The Cell The Cell CycleCycle

In the time that it In the time that it takes you to read takes you to read

this sentence, your this sentence, your body will have body will have

made millions of made millions of new cells! Making new cells! Making new cells allows new cells allows you to grow and you to grow and replace cells that replace cells that

have died.have died.

The Life of a CellThe Life of a Cell Cell cycle: the life cycle Cell cycle: the life cycle

of a cellof a cell Cell cycle begins when Cell cycle begins when

the cell is the cell is formedformed and and ends when the cell ends when the cell divides and forms new divides and forms new cellscells

Before a cell divides, it Before a cell divides, it must make a copy of its must make a copy of its DNADNA

DNA is organized into structures DNA is organized into structures called called CHROMOSOMESCHROMOSOMES

Copying chromosomes ensures Copying chromosomes ensures that each new cell will be an that each new cell will be an exactexact copy copy of its parent cellof its parent cell

How does a cell make more cells? How does a cell make more cells? Depends on whether it’s Depends on whether it’s

prokaryotic (no nucleus)prokaryotic (no nucleus)

or or

eukaryotic (with nucleus)eukaryotic (with nucleus)

Making More Prokaryotic CellsMaking More Prokaryotic Cells Prokaryotic cells are less Prokaryotic cells are less

complexcomplex than eukaryotic cells than eukaryotic cells Cell division is called “Cell division is called “binary binary

fissionfission”, which means ”, which means “splitting into two parts”“splitting into two parts”

Binary fission results in two Binary fission results in two cells that each contain cells that each contain oneone copy of the circle of DNAcopy of the circle of DNA

Eukaryotic Cells and Their DNAEukaryotic Cells and Their DNA

Eukaryotic cells Eukaryotic cells are more complexare more complex

The chromosomes The chromosomes of eukaryotic cells of eukaryotic cells contain more contain more DNADNA than prokaryotic than prokaryotic cellscells

Different kinds of Different kinds of eukaryotes have eukaryotes have different numbers different numbers of of chromosomeschromosomes

Example: humans Example: humans have 46 have 46 chromosomeschromosomes

Think “more chromosomes = better Think “more chromosomes = better organism”?organism”?

Not true! Humans have 46, but a lot of organisms have Not true! Humans have 46, but a lot of organisms have

more than us!more than us!

Butterfly = 380Butterfly = 380

Goldfish = 94Goldfish = 94

Horse = 64Horse = 64

Amoeba = 40Amoeba = 40

Tobacco plant = 48Tobacco plant = 48

Homologous chromosomes: Homologous chromosomes: chromosomes that have the chromosomes that have the samesame sequence of genes and sequence of genes and the same structurethe same structure

Making More Eukaryotic CellsMaking More Eukaryotic Cells

The eukaryotic cell cycle includes The eukaryotic cell cycle includes 3 3 stages:stages:

1.1. InterphaseInterphase: cell grows and copies its: cell grows and copies its

organelles and chromosomesorganelles and chromosomes

2.2. Mitosis:Mitosis: complicated process of complicated process of

chromosome separationchromosome separation

3.3. CytokinesisCytokinesis: cell splits into two cells; these: cell splits into two cells; these

cells are identical to each othercells are identical to each other

MitosisMitosis

•Cell division occurs in a series of stages, or phases

11stst: INTERPHASE: INTERPHASE Chromosomes are Chromosomes are

copied copied (# doubles)(# doubles) Chromosomes appear Chromosomes appear

as threadlike coils as threadlike coils ((chromatinchromatin) at the ) at the start, but each start, but each chromosome and its chromosome and its copy (copy (sistersister chromosome) change to chromosome) change to sister chromatids at end sister chromatids at end of this phaseof this phasecentromere

22ndnd: PROPHASE: PROPHASE

MitosisMitosis begins (cell begins (cell begins to divide)begins to divide)

CentriolesCentrioles (or (or poles) appear and poles) appear and begin to move to begin to move to opposite sides of opposite sides of cellcell

Spindle fibersSpindle fibers form form between the polesbetween the poles

33rdrd: METAPHASE: METAPHASE

ChromatidsChromatids (or (or pairs of pairs of chromosomes) chromosomes) attach to the attach to the spindle fibersspindle fibers

44thth: ANAPHASE: ANAPHASE

Chromatids (or Chromatids (or pairs of pairs of chromosomes) chromosomes) separateseparate and and begin to move to begin to move to oppositeopposite ends of ends of the cellthe cell

55thth: : TELOPHASETELOPHASE

Two new Two new nuclei nuclei formform

Chromosomes Chromosomes appear as appear as chromatin chromatin ((threadsthreads rather rather than than rodsrods))

MitosisMitosis ends ends

66thth: CYTOKINESIS: CYTOKINESIS

Cell membrane Cell membrane moves inward to moves inward to create two create two daughterdaughter cells – cells – each with its own each with its own nucleusnucleus with with identical identical chromosomeschromosomes

Ways to Remember the Order of Ways to Remember the Order of Mitosis!Mitosis!

II PProposed roposed MMarriage arriage AAfter fter TTuesday’s uesday’s CClass.lass.

II PPicked icked MMarigolds arigolds AAfter fter TTyping yping CClass.lass.

Can you think of any?Can you think of any?