A Tour of the Cell Friday Sept 16, 2005 BCOR 011 Lecture 8
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Transcript of A Tour of the Cell Friday Sept 16, 2005 BCOR 011 Lecture 8
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A Tour of the CellFriday Sept 16, 2005
BCOR 011
Lecture 8
10 µm
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Common features of all cells
Plasma Membrane – defines inside from outside
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Plasma membrane– Functions as a selective barrier– Specific portals for selective transport of
materials in and out of cell
Carbohydrate side chain
Figure 6.8 A, B
Outside of cell
Inside of cell
Hydrophilicregion
Hydrophobicregion
Hydrophilicregion
(b) Structure of the plasma membrane
Phospholipid ProteinsTEM of a plasmamembrane. Theplasma membrane,here in a red bloodcell, appears as apair of dark bandsseparated by alight band.
(a)
0.1 µm
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Common features of all cells
Plasma Membrane – defines inside from outside
DNA “chromosomes” - Genetic material – hereditary instructions
Ribosomes – “factories” to synthesize proteins
Cytosol- Semifluid “inside” of the cell
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– Carry out protein synthesis
ER
Cytosol
Free ribosomes
Membrane Bound ribosomes
Largesubunit
Smallsubunit
TEM showing ER and ribosomes
Diagram of a ribosome
0.5 µm
Figure 6.11
Ribosome – RNA & Protein Complex
ProteinsTo be exported
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Two Broad Two Broad Classes of CellsClasses of Cells
ProProkaryoteskaryotes EuEukaryoteskaryotesPro = before Eu = true
karyon = nucleus
DO NOT HAVEA NUCLEUS
NO internal membranes
HAVEA NUCLEUS
membrane-bound organelles
bacteria, cyanobacteria archaebacteria Plants, Animals,
Fungi, protists
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Bacterial Cell(Prokaryotic)
Nointernal
membranes
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(b) A thin section through the bacterium Bacillus coagulans (TEM)
Pili: attachment structures onthe surface of some prokaryotes
Nucleoid: region where thecell’s DNA is located (notenclosed by a membrane)
Ribosomes: organelles thatsynthesize proteins
Plasma membrane: membraneenclosing the cytoplasm
Cell wall: rigid structure outsidethe plasma membrane
Capsule: jelly-like outer coatingof many prokaryotes
Flagella: locomotionorganelles ofsome bacteria
(a) A typical rod-shaped bacterium
0.5 µmBacterial
chromosome
Figure 6.6 A, B
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Bacterial cell (Prokaryotic
On the samesize scale:
Animal Cell (Eukaryotic)
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Relative SizesRelative Sizes
“Typical” ~ 1-2 M Bacterium
“Typical” ~ 5 to 20 M diameter Animal Cell
“Typical” ~ 5 to 50 M diameter Plant Cell
M = micrometer or micron =10-6 meter
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11Animal Cell (Eukaryotic)
Internalmembrane-bound
organelles
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Why Internal Membranes?Why Internal Membranes?
CompartmentalizationCompartmentalization (Division of Labor)(Division of Labor)
I’m I’m sleepingsleeping
I’m watching
TV
I’m cookingdinner
I’m playing
mysax
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Rough ER Smooth ER
Centrosome
CYTOSKELETON
Microfilaments
Microtubules
Peroxisome
Lysosome
Golgi apparatus
Ribosomes
In animal cells but not plant cells:LysosomesCentriolesFlagella (in some plant sperm)
NUCLEUS
Intermediate filaments
ENDOPLASMIC RETICULUM (ER)
Mitochondrion
Plasma membrane
Figure 6.9
endoplasmic reticulum
nucleus
mitochondrionlysosome
Golgi apparatus
cytosol
ribosomes
Animal CellAnimal Cell
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Nucleus: Information storagedouble membrane
“Nuclear Envelope”
nucleolus
DNA housed, copied, read
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The NUCLEUSThe NUCLEUS
DoubleDouble membranemembrane
DNADNARNARNAproteinproteinlipid (membrane)lipid (membrane)
NuclearNuclearporespores
NucleolusNucleolus
EuchromatinEuchromatinHeterochromatinHeterochromatin
NuclearNuclearLaminaLamina
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nuclear envelope
Figure 6.10
Nucleus
NucleusNucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pores
Rough ER
Porecomplex
Surface of nuclear envelope.
Pore complexes (TEM). Nuclear lamina (TEM).
Close-up of nuclearenvelope
Ribosome
1 µm
1 µm
0.25 µm
Nuclear lamina
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NucleolusNucleolusSite of Site of Ribosome Ribosome Subunit Subunit Assembly Assembly
Note:Note:No membraneNo membrane
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Euchromatin regionEuchromatin regionSite of Site of mRNAmRNA synthesis synthesis
ExpressionExpressionOf Of InformationalInformationalRNAsRNAs
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Endoplasmic reticulum (ER)
1 m
Rough ER Smooth ER
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Endoplasmic reticulum (ER)[Reticulum – network] Continuous network of flattened sacs tubules, vesicles, throughout eukaryotic cytoplasm
Smooth ER
– Synthesizes membrane lipids
– Synthesizes steroids– Stores calcium– Detoxifies poison
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Example: detoxification in smooth ER
Benzo(a)pyrene charred meat, cigarette smoke
Oxidations –more soluble
Some metabolites are more toxic
Chronic use ofbarbiturates, alcohol-SER proliferation, resistance
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Rough ER – ribosomes attached to cytoplasmic face
• Large flattened sheets• Synthesizes secreted proteins, membrane proteins exported
• Protein modification; initial steps of carbohydrate addition
- glycoproteins
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Rough ERRough ER
Slips proteins Slips proteins Through ER Through ER membranemembrane
GlycosylationGlycosylationAdds Adds oligosaccharidesoligosaccharidesadded as protein being made
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24 Plasma membrane expandsby fusion of vesicles; proteinsare secreted from cell
Transport vesicle carriesproteins to plasma membrane for secretion
Lysosome availablefor fusion with anothervesicle for digestion
4 5 6
Nuclear envelope isconnected to rough ER, which is also continuous
with smooth ER
Nucleus
Rough ER
Smooth ERcis Golgi
trans Golgi
Membranes and proteinsproduced by the ER flow in
the form of transport vesiclesto the Golgi
Golgi pinches off transport Vesicles and other vesicles
that give rise to lysosomes and Vacuoles
1
3
2
Plasmamembrane
Figure 6.16
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Golgi Apparatus: protein secretion Processing, packaging and sorting center
Cis GolgiClose To RER
Trans GolgiFar sideAway From RER
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Functions of the Golgi ApparatusFunctions of the Golgi Apparatus
cis Golgi - processing center“near”
trans Golgi - sorting centersorting center“far”
Present wrapping
Service – modifies proteins
Fed Ex CentralFed Ex CentralSorts for delivery
To specific compartments
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Functions of the Golgi ApparatusFunctions of the Golgi Apparatus
•Trimming of Oligosaccharide side chains onglycosylated proteins
•Addition of new Oligosaccharide residues toexisting side chains of glycosylated proteins
•Phosphorylation of specific sugar residuesPhosphorylation of specific sugar residues on oligosaccharide side chains of glycosylated proteins
““molecular zip codes”molecular zip codes”
•“Maturation” Cleavages of specific proteinse.g., insulin
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Molecular tags route proteins to proper destination
P added in cis Golgi
Proteins with M-6-P tag bind receptorin trans Golgi
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Lysosomes: “Recycling Center”
sacs of digestive enzymes
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(a) Phagocytosis: lysosome digesting food
1 µm
Lysosome containsactive hydrolyticenzymes
Food vacuole fuses with lysosome
Hydrolyticenzymes digestfood particles
Digestion
Food vacuole
Plasma membrane
Lysosome
Digestiveenzymes
Lysosome
Nucleus
EndocytosisAnd
Phagocytosis
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EXTRACELLULARFLUID
PseudopodiumCYTOPLASM
“Food” or other particle
Foodvacuole
1 µm
Pseudopodiumof amoeba
Bacterium
Food vacuole
An amoeba engulfing a bacterium viaphagocytosis (TEM).
PINOCYTOSIS
Pinocytosis vesiclesforming (arrows) ina cell lining a smallblood vessel (TEM).
0.5 µm
In pinocytosis, the cell “gulps” droplets of extracellular fluid into tinyvesicles. It is not the fluiditself that is needed by the cell, but the molecules dissolved in the droplet. Because any and all included solutes are taken into the cell, pinocytosisis nonspecific in the substances it transports.
Plasmamembrane
Vesicle
In phagocytosis, a cellengulfs a particle by Wrapping pseudopodia around it and packaging it within a membrane-enclosed sac large enough to be classified as a vacuole. The particle is digested after the vacuole fuses with a lysosome containing hydrolytic enzymes.
Figure 7.20
PHAGOCYTOSIS
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320.25 µm
RECEPTOR-MEDIATED ENDOCYTOSIS
Receptor
Ligand
Coat protein
Coatedpit
Coatedvesicle
A coated pitand a coatedvesicle formedduringreceptor-mediatedendocytosis(TEMs).
Plasmamembrane
Coatprotein
Receptor-mediated endocytosis enables the cell to acquire bulk quantities of specific substances, even though those substances may not be very concentrated in the extracellular fluid. Embedded in the membrane are proteins with specific receptor sites exposed to the extracellular fluid. The receptor proteins are usually already clustered in regions of the membrane called coated pits, which are lined on their cytoplasmic side by a fuzzy layer of coat proteins. Extracellular substances (ligands) bind to these receptors. When binding occurs, the coated pit forms a vesicle containing the ligand molecules. Notice that there are relatively more bound molecules (purple) inside the vesicle, other molecules (green) are also present. After this ingested material is liberated from the vesicle, the receptors are recycled to the plasma membrane by the same vesicle.
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• Autophagy
Figure 6.14 B
(b) Autophagy: lysosome breaking down damaged organelle
Lysosome containingtwo damaged organelles 1 µ m
Mitochondrionfragment
Peroxisomefragment
Lysosome fuses withvesicle containingdamaged organelle
Hydrolytic enzymesdigest organellecomponents
Vesicle containingdamaged mitochondrion
Digestion
Lysosome
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Vesicles move thru the endomembrane system
exocytosis
endocytosis
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Mitochondria: Powerhouses of the cell
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Mitochondria Mitochondria singular = singular = mitochondrionmitochondrion
•powerhouse of the animal cell
produces ~ 90% of ATP•Carries out oxidative reactions
•Believed Derived from prokaryotic ancestor- DNA
- ribosomes- double membrane – inner and
outer *define two functional spaces
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Mitochondria are enclosed by two membranes– A smooth outer membrane– An inner membrane folded into cristae
Mitochondrion
Intermembrane space
Outermembrane
Freeribosomesin the mitochondrialmatrix
MitochondrialDNA
Innermembrane
Cristae
Matrix100 µmFigure 6.17
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Cell – organelles = CytosolGelImportant chemical reactionscytoskeleton - eukaryotes
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• The cytoskeleton– Is a network of fibers extending
throughout the cytoplasm– Structural Support– Movement of Materials and Organelles
Figure 6.20
Microtubule
0.25 µm MicrofilamentsFigure 6.20
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There are three types of fibers
that make up the cytoskeleton
Table 6.1
MicrotubulesMicrofilamentsIntermediateFilaments
Tubulin25 M dia
Actin7 M dia
various8-15 M dia
Cell shapeOrganelle movtChromosome separationFlagellar movt
Cell shapeCell cleavageCytoplasmic streaming Muscle contract
Nuclear laminaTension bearing elementsAnchors
Motors:DyneinKinesis
Motors:Myosin
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– Movement of Vesicles along Microtubules
VesicleATP
Receptor formotor protein
Motor protein(ATP powered)
Microtubuleof cytoskeleton
(a) Motor proteins that attach to receptors on organelles can “walk”the organelles along microtubules or, in some cases, microfilaments.
Microtubule Vesicles 0.25 µm
(b) Vesicles containing neurotransmitters migrate to the tips of nerve cell axons via the mechanism in (a). In this SEM of a squid giant axon, two vesicles can be seen moving along a microtubule. (A separate part of the experiment provided the evidence that they were in fact moving.)Figure 6.21 A, B
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Motor MAPs transport vesicles
MTOC
Dyneininbound
outboundkinesin
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– Contains a pair of centrioles
Centrosome
Microtubule
Centrioles
0.25 µm
Longitudinal sectionof one centriole
Microtubules Cross sectionof the other centrioleFigure 6.22
“microtubule-organizing center”
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• The ECM Is made up of glycoproteins
Collagen
Fibronectin
Plasmamembrane
EXTRACELLULAR FLUID
Micro-filaments
CYTOPLASM
Integrins
Polysaccharidemolecule
Carbo-hydrates
Proteoglycanmolecule
Coreprotein
Integrin
Figure 6.29
A proteoglycan complex
• Animal cells– Lack cell walls– Are covered by an elaborate matrix, the ECM
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• Functions of the ECM include– Cell-Cell adhesion– Cell-Cell recognition– Regulation of cellular processes
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plant cellplant cell
CYTOSKELETON
Ribosomes (small brown dots)
Central vacuole/Tonoplast
Microfilaments
Intermediate filaments
Microtubules
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
NUCLEUS
Chloroplast
PlasmodesmataWall of adjacent cell
Cell wall
Golgi apparatus
PeroxisomePlasma membrane
Mitochondrion
Figure 6.9
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Plant Central vacuoles - Tonoplasts– Are found in plant cells– Hold reserves of important organic
compounds and water– Regulates Turgor
Central vacuole
Cytosol
Tonoplast
Centralvacuole
Nucleus
Cell wall
Chloroplast
5 µm
Figure 6.15
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Chloroplast
ChloroplastDNA
Ribosomes
Stroma
Inner and outermembranes
Thylakoid
1 µm
Granum
Figure 6.18
In plant cells, chloroplasts capture energy from the sun
Photosynthesis
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ChloroplastsChloroplasts
-Contain DNA-Contain bacterial-like ribosomes-Believed derived from prokaryotic ancestor
cyanobacterium = blue-green alga
-Double membrane organelledefines three functional spaces
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StromaThylakoid
Space
Thylakoid Membrane
Intermembrane Space(transports things in and out of the chloroplast, but not central
to photosynthesis itself
Inner ChlorplastInner ChlorplastMembraneMembrane
OuterChlorplastMembrane
3 Central Players
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Cell Walls of Plants
• The cell wall– Is an extracellular structure of plant
cells that distinguishes them from animal cells
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• Plant cell walls– Are made of cellulose fibers embedded in
other polysaccharides and protein– May have multiple layers Central
vacuoleof cell
Plasmamembrane
Secondarycell wall
Primarycell wall
Middlelamella
1 µm
Centralvacuoleof cell
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
PlasmodesmataFigure 6.28
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• Plasmodesmata– Are channels that perforate plant cell walls
Interiorof cell
Interiorof cell
0.5 µm Plasmodesmata Plasma membranes
Cell walls
Figure 6.30
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Summary
Features of all cells
Features of Prokaryotes
Organelles of Animal Cells
Organelles of Plant Cells