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Biology
普通生物學
Biology
(7th edition)
Campbell, Reece
授課老師: 賴金美 (LS303)
[email protected]
Overview: The Importance of Cells
• All organisms are made of cells.
• The cell is the simplest collection of matter
that can live.
10 µm
• Concept 6.1: To study cells, biologists use
microscopes and the tools of biochemistry
• Scientists use microscopes to visualize cells too
small to see with the naked eye
• Light microscopes (LMs)
– Pass visible light through a specimen
– Magnify cellular structures with lenses
Light microscope (LM)
Two important parameters:
--- magnification
1000X
~ the ratio of an objects image to its real size
--- resolving power (or resolution)
~ a measure of the clarity of the image
Limit: ~ 0.2 mm (200 nm)
Resolution:
bad
good
–
Can be used to visualize
different sized cellular
Length of some
nerve and
muscle cells
0.1 m
Chicken egg
Light microscope
• Different types of microscopes
Human height
1m
Unaided eye
10 m
1 cm
structures
Frog egg
Most plant
and Animal cells
10 µ m
Measurements
1 centimeter (cm) = 102 meter (m) = 0.4 inch 1 µ m
1 millimeter (mm) = 10–3 m
100 nm
1 micrometer (µm) = 10–3 mm = 10–6 m
1 nanometer (nm) = 10–3 mm = 10–9 m
10 nm
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
Proteins
1 nm
Lipids
Small molecules
Figure 6.2
0.1 nm
Atoms
Electron microscope
100 µm
Electron microscope
1 mm
– Use different methods for enhancing
visualization of cellular structures
TECHNIQUE
RESULT
(a) Brightfield (unstained specimen).
Passes light directly through specimen.
Unless cell is naturally pigmented or
artificially stained, image has little
contrast. [Parts (a)–(d) show a
human cheek epithelial cell.]
50 µm
(b) Brightfield (stained specimen).
Staining with various dyes enhances
contrast, but most staining procedures
require that cells be fixed (preserved).
Figure 6.3
(c) Phase-contrast. Enhances contrast
in unstained cells by amplifying
variations in density within specimen;
especially useful for examining living,
unpigmented cells.
(d)
Differential-interference-contrast (Nomarski).
Like phase-contrast microscopy, it uses optical
modifications to exaggerate differences in
density, making the image appear almost 3D.
(e)
Fluorescence. Shows the locations of specific
molecules in the cell by tagging the molecules
with fluorescent dyes or antibodies. These
fluorescent substances absorb ultraviolet
radiation and emit visible light, as shown
here in a cell from an artery.
(f)
Confocal. Uses lasers and special optics for
“optical sectioning” of fluorescently-stained
specimens. Only a single plane of focus is
illuminated; out-of-focus fluorescence above
and below the plane is subtracted by a computer.
A sharp image results, as seen in stained nervous
tissue (top), where nerve cells are green, support
cells are red, and regions of overlap are yellow. A
standard fluorescence micrograph (bottom) of this
relatively thick tissue is blurry.
50 µm
However, most subcellular structures, or organelles,
are too small to be resolved by the LM.
 Until 1950s, with the introduction of the electron microscope
Electron microscope (EM)
--- Focus a beam of electrons through a specimen
(TEM) or onto its surface (SEM)
Limit: ~ 2 nm (0.002 nm theoretically)
(a hundredfold improvement over the light microscope)
“ Cell ultrastructure “
• The scanning electron microscope (SEM)
– Provides for detailed study of the surface of
a specimen.
TECHNIQUE
RESULTS
1 µm
Cilia
(a) Scanning electron microscopy (SEM). Micrographs taken
with a scanning electron microscope show a 3D image of the
surface of a specimen. This SEM
shows the surface of a cell from a
rabbit trachea (windpipe) covered
with motile organelles called cilia.
Beating of the cilia helps move
inhaled debris upward toward
the throat.
Figure 6.4 (a)
• The transmission electron microscope (TEM)
– Provides for detailed study of the internal
ultrastructure of cells
Longitudinal
section of
cilium
(b) Transmission electron microscopy (TEM). A transmission electron
microscope profiles a thin section of a
specimen. Here we see a section through
a tracheal cell, revealing its ultrastructure.
In preparing the TEM, some cilia were cut
along their lengths, creating longitudinal
sections, while other cilia were cut straight
across, creating cross sections.
Figure 6.4 (b)
Cross section
of cilium
1 µm
Isolating Organelles by Cell Fractionation
Why?  to study the function of the organelles
• Cell fractionation
– Takes cells apart and separates the major
organelles from one another
• The centrifuge
– Is used to fractionate cells into their component
parts (separate the cell components by size and
density)
• The process of cell fractionation
APPLICATION
Cell fractionation is used to isolate
(fractionate) cell components, based on size and density.
TECHNIQUE
First, cells are homogenized in a blender to
break them up. The resulting mixture (cell homogenate) is then
centrifuged at various speeds and durations to fractionate the
cell components, forming a series of pellets.
Figure 6.5
Homogenization
Tissue
cells
1000 g
(1000 times the
force of gravity)
10 min
Homogenate
Differential centrifugation
Supernatant poured
into next tube
 used microscopy to identify
the organelles in each pellet
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)
Figure 6.5
Pellet rich in
“microsomes”
(pieces of
plasma membranes and
cells’ internal
membranes)
Pellet rich in
ribosomes
 used biochemical methods to
determine the metabolic
functions associated with
each type of organelle.
Cytology
Biochemistry
Cell biologists can isolate organelles to study their functions
(a) rpm
(revolutions per minute)
(b) x g (force of gravity)
Cytology and biochemistry complement each other in
correlating cellular structure and function.
Concept 6.2: Eukaryotic cells have internal
membranes that compartmentalize their functions
• Two types of cells make up every organism
–
Prokaryotic
–
Eukaryotic
• All cells have several basic features in common
– They are bounded by a plasma membrane
– They contain a semifluid substance called the
cytosol
– They contain chromosomes
– They all have ribosomes
• Prokaryotic cells
– Do not contain a nucleus
– Have their DNA located in a region called the nucleoid
Pili: attachment structures on
the surface of some prokaryotes
Nucleoid: region where the
cell’s DNA is located (not
enclosed by a membrane)
Ribosomes: organelles that
synthesize proteins
Plasma membrane: membrane
enclosing the cytoplasm
Cell wall: rigid structure outside
the plasma membrane
Bacterial
chromosome
Capsule: jelly-like outer coating
of many prokaryotes
0.5 µm
Flagella: locomotion
organelles of
some bacteria
(a) A typical
rod-shaped bacterium
(b) A thin section through the
bacterium Bacillus coagulans
(TEM)
• Eukaryotic cells
– Contain a true nucleus, bounded by a membranous nuclear
envelope.
– Are generally quite a bit bigger than prokaryotic cells
ENDOPLASMIC RETICULUM (ER)
Rough ER
Smooth ER
Nuclear envelope
Nucleolus
NUCLEUS
cytoplasm
Chromatin
Flagelium
Plasma membrane
Centrosome
CYTOSKELETON
Ribosomes
Microvilli
Golgi apparatus
Mitochondrion
Lysosome
- Containing
a variety of
membranebounded
organelles.
Prokaryotic vs Eukaryotic cells
(原核)
(真核)
 Differ in size and complexity
 Basic features: plasma membrane, cytosol, chromosomes,
ribosomes, …
 Difference: as indicated by their names:
Chromosomes
location
Prokaryotic
Eukaryotic
nucleoid
nucleus
(no membrane)
(containing membranous
nuclear envelope)
cytoplasm
only ribosome
(organelles)
size
1-10 mm
10-100 mm
• The logistics of carrying out cellular metabolism
sets limits on the size of cells
• A smaller cell
– Has a higher surface to volume ratio,
Surface area increases while
total volume remains constant
which facilitates the exchange of
materials into and out of the cell
5
1
1
Total surface area
(height  width 
number of sides 
number of boxes)
6
150
750
Total volume
(height  width  length
 number of boxes)
1
125
125
Surface-to-volume
ratio
(surface area  volume)
6
1.2
6
• The plasma membrane
–
Functions as a selective barrier
–
Allows sufficient passage of nutrients
and waste
Outside of cell
Carbohydrate side chain
Hydrophilic
region
Inside of cell
0.1 µm
Figure 6.8 A, B
(a) TEM of a plasma
membrane. The
plasma membrane,
here in a red blood
cell, appears as a
pair of dark bands
separated by a
light band.
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
A Panoramic View of the Eukaryotic Cell
• Eukaryotic cells
–
Have extensive and elaborately arranged internal
membranes, which form organelles
ENDOPLASMIC RETICULUM (ER)
Rough ER
Smooth ER
Nuclear envelope
Nucleolus
NUCLEUS
Chromatin
Flagelium
Plasma membrane
Centrosome
CYTOSKELETON
Microfilaments
Intermediate filaments
Ribosomes
Microtubules
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome
In animal cells but not plant cells:
Lysosomes
Centrioles
Flagella (in some plant sperm)
• A plant cell
Nuclear envelope
Nucleolus
Chromatin
NUCLEUS
Centrosome
Rough
endoplasmic
reticulum
Smooth
endoplasmic reticulum
Ribosomes (small brwon dots)
Central vacuole
Tonoplast
Golgi apparatus
Microfilaments
Intermediate
filaments
CYTOSKELETON
Microtubules
Mitochondrion
Figure 6.9
Peroxisome
Plasma membrane
Chloroplast
Cell wall
Plasmodesmata
Wall of adjacent cell
In plant cells but not animal cells:
Chloroplasts
Central vacuole and tonoplast
Cell wall
Plasmodesmata
Concept 6.3: The eukaryotic cell’s genetic
instructions are housed in the nucleus and carried
out by the ribosomes.
• The nucleus
– Contains most of the genes in the eukaryotic cell
(some genes are located in mitochondria and chloroplasts)
• The nuclear envelope
–
Encloses the nucleus,
separating its contents
from the cytoplasm
Nucleolus
Chromatin
Nucleus
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Pore
complex
Rough ER
• The nuclear envelope
–
Is a double membrane (separated by a space of
20-40 nm)
- Nuclear pore
Nucleus
(100 nm in diameter)
- Nuclear lamina
- Nuclear matrix
- Chromatin
Nucleus
1 µm
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
(a complex of proteins
and DNA)
Nuclear pore
- nucleolus
Pore
complex
(rRNA & protein)
Rough ER
Surface of nuclear
envelope.
1 µm
Ribosome
0.25 µm
Close-up of
nuclear
envelope
Pore complexes (TEM).
Nuclear lamina (TEM).
Ribosomes: Protein Factories in the Cell
• Ribosomes
– Are particles made of ribosomal RNA and protein
– Carry out protein synthesis
• --- free ribosomes : in cytosol
bound ribosomes : attached to outside of the ER or nuclear envelop
Ribosomes
ER
Cytosol
Endoplasmic reticulum (ER)
Structurally
identical and
can alternate
Bound ribosomes
between the
Large two roles
Free ribosomes
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 in the
cell
• The endomembrane system
–
Includes many different structures
~ including the nuclear envelope, endoplasmic reticulum (ER),
Golgi apparatus, lysosomes, vacuoles, and the plasma
membrane. (related either through direct physical continuity
or by the transfer of membrane segment as tiny vesicles.)
• The endoplasmic reticulum (ER)
– Accounts for more than half the total membrane in
many eukaryotic cells
Endoplasmic reticulum (ER)
endoplasmic - “within the cytoplasm”
reticulum
- “ little net ”
* cisternae (membranous tubules and sacs; reservoir for a liquid)
cytosol --- ER lumen (cisternal space)
* smooth ER: lacks ribosomes
rough ER : containing ribosomes (cytoplasmic surface)
• The ER membrane
– Is continuous with the
nuclear envelope
• There are two distinct
Smooth ER
Nuclear
envelope
Rough ER
regions of ER
– Smooth ER, which lacks
ribosomes
ER lumen
Cisternae
– Rough ER, which contains
ribosomes
Ribosomes
Transport vesicle
Smooth ER
Figure 6.12
Transitional ER
Rough ER
200 µm
Smooth ER:
functions in diverse metabolic
processes in various cell types,
including synthesis of lipids,
metabolism of carbohydrates,
store Ca
2+
and detoxification
of drugs and poisons.
* steroids: sex hormones
(testes and ovaries are rich in smooth ER)
* Liver cells (detoxification ex. sedative phenobarbital
however, increase toleurance)
* Muscle cell: sER store Ca2+
Ca2+ pump (cytosol  ER lumen)
Rough ER :
* synthesize secretory proteins.
ex. Pancreas: insulin
~ most secretory proteins are glycoproteins (the carbohydrate
is attached to the protein
in the ER)
Transport vesicles
Smooth ER
Rough ER
Nuclear
envelope
* membrane factory:
 membrane production
ER lumen
Cisternae
Ribosomes
Transport vesicle
Transitional ER
The Golgi Apparatus: Shipping and Receiving Center
• The Golgi apparatus
– Receives many of the transport vesicles produced in the
rough ER
– As a center of manufacturing, warehousing, sorting, and
shipping
– Consists of flattened membranous sacs called cisternae
• Functions of the Golgi apparatus include
– Modification of the products of the rough ER
– Manufacture of certain macromolecules (ex. pectin and noncellulose polysaccharides)
• Golgi apparatus: has a distinct polarity
Golgi
apparatus
“cisternal maturation model”
cis face
(“receiving” side of
Golgi apparatus)
1 Vesicles move
2 Vesicles coalesce to
6 Vesicles also
form new cis Golgi cisternae
from ER to Golgi
transport certain
Cisternae
proteins back to ER
3 Cisternal
maturation:
Golgi cisternae
move in a cisto-trans
direction
Figure 6.13
5 Vesicles transport specific
proteins backward to newer
Golgi cisternae
0.1 0 µm
4 Vesicles form and
leave Golgi, carrying
specific proteins to
other locations or to
the plasma membrane for secretion
trans face
(“shipping” side of
Golgi apparatus)
TEM of Golgi apparatus
Lysosomes: Digestive Compartments
• A lysosome --- acidic pH (pH5)
– Is a membranous sac of hydrolytic enzymes
– Can digest all kinds of macromolecules
– Hydrolytic enzymes and lysosomal membrane are made by
rER  Golgi
• Lysosomes carry out intracellular digestion by
–
Phagocytosis (吞噬作用)
digestion products  pass into the cytosol and become the
nutrientsfor the cell.
- autophagy: recycle the cell’s own organic material.
ex. Liver.
• Lysosomes carry out intracellular digestion by
–
Phagocytosis
Nucleus
1 µm
Lysosome
Lysosome
contains
active hydrolytic
enzymes
Food vacuole
fuses with
lysosome
Hydrolytic
enzymes digest
food particles
Digestive
enzymes
Lysosome
Plasma membrane
Digestion
Figure 6.14 A
Food vacuole
(a) Phagocytosis: lysosome digesting food
• Autophagy
Lysosome containing
two damaged organelles
1µm
Mitochondrion
fragment
Peroxisome
fragment
* Tay-Sachs disease:
a lipid-digesting enzyme
is missing or inactive
Lysosome fuses with
vesicle containing
damaged organelle
Hydrolytic enzymes
digest organelle
components
Lysosome
Vesicle containing
damaged mitochondrion
Figure 6.14 B
Digestion
(b) Autophagy: lysosome breaking down damaged organelle
Vacuoles: Diverse Maintenance Compartments
• A plant or fungal cell
– May have one or several vacuoles
• Food vacuoles
– Are formed by phagocytosis
• Contractile vacuoles
– Pump excess water out of protist cells
• Central vacuoles
–
Are found in plant cells, enclosed by tonoplast.
–
Hold reserves of important organic compounds
and water
largest ~ 80%
function: storage,
waste disposal,
protection,
and growth.
Central vacuole
Cytosol
Tonoplast
Nucleus
Central
vacuole
Cell wall
Chloroplast
Figure 6.15
5 µm
The Endomembrane System: A Review
• Relationships among organelles of the
endomembrane system
1 Nuclear envelope is
connected to rough ER,
which is also continuous
with smooth ER
Nucleus
Rough ER
2 Membranes and proteins
produced by the ER flow in
the form of transport vesicles
to the Golgi
Figure 6.16
Smooth ER
cis Golgi
Nuclear envelop
3 Golgi pinches off transport
Vesicles and other vesicles
that give rise to lysosomes and
Vacuoles
trans Golgi
Plasma
membrane
4 Lysosome available 5 Transport vesicle carries 6 Plasma membrane expands
for fusion with another proteins to plasma
by fusion of vesicles; proteins
vesicle for digestion
membrane for secretion
are secreted from cell
• Concept 6.5: Mitochondria and chloroplasts change
energy from one form to another
• Mitochondria
– Are the sites of cellular respiration
• Chloroplasts
– Found only in plants, are the sites of photosynthesis
Other membranous organelles
Mitochondria & Chloroplasts
--- main energy transformers of cells.
--- not part of the endomembrane system.
membrane proteins are made by free ribosomes in the cytoso
and by ribosomes contained within themselves.
--- containing ribosomes, and a small amount of DNA.
--- semiautonomous organelles (growth and reproduce)
Mitochondria: cellular respiration
(generates ATP by extracting energy from sugars,
fats, and other fuels with the help of O2)
Chloroplasts: photosynthesis (only in plants and algae)
Mitochondria: Chemical Energy Conversion
• Mitochondria
– Are found in nearly all eukaryotic cells
• Mitochondria are enclosed by two membranes
– A smooth outer membrane
– An inner membrane folded into cristae
Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
Mitochondrial
DNA
100 µm
Chloroplasts: Capture of Light Energy
• The chloroplast
– Is a specialized member of a family of closely related plant
organelles called plastids (ex. amyloplast, chromoplast)
– Contains chlorophyll
– Are found in leaves and other green organs of plants and in
algae
Chloroplast
Chloroplast structure includes
- Thylakoids, membranous sacs
- Stroma, the internal fluid
Ribosomes
Stroma
Chloroplast
DNA
Inner and outer
membranes
Granum
1 µm
Thylakoid
Peroxisomes: Oxidation
• Peroxisomes
–
–
(proteins are made primarily in the cytosol, lipids
are made in the ER, and within the peroxisome itself)
Single membrane
Contain enzyme that transfer hydrogen from various substrates
to oxygen, producing hydrogen peroxide as a by-product.
Chloroplast
Peroxisome
Mitochondrion
* Break fatty acid down to
smaller molecules
 mitochondria
* Detoxification in liver
Also contain enzyme that
converts the H2O2 to
water
Figure 6.19
1 µm
Concept 6.6: The cytoskeleton is a network of fibers
that organizes structures and activities in the cell
• The cytoskeleton
– Is a network of fibers extending throughout the cytoplasm
Microtubule
Figure 6.20
0.25 µm
Microfilaments
Cytoskeleton
--- composed of three well-defined
filamentous structures
- Microtubules (tubulin)
- Microfilaments (actin)
- Intermediate filaments
Roles of the Cytoskeleton: Support, Motility, and
Regulation
The cytoskeleton
~ Gives mechanical support to the cell (maintain shape)
~ provides anchorage for many organelles and
cytosolic enzyme molecules
~ Is involved in cell motility (changes in cell location or
more limited movements of part of the cell) which
utilizes motor proteins
Cytoskeletal elements and motor proteins work together
with plasma membrane molecules to allow whole cells to
move along fivers outside the cell. (change in cell location)
The vesicles that bud off
from the ER travel to the
Golgi along tracks built of
cytoskeletal elements.
(movements of part of the
cell)
Figure 6.21 A, B
ATP
Vesicle
Receptor for
motor protein
Motor protein
Microtubule
(ATP powered)
of cytoskeleton
(a) Motor proteins that attach to receptors on organelles can “walk”
the organelles along microtubules or, in some cases, microfilaments.
Vesicles
Microtubule
0.25 µm
(b) Vesicles containing neurotransmitters migrate to the tips of nerve cell
axons via the mechanism in (a). In this SEM of a squid giant axon, two
vesicles can be seen moving along a microtubule. (A separate part of the
experiment provided the evidence that they were in fact moving.)
There are three main types of fibers that make up the
cytoskeleton
Table 6.1
Microtubules
--- hollow tubes; 25 nm (13 columns of tubulin molecules)
--- tubulin molecules: a dimer consisting a-, and b-tubulin
--- dynamic (200 nm~25 mm in length)
--- * compression-resisting
--- 1. shape and support the cell
2. serve as tracks for moving the organelles
(with motor protein)
ex. ~ guide secretory vesicles:
(Golgi apparatus
plasma membrane)
~ chromosome movements in cell division
--- construction of centrosomes, cilia and flagella
Centrosomes and centrioles
~ in many cells, microtubules grow out from a centrosome
(near nucleus)
“microtubule-organizing center” (MTOC)
* A pair of centrioles
(not essential for organizing
microtubule assembly; most
plants lack centrioles)
9 triplet MT
• Cilia and flagella
–
Contain specialized arrangements of microtubules
–
Are locomotor appendages that protrude from some cells
• Flagella beating
pattern
• Ciliary motion
Figure 6.23
Direction of swimming
• Cilia and flagella share a common ultrastructure
~ each has a core microtubules sheathed in an extension
of the plasma membrane.
moter protein
Figure 6.24 A-C
Outer microtubule
doublet
Dynein arms
0.1 µm
“9+2” pattern
Central
microtubule
(9 doublets & 2
central microtubule)
Outer doublets
cross-linking
proteins inside
Microtubules
Radial
spoke
Plasma
membrane
Basal body
(a)
(b)
0.5 µm
0.1 µm
Triplet
(c)
structurally identical
Cross section of basal body
to a centriole
Plasma
membrane
• The protein dynein --- motor protein
- Is responsible for the bending movement of cilia
and flagella
- “ATP” driving the conformational change of dynein
Microtubule
doublets
ATP
Dynein arm
(a) Powered by ATP, the dynein arms of one microtubule doublet
grip the adjacent doublet, push it up, release, and then grip again.
If the two microtubule doublets were not attached, they would slide
Figure 6.25 A
relative to each other.
* radial spokes
ATP
Outer doublets
cross-linking
proteins
1
2
Anchorage
in cell
(b) In a cilium or flagellum, two adjacent doublets cannot slide far because
they are physically restrained by proteins, so they bend. (Only two of
the nine outer doublets in Figure 6.24b are shown here.)
Figure 6.25 B
3
Microfilaments (Actin Filaments)
~ Are built from molecules of the protein actin
~ bear tension (pulling forces)
~ In combination with other proteins, they form a 3D network just
inside the plasma membrane, helping support the cell’s shape.
Microvillus
“Cortex”
outer cytoplasmic layer
--- semisolid gel
~ Ex. found in microvilli
Plasma membrane
Microfilaments
(actin filaments)
Intermediate filaments
Figure 6.26
0.25 µm
• Microfilaments that function in cellular motility
–
Contain the protein myosin in addition to actin
–
Contraction of the muscle cell results from the actin and
myosin filaments sliding past on another, shortening the cell
Muscle cell
Actin filament
Myosin filament
Myosin arm
Figure 6.27 A
(a) Myosin motors in muscle cell contraction.
• Amoeboid movement (localized contraction)
–
Involves the contraction of actin and myosin filaments
Cortex (outer cytoplasm):
gel with actin network
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
Figure 6.27 B
(b) Amoeboid movement
Pseudopodia extend and contract through the reversible assembly
of actin subunits into microfilaments and of microfilaments in
networks that convert cytoplasm from sol to gel.
• Cytoplasmic streaming
~ Is another form of locomotion created by microfilaments
~ Both actin-myosin interactions and sol-gel transformation
brought by actin may involved in.
~ Common in large plant cells, speeds the distribution of
materials within the cell.
Nonmoving
cytoplasm (gel)
Chloroplast
Streaming
cytoplasm
(sol)
Figure 6.27 C
Parallel actin
filaments
(b) Cytoplasmic streaming in plant cells
Cell wall
Intermediate filaments
--- 8~12 nm, specialized for bearing tension
--- are a diverse class of cytoskeletal elements
(belong to a family of protein containing “keratins”)
--- are more permanent fixtures of cells than
microfilaments and microtubules.
--- Maintenance of cell shape
(reinforcing the shape of a cell)
fix organelles in place
Formation of nuclear lamina
Concept 6.7: Extracellular components and
connections between cells help coordinate cellular
activities
Cell Walls of Plants
• The cell wall
–
Is an extracellular structure of plant cells that
distinguishes them from animal cells
–
Are made of cellulose fibers embedded in other
polysaccharides and protein
–
May have multiple layers
• Plant cell walls
–
Are made of cellulose fibers embedded in other
polysaccharides and protein
–
May have multiple layers
Central
vacuole
of cell
Plasma membrane
Secondary cell
wall
Primary
cell wall
Central
vacuole
of cell
Middle
lamella
1 µm
Central vacuole
sticky polysaccharide:
pectins
Cytosol
Plasma membrane
Plant cell walls
Figure 6.28
Plasmodesmata
The Extracellular Matrix (ECM) of Animal Cells
• Animal cells
– Lack cell walls
– Are covered by an elaborate matrix, the ECM
• The ECM
– Is made up of glycoproteins and other
macromolecules
• Functions of the ECM include
-
Support
Adhesion
Movement
Regulation
* The most abundant glycoprotein in the ECM of most
animal cells is collagen.
* Collagen accounts for about half of the total protein in the
human body. --- embedded in a network of proteoglycans.
(glycoprotein – up to 95% carbohydrate)
EXTRACELLULAR FLUID
Collagen
A proteoglycan
complex
Polysaccharide
molecule
Carbohydrates
Core
protein
Fibronectin
Plasma
membrane
Integrin
Figure 6.29
Integrins
Microfilaments
CYTOPLASM
Proteoglycan
molecule
Intercellular Junctions
Plants: Plasmodesmata
• Plasmodesmata
– Are channels that perforate plant cell walls
Cell walls
Interior
of cell
Interior
of cell
Figure 6.30
0.5 µm
Plasmodesmata
Plasma membranes
Intercellular Junctions help integrate cells into
higher levels of structure and function
• In animals, there are
three types of
intercellular junctions
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
- Tight junctions,
0.5 µm
- Desmosomes
- Gap junctions
Tight junctions
Intermediate filaments
Desmosome
Gap
junctions
Space
between
cells
Figure 6.31
Plasma membranes
of adjacent cells
1 µm
Extracellular
matrix
Gap junction
0.1 µm
The Cell:
~ A Living Unit Greater Than the Sum of Its Parts
5 µm
• Cells rely on the integration of structures and
organelles in order to function
Figure 6.32