CELLSCELLSThe Smallest Units Defined as Life

Wall WalkWall Walk

AristotleAristotle Gregorio RediGregorio Redi Robert HookeRobert Hooke Anton van Anton van

LeeuwenhoekLeeuwenhoek Lazzaro SpallanzaniLazzaro Spallanzani Louis PasteurLouis Pasteur

Jean-Baptiste de Jean-Baptiste de LamarkLamark

Matthias SchleidenMatthias Schleiden Theoror SchwannTheoror Schwann Rudolph VirchowRudolph Virchow

What is the Cell What is the Cell Theory?Theory?

Aristotle 384-322 B.C.Aristotle 384-322 B.C.“On the Generation of Animals”•Discussed fundamental questions of life: •How does reproduction occur?•How does development occur?•How does heredity take place?

“ … within each germ springs from a definite parent and gives rise to a predictable progeny. And thus it is the germ that is the ruling influence and fabricator of the offspring."

Spontaneous GenerationSpontaneous Generation

From pre-historic times to about 1850, most people believed that under the right conditions, living things could spontaneously appear from non-living material.

Francesco Redi 1668Francesco Redi 1668

Born 1626 in ItalyBorn 1626 in Italy FirstFirst to challenge the idea of to challenge the idea of

spontaneous generationspontaneous generation Did not accept the common Did not accept the common

belief that flies magically belief that flies magically appeared from rotting meatappeared from rotting meat

Hypothesis: If a jar containing Hypothesis: If a jar containing rotting meat is covered, then it rotting meat is covered, then it will produce no flieswill produce no flies

Redi’s ConclusionsRedi’s Conclusions

Flies lay eggs, Flies lay eggs, which grow into which grow into maggots, which maggots, which metamorphose metamorphose into fliesinto flies

If flies can’t lay If flies can’t lay eggs, then no new eggs, then no new flies can growflies can grow

We Object!We Object!

Many people rejected Redi’s claim that flies Many people rejected Redi’s claim that flies do not spontaneously generatedo not spontaneously generate

Their reasoning:Their reasoning: ““sealing the jar closed prevented a magical essence sealing the jar closed prevented a magical essence

from entering the rotting meat and brining it to from entering the rotting meat and brining it to life”life”

““Scientists seek only to challenge belief systems Scientists seek only to challenge belief systems and stir things up”and stir things up”

THE MICROSCOPETHE MICROSCOPE

This instrument This instrument opened up new opened up new

doors in the field of doors in the field of biology; Galileo biology; Galileo

designed a designed a compound compound microscopemicroscope

1665-Robert Hooke1665-Robert Hooke viewed thin slices of cork tree viewed thin slices of cork tree under a crude microscope and under a crude microscope and observed tiny hollow boxes. He observed tiny hollow boxes. He called these boxes called these boxes cells.cells.

Image Credit Cork cells

© 2010 Paul Billiet ODWS

1674- Anton van Leeuwenhoek 1674- Anton van Leeuwenhoek observed tiny living organisms in observed tiny living organisms in drops of pond water.drops of pond water.

Made over 250 microscopesMade over 250 microscopes Caused a sensation and scared people!Caused a sensation and scared people!

Lazzaro Lazzaro SpallanzaniSpallanzani 1729. Italian1729. Italian

Believed microbes that spoil Believed microbes that spoil food come from the air and food come from the air and can be killed by boilingcan be killed by boiling

Hypothesis: If air is allowed Hypothesis: If air is allowed to reach food, then microbes to reach food, then microbes will get in and cause it to will get in and cause it to spoilspoil

Spallanzani’s Experiment

Flask 1: boiled broth, openFlask 2: boiled broth, sealed shut

ResultsFlask 1 spoiled

Flask 2 did not spoil

Louis Pasteur 1862Louis Pasteur 1862

Anti-spontaneous generation experiments: Anti-spontaneous generation experiments: Improved on Spallanzani’s workImproved on Spallanzani’s work PasteurPasteur definitively demonstrated that microorganisms are present in definitively demonstrated that microorganisms are present in

air but not created by air. This was critical for refutation of the air but not created by air. This was critical for refutation of the concept of spontaneous generation and the for development of germ concept of spontaneous generation and the for development of germ

theory of disease.theory of disease.    

JEAN-BAPTISTE DE LAMARCKJEAN-BAPTISTE DE LAMARCK1744-18291744-1829

The majority of this Frenchman's work dealt with The majority of this Frenchman's work dealt with animal classification and evolution. He is credited animal classification and evolution. He is credited with taking steps towards the creation of the cell with taking steps towards the creation of the cell

theory with this saying: theory with this saying: "Every step which Nature takes when making her "Every step which Nature takes when making her direct creations consists in organizing into cellular direct creations consists in organizing into cellular

tissue the minute masses of viscous or mucous tissue the minute masses of viscous or mucous substances that she finds at her disposal under substances that she finds at her disposal under

favorable circumstancesfavorable circumstances

History of the Cell TheoryHistory of the Cell Theory

1838- Matthias Schleiden concludes 1838- Matthias Schleiden concludes that all plants are made up of cells.that all plants are made up of cells.

History of the Cell TheoryHistory of the Cell Theory

1839-Theodor Schwann 1839-Theodor Schwann concludes that all animals are concludes that all animals are made up of cells.made up of cells.

Created the term Cell Created the term Cell

TheoryTheory

History of the Cell TheoryHistory of the Cell Theory

1855-Rudolph Virchow completes 1855-Rudolph Virchow completes the cell theory by proposing all cells the cell theory by proposing all cells come from existing cells.come from existing cells.

Demonstrated that theDemonstrated that the

Cell Theory applies to Cell Theory applies to

diseased tissues as well diseased tissues as well

The Cell Theory:The Cell Theory: All organisms are composed All organisms are composed

of one or more cellsof one or more cells Evidence?Evidence?

The cell is the basic unit of The cell is the basic unit of organization for the organismorganization for the organism

All cells come from pre-All cells come from pre-existing cells existing cells

Technology ConnectionsTechnology Connections Light Microscope 1600’sLight Microscope 1600’s Differential Centrifugation – 1930sDifferential Centrifugation – 1930s

Procedure to separate organelles from whole cells Procedure to separate organelles from whole cells Separate nucleus from cytoplasm Separate nucleus from cytoplasm

Transmission Electron MicroscopeTransmission Electron Microscope A beam of electrons instead of light is passed A beam of electrons instead of light is passed

through an ultra thin specimen; those that pass through an ultra thin specimen; those that pass through onto photographic platesthrough onto photographic plates

Scanning Electron MicroscopeScanning Electron Microscope Forms a 3D image of the specimenForms a 3D image of the specimen

Two basic cell types:Two basic cell types:Prokaryotic & EukayoticProkaryotic & Eukayotic

Prokaryotic cellsProkaryotic cells Earliest cellsEarliest cells Lack membrane bound organelles Lack membrane bound organelles No nucleusNo nucleus No mitochondriaNo mitochondria Have membrane, cytoplasm, free DNA, Have membrane, cytoplasm, free DNA,

ribosomesribosomes

Prokayrotic cells: BacteriaProkayrotic cells: Bacteria

• May have evolved from Prokaryotic cell

• Have a nucleus that holds the DNA inside a membrane

• Have mitochondria• Also have cell membrane &

cytoplasm

Eukaryotic cells:

What are Organelles?What are Organelles?

Specific structures in the cytoplasm of the Specific structures in the cytoplasm of the cellcell

Perform specific functions for the cellPerform specific functions for the cell Organelles found only in plants includeOrganelles found only in plants include

Cell wallsCell walls ChloroplastsChloroplasts

Organelle found only in Animal Organelle found only in Animal CellsCells

CentriolesCentrioles