Chapter 3
Lecture Outline
3-1
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cellular Form and Function
•
•
•
•
Concepts of cellular structure
Cell surface
Membrane transport
Cytoplasm
3-2
Development of the Cell Theory
• cytology – scientific study of cells
– began when Robert Hooke coined the word, ‘cellulae’ to
describe empty cell walls of cork
• Theodor Schwann concluded, about two centuries
later, that all animal tissues are made of cells
• Louis Pasteur established beyond any reasonable
doubt that ‘cells arise only from other cells’
– refuting the idea of spontaneous generation - living things
arise from nonliving matter
• Modern Cell Theory emerged
3-3
Modern Cell Theory
• All organisms composed of cells and cell products.
• Cell is the simplest structural and functional unit of life.
– cells are alive
• An organism’s structure and functions are due to the activities
of its cells.
• Cells come only from preexisting cells, not from nonliving
matter.
– therefore, all life traces its ancestry to the same original cells
• Cells of all species have many fundamental similarities in their
chemical composition and metabolic mechanisms.
3-4
Cell Shapes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Squamous
Cuboidal
Columnar
Polygonal
Stellate
Spheroid
Discoid
Fusiform (spindle-shaped)
Figure 3.1
Fibrous
3-5
Cell Shapes
• about 200 types of cells in the human body
• Squamous - thin and flat with nucleus creating bulge
• Polygonal - irregularly angular shapes with 4 or more
sides
• Stellate – starlike shape
• Cuboidal – squarish and about as tall as they are wide
• Columnar - taller than wide
• Spheroid to Ovoid – round to oval
• Discoid - disc-shaped
• Fusiform - thick in middle, tapered toward the ends
• Fibrous – threadlike shape
• Note: some of these shapes are cell appearance in
tissue sections, but not their 3 dimensional shape
3-6
Cell Size
• Human cell size
– most from 10 - 15 micrometers (µm) in diameter
• egg cells (very large)100 µm diameter
– barely visible to the naked eye
• nerve cell at 1 meter long
– longest human cell
– too slender to be seen with naked eye
• Limitations on cell size
– cell growth increases volume more than surface area
– surface area of a cell is proportional to the square of its
diameter
– volume of a cell is proportional to the cube of its
diameter
• nutrient absorption and waste removal utilize surface area
– if cell becomes too large, may rupture like overfilled
water balloon
3-7
Cell Surface Area and Volume
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
20 mm
Growth
20 mm
Figure 3.2
10 mm
10 mm
Large cell
Diameter
= 20 mm
Surface area = 20 mm  20 mm  6 = 2,400 mm2
Volume
= 20 mm  20 mm  20 mm = 8,000 mm3
Small cell
Diameter
= 10 mm
Surface area = 10 mm  10 mm  6 = 600 mm2
Volume
= 10 mm  10 mm  10 mm = 1,000 mm3
Effect of cell growth:
Diameter (D) increased by a factor of 2
Surface area increased by a factor of 4 (= D2)
Volume increased by a factor of 8 (= D3)
3-8
General Cell Structure
• Light microscope reveals plasma membrane, nucleus
and cytoplasm
– cytoplasm – fluid between the nucleus and surface
membrane
• Resolution (ability to reveal detail) of electron
microscopes reveals ultrastructure
– organelles, cytoskeleton and cytosol (ICF)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Plasma membrane
Nucleus
Figure 3.3
Nuclear envelope
Mitochondria
Golgi vesicle
Golgi complex
Ribosomes
3-9
2.0 µm
© K.G. Muri/Visuals Unlimited
Magnification versus
Resolution
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a) Light microscope (LM)
From Cell Ultrastructure by William A. Jensen and Roderick B. Park. © 1967 by
Wadsworth Publishing Co., Inc. Reprinted by permission of the publisher
Figure 3.4a
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(b) Transmission electron
microscope (TEM)
2.0 µm
From Cell Ultrastructure by William A. Jensen and Roderick B. Park. © 1967 by
Wadsworth Publishing Co., Inc. Reprinted by permission of the publisher
Figure 3.4b
• Magnification of 750x seen through both light
and transmission electron microscope
• Increased resolution reveals the finer details
3-10
Magnification versus
Resolution
3-11
Major Constituents of Cell
• plasma (cell) membrane
– surrounds cell
– made of proteins and lipids
– composition and function can vary from one
region of the cell to another
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Apical cell surface
Microfilaments
Microvillus
• cytoplasm
– organelles
– cytoskeleton
– cytosol (intracellular
fluid - ICF)
Terminal web
Desmosome
Secretory vesicle
undergoing
exocytosis
Fat droplet
Secretory vesicle
Intercellular
space
Centrosome
Centrioles
Golgi vesicles
Golgi complex
Lateral cell surface
Free ribosomes
Intermediate filament
Nucleus
Lysosome
Nucleolus
Microtubule
Nuclear
envelope
Rough endoplasmic
reticulum
Smooth endoplasmic
reticulum
Mitochondrion
Plasma membranes
Hemidesmosome
• extracellular fluid – ECF
– fluid outside of cell
Basal cell surface
Figure 3.5
Basement
membrane
3-12
Plasma Membrane
unit membrane – forms the border of the cell and many of its organelles
-appears as a pair of dark parallel lines around cell
(viewed with the electron microscope)
plasma membrane – unit membrane at cell surface
-defines cell boundaries
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Plasma membrane
of upper cell
-governs interactions with other cells
Intercellular space
Plasma membrane
of lower cell
-controls passage of materials in and out of cell
-intracellular face – side that faces cytoplasm
-extracellular face – side that faces outward
Nuclear envelope
Nucleus
(a)
100 nm
a: © Don Fawcett/Photo Researchers, Inc.
Figure 3.6a
3-13
Plasma Membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Extracellular fluid
Peripheral
protein
Glycolipid
Glycoprotein
Carbohydrate
chains
Extracellular
face of
membrane
Phospholipid
bilayer
Channel
Peripheral
protein
Cholesterol
Transmembrane
protein
Intracellular fluid
Proteins of
cytoskeleton
Intracellular
face of
membrane
Figure 3.6b
(b)
• Oily film of lipids with diverse proteins embedded
3-14
Membrane Lipids
• 98% of molecules in plasma membrane are lipids
• Phospholipids
–
–
–
–
–
–
75% of membrane lipids are phospholipids
amphiphilic molecules arranged in a bilayer
hydrophilic phosphate heads face water on each side of membrane
hydrophobic tails – directed toward the center, avoiding water
drift laterally from place to place
movement keeps membrane fluid
• Cholesterol
– 20% of the membrane lipids
– holds phospholipids still and can stiffen membrane
• Glycolipids
– 5% of the membrane lipids
– phospholipids with short carbohydrate chains on extracellular face
– contributes to glycocalyx – carbohydrate coating on the
3-15
cells surface
Membrane Proteins
• Membrane proteins
– 2% of the molecules in plasma membrane
– 50% of its weight
• Transmembrane proteins
– pass through membrane
– have hydrophilic regions in contact with cytoplasm and extracellular
fluid
– have hydrophobic regions that pass back and forth through the lipid of
the membrane
– most are glycoproteins
Transmembrane
– can drift about freely in phospholipid film
protein:
– some anchored to cytoskeleton
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Peripheral proteins
– adhere to one face of the membrane
– usually tethered to the cytoskeleton
Figure 3.7
3-16
Membrane Protein Functions
• receptors, second-messenger systems,
enzymes, ion channels, carriers, cell-identity
markers, cell-adhesion molecules
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chemical
messenger
Breakdown
products
Ions
(a) Receptor
A receptor that
binds to chemical
messengers such
as hormones sent
by other cells
(b) Enzyme
An enzyme that
breaks down
a chemical
messenger and
terminates its
effect
(c) Ion Channel
A channel protein
that is constantly
open and allows
ions to pass
into and out of
the cell
CAM of
another cell
(d) Gated ion channel
A gated channel
that opens and
closes to allow
ions through
only at certain
times
Figure 3.8
(e) Cell-identity marker
A glycoprotein
acting as a cellidentity marker
distinguishing the
body’s own cells
from foreign cells
(f) Cell-adhesion
molecule (CAM)
A cell-adhesion
molecule (CAM)
that binds one
cell to another
3-17
Membrane Receptors
• Cell communication via chemical signals
– receptors – surface proteins on plasma
membrane of target cell
– bind these chemicals (hormones,
neurotransmitters)
– receptor usually specific for one substrate
3-18
Second Messenger System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 A messenger such as epinephrine (red triangle)
binds to a receptor in the plasma membrane.
First
messenger
Receptor
G
Adenylate cyclase
G
Pi
2 The receptor releases
a G protein, which
then travels freely in
the cytoplasm and
can go on to step 3
or have various other
effects on the cell.
ATP
Pi
3 The G protein
binds to an enzyme,
adenylate cyclase, in
the plasma membrane.
Adenylate cyclase
cAMP
converts ATP to cyclic (second
AMP (cAMP), the
messenger)
second messenger.
4 cAMP
activates a
cytoplasmic
enzyme called
a kinase.
Inactive
kinase
Activated
kinase
Inactive
enzymes
Figure 3.9
Pi
5 Kinases add
phosphate groups (Pi)
to other cytoplasmic
enzymes. This activates
some enzymes and
deactivates others, leading
to varied metabolic effects
in the cell.
Activated
enzymes
Various metabolic effects
3-19
Second Messenger System
• Chemical first messenger (epinephrine) binds to a surface receptor
– triggers changes within the cell that produces a second messenger in the
cytoplasm
• Receptor activates G protein
– an intracellular peripheral protein
– guanosine triphosphate (GTP) an ATP like compound
• G protein relays signal to adenylate cyclase which converts ATP to
cAMP (2nd messenger)
• cAMP activates a kinase in the cytosol
• Kinases add phosphate groups to other cellular enzymes
– activates some enzymes, and inactivates others triggering a wide variety of
physiological changes in cells
• Up to 60% of modern drugs work by altering activity of G proteins.
3-20
Membrane Enzymes
• enzymes in plasma membrane carry out
final stages of starch and protein digestion
in small intestine
• help produce second messengers (cAMP)
• break down chemical messengers and
hormones whose job is done
– stops excessive stimulation
3-21
Ion Channels
• Transmembrane proteins with pores that
allow water and dissolved ions to pass through
membrane
– some constantly open
– some are gated-channels that open and close in
response to stimuli
• ligand (chemically)-regulated gates
• voltage-regulated gates
• mechanically regulated gates (stretch and pressure)
• play an important role in the timing of nerve
signals and muscle contraction
3-22
Membrane Carriers or Pumps
• Transmembrane proteins bind to glucose,
electrolytes, and other solutes
– transfer them across membrane
• Pumps consume ATP in the process
3-23
Cell-Identity Markers
• Glycoproteins contribute to the glycocalyx
– carbohydrate surface coating
– acts like a cell’s ‘identification tag’
• Enables our bodies to identify which cells
belong to it and which are foreign invaders
3-24
Cell-Adhesion Molecules
• Adhere cells to each other and to
extracellular material
• cells do not grow or survive normally
unless they are mechanically linked to the
extracellular material
3-25
Glycocalyx
• Unique fuzzy coat external to the plasma
membrane
– carbohydrate moieties of membrane glycoproteins and
glycolipids
– unique in everyone, but identical twins
• Functions (see Table 3.2)
–
–
–
–
protection
immunity to infection
defense against cancer
transplant compatibility
- cell adhesion
- fertilization
- embryonic development
3-26
Microvilli
• Extensions of membrane (1-2 mm)
– serves to increase cell’s surface area
– best developed in cells specialized in absorption
– gives 15 – 40 times more absorptive surface area
• on some cells they are very dense and appear as a
fringe – “brush border”
– milking action of actin
• actin filaments shorten microvilli
– pushing absorbed contents down into cell
3-27
Microvilli
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glycocalyx
Microvillus
Actin
microfilaments
(a)
Figure 3.10a
1.0 µm
(b)
a: © Ed Reschke; b: Biophoto Associates/Photo Researchers, Inc.
0.1 µm
Figure 3.10b
Actin microfilaments are found in center of each microvilli.
3-28
Structure of Cilia
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cilia
(a)
Custom Medical Stock Photo, Inc.
Figure 3.11a
10 m
3-29
Cilia
• Hairlike processes 7-10mm long
– single, nonmotile primary cilium found on nearly every cell
– “antenna’ for monitoring nearby conditions
– sensory in inner ear, retina, nasal cavity, and kidney
• Motile cilia – respiratory tract, uterine tubes, ventricles of the brain,
efferent ductules of testes
– beat in waves
– sweep substances across surface in same direction
– power strokes followed by recovery strokes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mucus
Saline
layer
Epithelial
cells
1
2
3
Power stroke
(a)
Figure 3.12a
(b)
4
5
6
7
Recovery stroke
Figure 3.12b
3-30
Cross Section of a Cilium
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Axoneme - core of cilia that is
the structural basis for ciliary
movement
Axoneme:
Peripheral microtubules
Central microtubules
Dynein arms
Shaft of
cilium
• has 9 + 2 structure of
microtubules
Basal
body
Plasma membrane
(b)
– 9 pairs form basal body inside the
cell membrane
Dynein
arm
Central
microtubule
• anchors cilium
Axoneme
Figure 3.11b,d
Peripheral
microtubules
(d)
– dynein arms “crawls” up adjacent
microtubule bending the cilia
Cilia
• uses energy from ATP
• Saline Layer
– chloride pumps pump Cl- into ECF
– Na+ and H2O follows
– cilia beat freely in saline layer
Microvilli
Dynein
arm
Central
microtubule
Peripheral
microtubules
(c)
0.15 µm
c: © Biophoto Associates/Photo Researchers, Inc.
Figure 3.11c
3-31
Cilia & Cystic Fibrosis
• Saline layer at cell surface due to
chloride pumps move Cl- out of
cell. Na+ ions and H2O follow
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mucus
• Cystic fibrosis – hereditary
disease in which cells make
chloride pumps, but fail to install
them in the plasma membrane
Saline
layer
Epithelial
cells
– chloride pumps fail to create
adequate saline layer on cell surface
(a)
Figure 3.12a
• thick mucus plugs pancreatic
ducts and respiratory tract
– inadequate digestion of nutrients and
absorption of oxygen
– chronic respiratory infections
– life expectancy of 30
3-32
Flagella
• tail of the sperm - only functional flagellum
• whiplike structure with axoneme identical to
cilium
– much longer than cilium
– stiffened by coarse fibers that supports the tail
• movement is more undulating, snakelike
– no power stroke or recovery stroke as in cilia
3-33
Membrane Transport
• plasma membrane – a barrier and a gateway between the
cytoplasm and ECF
– selectively permeable – allows some things through, and prevents
other things from entering and leaving the cell
• passive transport mechanisms requires no ATP
– random molecular motion of particles provides the necessary
energy
– filtration, diffusion, osmosis
• active transport mechanisms consumes ATP
– active transport and vesicular transport
• carrier-mediated mechanisms use a membrane protein to
transport substances from one side of the membrane to the
3-34
other
Filtration
• Filtration - process in which
particles are driven through
Solute
a selectively permeable
membrane by hydrostatic Water
Capillary wall
pressure (force exerted
blood
on a membrane by water) Red
cell
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Examples
– filtration of nutrients through gaps in
blood capillary walls into tissue
fluids
Blood pressure in capillary
forces water and small
solutes such as salts through
narrow clefts between
capillary cells.
Clefts hold back
larger particles
such as red blood
cells.
Figure 3.13
– filtration of wastes from the blood in
the kidneys while holding back
blood cells and proteins
3-35
Simple Diffusion
• Simple Diffusion – the net
movement of particles from
area of high concentration
to area of low
concentration
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
– due to their constant,
spontaneous motion
• Also known as movement
down the concentration
gradient – concentration of a
substance differs from one
point to another
Down
gradient
Up
gradient
Figure 3.14
3-36
Diffusion Rates
• Factors affecting diffusion rate through a
membrane
– temperature -  temp.,  motion of particles
– molecular weight - larger molecules move slower
– steepness of concentrated gradient - difference,  rate
– membrane surface area -  area,  rate
– membrane permeability -  permeability,  rate
3-37
Membrane Permeability
• Diffusion through lipid bilayer
– Nonpolar, hydrophobic, lipid-soluble
substances diffuse through lipid layer
• Diffusion through channel proteins
– water and charged, hydrophilic solutes diffuse
through channel proteins in membrane
• Cells control permeability by regulating
number of channel proteins or by opening and
closing gates
3-38
Osmosis
• Osmosis - flow of water from
one side of a selectively
permeable membrane to the
other
– from side with higher water
concentration to the side with
lower water concentration
– reversible attraction of water to
solute particles forms hydration
spheres
– makes those water molecules less
available to diffuse back to the
side from which they came
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Side A
Side B
(a) Start
Figure 3.15a
• Aquaporins - channel
proteins specialized for
passage of water
3-39
Aquaporins
• Aquaporins - channel
proteins in plasma membrane
specialized for passage of water
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Side A
Side B
– cells can increase the rate of
osmosis by installing more
aquaporins
– decrease rate by removing them
• Significant amounts of water
diffuse even through the
hydrophobic, phospholipid
regions of the plasma
membrane
(a) Start
Figure 3.15a
3-40
Osmotic Pressure
• Osmotic Pressure amount of hydrostatic
pressure required to
stop osmosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Osmotic
pressure
Hydrostatic
pressure
• Osmosis slows due to
hydrostatic pressure
• Heart drives water out
of capillaries by reverse
osmosis – capillary
filtration
(b) 30 minutes later
Figure 3.15b
3-41
Osmolarity
• One osmole - 1 mole of dissolved particles
– 1M NaCl (1 mole Na+ ions + 1 mole Cl- ions) thus 1M
NaCl = 2 osm/L
• Osmolarity – number of osmoles of solute per liter
of solution
• Osmolality – number of osmoles of solute per
kilogram of water
• Physiological solutions are expressed in
milliosmoles per liter (mOsm/L)
– blood plasma = 300 mOsm/L
– osmolality similar to osmolarity at concentration
of body fluids – less than 1% difference
3-42
Tonicity
• Tonicity - ability of a solution to affect fluid volume and
pressure in a cell
– depends on concentration and permeability of solute
• Hypotonic solution
– has a lower concentration of nonpermeating solutes than intracellular
fluid (ICF)
• high water concentration
– cells absorb water, swell and may burst (lyse)
• Hypertonic solution
– has a higher concentration of nonpermeating solutes
• low water concentration
– cells lose water + shrivel (crenate)
• Isotonic solution
– concentrations in cell and ICF are the same
– cause no changes in cell volume or cell shape
– normal saline
3-43
Effects of Tonicity on RBCs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a) Hypotonic
(b) Isotonic
(c) Hypertonic
© Dr. David M. Phillips/Visuals Unlimited
Figure 3.16a
Figure 3.16b
Figure 3.16c
Hypotonic, isotonic and hypertonic solutions affect the fluid
volume of a red blood cell. Notice the crenated and swollen
cells.
3-44
Carrier-Mediated Transport
• Transport proteins in the plasma membrane that carry
solutes from one side of the membrane to the other
• Specificity:
– transport proteins specific for a certain ligand
– solute binds to a specific receptor site on carrier protein
– differs from membrane enzymes because carriers do not chemically
change their ligand
• simply picks them up on one side of the membrane, and release them,
unchanged, on the other
• Saturation:
– as the solute concentration rises, the rate of transport rises, but only
to a point – Transport Maximum (Tm)
• 2 types of carrier mediated transport
– facilitated diffusion and active transport
3-45
Membrane Carrier Saturation
Rate of solute transport
(molecules/sec passing
through plasma membrane)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Transport maximum (Tm)
Figure 3.17
Concentration of solute
• Transport maximum - transport rate when all
carriers are occupied
3-46
Membrane Carriers
• Uniport
– carries only one solute at a time
• Symport
– carries 2 or more solutes simultaneously in same direction
(cotransport)
• Antiport
– carries 2 or more solutes in opposite directions
(countertransport)
– sodium-potassium pump brings in K+ and removes Na+ from cell
• carriers employ two methods of transport
– facilitated diffusion
– active transport
3-47
Facilitated Diffusion
• facilitated diffusion - carrier-mediated transport of
solute through a membrane down its concentration
gradient
• does not consume ATP
• solute attaches to binding site on carrier, carrier
changes confirmation, then releases solute on other
side of membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ECF
Figure 3.18
ICF
1 A solute particle enters
the channel of a membrane
protein (carrier).
2 The solute binds to a receptor
site on the carrier and the
carrier changes conformation.
3 The carrier releases the
solute on the other side of
the membrane.
3-48
Active Transport
• active transport – carrier-mediated transport of
solute through a membrane up (against) its
concentration gradient
• ATP energy consumed to change carrier
• Examples of uses:
– sodium-potassium pump keeps K+ concentration
higher inside the cell
– bring amino acids into cell
– pump Ca2+ out of cell
3-49
Sodium-Potassium Pump
• each pump cycle consumes one ATP and exchanges three
Na+ for two K+
• keeps the K+ concentration higher and the Na+ concentration
lower with in the cell than in ECF
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• necessary because Na+ and K+
constantly leak through membrane
3 Na+ out
Extracellular
fluid
– half of daily calories utilized for
Na+ - K+ pump
Figure 3.19
ATP
ADP + Pi
Intracellular fluid
2 K+ in
3-50
Functions of
+
Na
+
-K
Pump
• Regulation of cell volume
– “fixed anions” attract cations causing osmosis
– cell swelling stimulates the Na+- K+ pump to
 ion concentration,  osmolarity and cell swelling
• Secondary active transport
– steep concentration gradient maintained between one side of the
membrane and the other – (water behind a dam)
– Sodium-glucose transport protein (SGLT) – simultaneously binds Na+
and glucose and carries both into the cell
– does not consume ATP
• Heat production
– thyroid hormone increase # of Na+ - K+ pumps
– consume ATP and produce heat as a by-product
• Maintenance of a membrane potential in all cells
– pump keeps inside more negative, outside more positive
– necessary for nerve and muscle function
3-51
Vesicular Transport
• Vesicular Transport – processes that move large particles, fluid
droplets, or numerous molecules at once through the membrane in
vesicles – bubblelike enclosures of membrane
– motor proteins consumes ATP
• Endocytosis –vesicular processes that bring material into the cell
– phagocytosis – “cell eating” - engulfing large particles
• pseudopods
phagosomes
macrophages
– pinocytosis – “cell drinking” taking in droplets of ECF containing
molecules useful in the cell
• pinocytic vesicle
– receptor-mediated endocytosis – particles bind to specific receptors
on plasma membrane
• clathrin-coated vesicle
• Exocytosis – discharging material from the cell
• Utilizes motor proteins energized by ATP
3-52
Phagocytosis or “Cell-Eating”
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Particle
7 The indigestible
residue is voided by
exocytosis.
1 A phagocytic cell encounters a
particle of foreign matter.
Pseudopod
Residue
2 The cell surrounds
the particle with its
pseudopods.
Nucleus
Phagosome
6 The phagolysosome
fuses with the
plasma membrane.
Lysosome
Vesicle fusing
with membrane
3 The particle is phagocytized
and contained in a
phagosome.
Phagolysosome
5 Enzymes from the
lysosome digest the
foreign matter.
4 The phagosome fuses
with a lysosome and
becomes a phagolysosome.
Figure 3.21
3-53
Keeps tissues free of debris and infectious microorganisms.
Pinocytosis or “Cell-Drinking”
• Taking in droplets of ECF
– occurs in all human cells
• Membrane caves in, then pinches off into
the cytoplasm as pinocytotic vesicle
3-54
Receptor Mediated Endocytosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Extracellular
molecules
Receptor
Coated
pit
Clathrin
1 Extracellular molecules bind to
receptors on plasma membrane;
receptors cluster together.
2 Plasma membrane sinks inward,
forms clathrin-coated pit.
Clathrincoated
vesicle
3 Pit separates from plasma
membrane, forms clathrin-coated
vesicle containing concentrated
molecules from ECF.
(all): Company of Biologists, Ltd.
Figure 3.22 (1,2 and 3)
3-55
Receptor Mediated Endocytosis
• more selective endocytosis
• enables cells to take in specific molecules
that bind to extracellular receptors
• Clathrin-coated vesicle in cytoplasm
– uptake of LDL from bloodstream
3-56
Transcytosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Capillary endothelial cell
Intercellular cleft
Capillary lumen
Pinocytotic vesicles
Muscle cell
Figure 3.23
Tissue fluid
0.25 µm
© Don Fawcett/Photo Researchers, Inc.
• Transport of material across the cell by capturing it
on one side and releasing it on the other
• Receptor-mediated endocytosis moves it into cell
and exocytosis moves it out the other side
– insulin
3-57
Exocytosis
• Secreting material
• replacement of plasma membrane removed
by endocytosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dimple
Fusion pore
Secretion
Plasma
membrane
Linking
protein
Secretory
vesicle
(a)
(b)
1 A secretory vesicle approaches
2 The plasma membrane and
vesicle unite to form a fusion
the plasma membrane and docks
pore through which the vesicle
on it by means of linking proteins.
contents are released.
The plasma membrane caves in
at that point to meet the vesicle.
Courtesy of Dr. Birgit Satir, Albert Einstein College of Medicine
Figure 3.24a,b
3-58
The Cell Interior
• structures in the cytoplasm
– organelles, cytoskeleton, and inclusions
– all embedded in a clear gelatinous cytosol
• Organelles – internal structures of a cell that carry out
specialized metabolic tasks
– membranous organelles – those surrounded by one or two layers of
unit membrane
• nucleus, mitochondria, lysosome, peroxisome, endoplasmic reticulum, and
Golgi complex
– organelles not surrounded by membranes
• ribosome, centrosome, centriole, basal bodies
• Cytoskeleton
– collection of protein filaments
– microfilaments, intermediate filaments, and microtubules
• Inclusions
– stored cellular components and fat droplets
3-59
Nucleus
• Largest organelle (5 mm in diameter)
– most cells have one nucleus
– a few cells are anuclear or multinucleate
• nuclear envelope - two unit membranes surround nucleus
– perforated by nuclear pores formed by rings of protein
• regulate molecular traffic through envelope
• hold two unit membranes together
– supported by nuclear lamina
•
•
•
•
web of protein filaments
supports nuclear envelope and pores
provides points of attachment and organization for chromatin
plays role in regulation of the cell life cycle
• nucleoplasm – material in nucleus
– chromatin (thread-like matter) composed of DNA and protein
– nucleoli – one or more dark masses where ribosomes are
produced
3-60
Micrograph of The Nucleus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nuclear
pores
Nucleolus
Nucleoplasm
Nuclear
envelope
(a) Interior of nucleus
2 mm
(b) Surface of nucleus
1.5 mm
a: © Richard Chao; b: © E.G. Pollock
Figure 3.25a
Figure 3.25b
3-61
Endoplasmic Reticulum
• endoplasmic reticulum - system of interconnected
channels called cisternae enclosed by unit
membrane
• rough endoplasmic reticulum – composed of
parallel, flattened sacs covered with ribosomes
– continuous with outer membrane of nuclear envelope
– adjacent cisternae are often connected by perpendicular
bridges
– produces the phospholipids and proteins of the plasma
membrane
– synthesizes proteins that are packaged in other
organelles or secreted from cell
3-62
Endoplasmic Reticulum
• smooth endoplasmic reticulum
– lack ribosomes
– cisternae more tubular and branching
– cisternae are thought to be continuous with
those of rough ER
– synthesizes steroids and other lipids
– detoxifies alcohol and other drugs
– manufactures all membranes of the cell
• rough and smooth ER are functionally
different parts of the same network
3-63
Smooth and Rough ER
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Rough endoplasmic
reticulum
Ribosomes
Cisternae
(c)
Smooth
endoplasmic
reticulum
Figure 3.26c
3-64
Endoplasmic Reticulum
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cisternae of
rough ER
Oil droplet
(inclusion)
Nucleus
Ribosomes
of rough ER
Smooth
endoplasmic
reticulum
(a)
1 µm
(b)
1 µm
© Don Fawcett/Photo Researchers, Inc.
Figure 3.26a
Figure 3.26b
3-65
Ribosomes
• Ribosomes - small granules of protein and
RNA
– found in nucleoli, in cytosol, and on outer
surfaces of rough ER, and nuclear envelope
• they ‘read’ coded genetic messages
(messenger RNA) and assemble amino
acids into proteins specified by the code
3-66
Golgi Complex
• Golgi complex - a small system of cisternae that
synthesize carbohydrates and put the finishing
touches on protein and glycoprotein synthesis
– receives newly synthesized proteins from rough ER
– sorts them, cuts and splices some of them, adds
carbohydrate moieties to some, and packages the protein
into membrane-bound Golgi vesicles
• some become lysosomes
• some migrate to plasma membrane and fuse to it
• some become secretory vesicles for later release
3-67
Golgi Complex
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Golgi vesicles
Golgi
complex
Figure 3.27
600 nm
Visuals Unlimited
3-68
Lysosomes
• Lysosomes - package of enzymes bound by a
single unit membrane
– extremely variable in shape
• Functions
– intracellular hydrolytic digestion of proteins, nucleic acids,
complex carbohydrates, phospholipids, and other
substances
– autophagy – digest and dispose of worn out mitochondria
and other organelles
– autolysis – ‘cell suicide’ – some cells are meant to do a
certain job and then destroy themselves
3-69
Lysosomes and Peroxisomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mitochondria
Peroxisomes
Lysosomes
Smooth ER
Golgi
complex
(a) Lysosomes
1 mm
(b) Peroxisomes
0.3 mm
© Don Fawcett/Photo Researchers, Inc.
Figure 3.28a
Figure 3.28b
3-70
Peroxisomes
• Peroxisomes - resemble lysosomes but contain
different enzymes and are not produced by the
Golgi complex
• General function is to use molecular oxygen to
oxidize organic molecules
– these reactions produce hydrogen peroxide (H2O2)
– catalase breaks down excess peroxide to H2O and O2
– neutralize free radicals, detoxify alcohol, other drugs,
and a variety of blood-borne toxins
– breakdown fatty acids into acetyl groups for
mitochondrial use in ATP synthesis
• In all cells, but abundant in liver and kidney
3-71
Mitochondrion
• mitochondria – organelles specialized
for synthesizing ATP
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• variety of shapes – spheroid, rodshaped, kidney bean-shaped, or
threadlike
• surrounded by a double unit membrane
– inner membrane has folds called cristae
– spaces between cristae are called matrix
• matrix contains ribosomes, enzymes used for
ATP synthesis, small circular DNA molecule
– mitochondrial DNA (mtDNA)
• “Powerhouses” of the cell
– energy is extracted from organic
molecules and transferred to ATP
Matrix
Outer membrane
Inner membrane
Mitochondrial
ribosome
Intermembrane
space
Crista
Figure 3.29b
3-72
Mitochondrion
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Matrix
Outer membrane
Inner membrane
Figure 3.29a,b
Mitochondrial
ribosome
Intermembrane
space
Crista
1 µm
3-73
(Left): Dr. Donald Fawcett & Dr. Porter/Visuals Unlimited
Evolution of Mitochondrion
• It is a virtual certainty that mitochondria evolved from bacteria
that invaded another primitive cell, survived in the cytoplasm,
and became permanent residents
– its two unit membranes suggests that the original bacterium provided
the inner membrane, and the host cell’s phagosome provided the outer
membrane
– mitochondrial ribosomes more like bacterial ribosomes
– has its own mtDNA
• small circular molecule resembling bacterial DNA
• replicates independently of nuclear DNA
– when a sperm fertilizes the egg, any mitochondria introduced by the
sperm are usually destroyed, and only those provided by the egg are
passed on to the developing embryo
• mitochondrial DNA is almost exclusively inherited through the mother
– mutates more readily than nuclear DNA
• no mechanism for DNA repair
• produces rare hereditary diseases
• mitochondrial myopathy , mitochondrial encephalomyopathy,
and others
3-74
Centrioles
• centriole – a short cylindrical assembly of
microtubules arranged in nine groups of three
microtubules each
• two centrioles lie perpendicular to each other within
a small clear area of cytoplasm - centrosome
– play role in cell division
• cilia and flagella formation
– each basal body of a cilium or flagellum is a single
centriole oriented perpendicular to plasma membrane
– basal bodies originate in centriolar organizing center
• migrates to plasma membrane
– two microtubules of each triplet elongate to form the nine
pairs of peripheral microtubules of the axoneme
3-75
– cilium reaches full length in less than one hour
Centrioles
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.30a,b
Microtubules
Protein
link
Longitudinal
view
Cross
section
0.1 µm
(a) Cross-section (TEM)
Microtubules
(b) Pair of centrioles
3-76
a: From: Manley McGill, D.P. Highfield, T.M. Monahan, and B.R. Brinkley Effects of Nucleic Acid Specific Dyes on Centrioles
of Mammalian Cells, published in the Journal of Ultrastructure Research 57, 43-53 (1976), pg. 48, fig. 6, with permission from Elsevier
Cytoskeleton
• Cytoskeleton - collection of filaments and cylinders
– determines shape of cell, lends structural support, organizes its
contents, directs movement of substances through the cell, and
contributes to the movements of cell as a whole.
• Composed of:
– microfilaments – made of protein actin
• form network on cytoplasmic side of plasma membrane called the
terminal web (membrane skeleton)
– provides physical support for phospholipid bilayer
– actin supports microvilli and produces cell movements
– intermediate fibers – thicker and stiffer than microfilaments
• resist stresses placed on cell
• participate in junctions that attach some cells to their neighbors
• line nuclear envelope and form cagelike nuclear lamina that encloses DNA
– microtubules – cylinders made of 13 parallel strands called
protofilaments
3-77
Microtubules
• a microtubule is a cylinder of 13 parallel strands called protofilaments
– each protofilament is a long chain of globular proteins called tubulin
• microtubules radiate from centrosome and hold organelles in place, form
bundles that maintain cell shape and rigidity, and act somewhat like
railroad tracks
– motor proteins ‘walk’ along these tracks carrying organelles and other
macromolecules to specific locations in the cell
• not permanent structures, they come and go moment by moment
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a)
(b)
(c)
Microtubule
Protofilaments
Dynein arms
Tubulin
Figure 3.32
3-78
Cytoskeleton
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Microvilli
Microfilaments
Terminal web
Secretory
vesicle in
transport
Desmosome
Lysosome
Kinesin
Microtubule
Intermediate
filaments
Intermediate
filaments
Microtubule
in the process
of assembly
Centrosome
Microtubule
undergoing
disassembly
Nucleus
Mitochondrion
(a)
Basement
membrane
Hemidesmosome
Figure 3.31a
3-79
EM and Fluorescent Antibodies
demonstrate Cytoskeleton
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(b)
15 µm
© K.G. Murti/Visuals Unlimited
Figure 3.31b
3-80
Inclusions
• two kinds of inclusions
– Stored cellular products
• glycogen granules, pigments and fat droplets
– Foreign bodies
• viruses, intracellular bacteria, and dust particles and
other debris phagocytized by cell
• never enclosed in a unit membrane
• not essential for cell survival
3-81
Table 3.4
• Summary of
organelles: their
appearance and
function
3-82