertilized single fertilized cell.cell.

Humans begin as Humans begin as a fertilized a fertilized OVUM or OVUM or human egg cell.human egg cell.

The egg cell …The egg cell … …….then begins to .then begins to

divide into exact divide into exact duplicate “stem duplicate “stem cells”.cells”.

these first cells will these first cells will be the basis for all be the basis for all future cells in the future cells in the human body. human body.

---->note the ovum ---->note the ovum has divided into 8 has divided into 8 stem cellsstem cells

How does this work?How does this work? Let’s go back to Let’s go back to

the little batch of the little batch of 8…8…

We will now look We will now look at cells when they at cells when they are dividing…and are dividing…and when they aren’t!when they aren’t!

This little batch of cells…This little batch of cells… ……will not will not

stay the stay the same. Cells same. Cells specialize specialize and take on and take on different different jobs. jobs.

InterphaseInterphase The time The time

between cell between cell divisiondivision

Cell is doing its Cell is doing its jobjob

DNA DNA duplicates-duplicates-chromosomes chromosomes make exact make exact copies of copies of themselvesthemselves

Genetic material is all strung out as chromatin

Nuclear membraneclearly in place

G0

The Cell CycleThe Cell Cycle

The Cell Cycle: InterphaseThe Cell Cycle: InterphaseWhen a cell is not dividing it When a cell is not dividing it is said to be in Interphase:is said to be in Interphase:

  G1: Gap, cells are G1: Gap, cells are recovering from an earlier recovering from an earlier cell division cell division

  S: Synthesis, DNA S: Synthesis, DNA replication occursreplication occurs

The Cell Cycle: Interphase The Cell Cycle: Interphase G2G2

Gap, cells are making sure all Gap, cells are making sure all the DNA was replicated the DNA was replicated correctly; a little more correctly; a little more growth; the chromosomes growth; the chromosomes start to become tightly start to become tightly coiled; Centrioles replicate coiled; Centrioles replicate and one centriole moves to and one centriole moves to each pole. *Animal Cells*each pole. *Animal Cells*

REVIEW:REVIEW:

In a non-dividing cell, the DNA is called In a non-dividing cell, the DNA is called

CHROMATIN.CHROMATIN. During theDuring the S phase of the cell S phase of the cell

cycle, the DNA replicates to cycle, the DNA replicates to form sister form sister CHROMATIDSCHROMATIDS..

In a dividing cell, the DNA is called In a dividing cell, the DNA is called

CHROMOSOMES.CHROMOSOMES.

Cell cycleCell cycle Two main parts:Two main parts:

IInterphasenterphase

Cell divisionCell division

Eukaryotic Chromosome Eukaryotic Chromosome StructureStructure

Normally, Normally, chromosomes chromosomes are spread out in are spread out in a form called a form called chromatinchromatin

During mitosis, During mitosis, chromosomes chromosomes fold up and fold up and condensecondense

Chromosome structureChromosome structure

The replicated chromosomes The replicated chromosomes stay together and are called stay together and are called sister chromatidssister chromatids

Sister chromatids are attached at Sister chromatids are attached at the the centromerecentromere

The Cell Cycle: Cell DivisionThe Cell Cycle: Cell Division Mitosis (M Phase)Mitosis (M Phase)

Nuclear DivisionNuclear Division

Cytokinesis (C phase)Cytokinesis (C phase)Cytoplasmic DivisionCytoplasmic Division

The Cell CycleThe Cell Cycle The length of time the cell cycle The length of time the cell cycle

takes depends on the type of cell. takes depends on the type of cell. Usually the more specialized the Usually the more specialized the cell the less likely it is to divide.cell the less likely it is to divide.

Red blood cells are replaced at a Red blood cells are replaced at a rate of 2-3 million/secrate of 2-3 million/sec

Nerve cells usually never divide, Nerve cells usually never divide, they enter they enter G0G0

MitosisMitosis

Cell divides to form two new cellsCell divides to form two new cells Can look at four different stagesCan look at four different stages

PProphaserophaseMMetaphaseetaphaseAAnaphasenaphaseTTelophaseelophase

ProphaseProphase DNA DNA

condenses to condenses to form distinct form distinct chromosomeschromosomes

Nuclear Nuclear membrane membrane disappearsdisappears

MetaphaseMetaphase Chromosomes Chromosomes

line up in the line up in the middle middle (equator) of (equator) of the cellthe cell

Spindle fibers Spindle fibers attachattach

AnaphaseAnaphase ChromosomeChromosome

s separate s separate and move and move toward the toward the opposite opposite ends of the ends of the cell (poles)cell (poles)

TelophaseTelophase Chromosomes Chromosomes

reach the polesreach the poles New nuclear New nuclear

membrane formsmembrane forms Chromosomes Chromosomes

unwind to unwind to become thread-become thread-like chromatin like chromatin againagain

Cytokinesis (End of Cytokinesis (End of Telophase)Telophase)

The cytoplasm is The cytoplasm is evenly dividedevenly divided

New cell New cell membrane membrane forms in animal forms in animal cellscells

New cell wall is New cell wall is built across for built across for plant cellsplant cells

OK, fine…but who really cares about MITOSIS and dividing cells???

Nerve cells…Nerve cells…

……remain in remain in INTERPHASE for INTERPHASE for long periods of long periods of time.time.

They go through They go through mitosis about once mitosis about once every 75 years. every 75 years.

So?…So?…

Damage to these cells…Damage to these cells…

……is often very is often very serious.serious.

Some damage is not Some damage is not permanentpermanent

Gloria Estefan was Gloria Estefan was involved in a tragic tour involved in a tragic tour bus accident. bus accident.

Surgeons were able to Surgeons were able to repair her nearly repair her nearly severed spinal chord.severed spinal chord.

She recently donated She recently donated $1,000,000 for spinal $1,000,000 for spinal cord injury research---> cord injury research--->

Cancer cells…Cancer cells… ……behave much differently behave much differently

than nerve cells.than nerve cells.

……spend very little time in spend very little time in interphase and go through interphase and go through mitosis uncontrollably.mitosis uncontrollably.

Approx. 1/10,000 of your Approx. 1/10,000 of your cells are cancerous-the cells are cancerous-the good news-your defense good news-your defense cells usually kill them fast.cells usually kill them fast.