Transcript Ch 6 Tour of Cell

Chapter 6
A Tour of the Cell
(modified: 38 illustrations, 78
slides total )
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview: The Fundamental Units of Life
• All organisms are made of cells
• The cell is the simplest collection of matter
that can live
• Cell structure and cell function are related
• All cells come from earlier cells
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Concept 6.1: To study cells, biologists use
microscopes and the tools of biochemistry
• Microscopes are used to see cells and the
complex details of cells invisible to the unaided
eye
• Light microscope is the simplest
• In a light microscope (LM), visible light
passes through a specimen and then through
glass lenses, magnifying the image
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• The quality of an image depends on
– Magnification- ratio of an object’s image size
to its real size
– Resolution- measure of the image’s clarity, or
the minimum distance between two
distinguishable points
– Contrast- visible differences in parts of the
sample
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10 m
1m
Human height
Length of some
nerve and
muscle cells
0.1 m
Chicken egg
1 cm
Unaided eye
Fig. 6-2
Frog egg
Limitations of
the light and
electron
microscopes
Most plant and
animal cells
10 µm
Nucleus
Most bacteria
1 µm
100 nm
10 nm
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
Proteins
Lipids
1 nm
Small molecules
0.1 nm
Atoms
Electron microscope
100 µm
Light microscope
1 mm
• LM’s effectively magnify a specimen’s image to
about 1,000 times its actual size.
• Various techniques increase contrast and help
cell components to be stained or labeled
• Most subcellular structures, including
organelles (membrane-enclosed
compartments), are too small to be resolved by
an LM
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TECHNIQUE
RESULTS
(a) Brightfield
(unstained
specimen)
TECHNIQUE
RESULTS
(e) Fluorescence
100 µm
(b) Brightfield (stained
specimen)
(f) Confocal
(c) Phase-contrast
(d) Differentialinterferencecontrast (Nomarski)
Fig. 6-3
100 µm
• Electron microscopes (EMs) are used to
study subcellular structures
• Scanning electron microscopes (SEMs)
focus a beam of electrons onto the surface of a
specimen, giving images that look 3-D
• Transmission electron microscopes (TEMs)
focus a beam of electrons through a specimen
to study the internal structure of cells
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Fig. 6-4
TECHNIQUE
(a) Scanning electron
microscopy (SEM)
RESULTS
Cilia
1 µm
(b) Transmission electron Longitudinal Cross section
section of
of cilium
microscopy (TEM)
1 µm
cilium
Cell Fractionation
• Cell fractionation breaks cells and separates
major organelles from each other using
ultracentrifuges
• This lets scientists determine the functions of
organelles
• Biochemistry and cytology help correlate cell
function with structure
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Fig. 6-5a
TECHNIQUE
Homogenization
Tissue
cells
Differential centrifugation
Homogenate
Fig. 6-5b
TECHNIQUE (cont.)
1,000 g
(1,000 times the
force of gravity)
10 min
Supernatant poured
into next tube
20,000 g
20 min
80,000 g
60 min
Pellet rich in
nuclei and
cellular debris
150,000 g
3 hr
Pellet rich in
mitochondria
(and chloroplasts if cells
are from a plant)
Pellet rich in
“microsomes”
(pieces of plasma
membranes and
cells’ internal
membranes)
Pellet rich in
ribosomes
Concept 6.2: Eukaryotic cells have internal
membranes that compartmentalize their functions
• All cells are either prokaryotic or eukaryotic cells
• Bacteria & Archaeabacteria are prokaryotic cells
• Protists, fungi, animals, and plants are
eukaryotic cells
• Basic features of all cells:
– Plasma membrane
– Semifluid substance called cytosol
– Chromosomes (carry genes)
– Ribosomes (make proteins)
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Comparing Prokaryotic and Eukaryotic Cells
• Prokaryotic cells are characterized by having
–
–
–
–
No nucleus
DNA in an unbound region called the nucleoid
No membrane-bound organelles
Cytoplasm bound by the plasma membrane
• Eukaryotic cells are much larger than prokaryotic
cells and are characterized by:
– A membrane-bound nucleus containing the DNA
– Membrane-bound organelles
– Cytoplasm between the plasma membrane and
nucleus
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Fig. 6-6
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 µm
(a) A typical
rod-shaped
bacterium
Flagella
(b) A thin section
through the
bacterium
Bacillus
coagulans (TEM)
Cellular Membranes
• The plasma membrane is a selective barrier
allowing passage of oxygen, nutrients, and
waste to feed & clean the volume of a cell
• Nearly all biological membrane consist of a
double layer of phospholipids
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Fig. 6-7
Outside of cell
Inside of
cell
0.1 µm
(a) TEM of a plasma
membrane
Carbohydrate side chain
Hydrophilic
region
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
Size limitations in a cell
• The surface area to volume ratio of a cell sets
limits on size because cells depend on
diffusion for nutrition & waste removal
• As the surface area increases by a factor of n2,
the volume increases by n3
• So, small cells have a greater surface area
relative to their volume
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Fig. 6-8
Surface area increases while
total volume remains constant
5
1
1
Total surface area
[Sum of the surface areas
(height  width) of all boxes
sides  number of boxes]
Total volume
[height  width  length 
number of boxes]
Surface-to-volume
(S-to-V) ratio
[surface area ÷ volume]
6
150
750
1
125
125
6
1.2
6
Concept 6.3: The eukaryotic cell’s genetic info. is
housed in the nucleus and carried out by ribosomes
• A eukaryotic cell has internal membranes that
partition the cell into organelles
• Plant and animal cells have almost the same
organelles
• The nucleus contains most of the DNA in a
eukaryotic cell
• Ribosomes use the information from the DNA
to make proteins
BioFlix: Tour Of An Animal Cell
BioFlix: Tour Of A Plant Cell
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Fig. 6-9a
Nuclear
envelope
ENDOPLASMIC RETICULUM (ER)
Flagellum
Rough ER
NUCLEUS
Nucleolus
Smooth ER
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate
filaments
Microtubules
Ribosomes
Microvilli
Golgi
apparatus
Peroxisome
Mitochondrion
Lysosome
Fig. 6-9b
NUCLEUS
Nuclear envelope
Nucleolus
Chromatin
Rough endoplasmic
reticulum
Smooth endoplasmic
reticulum
Ribosomes
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
Microtubules
Mitochondrion
Peroxisome
Chloroplast
Plasma
membrane
Cell wall
Plasmodesmata
Wall of adjacent cell
CYTOSKELETON
The Nucleus: Information Central
• Nucleus- holds most genes; usually largest
organelle
• Nuclear envelope (membrane)- encloses
nucleus, separates it from cytoplasm; is a double
membrane; each membrane is a lipid bilayer
• Pores regulate entry/exit of molecules from the
nucleus
• Nuclear lamina maintains shape of the nucleus;
composed of protein
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Fig. 6-10
Nucleus
1 µm
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Pore
complex
Surface of
nuclear envelope
Rough ER
Ribosome
1 µm
0.25 µm
Close-up of nuclear
envelope
Pore complexes (TEM)
Nuclear lamina (TEM)
• DNA and proteins form genetic material called
chromatin
• Chromatin condenses to form chromosomes
• Nucleolus- an area within the nucleus; the site
of ribosomal RNA (rRNA) synthesis
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Ribosomes: Protein Factories
• Ribosomes- particles made of rRNA & protein
• Ribosomes carry out protein synthesis in two
locations:
– In cytosol (free ribosomes)
– On outside of the endoplasmic reticulum or the
nuclear envelope (bound ribosomes)
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Fig. 6-11
Cytosol
Endoplasmic reticulum (ER)
Free ribosomes
Bound ribosomes
Large
subunit
0.5 µm
TEM showing ER and ribosomes
Small
subunit
Diagram of a ribosome
Concept 6.4: The endomembrane system regulates
protein traffic and performs metabolic functions
• Components of the endomembrane system:
– Nuclear envelope
– Endoplasmic reticulum
– Golgi apparatus
– Lysosomes
– Vacuoles
– Plasma membrane
• The components are either continuous or
connected via transfer by vesicles
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The Endoplasmic Reticulum: Biosynthetic Factory
• Endoplasmic reticulum (ER) is more than half
the total membrane in most eukaryotic cells
• The ER is continuous with the nuclear envelope
• Two distinct regions:
– Smooth ER- no ribosomes
– Rough ER- has ribosomes on its surface
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Fig. 6-12
Smooth ER
Rough ER
ER lumen
Cisternae
Ribosomes
Transport vesicle
Smooth ER
Nuclear
envelope
Transitional ER
Rough ER
200 nm
Functions of Smooth & Rough ER
• Smooth ER
–
–
–
–
Synthesizes lipids
Metabolizes carbohydrates
Detoxifies poison
Stores calcium
• The rough ER
– Has bound ribosomes to secrete
glycoproteins (proteins covalently bonded to
carbohydrates)
– Distributes transport vesicles, proteins
surrounded by membranes
– Is a membrane factory for the cell
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The Golgi Apparatus: Shipping and
Receiving Center
• Golgi apparatus- group of flattened
membranous sacs called cisternae
• Functions of the Golgi apparatus:
– Modifies products of ER
– Manufactures certain macromolecules
– Sorts and packages materials into transport
vesicles
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Fig. 6-13
cis face
(“receiving” side of
Golgi apparatus)
0.1 µm
Cisternae
trans face
(“shipping” side of
Golgi apparatus)
TEM of Golgi apparatus
Lysosomes: Digestive Compartments
• Lysosome- membranous sac of hydrolytic
enzymes that digest macromolecules
– Lysosomal enzymes hydrolyze proteins, fats,
polysaccharides, & nucleic acids
• Phagocytosis- when certain cells can engulf
another cell to form a food vacuole
– A lysosome fuses with the food vacuole and
digests the molecules
• Autophagy- lysosomes also use enzymes to
recycle old organelles and macromolecules
Animation: Lysosome Formation
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Fig. 6-14
Nucleus
1 µm
Vesicle containing
two damaged organelles
1 µm
Mitochondrion
fragment
Peroxisome
fragment
Lysosome
Lysosome
Digestive
enzymes
Plasma
membrane
Lysosome
Peroxisome
Digestion
Food vacuole
Vesicle
(a) Phagocytosis
(b) Autophagy
Mitochondrion
Digestion
Vacuoles: Diverse Maintenance Compartments
• A plant cell or fungal cell may have one or
several vacuoles
• Food vacuoles are formed by phagocytosis
• Contractile vacuoles, found in many
freshwater protists, pump excess water out of
cells
• Central vacuoles, found in many mature plant
cells, hold organic compounds and water
Video: Paramecium Vacuole
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Fig. 6-15
Central vacuole
Cytosol
Nucleus
Central
vacuole
Cell wall
Chloroplast
5 µm
Fig. 6-16-3
Nucleus
Rough ER
Smooth ER
cis Golgi
trans Golgi
Plasma
membrane
Concept 6.5: Mitochondria and chloroplasts
change energy from one form to another
• Mitochondria- sites of cellular respiration, a
metabolic process that generates ATP
• Chloroplasts- plants & algae; sites of
photosynthesis
• Peroxisomes- oxidative organelles; break down
free radicles
• Mitochondria and chloroplasts
–
–
–
–
Are not part of the endomembrane system
Have a double membrane
Have proteins made by free ribosomes
Contain their own DNA
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Mitochondria: Chemical Energy Conversion
• Mitochondria are in nearly all eukaryotic cells
• 2 membranes
– Outer membrane
– Cristae- inner, folded membrane
• Cristae create two compartments:
– intermembrane space
– mitochondrial matrix- where some metabolic
steps of cell respiration are catalyzed
• Cristae present a large surface area for
enzymes that synthesize ATP
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Fig. 6-17
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
0.1 µm
Chloroplasts: Capture of Light Energy
• Chloroplast are
– plastids- pigment containing organelles
– found in leaves & green organs of plants &
algae
• Chloroplasts contain
– Chlorophyll- a green pigment
– Enzymes & molecules that function in
photosynthesis
• Chloroplast structures include:
– Thylakoids, membranous sacs, stacked to
form a granum
– Stroma, the internal fluid
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Fig. 6-18
Chloroplast Structure
Ribosomes
Stroma
Inner and outer
membranes
Granum
Thylakoid
1 µm
Peroxisomes: Oxidation- Single membrane
• Peroxisomes are specialized metabolic
compartments
– bounded by a single membrane
– produce hydrogen peroxide &convert it to water
– Liberate oxygen as a by product
• Oxygen is used to break down different types of
molecules
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Fig. 6-19
Chloroplast
Relative sizes of organelles
Peroxisome
Mitochondrion
1 µm
Concept 6.6: The cytoskeleton is a network of fibers
that organizes structures and activities in the cell
• Cytoskeleton- network of fibers extending
throughout the cytoplasm
– organizes the cell’s structures and activities
– anchors many organelles
• Three main types of fibers in the cytoskeleton:
– Microtubules- thickest fiber of the cytoskeleton
– Microfilaments- also called actin filaments;
thinnest components
– Intermediate filaments- fibers with diameters in
a mid-range
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Fig. 6-20
Microtubule
0.25 µm
Microfilaments
Roles of a Cytoskeleton: Support, Motility, Regulation
• Cytoskeleton- supports cell & maintains its shape
• It interacts with motor proteins to create motility
– In cells, vesicles move on cytoskeleton
monorails
• Cytoskeletons may regulate biochem. Activities
• Microtubules- hollow rods ~ 25 nm in diameter
& ~ 200 nm to 25 microns long
• Functions of microtubules:
– Shaping the cell
– Guiding movement of organelles
– Separating chromosomes during cell division
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Fig. 6-21
ATP
Vesicle
Receptor for
motor protein
Motor protein Microtubule
(ATP powered) of cytoskeleton
(a)
Microtubule
(b)
Vesicles
0.25 µm
Table 6-1a
10 µm
Column of tubulin dimers
25 nm


Tubulin dimer
Table 6-1b
10 µm
Actin subunit
7 nm
Table 6-1c
5 µm
Keratin proteins
Fibrous subunit (keratins
coiled together)
8–12 nm
Centrosomes & Centrioles; Cilia & Flagella
• Centrosome- a “microtubule-organizing center”
• In many cells, microtubules grow out from a
centrosome near the nucleus
• In animal cells, the centrosome has a pair of
centrioles, each with nine triplets of
microtubules arranged in a ring
• Microtubules control the beating of cilia and
flagella, locomotor appendages of some cells
• Cilia and flagella differ in their beating patterns
Video: Chlamydomonas
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Video: Paramecium Cilia
Fig. 6-22
Centrosome
Microtubule
Centrioles
0.25 µm
Longitudinal section Microtubules Cross section
of one centriole
of the other centriole
Fig. 6-23
Direction of swimming
(a) Motion of flagella
5 µm
Direction of organism’s movement
Power stroke Recovery stroke
(b) Motion of cilia
15 µm
• Cilia and flagella share a common ultrastructure:
– Core of microtubules sheathed by the plasma
membrane
– Basal body- anchors the cilium or flagellum
– Motor protein called dynein, which drives the
bending movements of a cilium or flagellum
Animation: Cilia and Flagella
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Fig. 6-24
Outer microtubule
doublet
0.1 µm
Dynein proteins
Central
microtubule
Radial
spoke
Protein crosslinking outer
doublets
Microtubules
Plasma
membrane
(b) Cross section of
cilium
Basal body
0.5 µm
(a) Longitudinal
section of cilium
0.1 µm
Triplet
(c) Cross section of basal body
Plasma
membrane
• How dynein “walking” moves flagella and cilia:
− Dynein arms alternately grab, move, and
release the outer microtubules
– Protein cross-links limit sliding
– Forces exerted by dynein arms cause doublets
to curve, bending the cilium or flagellum
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Fig. 6-25
How dynein “walking” moves flagella and cilia
Microtubule doublets
ATP
Dynein
protein
(a) Effect of unrestrained dynein movement
ATP
Cross-linking proteins
inside outer doublets
Anchorage
in cell
(b) Effect of cross-linking proteins
1
3
2
(c)
Wavelike motion
Microfilaments (Actin Filaments)
• Microfilaments- twisted double chain of actin
subunits forming solid rods ~ 7 nm in diameter
• Microfilaments form a 3-D network, the cortex,
just inside the plasma membrane to:
– bear tension
– resist pulling forces within the cell
– support the cell’s shape
• Bundles of microfilaments form the core of microvilli on
intestinal cells
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Fig. 6-26
Microvillus
Plasma membrane
Microfilaments (actin
filaments)
Intermediate filaments
0.25 µm
Uses of Actin & Myosin
• Microfilaments used in motility have myosin &
actin.
• In muscle cells- the “myosin motor”
– thousands of actin filaments are arranged parallel
– Thicker myosin filaments inter-layer with thinner
actin fibers
– Muscles contract when fibers slide past each other
• In ameba- in pseudopods (cellular extensions)
– Actin and myosin contraction drives amoeboid
movement
– Actin subunits assemble into microfilaments and
contract; & then disassemble
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Fig, 6-27a
Muscle cell
Actin filament
Myosin filament
Myosin arm
(a) Myosin motors in muscle cell contraction
Fig. 6-27bc
Cortex (outer cytoplasm):
gel with actin network
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
(b) Amoeboid movement
Nonmoving cortical
cytoplasm (gel)
Chloroplast
Streaming
cytoplasm
(sol)
Vacuole
Parallel actin
filaments
(c) Cytoplasmic streaming in plant cells
Cell wall
• Cytoplasmic streaming- circular flow of
cytoplasm within cells
– Streaming distributes materials within the cell
– In plants, actin-myosin interactions & sol-gel
transformations drive streaming
• Intermediate filaments
– range in diameter from 8–12 nanometers;
– In size, microtubules>intermediate filaments >
microfilaments
– support cell shape & fix organelles in place
– are more permanent than the other 2 classes
Video: Cytoplasmic Streaming
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Concept 6.7: Extracellular components & connections
between cells coordinate cellular activities
• Cells make and secrete materials external to
the plasma membrane
• Extracellular structures include:
– Plant cell walls
– Extracellular matrix (ECM) of animal cells
– Intercellular junctions
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Cell Walls of Plants
• Plants, prokaryotes, fungi, and some protists all
have cell walls; animal cells don’t
• Cell wall are extracellular structures
• Cell walls
– protect plant cells
– maintain their shape
– prevents excessive water uptake
• Plant cell walls are of cellulose fibers embedded
in polysaccharides and protein
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• Plant cell walls may have multiple layers:
– Primary cell wall: relatively thin and flexible
– Middle lamella: thin layer between primary
walls of adjacent cells
– Secondary cell wall (in some cells): added
between the plasma membrane and the
primary cell wall
• Plasmodesmata- channels between adjacent
plant cells
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Fig. 6-28
Secondary
cell wall
Primary
cell wall
Middle
lamella
1 µm
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
Plasmodesmata
The Extracellular Matrix (ECM) of Animal Cells
• Animal cells are covered by an extracellular
matrix (ECM)
• ECM- made of glycoproteins like collagen,
proteoglycans, and fibronectin
• ECM proteins bind to integrins- receptor
proteins in the plasma membrane
• Functions of the ECM:
–
–
–
–
Support
Adhesion
Movement
Regulation
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Fig. 6-30
Collagen
Proteoglycan
complex
EXTRACELLULAR FLUID
Polysaccharide
molecule
Carbohydrates
Fibronectin
Core
protein
Integrins
Proteoglycan
molecule
Plasma
membrane
Proteoglycan complex
Microfilaments
CYTOPLASM
Intercellular Junctions
• Neighboring cells in tissues, etc. will adhere,
interact, and communicate through direct contact
• Intercellular junctions aid this contact
• Types of intercellular junctions:
– Plasmodesmata
– Tight junctions
– Desmosomes
– Gap junctions
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Plasmodesmata in Plant Cells
• Plasmodesmata-channels in plant cell walls
• Through these, water, small solutes, proteins
and RNA can pass from cell to cell
Cell walls
Interior
of cell
Interior
of cell
0.5 µm
Plasmodesmata Plasma membranes
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Tight Junctions, Desmosomes, and Gap Junctions in
Animal Cells
• Tight junctions- membranes of neighboring cells
pressed together; prevents leakage of extracellular
fluid
• Desmosomes (anchoring junctions) fasten cells
together into strong sheets
• Gap junctions (communicating junctions) make
cytoplasmic channels between adjacent cells
Animation: Tight Junctions
Animation: Desmosomes
Animation: Gap Junctions
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Fig. 6-32
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
Tight junction
Intermediate
filaments
Desmosome
Gap
junctions
Space
between
cells
Plasma membranes
of adjacent cells
Desmosome
1 µm
Extracellular
matrix
Gap junction
0.1 µm
Tight
junction
0.5 µm
Desmosome 1 µm
Gap
junction
Fig. 6-32b-d
0.1 µm
The Cell: Living Unit Greater Than the Sum of Its Parts
• Cells can’t function unless their structures &
organelles work together
Fig. 6-
An electron
micrograph
of a
macrophage
consuming
bacteria
3
3
• Ex. Macrophage must coordinate components
such as the cytoskeleton, lysosomes, and
plasma membrane to destroy bacteria.
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The Endomembrane System: A Review
(optional slide)
• The endomembrane system is a complex and
dynamic player in the cell’s compartmental
organization
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