A TOUR OF THE CELL the fundamental unit of the fundamental unit of life life
Jan 20, 2016
A TOUR OF THE CELL
the fundamental unit of lifethe fundamental unit of life
The discovery and early study of cells The discovery and early study of cells progressed with the invention and progressed with the invention and improvement of microscopes in the 17th improvement of microscopes in the 17th century.century. Robert HookeRobert Hooke Anton van LeeuwenhoekAnton van Leeuwenhoek
Microscopes are a major tool in Microscopes are a major tool in cytologycytology, the , the study of cell structuresstudy of cell structures Cytology coupled with Cytology coupled with biochemistrybiochemistry, the study of molecules , the study of molecules
and chemical processes in metabolism, developed modern and chemical processes in metabolism, developed modern cell biology.cell biology.
Microscopes - windows to the Microscopes - windows to the world of the cellworld of the cell
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
From Monk’s Room to From Monk’s Room to Unit of Life Unit of Life
Robert Hooke Robert Hooke thought what he thought what he was looking at was looking at resembled the resembled the rooms monk’s rooms monk’s occupied…..occupied…..
CellsCells
The InstrumentsThe Instruments
D arkfie ld M icroscopy
P hase C ontrast M icroscopy
D ifferentia l In terference C ontrast M icroscopy
F luorescence M icroscopy
C onfocal M icroscopy
C om pound L ight M icroscope
S canning E lectron M icroscopy
Transm iss ion E lectron M icroscopy
A tom ic F orce E lectron M icroscopy
E lectron M icroscopes
Compound Light Compound Light MicroscopeMicroscope
Uses visible lightUses visible light Has at least 2 sets Has at least 2 sets
of lensesof lenses Can achieve Can achieve
maximum 2000X maximum 2000X magnificationmagnification
Resolution of Resolution of objects as small as objects as small as 0.2 0.2 mm
Light MicroscopyLight Microscopy
In a In a light microscope light microscope visible lightvisible light passes through the specimen and passes through the specimen and then through glass lenses.then through glass lenses. The lenses refract light such that the The lenses refract light such that the
image is magnified into the eye or a image is magnified into the eye or a video screen.video screen.
Brightfield IlluminationBrightfield Illumination
Usual operationsUsual operations Specimens must be Specimens must be
stained for viewingstained for viewing Best magnification Best magnification
and resolution with and resolution with the oil immersion the oil immersion objectiveobjective
Oil has same Oil has same refractive index as refractive index as glassglass
Microscopes vary in magnification and Microscopes vary in magnification and resolving power.resolving power.
MagnificationMagnification is the ratio of an object’s is the ratio of an object’s image to its real size.image to its real size.
Resolving powerResolving power is a measure of image is a measure of image clarity.clarity. It is the minimum distance two points It is the minimum distance two points
can be separated and still viewed as two can be separated and still viewed as two separate points.separate points.
Resolution is limited by the shortest Resolution is limited by the shortest wavelength of the source, in this case wavelength of the source, in this case light.light.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Light MicroscopesLight Microscopes
The minimum resolution The minimum resolution of a light microscope is of a light microscope is about 2 microns, the size about 2 microns, the size of a small bacteriumof a small bacterium
Light microscopes can Light microscopes can magnify effectively to magnify effectively to about 1,000 times the about 1,000 times the size of the actual size of the actual specimen.specimen. At higher At higher
magnifications, the magnifications, the image blurs.image blurs.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 7.1
Resolution of Light Resolution of Light MicroscopesMicroscopes
Electron MicroscopyElectron Microscopy
Beam of electrons has shorter Beam of electrons has shorter so so gives better resolution than visible gives better resolution than visible lightlight
Electromagnetic lenses rather than Electromagnetic lenses rather than glassglass
Done in a vacuumDone in a vacuum Can resolve to 0.5nm and magnify up Can resolve to 0.5nm and magnify up
to 100,000 times.to 100,000 times. Specimen must be dry….deadSpecimen must be dry….dead
Electron micrographsElectron micrographs
The goal of The goal of cell fractionationcell fractionation is to separate is to separate the major organelles of the cells so that their the major organelles of the cells so that their individual functions can be studiedindividual functions can be studied..
Cell FractionationCell Fractionation
Fractionation begins with homogenization, begins with homogenization, gently disrupting the cell gently disrupting the cell
Then, the homogenate is spun in a Then, the homogenate is spun in a centrifuge to separate heavier pieces into centrifuge to separate heavier pieces into the pellet while lighter particles remain in the pellet while lighter particles remain in the supernatant. the supernatant.
As the process is repeated at higher speeds As the process is repeated at higher speeds and longer durations, smaller and smaller and longer durations, smaller and smaller organelles can be collected in subsequent organelles can be collected in subsequent pelletspellets ultracentrifuge ultracentrifuge
can spin at up to 130,000 revolutions per minute can spin at up to 130,000 revolutions per minute and apply forces more than 1 million times and apply forces more than 1 million times gravity (1,000,000 gravity (1,000,000 gg).).
The ProcedureThe Procedure
Cell fractionation prepares quantities of Cell fractionation prepares quantities of specific cell components.specific cell components. enables the functions of these organelles to be isolated, enables the functions of these organelles to be isolated,
especially by the reactions or processes catalyzed by their especially by the reactions or processes catalyzed by their proteins.proteins.
For example, one cellular fraction is enriched in For example, one cellular fraction is enriched in enzymes that function in cellular respirationenzymes that function in cellular respiration..
Electron microscopy reveals that this fraction is Electron microscopy reveals that this fraction is rich in the organelles called mitochondria.rich in the organelles called mitochondria.
Cytology and biochemistry complement each Cytology and biochemistry complement each other in connecting cellular structure and other in connecting cellular structure and functionfunction..
Why Look at the Parts Why Look at the Parts rather than the Wholerather than the Whole
Fluorescent stain of cellFluorescent stain of cell
Cell Structure and FunctionCell Structure and Function
Mid 1600s - Robert Hooke observed Mid 1600s - Robert Hooke observed
and described cells in corkand described cells in cork
Late 1600s - Antony van Leeuwenhoek Late 1600s - Antony van Leeuwenhoek
observed sperm, microorganismsobserved sperm, microorganisms
1820s - Robert Brown observed and 1820s - Robert Brown observed and
named nucleus in plant cellsnamed nucleus in plant cells
Early DiscoveriesEarly Discoveries
Cell TheoryCell Theory
Schleiden and SchwannSchleiden and Schwann Every organism is composed of one or more Every organism is composed of one or more
cellscells
Cell is smallest unit having properties of lifeCell is smallest unit having properties of life
VirchowVirchow All exisiting cells arise from pre-existing All exisiting cells arise from pre-existing
cells.cells.
Smallest unit of lifeSmallest unit of life
Can survive on its own or has Can survive on its own or has
potential to do sopotential to do so
Is highly organized for metabolismIs highly organized for metabolism
Senses and responds to environmentSenses and responds to environment
Has potential to reproduceHas potential to reproduce
CellCell
Measuring Measuring
Cells Vary in SizeCells Vary in Size
Why Are Cells So Small?Why Are Cells So Small?
Surface-to-volume ratioSurface-to-volume ratio
The bigger a cell is, the less surface The bigger a cell is, the less surface
area there is per unit volumearea there is per unit volume
Above a certain size, material cannot Above a certain size, material cannot
be moved in or out of cell fast be moved in or out of cell fast
enoughenough
Size is Limited Size is Limited
Fig. 7.5
Metabolic requirements also set an upper limit to the size of Metabolic requirements also set an upper limit to the size of a single cell.a single cell.
As a cell increases in size its volume increases faster than its As a cell increases in size its volume increases faster than its surface area.surface area. Smaller objects have a greater Smaller objects have a greater
ratio of surface area to volume.ratio of surface area to volume.
Structure of CellsStructure of Cells Two or Three types of cellsTwo or Three types of cells
Archeo - cell typeArcheo - cell type There is much evidence that this is a third cell typeThere is much evidence that this is a third cell type
ProkaryoticProkaryotic EukaryoticEukaryotic
All cells have:All cells have: Plasma membrane Plasma membrane Region where DNA is storedRegion where DNA is stored Cytoplasm Cytoplasm ribosomesribosomes
Archeo-cell type and Archeo-cell type and ProkaryotesProkaryotes
No nucleusNo nucleus Nucleoid area where DNA residesNucleoid area where DNA resides
No membrane bound organelles.No membrane bound organelles. 70s ribosomes70s ribosomes Cell walls contain petidoglycan Prokaryotic Cell walls contain petidoglycan Prokaryotic
OrganismsOrganisms EubacteriaEubacteria CyanobacteriaCyanobacteria
Archeo-cell typeArcheo-cell type Pseudomurein rather than peptidoglycanPseudomurein rather than peptidoglycan Organisms belong to the ArcheobacterOrganisms belong to the Archeobacter
A prokaryotic cellA prokaryotic cell
E. coliE. coli
Eukaryotic CellsEukaryotic Cells
Have a nucleus and Have a nucleus and other organellesother organelles
Eukaryotic organismsEukaryotic organisms ProtistansProtistans Fungi Fungi PlantsPlants AnimalsAnimals
Overview of a plant cellOverview of a plant cell
Overview of an animal cellOverview of an animal cell
contains most of the genes in a contains most of the genes in a eukaryotic cell.eukaryotic cell. Some genes are located in mitochondria Some genes are located in mitochondria
and chloroplasts.and chloroplasts. The nucleus averages about 5 microns The nucleus averages about 5 microns
in diameter.in diameter. The nucleus is separated from the The nucleus is separated from the
cytoplasm by a double membrane.cytoplasm by a double membrane. These are separated by 20-40 nm.These are separated by 20-40 nm.
Where the double membranes are Where the double membranes are fused, a pore allows large fused, a pore allows large macromolecules and particles to pass macromolecules and particles to pass through.through.
The nucleus contains a The nucleus contains a eukaryotic cell’s genetic libraryeukaryotic cell’s genetic library
NucleolusNucleolus
In the nucleus is a region of densely stained In the nucleus is a region of densely stained fibers and granules adjoining chromatin, the fibers and granules adjoining chromatin, the nucleolusnucleolus. . ribosomal RNA (rRNA) is synthesized ribosomal RNA (rRNA) is synthesized assembled with proteins from the assembled with proteins from the
cytoplasm to form ribosomal subunits.cytoplasm to form ribosomal subunits. The subunits pass from the nuclear pores The subunits pass from the nuclear pores
to the cytoplasm where they combine to to the cytoplasm where they combine to form ribosomes.form ribosomes.
The nucleus and its envelope The nucleus and its envelope
Keeps the DNA molecules of Keeps the DNA molecules of eukaryotic cells separated from eukaryotic cells separated from metabolic machinery of cytoplasmmetabolic machinery of cytoplasm
Makes it easier to organize DNA and Makes it easier to organize DNA and to copy it before parent cells divide to copy it before parent cells divide into daughter cells into daughter cells
Functions of NucleusFunctions of Nucleus
The nucleus and its envelope The nucleus and its envelope
Group of related organelles in which lipids Group of related organelles in which lipids are assembled and new polypeptide are assembled and new polypeptide chains are modifiedchains are modified
Products are sorted and shipped to various Products are sorted and shipped to various destinationsdestinations
Components of the cytomembrane systemComponents of the cytomembrane system Endoplasmic reticulumEndoplasmic reticulum Golgi apparatusGolgi apparatus vesiclesvesicles
Cytomembrane SystemCytomembrane System
Endoplasmic ReticulumEndoplasmic Reticulum
In animal cells, continuous with In animal cells, continuous with
nuclear membranenuclear membrane
Extends throughout cytoplasmExtends throughout cytoplasm
Two regions - rough and smoothTwo regions - rough and smooth
Rough ERRough ER
Arranged into flattened sacsArranged into flattened sacs Ribosomes on surface give it a rough Ribosomes on surface give it a rough
appearanceappearance Some polypeptide chains enter rough Some polypeptide chains enter rough
ER and are modifiedER and are modified Cells that specialize in secreting Cells that specialize in secreting
proteins have lots of rough ERproteins have lots of rough ER
Smooth ERSmooth ER
A series of interconnected tubules A series of interconnected tubules No ribosomes on surfaceNo ribosomes on surface Lipids assembled inside tubulesLipids assembled inside tubules Smooth ER of liver inactivates Smooth ER of liver inactivates
wastes, drugswastes, drugs Sarcoplasmic reticulum of muscle is Sarcoplasmic reticulum of muscle is
a specialized forma specialized form
Endoplasmic reticulum (ER)Endoplasmic reticulum (ER)
Golgi BodiesGolgi Bodies
Put finishing touches on proteins and Put finishing touches on proteins and lipids that arrive from ERlipids that arrive from ER
Package finished material for Package finished material for shipment to final destinationsshipment to final destinations
Material arrives and leaves in vesiclesMaterial arrives and leaves in vesicles
The Golgi apparatusThe Golgi apparatus
VesiclesVesicles
Membranous sacs that Membranous sacs that
move through the move through the
cytoplasmcytoplasm
LysosomesLysosomes
PeroxisomesPeroxisomes
LysosomesLysosomes
Review: relationships among organelles of the Review: relationships among organelles of the endomembrane systemendomembrane system
The mitochondrion, site of cellular The mitochondrion, site of cellular respirationrespiration
PlastidsPlastids
Central VacuoleCentral Vacuole
Specialized Plant Specialized Plant OrganellesOrganelles
The chloroplast, site of The chloroplast, site of photosynthesisphotosynthesis
Other PlastidsOther Plastids
Chromoplasts Chromoplasts No chlorophyllNo chlorophyll Abundance of carotenoidsAbundance of carotenoids Color fruits and flowers red-to-yellowColor fruits and flowers red-to-yellow
AmyloplastsAmyloplasts No pigmentsNo pigments Store starchStore starch
The plant cell vacuole The plant cell vacuole
Organelles with no Organelles with no MembranesMembranes
RibosomesRibosomes Function in protein synthesisFunction in protein synthesis
CytoskeletonCytoskeleton Function in maintenance of cell shape Function in maintenance of cell shape
and positioning of organellesand positioning of organelles Centrioles (animals only)Centrioles (animals only)
Function during cell divisionFunction during cell division
Figure 7.10 RibosomesFigure 7.10 Ribosomes
Ribosomes contain rRNA and protein.Ribosomes contain rRNA and protein. A ribosome is composed of two subunits that A ribosome is composed of two subunits that
combine to carry out protein synthesis.combine to carry out protein synthesis.
Ribosomes build a cell’s Ribosomes build a cell’s proteinsproteins
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 7.10
Present in all eukaryotic cellsPresent in all eukaryotic cells
Basis for cell shape and internal Basis for cell shape and internal organizationorganization
Allows organelle movement within Allows organelle movement within cells and, in some cases, cell motilitycells and, in some cases, cell motility
CytoskeletonCytoskeleton
Cytoskeletal ElementsCytoskeletal Elements
microtubule
microfilament
intermediatefilament
MicrotubulesMicrotubules
Largest elementsLargest elements
Composed of the protein tubulinComposed of the protein tubulin
Arise from microtubule organizing Arise from microtubule organizing
centers (MTOCs)centers (MTOCs)
Polar and dynamicPolar and dynamic
Involved in shape, motility, cell Involved in shape, motility, cell
divisiondivision
MicrofilamentsMicrofilaments
Thinnest cytoskeletal elementsThinnest cytoskeletal elements
Composed of the protein actin Composed of the protein actin
Polar and dynamicPolar and dynamic
Take part in movement, formation Take part in movement, formation
and maintenance of cell shapeand maintenance of cell shape
Intermediate FilamentsIntermediate Filaments
Present only in animal cells of certain Present only in animal cells of certain tissuestissues
Most stable cytoskeletal elementsMost stable cytoskeletal elements Six known groupsSix known groups Different cell types usually have 1-2 Different cell types usually have 1-2
different kindsdifferent kinds
Cell-to-Cell JunctionsCell-to-Cell Junctions
Plants Plants Plasmodesmata Plasmodesmata
Animals Animals Tight junctionsTight junctions Adhering Adhering
junctionsjunctions Gap junctionsGap junctions
plasmodesma
Animal Cell JunctionsAnimal Cell Junctions
tightjunctions
adhering junction
gapjunction