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Transcript
Chapter 6
A Tour of the Cell
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
• Cell structure is correlated to cellular function
• All cells are related by their descent from
earlier cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-1
Cytoskeleton: microtubule, intermediate filament,
Concept 6.1: To study cells, biologists use
microscopes and the tools of biochemistry
Microscopy
• Scientists use microscopes to visualize cells
too small to see with the naked eye
• In a light microscope (LM), visible light
passes through a specimen and then through
glass lenses, which magnify the image
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• The quality of an image depends on
– 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
10 m
1m
Human height
Length of some
nerve and
muscle cells
0.1 m
Chicken egg
1 cm
Unaided eye
Frog egg
100 µm
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
1 mm
Light microscope
Fig. 6-2
• LMs can magnify effectively to about 1,000
times the size of the actual specimen
• Various techniques enhance contrast and
enable cell components to be stained or
labeled
• Most subcellular structures, including
organelles (membrane-enclosed
compartments), are too small to be resolved by
an LM
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
– Use different methods for enhancing
visualization
RESULT
TECHNIQUEof cellular structures
(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).
(c) Phase-contrast. Enhances contrast
in unstained cells by amplifying
variations in density within specimen;
especially useful for examining living,
unpigmented cells.
Figure 6.3
(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.
50 µm
(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
• 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• 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
Cell Fractionation
• Cell fractionation takes cells apart and
separates the major organelles from one
another
• Ultracentrifuges fractionate cells into their
component parts
• Cell fractionation enables scientists to
determine the functions of organelles
• Biochemistry and cytology help correlate cell
function with structure
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-5
TECHNIQUE
Homogenization
Tissue
cells
Homogenate
1,000 g
(1,000 times the
force of gravity)
Differential centrifugation
10 min
Supernatant poured
into next tube
20,000 g
20 min
Pellet rich in
nuclei and
cellular debris
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
membranes)
Pellet rich in
ribosomes
Concept 6.2: Eukaryotic cells have internal
membranes that compartmentalize their functions
• The basic structural and functional unit of every
organism is one of two types of cells:
prokaryotic or eukaryotic
• Only organisms of the domains Bacteria and
Archaea consist of prokaryotic cells
• Protists, fungi, animals, and plants all consist of
eukaryotic cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Comparing Prokaryotic and Eukaryotic Cells
• Basic features of all cells:
– Plasma membrane
– Semifluid substance called cytosol
– Chromosomes (carry genes)
– Ribosomes (make proteins)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Bacterial
chromosome
(a) A typical
rod-shaped bacterium
Figure 6.6 A, B
Plasma membrane: membrane
enclosing the cytoplasm
Cell wall: rigid structure outside
the plasma membrane
Capsule: jelly-like outer coating
of many prokaryotes
0.5 µm
Flagella: locomotion
organelles of
some bacteria
(b) A thin section through the
bacterium Bacillus coagulans
(TEM)
• 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• The plasma membrane is a selective barrier
that allows sufficient passage of oxygen,
nutrients, and waste to service the volume of
every cell
• The general structure of a biological membrane
is a double layer of phospholipids
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
• The logistics of carrying out cellular metabolism
sets limits on the size of cells
• The surface area to volume ratio of a cell is
critical
• As the surface area increases by a factor of n2,
the volume increases by a factor of n3
• Small cells have a greater surface area relative
to volume
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
A Panoramic View of the Eukaryotic Cell
• A eukaryotic cell has internal membranes that
partition the cell into organelles
• Plant and animal cells have most of the same
organelles
BioFlix: Tour Of An Animal Cell
BioFlix: Tour Of A Plant Cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
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 DNA in a
eukaryotic cell
• Ribosomes use the information from the DNA
to make proteins
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Nucleus: Information Central
• The nucleus contains most of the cell’s genes
and is usually the most conspicuous organelle
(additional DNA where?)
• The nuclear envelope encloses the nucleus,
separating it from the cytoplasm
• The nuclear membrane is a double membrane;
each membrane consists of a lipid bilayer
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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)
• Pores regulate the entry and exit of molecules
from the nucleus
• The shape of the nucleus is maintained by the
nuclear lamina, which is composed of protein
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• In the nucleus, DNA and proteins form genetic
material called chromatin
• Chromatin condenses to form discrete
chromosomes
• The nucleolus is located within the nucleus
and is the site of ribosomal RNA (rRNA)
synthesis
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Ribosomes: Protein Factories
• Ribosomes are particles made of ribosomal
RNA and protein
• Ribosomes carry out protein synthesis in two
locations:
– In the cytosol (free ribosomes)
– On the outside of the endoplasmic reticulum or
the nuclear envelope (bound ribosomes)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Crystal Structure of the large ribosomal subunit
•Harry Noller at the University of
California Santa Cruz
•Venki Ramakrishnan at the University
of Cambridge,
•Thomas Steitz at Yale University
Concept 6.4: The endomembrane system regulates
protein traffic and performs metabolic functions in
the cell
• Components of the endomembrane system:
– Nuclear envelope
– Endoplasmic reticulum
– Golgi apparatus
– Lysosomes
– Vacuoles
– Plasma membrane
• These components are either continuous or
connected via transfer by vesicles
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Endoplasmic Reticulum: Biosynthetic Factory
• The endoplasmic reticulum (ER) accounts for
more than half of the total membrane in many
eukaryotic cells
• The ER membrane is continuous with the
nuclear envelope
• There are two distinct regions of ER:
– Smooth ER, which lacks ribosomes
– Rough ER, with ribosomes studding its
surface
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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 ER
• The smooth ER
– Synthesizes lipids
– Metabolizes carbohydrates
– Detoxifies poison
– Stores calcium
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Functions of Rough ER
• The rough ER
– Has bound ribosomes, which secrete
glycoproteins (proteins covalently bonded to
carbohydrates)
– Distributes transport vesicles, proteins
surrounded by membranes
– Is a membrane factory for the cell; adding
membrane proteins and phospholipids to its
own membrane and other endomembrane
system by transport vesicles
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Golgi Apparatus: Shipping and
Receiving Center
• 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
• A lysosome is a membranous sac of hydrolytic
enzymes that can digest macromolecules
• Lysosomal enzymes can hydrolyze proteins,
fats, polysaccharides, and nucleic acids
Animation: Lysosome Formation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-15
Central vacuole
Cytosol
Nucleus
Central
vacuole
Cell wall
Chloroplast
5 µm
The Endomembrane System: A Review
• The endomembrane system is a complex and
dynamic player in the cell’s compartmental
organization
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-16-1
Nucleus
Rough ER
Smooth ER
Plasma
membrane
Fig. 6-16-2
Nucleus
Rough ER
Smooth ER
cis Golgi
trans Golgi
Plasma
membrane
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 are the sites of cellular
respiration, a metabolic process that generates
ATP
• Chloroplasts, found in plants and algae, are
the sites of photosynthesis
• Peroxisomes are oxidative organelles
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Mitochondria and chloroplasts
– Are not part of the endomembrane system
– Have a double membrane
– Have proteins made by free ribosomes
– Contain their own DNA
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Mitochondria: Chemical Energy Conversion
• Mitochondria are in nearly all eukaryotic cells
• They have a smooth outer membrane and an
inner membrane folded into cristae
• The inner membrane creates two
compartments: intermembrane space and
mitochondrial matrix
• Some metabolic steps of cellular respiration
are catalyzed in the mitochondrial matrix
• Cristae present a large surface area for
enzymes that synthesize ATP
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
• The chloroplast is a member of a family of organelles
called plastids
• Chloroplasts contain the green pigment chlorophyll, as
well as enzymes and other molecules that function in
photosynthesis
• Chloroplasts are found in leaves and other green organs of
plants and in algae
• Chloroplast structure includes:
– Thylakoids, membranous sacs, stacked to form a
granum
– Stroma, the internal fluid contain chloroplast DNA &
ribosome
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-18
Ribosomes
Stroma
Inner and outer
membranes
Granum
Thylakoid
1 µm
Peroxisomes: Oxidation
• Peroxisomes
–
Transfer hydrogen from substrates to oxygen producing hydrogen
peroxide (H2O2) as a by-product; detoxification
–
break fatty acids down into smaller molecules
–
Glyoxysome in plant seed converts faty acids to sugar
–
Grow larger by incorporating proteins and lipids and increase in
number by splitting
Chloroplast
Peroxisome
Mitochondrion
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
• It organizes the cell’s structures and activities,
anchoring many organelles
• It is composed of three types of molecular
structures:
– Microtubules
– Microfilaments
– Intermediate filaments
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-20
Microtubule
0.25 µm
Microfilaments
Roles of the Cytoskeleton: Support, Motility, and
Regulation
• The cytoskeleton helps to support the cell and
maintain its shape
• It interacts with motor proteins to produce
motility
• Inside the cell, vesicles can travel along
“monorails” provided by the cytoskeleton
• Recent evidence suggests that the
cytoskeleton may help regulate biochemical
activities
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-21
ATP
Vesicle
Receptor for
motor protein
Motor protein Microtubule
(ATP powered) of cytoskeleton
(a)
Microtubule
(b)
Vesicles
0.25 µm
Components of the Cytoskeleton
• 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
More permanent than microtubule and microfilament
Fibrous subunit (keratins
coiled together)
8–12 nm
Microtubules
• Microtubules are hollow rods about 25 nm in
diameter and about 200 nm to 25 microns long
• Functions of microtubules:
– Shaping the cell
– Guiding movement of organelles
– Separating chromosomes during cell division
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Centrosomes and Centrioles
• In many cells, microtubules grow out from a
centrosome near the nucleus
• The centrosome is a “microtubule-organizing
center”
• In animal cells, the centrosome has a pair of
centrioles, each with nine triplets of
microtubules arranged in a ring
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-22
Centrosome
Microtubule
Centrioles
0.25 µm
Longitudinal section Microtubules Cross section
of one centriole
of the other centriole
Cilia and Flagella
• Microtubules control the beating of cilia and
flagella, locomotor appendages of some cells
• Cilia and flagella differ in their beating patterns
Video: Chlamydomonas
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Video: Paramecium Cilia
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:
– A core of microtubules sheathed by the plasma
membrane
– A basal body that anchors the cilium or
flagellum
– A motor protein called dynein, which drives
the bending movements of a cilium or
flagellum
Animation: Cilia and Flagella
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-25
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 are solid rods about 7 nm in
diameter, built as a twisted double chain of
actin subunits
• The structural role of microfilaments is to bear
tension, resisting pulling forces within the cell
• They form a 3-D network called the cortex just
inside the plasma membrane to help support
the cell’s shape
• Bundles of microfilaments make up the core of
microvilli of intestinal cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-26
Microvillus
Plasma membrane
Microfilaments (actin
filaments)
Intermediate filaments
0.25 µm
• Microfilaments that function in cellular motility
contain the protein myosin in addition to actin
• In muscle cells, thousands of actin filaments
are arranged parallel to one another
• Thicker filaments composed of myosin
interdigitate with the thinner actin fibers
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-27
Muscle cell
Actin filament
Myosin filament
Myosin arm
(a) Myosin motors in muscle cell contraction
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
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
• Localized contraction brought about by actin
and myosin also drives amoeboid movement
• Pseudopodia (cellular extensions) extend and
contract through the reversible assembly and
contraction of actin subunits into microfilaments
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Cytoplasmic streaming is a circular flow of
cytoplasm within cells
• This streaming speeds distribution of materials
within the cell
• In plant cells, actin-myosin interactions and solgel transformations drive cytoplasmic
streaming
Video: Cytoplasmic Streaming
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Intermediate Filaments
• Intermediate filaments range in diameter from
8–12 nanometers, larger than microfilaments
but smaller than microtubules
• They support cell shape and fix organelles in
place
• Intermediate filaments are more permanent
cytoskeleton fixtures than the other two classes
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Concept 6.7: Extracellular components and
connections between cells help coordinate cellular
activities
• Most cells synthesize and secrete materials
that are external to the plasma membrane
• These extracellular structures include:
– Cell walls of plants
– The extracellular matrix (ECM) of animal cells
– Intercellular junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cell Walls of Plants
• The cell wall is an extracellular structure that
distinguishes plant cells from animal cells
• Prokaryotes, fungi, and some protists also have
cell walls
• The cell wall protects the plant cell, maintains its
shape, and prevents excessive uptake of water
• Plant cell walls are made of cellulose fibers
embedded in other polysaccharides and protein
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Plant cell walls may have multiple layers:
– Primary cell wall: relatively thin and flexible
– Middle lamella: thin layer between primary
walls of adjacent cells (pectin)
– Secondary cell wall (in some cells): added
between the plasma membrane and the
primary cell wall
• Plasmodesmata are channels between
adjacent plant cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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 lack cell walls but are covered by
an elaborate extracellular matrix (ECM)
• The ECM is made up of glycoproteins such as
collagen, proteoglycans, and fibronectin
• ECM proteins bind to receptor proteins in the
plasma membrane called integrins
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-30
Collagen is about half of the total protein in human body
Collagen
Proteoglycan
complex
EXTRACELLULAR FLUID
Polysaccharide
molecule
Carbohydrates
Fibronectin
Core
protein
Integrins
Proteoglycan
molecule
Plasma
membrane
Proteoglycan complex
Microfilaments
CYTOPLASM
Integrins are the linker between microfilaments in cytoskeleton and ECM in extracellular fluid
And transmit signals between the ECM and the cytoskeleton and result in changes in cell behavior
• Functions of the ECM:
– Support
– Adhesion
– Movement
– Regulation of genes :
information of ECM reaches the nucleus by a combination of mechanical
and chemical signaling pathways. Changes in the cytoskeleton may in
turn trigger chemical signaling pathways inside the cell, leading to
change in proteins and functions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Intercellular Junctions
• Neighboring cells in tissues, organs, or organ
systems often adhere, interact, and
communicate through direct physical contact
• Intercellular junctions facilitate this contact
• There are several types of intercellular junctions
– Plasmodesmata
– Tight junctions
– Desmosomes
– Gap junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Plasmodesmata in Plant Cells
• Plasmodesmata are channels that perforate
plant cell walls
• Through plasmodesmata, water and small
solutes (and sometimes proteins and RNA) can
pass from cell to cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-31
Cell walls
Interior
of cell
Interior
of cell
0.5 µm
Plasmodesmata Plasma membranes
Tight Junctions, Desmosomes, and Gap Junctions in
Animal Cells
• At tight junctions, membranes of neighboring cells are
pressed together, preventing leakage of extracellular fluid.
Continuous sealing in an intestine
• Desmosomes (anchoring junctions) fasten cells together
into strong sheets; anchor intermediate filament in
cytoplasm and attach muscle cells to each other in a
muscle. “muscle tears” involve the rupture of desmosomes.
• Gap junctions (communicating junctions) provide
cytoplasmic channels between adjacent cells, just like
plasmodesmata in plants. Necessary for communication
between cells in heart, muscle and in animal embryos.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Fig. 6-32a
Tight junctions prevent
fluid from moving
across a layer of cells
Tight junction
Animation: Tight Junctions
Intermediate
filaments
Desmosome
Animation: Desmosomes
Animation: Gap Junctions
Gap
junctions
Space
between
cells
Plasma membranes
of adjacent cells
Extracellular
matrix
The Cell: A Living Unit Greater Than the Sum of
Its Parts
• Cells rely on the integration of structures and
organelles in order to function
• For example, a macrophage’s ability to destroy
bacteria involves the whole cell, coordinating
components such as the cytoskeleton,
lysosomes, and plasma membrane
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
TAXOL
•
Paclitaxel은 Taxus brevifolia Nutt. (Taxaceae)(미국 주목나무-Western Yew)의
주피(bark)에서 추출한 diterpenoid taxane 유도체로 천연 taxane ring을 가진
alkaloid이다. (1) 이 taxane ring과 ester side chain이 cytotoxicity 작용을 가지는 것으로
알려졌다.(1) Paclitaxel은 수용성이 극히 낮아 제제화하기 위해 polyoxyethylated castor
oil과 absolute ethanol의 혼합물인 Cremorphor® EL이라는 용제를 사용하고 있다. (3)
따라서 임상적으로 이러한 용제가 과량 투여되므로 심장독성과 과민반응이 발생하는
것으로 보고되고 있다.
Taxol 와 -, - tubulin complex 구조
1.2 Mechanism of Action
Paclitaxel은 1992년12월에 난치성 난소암의 치료제로 FDA의 승인을 받은 항암제로 세포
내 microtubule의 assembly를 증진시키고 disassembly를 저해함으로써 항암효과를
나타내는 독특한 약물이다.(2) Microtubule이란 세포질(cytoplasm)에 있는 가는 tube 같은
구조로써 세포의 골격 형성과 motility를 유지하며 유사분열 중기에서 방추사의 형성과
분열시 이동에 관여한다.(2) Microtubule은 tubulin dimer라는 고유의 subunit로
이루어졌고 이 tubulin이 assembly되어 microtubule을 형성한다. .(2) 형성된
microtubule은 유사분열시 기능수행을 위해서는 disassembly 되어야 한다. .(2)
Paclitaxel은 암세포의 microtubule의 assembly를 증진 시키고 일단 형성된 microtubule을
안정화시켜 polymerization 상태로 남아있게 한다.(2) Fuchs과 Johnson의 초기 발견에
의하면, microtubule의 disassembly를 저해하여 유사분열에 필요한 방추사의 형성을
억제하므로 세포 주기상 암 세포가 G2기와 M기에 머무르게 되어 cytotoxic effect를
가진다. 이는 vincristine, vinblastine, colchicines, podophyllotoxin, maytansine과 같은
항암제와 같은 작용이나,(1) paclitaxel은 다른 항암제와 달리 microtubule을
stabilize시키고, depolymerization을 억제시킨다.(2) 또한 이 G2기와 M기 는 방사선에
매우 민감한 주기이므로 radiation therapy와 병용할 시 cytotoxicity가 증가하게 된다. (6)
Fig. 6-UN1a
Structure
Cell Component
Concept 6.3
The eukaryotic cell’s genetic
instructions are housed in
the nucleus and carried out
by the ribosomes
Nucleus
Function
Surrounded by nuclear
envelope (double membrane)
perforated by nuclear pores.
The nuclear envelope is
continuous with the
endoplasmic reticulum (ER).
Houses chromosomes, made of
chromatin (DNA, the genetic
material, and proteins); contains
nucleoli, where ribosomal
subunits are made. Pores
regulate entry and exit os
materials.
Two subunits made of ribosomal RNA and proteins; can be
free in cytosol or bound to ER
Protein synthesis
(ER)
Ribosome
Fig. 6-UN1b
Cell Component
Concept 6.4
Endoplasmic reticulum
The endomembrane system
(Nuclear
regulates protein traffic and
envelope)
performs metabolic functions
in the cell
Golgi apparatus
Lysosome
Vacuole
Structure
Function
Extensive network of
membrane-bound tubules and
sacs; membrane separates
lumen from cytosol;
continuous with
the nuclear envelope.
Smooth ER: synthesis of
lipids, metabolism of carbohydrates, Ca2+ storage, detoxification of drugs and poisons
Stacks of flattened
membranous
sacs; has polarity
(cis and trans
faces)
Rough ER: Aids in sythesis of
secretory and other proteins
from bound ribosomes; adds
carbohydrates to glycoproteins;
produces new membrane
Modification of proteins, carbohydrates on proteins, and phospholipids; synthesis of many
polysaccharides; sorting of
Golgi products, which are then
released in vesicles.
Breakdown of ingested subMembranous sac of hydrolytic stances cell macromolecules,
enzymes (in animal cells)
and damaged organelles for
recycling
Large membrane-bounded
vesicle in plants
Digestion, storage, waste
disposal, water balance, cell
growth, and protection
Fig. 6-UN1c
Cell Component
Concept 6.5
Mitochondrion
Mitochondria and chloroplasts change energy from
one form to another
Structure
Bounded by double
membrane;
inner membrane has
infoldings (cristae)
Function
Cellular respiration
Chloroplast
Typically two membranes
around fluid stroma, which
contains membranous thylakoids
stacked into grana (in plants)
Photosynthesis
Peroxisome
Specialized metabolic
compartment bounded by a
single membrane
Contains enzymes that transfer
hydrogen to water, producing
hydrogen peroxide (H2O2) as a
by-product, which is converted
to water by other enzymes
in the peroxisome