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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Lectures by
Erin Barley
Kathleen Fitzpatrick
1
© 2011 Pearson Education, Inc.
1. Biologists use microscopes and the tools of
biochemistry to study cells
2. Eukaryotic cells have internal membranes that
compartmentalize their functions
3. The eukaryotic cell’s genetic instructions are housed
in the nucleus and carried out by the ribosomes
4. The endomembrane system regulates protein traffic
and performs metabolic functions in the cell
5. Mitochondria and chloroplasts change energy from
one form to another
6. The cytoskeleton is a network of fibers that organizes
structures and activities in the cell
7. Extracellular components and connections between
cells help coordinate cellular activities
2
1. All organisms are made of cells.
2. The cell is the simplest collection of matter
that can be alive. Indeed, many forms of life
exist as single-celled organisms.
3. Even when cells are arranged into higher
levels of organization, such as tissues and
organs, the cell remains the organism’s basic
unit of structure and function.
4. All cells are related by their descent from
earlier cells.
3
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Figure 6.1 How do your brain cells help you learn about biology?
4
 How can cell biologists investigate the inner
workings of a cell, usually too small to be seen by
the unaided eye?
5
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 The microscopes first used by Renaissance
scientists, as well as the microscopes you are
likely to use in the laboratory, are all light
microscopes.
 In a light microscope (LM), visible light is
passed through a specimen and then through
glass lenses.
 The lenses refract (bend) the light, so that the
image of the specimen is magnified
6
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Three important parameters of microscopy
 Magnification, the ratio of an object’s image
size to its real size
 Resolution, the measure of the clarity of the
image, or the minimum distance of two
distinguishable points
 Contrast, visible differences in parts of the
sample
7
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 LMs can magnify effectively to about 1,000 times
the actual size of the specimen
 Improvements in light microscopy have included
new methods for enhancing contrast, such as
staining or labeling cell components to stand out
visually.
 The resolution barrier prevented cell biologists
from using standard light microscopy to study
organelles, the membrane-enclosed structures
within eukaryotic cells.
8
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10 m
0.1 m
Length of some
nerve and
muscle cells
Chicken egg
1 cm
Frog egg
1 mm
Human egg
Most plant and
animal cells
10 m
1 m
100 nm
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
10 nm
Superresolution
microscopy
Electron microscopy
100 m
Light microscopy
 1 cm= 10-2 m= 0.4 inch
 1 mm= 10-3 m
 1 m= 10-3 mm= 10-6 m
 1 nm= 10-3 m= 10-9 m
Unaided eye
Figure 6.2 The size range of cells
Human height
1m
Proteins
Lipids
1 nm
0.1 nm
Small molecules
Atoms
9
Light Microscopy (LM)
Brightfield
(unstained specimen)
Electron Microscopy (EM)
Longitudinal section
of cilium
Confocal
Cross section
of cilium
50 m
Cilia
50 m
Brightfield
(stained specimen)
2 m
2 m
Scanning electron
microscopy (SEM)
Deconvolution
Transmission electron
microscopy (TEM)
10 m
Phase-contrast
Differential-interferencecontrast (Nomarski)
Super-resolution
Figure 6.3 Exploring Microscopy
10 m
1 m
Fluorescence
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Figure 6.3a
50 m
Brightfield
(unstained specimen)
11
Figure 6.3b
Brightfield
(stained specimen)
12
Figure 6.3c
Phase-contrast
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Figure 6.3d
Differential-interferencecontrast (Nomarski)
微分干涉顯微鏡
14
Figure 6.3e
Fluorescence
10 m
15
Figure 6.3f
50 m
Confocal
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Figure 6.3g
10 m
Deconvolution
17
Figure 6.3h
1 m
Super-resolution
18
Figure 6.3i
Scanning electron microscopy (SEM)
Cilia
2 m
19
Figure 6.3j
Transmission electron microscopy (TEM)
Longitudinal section
of cilium
Cross section
of cilium
2 m
20
 In the 1950s, the electron microscope was
introduced to biology.
 Two basic types of electron microscopes (EMs)
are used to study subcellular structures
– Scanning electron microscopes (SEMs) focus a beam
of electrons onto the surface of a specimen, providing
images that look 3-D
– Transmission electron microscopes (TEMs) focus a
beam of electrons through a specimen
• TEMs are used mainly to study the internal structure of cells
21
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• Recent advances in light microscopy
– Both confocal and deconvolution
microscopy have sharpened images of threedimensional tissues and cells.
– As this “super-resolution microscopy”
becomes more widespread, the images we’ll
see of living cells may well be as awe-inspiring
to us as Van Leeuwenhoek’s were to Robert
Hook 350 years ago.
22
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• A useful technique for studying cell structure and
function is cell fractionation, which takes cells apart
and separates major organelles and other subcellular
structures from one another.
• Cell fractionation enables researchers to prepare
specific cell components in bulk and identify their
functions, a task not usually possible with intact cells.
• Biochemistry and cytology thus complement each
other in correlating cell function with structure.
23
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Figure 6.4
TECHNIQUE
Homogenization
Tissue
cells
Homogenate
Centrifuged at
1,000 g
(1,000 times the
force of gravity)
for 10 min Supernatant
poured into
next tube
20,000 g
20 min
Pellet rich in
nuclei and
cellular debris
Centrifugation
Differential
centrifugation
80,000 g
60 min
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
Pellet rich in
membranes)
ribosomes
24
Figure 6.4a
TECHNIQUE
Homogenization
Tissue
cells
Homogenate
Centrifugation
25
Centrifuged at
1,000 g
(1,000 times the
force of gravity)
for 10 min Supernatant
poured into
next tube
20,000 g
20 min
Pellet rich in
nuclei and
cellular debris
Differential
centrifugation
80,000 g
60 min
150,000 g
3 hr
Pellet rich in
mitochondria
(and chloroplasts if cells
are from a plant)
Pellet rich in
“microsomes”
Pellet rich in
ribosomes
26
 The basic structural and functional unit of every
organism is one of two types of cells:
prokaryotic or eukaryotic
 Organisms of the domains Bacteria and Archaea
consist of prokaryotic cell. Protists, fungi,
animals, and plants all consist of eukaryotic cells.
27
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• All cells share certain basic features:
– Plasma membrane ：cytosol
– Chromosomes ：carry genes in the form of DNA
– Ribosomes ：make proteins according to
instructions from the genes.
28
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• 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
29
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Figure 6.5
Fimbriae
Nucleoid
Ribosomes
Plasma
membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 m
Flagella
(a)
(b) A thin section
through the
bacterium Bacillus
coagulans (TEM)
A typical rod-shaped bacterium
30
• Eukaryotic cells are characterized by having
– DNA in a nucleus that is bounded by a
membranous nuclear envelope
– Membrane-bound organelles
– Cytoplasm in the region between the
plasma membrane and nucleus
• Eukaryotic cells are generally much larger
than prokaryotic cells
31
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 At the boundary of every cell, the plasma
membrane functions as a selective barrier
that allows passage of enough oxygen,
nutrients, and wastes to service the entire cell.
 As a cell (or any other object) increases in size,
its volume grows proportionately more than
its surface area.
 Thus, a smaller object has a greater ratio of
surface area to volume.
32
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Figure 6.6
Outside of cell
(a) TEM of a plasma
membrane
劃出結構圖
Inside of cell
0.1 m
Carbohydrate side chains
Hydrophilic
region
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
33
Figure 6.7
Surface area increases while
total volume remains constant
解釋細胞為什麼要
愈小愈好?
5
1
1
Total surface area
[sum of the surface areas
(height  width) of all box
sides  number of boxes]
6
150
750
Total volume
[height  width  length
 number of boxes]
1
125
125
Surface-to-volume
(S-to-V) ratio
[surface area  volume]
6
1.2
6
34
 A eukaryotic cell has extensive and elaborately
arranged internal membranes that divide the cell
into compartments- the organelles mentioned
earlier.
 The generalized diagrams of an animal cell and a
plant cell introduce the various organelles and
highlight the key differences between animals
and plant cells.
BioFlix: Tour of an Animal Cell
BioFlix: Tour of a Plant Cell
© 2011 Pearson Education, Inc.
35
Figure 6.8a
ENDOPLASMIC RETICULUM (ER)
Flagellum
Nuclear
envelope
Nucleolus
Rough Smooth
ER
ER
NUCLEUS
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate filaments
Microtubules
Ribosomes
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome
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Figure 6.8ba
10 m
Animal Cells
Cell
Nucleus
Nucleolus
Human cells from lining
of uterus (colorized TEM)
37
Figure 6.8bb
Fungal Cells
Parent
cell
5 m
Buds
Yeast cells budding
(colorized SEM)
38
Figure 6.8bc
1 m
Cell wall
Vacuole
Nucleus
Mitochondrion
A single yeast cell
(colorized TEM)
39
Figure 6.8c
Nuclear
envelope
NUCLEUS
Nucleolus
Chromatin
Rough
endoplasmic
reticulum
Smooth
endoplasmic
reticulum
Ribosomes
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
Microtubules
CYTOSKELETON
Mitochondrion
Peroxisome
Chloroplast
Plasma membrane
Cell wall
Plasmodesmata
Wall of adjacent cell
40
Figure 6.8da
Plant Cells
5 m
Cell
Cell wall
Chloroplast
Mitochondrion
Nucleus
Nucleolus
Cells from duckweed
(colorized TEM)
41
Figure 6.8db
8 m
Protistan Cells
Chlamydomonas
(colorized SEM)
42
Figure 6.8dc
Protistan Cells
1 m
Flagella
Nucleus
Nucleolus
Vacuole
Chloroplast
Cell wall
Chlamydomonas
(colorized TEM)
43
 The nucleus, which houses most of the cell’s
DNA, and the ribosomes, which use
information from the DNA to make proteins
44
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 The nucleus contains most of the genes in the
eukaryotic cell.
 It is generally the most conspicuous organelle in
a eukaryotic cell, averaging about 5m in
diameter.
 The nuclear envelope encloses the nucleus,
separating its contents from the cytoplasm.
 The two membrane, each a lipid bilayer with
associated proteins, are separated by a space of
30-40 nm.
45
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 Except at the pores, the nuclear side of the
envelope is lined by the nuclear lamina, a netlike
array of protein filaments that maintains the
shape of the nucleus by mechanically supporting
the nuclear envelope.
 Within the nucleus, the DNA is organized into
discrete units called chromosomes, structures
that carry the genetic information.
 Each chromosome contains one long DNA
molecule associated with many proteins.
46
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Figure 6.9
1 m
Nucleus
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Rough ER
Surface of nuclear
envelope
Pore
complex
Ribosome
Chromatin
1 m
0.25 m
Close-up
of nuclear
envelope
Pore complexes (TEM)
Nuclear lamina (TEM)
47
• The complex of DNA and proteins making up
chromosomes is called chromatin.
• Each eukaryotic species has a characteristic
number of chromosomes.
• A prominent structure within the nondividing
nucleus is the nucleolus, which appears through
the electron microscope as a mass of density
stained granules and fibers adjoining part of the
chromatin.
• ribosomal RNA (rRNA) is synthesized from
instructions in the DNA.
48
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• Ribosomes, which are complexes made of
ribosomal RNA and protein, are the cellular
components that carry out protein synthesis.
• Ribosomes build proteins in two cytoplasmic
locales.
– In the cytosol (free ribosomes)
– On the outside of the endoplasmic reticulum
or the nuclear envelope (bound ribosomes)
49
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Figure 6.10
0.25 m
Free ribosomes in cytosol
Endoplasmic reticulum (ER)
Ribosomes bound to ER
Large
subunit
TEM showing ER and
ribosomes
Small
subunit
Diagram of a ribosome
50
• Many of the different membranes of the
eukaryotic cell are part of the endomembrane
system, which includes
– Nuclear envelope
– Endoplasmic reticulum
– Golgi apparatus
– Lysosomes
– Vesicles and Vacuoles
– Plasma membrane
51
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 Many of the different membranes of the
eukaryotic cell are part of the endomembrane
system, which includes the nuclear envelope,
the Golgi apparatus, lysosomes, various kinds
of vesicles and vacuoles, and the plasma
membrane.
 There are two distinct regions of ER
 Smooth ER, which lacks ribosomes
 Rough ER, surface is studded with ribosomes
52
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Figure 6.11
Smooth ER
Nuclear
envelope
Rough ER
ER lumen
Cisternae
Ribosomes
Transport vesicle
Smooth ER
Transitional ER
Rough ER
200 nm
53
• The smooth ER
考
– Synthesizes of lipids
– Metabolism of carbohydrates
– Detoxification of drugs and poisons
– Storage of calcium ions
54
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• The rough ER
考
– Most secretory proteins are glycoproteins,
proteins that have carbohydrates covalently
bonded to them.
– Vesicles in transit from one part of the cell to
another are called transport vesicles;
– Is a membrane factory for the cell
55
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• The Golgi apparatus consists of flattened
membranous sacs called cisternae
• Functions of the Golgi apparatus
– Modifies products of the ER
– Manufactures certain macromolecules
– Sorts and packages materials into transport
vesicles
56
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Figure 6.12
cis face
(“receiving” side of
Golgi apparatus)
0.1 m
Cisternae
trans face
(“shipping” side of
Golgi apparatus)
TEM of Golgi apparatus
57
 A lysosome is a membranous sac of hydrolytic
enzymes that an animal cell uses to digest
macromolecules
 Lysosomes carry out intracellular digestion in a
variety of circumstances. Amoebas and many
other protists eat by engulfing smaller organisms
or food particles, a process called phagocytosis.
 Lysosomes also use their hydrolytic enzymes to
recycle the cell’s own organic material, a process
called autophagy.
Animation: Lysosome Formation
© 2011 Pearson Education, Inc.
58
Figure 6.13
Nucleus
Vesicle containing
two damaged
organelles
1 m
1 m
Mitochondrion
fragment
Peroxisome
fragment
Lysosome
Digestive
enzymes
Lysosome
Lysosome
Plasma membrane
Peroxisome
Digestion
Food vacuole
Vesicle
(a) Phagocytosis
Mitochondrion
Digestion
(b) Autophagy
比較phagocytosis與autophagy的不同
59
• Vacuoles are large vesicles derived from the
endoplasmic reticulum and Golgi apparatus.
– 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
60
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Figure 6.14
Central vacuole
Cytosol
Nucleus
Central
vacuole
Cell wall
Chloroplast
5 m
61
• As the membrane moves from the ER to the
Golgi and then elsewhere, its molecular
composition and metabolic function are
modified, along with those of its contents.
62
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Figure 6.15-1
Nucleus
Rough ER
Smooth ER
Plasma
membrane
63
Figure 6.15-2
Nucleus
Rough ER
Smooth ER
cis Golgi
trans Golgi
Plasma
membrane
64
Figure 6.15-3
Nucleus
Rough ER
Smooth ER
cis Golgi
trans Golgi
Plasma
membrane
65
• Mitochondria are the sites of cellular
respiration, the metabolic process that uses
oxygen to generate ATP by extracting energy
from sugars, fats, and other fuels.
• Chloroplasts, found in plants and algae, are
the sites of photosynthesis.
• Peroxisome are an oxidative organelles
66
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• Mitochondria and chloroplasts display
similarities with bacteria that led to the
endosymbiont theory
– Enveloped by a double membrane
– Contain free ribosomes and circular DNA
molecules
– Grow and reproduce somewhat
independently in cells
解釋粒線體與葉綠體和細菌相似之處
© 2011 Pearson Education, Inc.
67
• The Endosymbiont theory
內共生學說
– An early ancestor of eukaryotic cells engulfed a
nonphotosynthetic prokaryotic cell, which
formed an endosymbiont relationship with its
host
– The host cell and endosymbiont merged into a
single organism, a eukaryotic cell with a
mitochondrion
– At least one of these cells may have taken up a
photosynthetic prokaryote, becoming the
ancestor of cells that contain chloroplasts
68
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Figure 6.16
Endoplasmic
reticulum
Nucleus
Engulfing of oxygenNuclear
using nonphotosynthetic envelope
prokaryote, which
becomes a mitochondrion
Ancestor of
eukaryotic cells
(host cell)
Mitochondrion
Nonphotosynthetic
eukaryote
At least
one cell
Engulfing of
photosynthetic
prokaryote
Chloroplast
Mitochondrion
Photosynthetic eukaryote
69
 Mitochondria are found in nearly all eukaryotic
cells, including those of plants, animals, fungi,
and most protists.
 The outer membrane is smooth, but inner
membrane is convoluted, with infoldings called
cristae.
 The inner membrane divides the mitochondrion
into two internal compartments. (mitochondrial
matrix)
70
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Figure 6.17a
請劃出粒線體的構造
Intermembrane space
Outer
membrane
DNA
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
0.1 m
(a) Diagram and TEM of mitochondrion
71
Figure 6.17b
10 m
Mitochondria
Mitochondrial
DNA
Nuclear DNA
(b) Network of mitochondria in a protist
cell (LM)
72
 Chloroplasts contain the green pigment chlorophyll,
along with enzymes and other molecules that function in
the photosynthetic production of sugar.
 Inside the chloroplast is another membranous system in
the form of flattened, interconnected sacs called
thylakoids.
 In some regions, thylakoids are stacked like poker chips;
each stack is called a granum.
 The fluid outside the thylakoids is the stroma, which
contains the chloroplast DNA and ribosomes as well as
many enzymes.
 The chloroplast is a specialized member of a family of
closely related plant organelles called plastids.
73
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Figure 6.18
50 m
Ribosomes
Stroma
Inner and outer
membranes
Granum
DNA
Intermembrane space
Thylakoid
(a) Diagram and TEM of chloroplast
Chloroplasts
(red)
1 m
(b) Chloroplasts in an algal cell
74
 The peroxisome is a specialized metabolic
compartment bounded by a single membrane.
 Peroxisomes contain enzymes that remove hydrogen
atoms from various substrates and transfer them to
oxygen (O2), thus producing hydrogen peroxide (H2O2)
as a by-product.
 Peroxisomes in the liver detoxify alcohol and other
harmful compounds by transferring hydrogen from
the poisons to oxygen.
 Specialized peroxisomes called glyoxysomes are
found in the fat-storing tissues of plant seeds.
75
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Figure 6.19
1 m
Chloroplast
Peroxisome
Mitochondrion
76
• The cytoskeleton is a network of fibers extending
throughout the cytoplasm.
• It organizes the cell’s structures and activities,
anchoring many organelles
• It is composed of three types of molecular
structures
– Microtubules
考
– Microfilaments
– Intermediate filaments
77
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10 m
Figure 6.20
78
• The remarkable strength and resilience of the
cytoskeleton as a whole is based on its
architecture.
• Several types of cell motility also involve the
cytoskeleton. The term cell motility
encompasses both changes in cell location and
more limited movements of parts of the cell.
• It interacts with motor proteins to produce
motility
79
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Figure 6.21
ATP
Vesicle
Receptor for
motor protein
Motor protein Microtubule
(ATP powered) of cytoskeleton
(a)
Microtubule
(b)
Vesicles
0.25 m
80
• Three main types of fibers make up the
cytoskeleton
– Microtubules are the thickest of the three
components of the cytoskeleton
– Microfilaments, also called actin filaments, are the
thinnest components
– Intermediate filaments are fibers with diameters
in a middle range
81
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Table 6.1
10 m
10 m
5 m
Column of tubulin dimers
Keratin proteins
Fibrous subunit (keratins
coiled together)
Actin subunit
25 nm
7 nm


812 nm
Tubulin dimer
82
Table 6.1a
10 m
Column of tubulin dimers
25 nm


Tubulin dimer
83
Table 6.1b
10 m
Actin subunit
7 nm
84
Table 6.1c
5 m
Keratin proteins
Fibrous subunit (keratins
coiled together)
812 nm
85
Figure 6.22
Centrosome
Microtubule
Centrioles
0.25 m
Longitudinal
section of
one centriole
Microtubules
Cross section
of the other centriole
86
Figure 6.23
Direction of swimming
(a) Motion of flagella
5 m
Direction of organism’s movement
Power stroke Recovery stroke
(b) Motion of cilia
15 m 87
Figure 6.24
0.1 m
Outer microtubule
doublet
Dynein proteins
Plasma membrane
Central
microtubule
Radial
spoke
Microtubules
Plasma
membrane
(b) Cross section of
motile cilium
Cross-linking
proteins between
outer doublets
Basal body
0.5 m
(a) Longitudinal section
of motile cilium
0.1 m
Triplet
(c) Cross section of
basal body
88
Figure 6.25a
Microtubule
doublets
ATP
Dynein protein
(a) Effect of unrestrained dynein movement
89
Figure 6.25b
Cross-linking proteins
between outer doublets
ATP
3
1
2
Anchorage
in cell
(b) Effect of cross-linking proteins
(c) Wavelike motion
90
Figure 6.26
Microvillus
Plasma membrane
Microfilaments (actin
filaments)
Intermediate filaments
0.25 m
91
Figure 6.27
Muscle cell
0.5 m
Actin
filament
Myosin
filament
Myosin
head
(a) Myosin motors in muscle cell contraction
Cortex (outer cytoplasm):
gel with actin network
100 m
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
(b) Amoeboid movement
Chloroplast
(c) Cytoplasmic streaming in plant cells
30 m
92
Figure 6.27a
Muscle cell
0.5 m
Actin
filament
Myosin
filament
Myosin
head
(a) Myosin motors in muscle cell contraction
93
 The cell wall is an extracellular structure of plant
cells that distinguishes them from animal cells.
 Prokaryotes, fungi, and some protists also have
cell walls
 Microfibrils made of the polysaccharide cellulose.
 The matrix of polysaccharides and proteins
makes a “ground substance”, which is the
same basic architectural design found in steelreinforced concrete and in fiberglass.
94
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Figure 6.28
Secondary cell wall
Primary cell wall
Middle lamella
1 m
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
Plasmodesmata
95
Figure 6.29
RESULTS
10 m
Distribution of cellulose
synthase over time
Distribution of
microtubules
over time
96
 Although animal cells lack cell walls akin to
those of plant cells, they do have an elaborate
extracellular matrix (ECM)
 The most abundant glycoprotein in the ECM of
most animal cells is collagen, proteoglycans,
and fibronectin
 Fibronectin and other ECM proteins bind to cellsurface receptor proteins called integrins that
are built into the plasma membrane.
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Figure 6.30
Collagen
Polysaccharide
molecule
EXTRACELLULAR FLUID
Proteoglycan
complex
Fibronectin
Carbohydrates
Core
protein
Integrins
Proteoglycan
molecule
Plasma
membrane
Proteoglycan complex
Microfilaments
CYTOPLASM
98
• Cells in an animal or plant are organized into
tissues, organs, and organ systems.
• Neighboring cells often adhere, interact, and
communicate via sites of direct physical contact.
• There are several types of intercellular junctions
– Plasmodesmata
– Tight junctions
– Desmosomes
– Gap junctions
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Figure 6.31
Cell walls
Interior
of cell
Interior
of cell
0.5 m
Plasmodesmata
Plasma membranes
100
Tight Junctions, Desmosomes, and Gap
Junctions in Animal Cells
• At tight junctions, membranes of neighboring
cells are pressed together, preventing leakage of
extracellular fluid
• Desmosomes (anchoring junctions) fasten cells
together into strong sheets
• Gap junctions (communicating junctions) provide
cytoplasmic channels between adjacent cells
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Figure 6.32
Tight junctions prevent
fluid from moving
across a layer of cells
Tight junction
TEM
0.5 m
Tight junction
Intermediate
filaments
Desmosome
TEM
1 m
Gap
junction
Space
between cells
Plasma membranes
of adjacent cells
Extracellular
matrix
TEM
Ions or small
molecules
0.1 m
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