1. A Tour of the CellA Tour of the Cell
Ch. 6Ch. 6
Sections 6.1, 6.2Sections 6.1, 6.2

2. 3 Objectives in the Section3 Objectives in the Section
1.1. Microscope types – what kindMicroscope types – what kind
is best for different jobsis best for different jobs
2.2. Differences betweenDifferences between
prokaryotes and eukaryotesprokaryotes and eukaryotes
3.3. Why cells need to be smallWhy cells need to be small

3. MicroscopesMicroscopes
how we view cellshow we view cells

4. Early MicroscopesEarly Microscopes
 First microscopeFirst microscope
 Jansen (Dutch) -Jansen (Dutch) -
15951595
 Christopher Cock’sChristopher Cock’s
compound scopescompound scopes
(1665) used by(1665) used by RobertRobert
HookHook, Father of cell, Father of cell
biologybiology

5. Leeuwenhoek’sLeeuwenhoek’s MicroscopesMicroscopes
 Brightest, clearest lensesBrightest, clearest lenses
 Single lens,Single lens, magnified overmagnified over
200x200x
 Impressive observerImpressive observer
of protistsof protists

6.  500500 timestimes
better thanbetter than
human eyehuman eye
LightLight
MicroscopeMicroscope

7. Light MicroscopesLight Microscopes
 Early scopes and modern scopes are lightEarly scopes and modern scopes are light
microscopes (LMs)microscopes (LMs)
Visible light passes through the specimenVisible light passes through the specimen
Image magnified by a series of lensesImage magnified by a series of lenses

8. MagnificationMagnification
 The ratio of the projected image to the realThe ratio of the projected image to the real
size of the objectsize of the object
 LMs can effectively magnify to ~ 1000xLMs can effectively magnify to ~ 1000x

9. Sizes of cellsSizes of cells
 OneOne MICROMETERMICROMETER = 1/ 1,000,000 m= 1/ 1,000,000 m
 OneOne NANOMETERNANOMETER = 1/1,000,000,000 m= 1/1,000,000,000 m

10. ResolutionResolution
 A measure of how clear an image isA measure of how clear an image is
 Determined by the minimum distance atDetermined by the minimum distance at
which 2 points can still be distinguished aswhich 2 points can still be distinguished as
2 separate points2 separate points
 LMs have resolution of ~0.2 micrometersLMs have resolution of ~0.2 micrometers
at bestat best
Poor resolution
At what point can
you no longer
distinguish these
as separate lines?

11. ResolutionResolution
 Human eye's resolving powerHuman eye's resolving power
 Ability to distinguish betweenAbility to distinguish between
lines =lines = 1/10 mm1/10 mm
 If closer, lines merge into 1 lineIf closer, lines merge into 1 line

12.  Reverses image under field of viewReverses image under field of view
Light MicroscopeLight Microscope

13. Dark-Field MicroscopesDark-Field Microscopes
 Light comes from the sideLight comes from the side,, makesmakes hugehuge
shadowsshadows and contrastsand contrasts
Good for LIVING CELLS

14. Phase-contrast MicroscopePhase-contrast Microscope
 Waves of lightWaves of light
are set up,are set up,
bounced offbounced off
the specimenthe specimen
 InterferenceInterference
causedcaused
byby
shape of cells isshape of cells is
plotted byplotted by

15. Electron MicroscopesElectron Microscopes
 Developed in theDeveloped in the
1950s1950s
 Instead of light, aInstead of light, a
beam of electrons isbeam of electrons is
focused on specimenfocused on specimen

16. Transmission Electron MicroscopeTransmission Electron Microscope
(T.E.M.)(T.E.M.)
 Aims aAims a beam of electronsbeam of electrons instead ofinstead of
light waveslight waves THROUGHTHROUGH a section ofa section of
thethe specimenspecimen
 200,000200,000 times bettertimes better
than the eyethan the eye

17. T.E.M. X-secT.E.M. X-sec
Golgi
Actin Filament
Mitochondrion

18. Preparation of specimenPreparation of specimen
 Since cells are mostly water,Since cells are mostly water, need dye toneed dye to
show up,show up, block light raysblock light rays
 Hydrophobic andHydrophobic and
hydrophillichydrophillic stainsstains
will dye organelleswill dye organelles
different densitiesdifferent densities

19. Scanning Electron MicroscopeScanning Electron Microscope
(S.E.M.)(S.E.M.)
 Works like sonar, usingWorks like sonar, using electronselectrons toto
bounce off specimen's surfacebounce off specimen's surface
 Limited resolutionLimited resolution butbut greatgreat 3-D3-D effecteffect!!

20. S.E.M.S.E.M.

21. Pollen grains
Ant
Red and
white
blood
cells

22. Preparation of specimensPreparation of specimens
 First embedded in waxFirst embedded in wax
 Sliced with aSliced with a
MICROTOMEMICROTOME
 Specimens "shadowed"Specimens "shadowed"
with metalwith metal,,
for reflection, contrastfor reflection, contrast
 ALL THESEALL THESE
PROCESSESPROCESSES
KILLKILL
CELLSCELLS

23. Pros & Cons of Microscope TypesPros & Cons of Microscope Types
LightLight ScanningScanning
ElectronElectron
TransmissionTransmission
ElectronElectron
ProsPros Can studyCan study
living cellsliving cells
Gives details onGives details on
surface of specimen;surface of specimen;
resolution 0.002resolution 0.002
micrometersmicrometers
Good for studyingGood for studying
internal cellinternal cell
structures; resolutionstructures; resolution
0.002 micrometers0.002 micrometers
ConsCons MagnificationMagnification
to only 1000x,to only 1000x,
resolutionresolution
only 0.2only 0.2
micrometermicrometer
Preparation of cellsPreparation of cells
kills them; limitedkills them; limited
resolutionresolution
Preparation of cellsPreparation of cells
kills them; need verykills them; need very
thin sections of cellthin sections of cell
parts (no depth)parts (no depth)

24. Quick ThinkQuick Think
 With your neighbor, DISCUSS:With your neighbor, DISCUSS:
 What type of microscope wouldWhat type of microscope would
you use to studyyou use to study
1.1. A living white blood cell?A living white blood cell?
2.2. The details of surface texture ofThe details of surface texture of
hair?hair?
3.3. The detailed structure of anThe detailed structure of an
organelle?organelle?

25. Separation of Organelles bySeparation of Organelles by CellCell
FractionationFractionation
 Using a centrifuge to separate out successivelyUsing a centrifuge to separate out successively
smaller cell components for studysmaller cell components for study
 Cell parts separated by size and densityCell parts separated by size and density

26. Prokaryotic Cells vs.Prokaryotic Cells vs.
Eukaryotic CellsEukaryotic Cells

27. PROKARYOTESPROKARYOTES
TheyThey are:are:
BacteriaBacteria

28.  Have plasma membraneHave plasma membrane (aka cell membrane)(aka cell membrane)
++ cell wallcell wall
 NoNo membrane-boundmembrane-bound organellesorganelles
 NONO NUCLEAR MEMBRANE (NUCLEAR MEMBRANE (no nucleusno nucleus))
DNA in strands in mid-cellDNA in strands in mid-cell
 Heterotrophic, phototrophic & chemotrophicHeterotrophic, phototrophic & chemotrophic
formsforms
ProkaryotesProkaryotes

30. EUKARYOTESEUKARYOTES
 Much moreMuch more complexcomplex
 Contain MANYContain MANY membrane-boundmembrane-bound organellesorganelles
 DNADNA containedcontained in a nucleusin a nucleus
membranemembrane
 IncludesIncludes ALLALL
animals,animals,
plants, protists, &plants, protists, &
fungifungi

31. Cell SizeCell Size
InIn eukaryoteseukaryotes – cells– cells
varyvary greatly,greatly, butbut
basically allbasically all similar insimilar in
structure & sizestructure & size
10 30 micrometers‑10 30 micrometers‑
 Largest cell =Largest cell = eggseggs
 Zygote divides rapidly toZygote divides rapidly to
get new cells to correct sizeget new cells to correct size

33. Critical Question:Critical Question:
Why Do Cells Need to BeWhy Do Cells Need to Be
ExtremelyExtremely Small?Small?

34. Answer:Answer:
 Surface to volume ratioSurface to volume ratio needs to be largeneeds to be large
 LOTS of materialsLOTS of materials need to pass through plasmaneed to pass through plasma
membranemembrane
 DiffusionDiffusion only works well across very shortonly works well across very short
distancesdistances
 NucleusNucleus can only handle so much info at oncecan only handle so much info at once
would “short out” if cells were much larger‑would “short out” if cells were much larger‑

35. Diffusion of substances across theDiffusion of substances across the
plasma membraneplasma membrane
 Only so much stuff can pass across theOnly so much stuff can pass across the
membrane at any particular locationmembrane at any particular location
 Larger cells cannot move enoughLarger cells cannot move enough
materials in and out to support the cellmaterials in and out to support the cell

36. Increase Surface/Volume RatioIncrease Surface/Volume Ratio

37. Cell ShapeCell Shape
Tend to beTend to be sphericalspherical
because of cohesion &because of cohesion &
surface tensionsurface tension
 Strongest structuralStrongest structural
shape, stableshape, stable (like bubbles(like bubbles
& balloons)& balloons)
 If NOT spherical,If NOT spherical,
cell needscell needs internalinternal
and/orand/or
externalexternal

38. OrganellesOrganelles
 Eukaryotic cells haveEukaryotic cells have
elaborateelaborate internalinternal
membranesmembranes that divide thethat divide the
interior of the cell intointerior of the cell into
compartmentscompartments
 TheseThese membrane boundmembrane bound
compartments are calledcompartments are called
organellesorganelles
 Each has a specific functionEach has a specific function
 Each has a specific structureEach has a specific structure

39. Cell ComponentsCell Components
Animal CellAnimal Cell

40. Plant CellPlant Cell

41. The Cell Parts ProjectThe Cell Parts Project
 NucleusNucleus
 NucleolusNucleolus
 RibosomesRibosomes
 Smooth ERSmooth ER
 Rough ERRough ER
 GolgiGolgi
 Vacuoles (food,Vacuoles (food,
contractile, central)contractile, central)
 CentriolesCentrioles
 MitochondriaMitochondria
 ChloroplastChloroplast
 CytoskeletonCytoskeleton
 Cilia and flagellaCilia and flagella
 Cell wallCell wall
 LysosomesLysosomes
 Plasma membranePlasma membrane
Do not
need
details of
p/s or c/r

42. Groups and TopicsGroups and Topics
You can choose your partner,You can choose your partner,
but topics will be assigned onbut topics will be assigned on
a first come, first serveda first come, first served
RANDOM basisRANDOM basis