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Development of the cell theory:
Hooke in 1663, observed cork
(plant): named the cell Schwann in 1800s states:
all animals are made of cells
Pasteurs work with bacteria ~ 1860 disprovedidea of spontaneous generation (living things
from nonliving)
Modern cell theory emerged by 1900
Chapter 4:
Cellular Form and Function
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Modern Cell Theory All organisms composed of cells and cell products.
A cell is the simplest structural and functional unit of life. Thereare no smaller subdivisions of a cell or organism that, in themselves,
are alive.
An organisms structure and all of its functions are ultimately due to
the activities of its cells. Cells come only from preexisting cells, not from nonliving
matter. All life, therefore, traces its ancestry to the same original
cells.
Because of this common ancestry, the cells of all species have manyfundamental similarities in their chemical composition and
metabolic mechanisms.
Cells carry genetic information in the form of DNA, which is
passed from the parent to the daughter cell.
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Methods and tools
MicroscopyCompound light microscope
Magn. = eyepiecex objective, eg. 10x times 4x = 40x
Mostly for non-living specimen (dyes used)
Phase contrast microscope Allows visualization of living cells
Electron microscope Uses a beam of e-, resolution is thus not limited to light wavelength
Order of pm
Autoradiography Label cells with radioactive atoms or molecules and follow their
location
Centrifugation Sedimentation coefficient:
Depends on mass and particles size (radius)
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Prokaryotes
bacteria, cyanobacteria (blue-green algae) and archaeaabsent nucleus, no mitochondria or chloroplasts, no ER and
Golgi
size of ribosomes similar to mitochondrial ribosomes ineukaryotes
circular DNA is held within irregular nucleoid
oxidative phosphorylation takes place directly on plasmamembrane
do have ribosomes (30,50,70) and cytoskeletons
contain plasmidssome may organize into cellular communities (biofilms)
asexual reproduction (binary fission or budding) andconjugation
have flagellum and cell walls (except gen. mycoplasma)
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Cell Shapes
thin, flat, angular contours
irregular angular shapes,
> 4 sides
round to oval
disc shaped
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Cell Shapes 2
squarish thick middle, tapered ends
taller than wide long, slender
Stellate
nerve cells have extensions,look starlike
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Epithelial Cell Surfaces
Epithelial cells line organ surfaces andcavities
Basal surface
cell rests on this lower surface
Lateral surface
the sides of the cell
Apical surface
exposed upper surface
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Cell Size
Human cell sizemost range from 10 - 15 m
egg cells (very large)100 m diameter, visible to
naked eyenerve cell over 1 meter, muscle cell up to 30 cm,
(too slender to be seen)
Limitations on cell size
as cell enlarges, volume increases faster than
surface area so the need for increased nutrients
and waste removal exceeds ability of membrane
surface to exchange
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Cell Surface Area and Volume
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Evolving Perspective on Cells
Early study with light microscope revealedsurface membrane, nucleus and cytoplasm
Electron microscopes have much higher resolution
and revealed much greater details, such as the cellultrastructure of the cytoplasm
fibers, passageways and compartments, and organelles
surrounded by cytosol (a clear gelatinous component
also called intracellular fluid)
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Cell Structure
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Cell Structure 2
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Defines cell boundaries Controls interactions with other cells
Controls passage of materials in and out of cell
Appears as pair of dark parallel lines around cell(viewed with the electron microscope)
intracellular face - side faces cytoplasm
extracellular face - side faces outwards
Structure described by fluid-mosaic theory
arrangement of mobile globular proteins embedded in
an oily film of phospholipids
Plasma Membrane
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Plasma Membrane Preview
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Membrane Lipids
Lipids constitute90 to 99% of the
plasma membrane
Glycolipids5% of the lipids, found
only on extracellularface, contribute to
glycocalyx
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Cholesterol20% of the lipids, affects membrane
fluidity (low conc.. more rigid, highconc.. more fluid)
Phospholipid bilayer75% of the lipids, with hydrophilic heads
(phosphate) on each side andhydrophobic tails in the center
motion of these molecules createsmembrane fluidity, an important qualitythat allows self repair
Membrane Lipids 2
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Membrane Proteins
Proteins constituteonly 1 to 10% of the plasma
membrane, but they are larger andaccount for half its weight
Integral (transmembrane) proteinspass through membrane, have
hydrophobic regions embedded inphospholipid bilayer and hydrophilicregions extending into intra- andextracellular fluids
most are glycoproteins, conjugatedwith oligosaccharides on theextracellularside of membrane
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Integral proteins (cont.)may cross the plasma
membrane once or multiple
times
Peripheral proteins
adhere to intracellular
surface of membrane
anchors integral proteins to
cytoskeleton
Membrane Proteins 2
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Membrane Protein Functions
Receptors Second messenger systems
Enzymes
Channel proteins
Carriers and pumps
Motor molecules
Cell-identity markers
Cell-adhesion molecules
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Protein Functions - Receptors
Cells communicate with chemicalsignals that cannot enter target
cells
Receptors bind these messengers(hormones, neurotransmitters)
Each receptor is usually specific
for one messenger
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Second Messenger System
A messenger (epinephrine)binds to a receptor 1
Receptor releases a Gprotein
2
G protein binds to anenzyme, adenylate cyclase,which converts ATP to
cAMP, the 2ndmessenger 3 cAMP activates a kinase 4
Kinases add Pi, activates or
inactivates other enzymes
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Enzymes in Plasma Membrane
Break down chemicalmessengers to stop their effects
Final stages of starch and
protein digestion in smallintestine
Involved in producing second
messengers (cAMP)
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Protein Functions - Channel Proteins
Formed by integral proteins
Channels are constantly open,
allow water and hydrophilic
solutes in and out
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Gates open to three type of stimulantsligand-regulated gates: bind to chemicalmessenger
voltage-regulated gates: potential changes
across plasma membranemechanically regulated gates:physicalstress such as stretch and pressure
Gates control passage of electrolytes so
are important in nerve signals andmuscle contraction
Protein Functions - Channel Proteins 2
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Protein Functions - Motor Molecules
A filamentous protein that arisesdeep in the cytoplasm and pulls
on membrane proteins causing
movement:within a cell (organelles)
of a cell (WBCs)
shape of cell (cell division,
phagocytosis)
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Protein Functions - Carriers
Integral proteins that bind to solutes andtransfer them across membrane
Carriers that consume ATP are called
pumps
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Protein Functions - Cell-identity Markers
Glycoproteins contribute tothe glycocalyx, a surface
coating that acts as a cells
identity tag
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Protein Functions - Cell-adhesion Molecules
Membrane proteins thatadhere cells together and
to extracellular material
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Glycocalyx
Surface of animal cellsCHO moieties of membrane glycoproteins
and glycolipids that retains a film of water
Functionsimmune response to infection and cancer
basis of tissue transplant compatibility
cellular uptake of water, dissolved solutesassists in cell adhesion, fertilization and
embryonic development
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Structure extensions of plasma membrane (1-2m) that
increase surface area for absorptive cells (by 15-
40x in intestine, kidney)
Brush border
on some cells, they are very dense and appear as
a fringe on apical cell surface
Milking actionprotein filaments (actin) attach from the tip of
microvillus to its base, anchors to a protein mesh
in the cytoplasm called the terminal web and can
shorten pushing absorbed contents into cell
Microvilli
Cross Section of a Microvillus reveals
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Cross Section of a Microvillus reveals
actin filaments
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Cilia
Hairlike processes 7-10m long, 50-200 on cell surfacemove mucus, egg cells note that microvilli, unlike cilia, are extensions of the plasma
membrane
Covered by saline layer created by chloride pumps
Cilia beat in waves, sequential power strokes followed byrecovery strokes
Cross Section of a Cilium reveals
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Cross Section of a Cilium reveals
microtubules
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Cilia 2
Axonemehas a 9+2 structure of microtubules2 central microtubules stop at cell surface
9 pairs of peripheral microtubules continue into cell as
abasal bodythat acts as an anchor
dynein (motor protein) arms on one pair of peripheral
microtubules crawls up adjacent pair bending cilia
Sensory cells
some cilia lose motility and are involved in vision,
smell, hearing and balance
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Cilium At Cell Surface
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Flagella
Long whiplike structure that has an axonemeidentical to that of a cilium
the only functional flagellum in humans is the tail
of the sperm
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Nucleus
Largest organelle Nuclear envelope surrounds nucleus with a double
membrane punctures with nuclear pores
Contains DNA, the genetic program for a cellsstructure and function
nucleolus = a subsection within the nucleus, where
rRNA is synthesized
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Cell Structure
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Rough ERextensive sheets of parallel unit membranes with cisternae
between them and covered with ribosomes, continuous withnuclear envelope
protein synthesis, in particular secretory proteins,production of cell membranes
protein folding environment
Ca2+ homeostasis
Smooth ER lack ribosomes, cisternae more tubular and branch more
extensively, continuous with rough ER
function in lipid synthesis, detoxification, Ca2+storage and
signaling
Endoplasmic Reticulum
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Endoplasmic Reticulum Diagram
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Ribosomes
Small dark granules of protein and RNA free incytosol or on surface of rough ER
Interpret the genetic code and synthesize
polypeptides
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Golgi Complex
Synthesizes CHOs, processes proteins from RERand packages them into golgi vesicles
Golgi vesiclesirregular sacs near golgi complex that bud off cisternae
some become lysosomes, some fuse with plasmamembrane and some become secretory vesicles
Secretory vesiclesstore a cell product
for later release Note: in plants
vesicles are larger and
are called vacuoles
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Lysosomes
Package of enzymes in a single unit membrane,variable in shape
garbage brought by endosomes
Functions
intracellular digestion - hydrolyze proteins, nucleic acids,complex carbohydrates, phospholipids and other substrates
hydrolytic enzymes work at pH = 5
autophagy - the digestion of worn out organelles andmitochondrion
autolysis/apoptosis - programmed cell death
glucose mobilization - lysosomes in liver cells break downglycogen
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Microbodies
Peroxisome Appear similar to lysosomes, lighter in color
Abundant in liver and kidney
Function
neutralize free radicalsproduce H2O2in process of alcohol detoxification in the
liver, and in killing bacteria
break down excess H2O2 with the enzyme catalase
break down fatty acids into acetyl groupsGlyosome (in plants)
important during germination
allows plants to break down fats into carbohydrates for
energy
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Mitochondrion
Double unit membrane Inner membrane contains folds called cristae
ATP synthesized by enzymes on cristae from energy extractedfrom organic compounds
Space between cristae called the matrix contains ribosomes and small, circular DNA (mitochondrial
DNA) are semiautonomous: mDNA is replicated independently,
encodes for many proteins others proteins (e.g. ribosomes) are encoded by nuclear DNA
Reproduce independentlyof cell and live for 10 days
capable of triggering apoptosis in plants:
chloroplasts contain their own DNA
carry out photosynthesis
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Mitochondrion, Electron Micrograph
ll ll
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Cell wall
present in all procaryotes and some eukaryotes:fungi, made of chitin
plants composed of cellulose
protection, structural support notpresent in animals
C i l
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Centrioles
not present in plants Short cylindrical assembly of microtubules,
arranged in nine groups of three microtubules each
Two centrioles, perpendicular to each other, lienear the nucleus in an area called the centrosome
these play a role in cell division
Other single centrioles migrate to plasmamembrane formingbasal bodiesof cilia or flagella
two microtubules of each triplet elongate to form the
nine pairs of peripheral microtubules of the axoneme
P di l C i l Di
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Perpendicular Centrioles Diagram
C k l
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Cytoskeleton
Microfilaments (actin filaments)made of protein actin, form network on cytoplasmic
side of plasma membrane called the membrane skeleton
supports phospholipids of plasma membrane, supports
microvilli and produces cell movement,
with myosin causes muscle contraction
Intermediate fibers
in junctions that hold epithelial cells together and resist
stresses on a cell
Microtubules
Mi b l
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Microtubules
Hollow cylinder of 13 parallel strands calledprotofilaments
(a long chain of globular protein units called tubulin)
Hold organelles in place and maintain cell shape Form tracks to guide organelles and molecules to
specific destinations in a cell
Form axonemes of cilia and flagella, centrioles,basal bodies and mitotic spindle
Not all are permanent structures and can be
disassembled and reassembled where needed
Mi b l Di
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Microtubule Diagram
C t k l t Di
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Cytoskeleton Diagram
I l i
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Inclusions
Highly variable appearance, no unit membrane Stored cellular products
glycogen granules,pigments and fat droplets
in plants: water vacuoles Foreign bodies
dust particles, viruses and intracellular bacteria
M b T S l i P bili
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Membrane Transport: Selective Permeability
Plasma membrane allows passage of some things
between cytoplasm and ECF but not others
Passive transport requires no ATP, movement of
particles across selectively permeable membrane,
down concentration gradient filtration
simple diffusion
facilitated diffusion through channels Active transport requires ATP, transports particles
up concentration gradient
carrier mediated (active transport) and bulk transport
M b T t Filt ti
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Membrane Transport: Filtration
Movement of particles through a selectivelypermeable membrane by hydrostatic pressure
Hydrostatic pressure - the force exerted on the
membrane by water
In capillaries, blood pressure forces water, salts,
nutrients and solutes into tissue fluid, while larger
particles like blood cells and protein are held back
Si l Diff i
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Simple Diffusion
Simple diffusion is the movement of particles as aresult of their constant, random motion
Net diffusion is the movement of particles from an
area of high concentration to an area of lowconcentration (down or with the concentration
gradient)
Diff i R t
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Diffusion Rates
Factors that affect rate of diffusion through amembrane
Temperature - temp., motion of particles
Molecular weight - larger molecules move slower
Steepness of conc.gradient - difference, rate
Membrane surface area - area, rate
Membrane permeability - permeability, rate
O i
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Osmosis
Net diffusion of waterthrough a selectively
permeable membrane from
an area of more water, sideB (less dissolved solute) to
an area of less water, side
A (more dissolved solute)
O ti P
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Osmotic Pressure
Osmosis opposed byfiltration of water
back across
membrane due to hydrostatic pressure
Amount of
hydrostatic pressure
required to stop
osmosis is called
osmotic pressure
O l it
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Osmolarity
One osmole is 1 mole of dissolved particles1M NaCl contains 1 mole Na+ions and 1 mole Cl-
ions/L, both affect osmosis, thus 1M NaCl = 2 osm/L
Osmolarity = # osmoles/liter solution
Tonicit
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Tonicity
Tonicity - ability of a solution to affect fluidvolume and pressure within a celldepends on concentration and permeability of solute
Hypotonic solution
has low concentration of nonpermeating solutes (highwater concentration)
cells in this solution would absorb water, swell and mayburst (lyse)
Hypertonic solutionhas high concentration of nonpermeating solutes (low
water concentration)cells in this solution would lose water +shrivel (crenate)
Isotonic: no net movement
M b T C i M di d T
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Membrane Transport: Carrier Mediated Transport
Proteins in cell membrane carry solutes through it Specificity
solute binds to a receptor site on carrier protein that is
specific for that solute Two types of carrier mediated transport are
facilitated diffusion and active transport
Exhibits saturation (see next slide)
Carrier Saturation
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Carrier Saturation
As concentration of solute , rate of transport upto the point when all carriers are occupied and rate
of transport levels off at the transport maximum
Membrane Transport: Facilitated Diffusion
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Membrane Transport: Facilitated Diffusion
Passivetransport of solute downits concentrationgradient, across membrane, with aid of a carrier
Solute binds to carrier, carrier changes shape andreleases solute on other side of membrane
Active Transport
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Active Transport
Activetransport of solute upits concentrationgradient, across membrane, carrier requires ATP
Carrier binds to ligand ATP phosphorylates carrier
Carrier changes conformation
Carrier releases ligand on other side
Prominent example is the sodium-potassium pump
Sodium Potassium Pump
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Sodium-Potassium Pump
3Na+
bind to receptor, carrier phosphorylated,changes conformation, releases Na+in ECF, binds
2K+, releases Pi, resumes conformation, releases K+
Na+ = naverx,
3 signs
K+ = 2 signs
Functions of Sodium Potassium Pump
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Functions of Sodium-Potassium Pump
Regulation of cell volumecell swelling stimulates the Na+-K+pump:
ion concentration, osmolarity and cell swelling
Heat production
Maintenance of a membrane potential
Na+-K+pump keeps inside of membrane negative,
outside of membrane positive
Secondary active transport
transport of solute particles by carrier that does not
need ATP, but depends on the concentration gradient
provided by active transport pumps ...
Secondary Active Transport
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Secondary Active Transport
Transport of glucose byfacilitated diffusion, along with
Na+by SGLT carrier (no ATP),
depends on Na+
-
K+
pump (usesATP)
Cotransport
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Cotransport
When carrier transports 2 different solutessimultaneously, or within one transport cycle
Symport - a carrier that transports both solutes in
the same direction Antiport - a carrier that transports solutes in
opposite directions
Bulk Transport
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Bulk Transport
Transport of large particles and fluid dropletsthrough membrane, using vacuoles or vesicles of
plasma membrane, uses a lot of ATP
Endocytosis - bulk transport intocell Exocytosis - bulk transport out of cell
Endocytosis has three forms
phagocytosis- engulfing large particles by pseudopodsfluid phase pinocytosis
receptor mediated endocytosis
Phagocytosis
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Phagocytosis
Fluid phase Pinocytosis
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Fluid-phase Pinocytosis
Cell takes in droplets of ECF (along with dissolvedor broken down particles)
Plasma membrane dimples, then pinches off as
pinocytotic vesicle Occurs in all human cells
Receptor Mediated Endocytosis
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Receptor Mediated Endocytosis
Receptors on membrane bind to specific moleculesin ECF, cluster together, then sink in, become
coated with a peripheral protein, clathrin, and
pinch off into cell as clathrin-coated vesicle
This occurs in the uptake of LDLs by endothelium
of blood vessels
Transcytosis uses this process to move a substance
across a cell
insulin absorbed into endothelial cell from blood by
RME, then transported out into tissues
Receptor Mediated Endocytosis
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Receptor Mediated Endocytosis
Receptor Mediated Endocytosis EM
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Receptor Mediated Endocytosis EM
Exocytosis
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Exocytosis
Eliminating or secreting material from cell andreplacement of plasma membrane
Exocytosis EM
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Exocytosis EM
Viruses are not living organisms
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Viruses are not living organisms
cells are 1-10 um viruses are about two orders of magnitude smaller
main features:
protein coat = capsidDNA or RNA, single or double stranded
obligate intracellulare parasites
bacteriophages target bacteria