A Tour of the CellA Tour of the Cell

Ch. 6Ch. 6

Sections 6.1, 6.2Sections 6.1, 6.2

3 Objectives in the Section3 Objectives in the Section

1.1. Microscope types – what kind Microscope types – what kind is best for different jobsis best for different jobs

2.2. Differences between Differences between prokaryotes and eukaryotesprokaryotes and eukaryotes

3.3. Why cells need to be smallWhy cells need to be small

MicroscopesMicroscopeshow we view cellshow we view cells

Early MicroscopesEarly Microscopes

First microscopeFirst microscope Jansen (Dutch) -Jansen (Dutch) -

15951595

Christopher Cock’s Christopher Cock’s compound scopes compound scopes (1665) used by (1665) used by Robert Robert HookHook, Father of cell , Father of cell biologybiology

Leeuwenhoek’sLeeuwenhoek’s Microscopes MicroscopesBrightest, clearest lensesBrightest, clearest lensesSingle lens, Single lens, magnified over magnified over

200x200x Impressive observer Impressive observer

of protists of protists

500500 times times better than better than human eyehuman eye

Light Light MicroscopeMicroscope

Light MicroscopesLight Microscopes

Early scopes and modern scopes are light Early 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

MagnificationMagnification

The ratio of the projected image to the real The 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

Sizes of cellsSizes of cells

One One MICROMETERMICROMETER = 1/ 1,000,000 m = 1/ 1,000,000 m One One NANOMETERNANOMETER = 1/1,000,000,000 m = 1/1,000,000,000 m

ResolutionResolutionA measure of how clear an image isA measure of how clear an image isDetermined by the minimum distance at Determined by the minimum distance at

which 2 points can still be distinguished as which 2 points can still be distinguished as 2 separate points2 separate points

LMs have resolution of ~0.2 micrometers LMs have resolution of ~0.2 micrometers at bestat best

Poor resolution

At what point can you no longer distinguish these as separate lines?

ResolutionResolution

Human eye's resolving powerHuman eye's resolving power Ability to distinguish between Ability to distinguish between

lines = lines = 1/10 mm1/10 mm If closer, lines merge into 1 lineIf closer, lines merge into 1 line

Reverses image under field of viewReverses image under field of view

Light MicroscopeLight Microscope

Dark-Field MicroscopesDark-Field Microscopes

Light comes from the sideLight comes from the side, , makes makes huge huge shadowsshadows and contrasts and contrasts

Good for LIVING CELLS

Phase-contrast MicroscopePhase-contrast Microscope

Waves of lightWaves of light are set up, are set up, bounced offbounced off the specimenthe specimen

InterferenceInterference caused caused by by shape of cells is shape of cells is plotted by plotted by computer, computer, projected projected

Electron MicroscopesElectron Microscopes

Developed in theDeveloped in the 1950s1950s

Instead of light, a Instead of light, a beam of electrons is beam of electrons is focused on specimenfocused on specimen

Transmission Electron MicroscopeTransmission Electron Microscope (T.E.M.)(T.E.M.)

Aims a Aims a beam of electronsbeam of electrons instead of instead of light waves light waves THROUGHTHROUGH a section of a section of the the specimenspecimen

200,000200,000 times better times better than the eye than the eye

T.E.M. X-secT.E.M. X-secGolgi

Actin Filament

Mitochondrion

Preparation of specimenPreparation of specimen

Since cells are mostly water, Since cells are mostly water, need dye to need dye to show up, show up, block light raysblock light rays

Hydrophobic and Hydrophobic and hydrophillic hydrophillic stainsstains will dye organelles will dye organelles different densitiesdifferent densities

Scanning Electron MicroscopeScanning Electron Microscope (S.E.M.)(S.E.M.)

Works like sonar, using Works like sonar, using electronselectrons to to bounce off specimen's surfacebounce off specimen's surface

Limited resolutionLimited resolution but but great great 3-D3-D effect effect!!

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

Pollen grains

Ant

Red and white blood cells

Preparation of specimensPreparation of specimens

First embedded in waxFirst embedded in wax Sliced with a Sliced with a

MICROTOMEMICROTOME Specimens "shadowed" Specimens "shadowed"

with metal with metal, , for reflection, contrastfor reflection, contrast

ALL THESE ALL THESE PROCESSES PROCESSES KILL KILL CELLSCELLS

Pros & Cons of Microscope TypesPros & Cons of Microscope TypesLightLight Scanning Scanning

ElectronElectronTransmission Transmission ElectronElectron

ProsPros Can study Can study living cellsliving cells

Gives details on Gives details on surface of specimen; surface of specimen; resolution 0.002 resolution 0.002 micrometersmicrometers

Good for studying Good for studying internal cell internal cell structures; resolution structures; resolution 0.002 micrometers0.002 micrometers

ConsCons Magnification Magnification to only 1000x, to only 1000x, resolution resolution only 0.2 only 0.2 micrometermicrometer

Preparation of cells Preparation of cells kills them; limited kills them; limited resolutionresolution

Preparation of cells Preparation of cells kills them; need very kills them; need very thin sections of cell thin sections of cell parts (no depth)parts (no depth)

Quick ThinkQuick Think

With your neighbor, DISCUSS:With your neighbor, DISCUSS: What type of microscope would What type of microscope would

you use to study you use to study 1.1. A living white blood cell?A living white blood cell?

2.2. The details of surface texture of The details of surface texture of hair?hair?

3.3. The detailed structure of an The detailed structure of an organelle?organelle?

Separation of Organelles by Separation of Organelles by Cell Cell FractionationFractionation

Using a centrifuge to separate out successively Using 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

Prokaryotic Cells vs. Prokaryotic Cells vs. Eukaryotic CellsEukaryotic Cells

PROKARYOTESPROKARYOTES

They They are:are:BacteriaBacteria

Have plasma membraneHave plasma membrane (aka cell membrane) (aka cell membrane) + + cell wallcell wall

NoNo membrane-bound membrane-bound organellesorganellesNONO NUCLEAR MEMBRANE ( NUCLEAR MEMBRANE (no nucleusno nucleus))

DNA in strands in mid-cellDNA in strands in mid-cellHeterotrophic, phototrophic & chemotrophic Heterotrophic, phototrophic & chemotrophic

formsforms

ProkaryotesProkaryotes

EUKARYOTESEUKARYOTES

Much more Much more complexcomplex Contain MANYContain MANY membrane-bound membrane-bound organellesorganelles DNA DNA contained contained in a nucleusin a nucleus

membrane membrane Includes Includes ALL ALL

animals, animals, plants, protists, & plants, protists, & fungi fungi

Cell SizeCell Size

In In eukaryoteseukaryotes – cells – cells varyvary greatly, greatly, butbut basically allbasically all similar in similar in structure & sizestructure & size

10 30 micrometers‑10 30 micrometers‑Largest cell = Largest cell = eggseggs

Zygote divides rapidly to Zygote divides rapidly to get new cells to correct sizeget new cells to correct size

Critical Question:Critical Question:Why Do Cells Need to Be Why Do Cells Need to Be

ExtremelyExtremely Small? Small?

Answer:Answer: Surface to volume ratio Surface to volume ratio needs to be largeneeds to be large

LOTS of materialsLOTS of materials need to pass through plasma need to pass through plasma membrane membrane

DiffusionDiffusion only works well across very short only works well across very short distancesdistances

Nucleus Nucleus can only handle so much info at once can only handle so much info at once would “short out” if cells were much larger‑would “short out” if cells were much larger‑

Diffusion of substances across the Diffusion of substances across the plasma membraneplasma membrane

Only so much stuff can pass across the Only so much stuff can pass across the membrane at any particular locationmembrane at any particular location

Larger cells cannot move enough Larger cells cannot move enough materials in and out to support the cellmaterials in and out to support the cell

Increase Surface/Volume RatioIncrease Surface/Volume Ratio

Cell ShapeCell ShapeTend to be Tend to be sphericalspherical

because of cohesion & because of cohesion & surface tensionsurface tension Strongest structural Strongest structural

shape, stableshape, stable (like bubbles (like bubbles & balloons)& balloons)

If NOT spherical, If NOT spherical, cell needs cell needs internal internal and/or and/or external external supportsupport maintain maintain shapeshape

OrganellesOrganelles Eukaryotic cells haveEukaryotic cells have

elaborate elaborate internal internal membranesmembranes that divide the that divide the interior of the cell into interior of the cell into compartmentscompartments

These These membrane bound membrane bound compartments are called compartments are called organellesorganelles Each has a specific function Each has a specific function Each has a specific structureEach has a specific structure

Cell ComponentsCell ComponentsAnimal CellAnimal Cell

Plant CellPlant Cell

The Cell Parts ProjectThe Cell Parts Project Nucleus Nucleus NucleolusNucleolus RibosomesRibosomes Smooth ERSmooth ER Rough ER Rough ER GolgiGolgi Vacuoles (food, Vacuoles (food,

contractile, central)contractile, central) CentriolesCentrioles

Mitochondria Mitochondria ChloroplastChloroplast Cytoskeleton Cytoskeleton Cilia and flagella Cilia and flagella Cell wall Cell wall Lysosomes Lysosomes Plasma membranePlasma membrane

Do not need details of p/s or c/r

Groups and TopicsGroups and Topics

You can choose your partner, You can choose your partner, but topics will be assigned on but topics will be assigned on a first come, first served a first come, first served RANDOM basisRANDOM basis