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How are cells able
to move? List some different
techniques of cell locomotion.
Amoeba in Motion
http://viewpure.com/7pR7TNzJ_pA
Ciliates and Flagellates
http://viewpure.com/E1L27sUzwQ0
Cytoskeleton
http://viewpure.com/5rqbmLiSkpk
Actin Microfilaments
• two gently twisted strands of actin subunits
– long but only 7nm in diameter
– maintain shape of the cell
– bearing tension (pull) rather than resistance (push)
– instrumental in major changes of cell shape such as
• Pseudopodia
• muscle contractions
• cleavage that occurs during cell division.
Tubulin - Microtubules
• The microtubule subunits wind around in a
continuously growing strand and can be added to
lengthen the hollow tube that is formed
– 25nm in diameter
– Hollow tube part is 15 nm in diameter
• used in cell motility by flagella and cilia
• Maintains the shape of a cell by resisting compression
• used to move around items inside the cell, such as
organelles or chromosomes during cell division.
Dividing newt lung cell seen under a light microscope and colored using
fluorescent dyes: chromosomes in blue, intermediate filaments in red, and
spindle fibers (bundled microtubules assembled for cell division) in green.
Fig. 6-21
ATP
Vesicle
Receptor for
motor protein
Motor protein Microtubule
(ATP powered) of cytoskeleton
(a)
Microtubule
(b)
Vesicles
0.25 µm
Intermediate Filaments
• Keratin protein fibers
– arranged in cords of differing diameters of 8-12nm
(depending on the function in the cell)
• Serve as permanent structures, unlike the
microtubules and microfilaments
– part of a permanent scaffolding
– serve to maintain rigid cell shape
– anchor organelles in fixed positions when necessary
• the nucleus is fixed in a position with rigid intermediate
filaments
Name the three types of structures
which make up the cytoskeleton.
– Microtubules
– Microfilaments
– Intermediate filaments
• Describe the differences in size between
microtubules, microfilaments and intermediate
filaments.
Components of 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 6-1
10 µm
10 µm
10 µm
Column of tubulin dimers
Keratin proteins
Actin subunit
Fibrous subunit (keratins
coiled together)
25 nm
7 nm


Tubulin dimer
8–12 nm
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 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
• Cilia and flagella differ in their beating patterns
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
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. 6-25a
Microtubule
doublets
ATP
Dynein
protein
(a) Effect of unrestrained dynein movement
Fig. 6-25b
ATP
Cross-linking proteins
inside outer doublets
Anchorage
in cell
(b) Effect of cross-linking proteins
1
3
2
(c) Wavelike motion
Hypothesis of Flagellar Beating
https://www.youtube.com/watch?v=SlZtSD
alef0
• 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, 6-27a
Muscle cell
Actin filament
Myosin filament
Myosin arm
(a) Myosin motors in muscle cell contraction
Actin – Myosin Interaction
http://viewpure.com/zQocsLRm7_A
• actin and myosin drive 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
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
– a circular flow of cytoplasm within cells
– speeds distribution of materials within the cell
– In plant cells, actin-myosin interactions and
sol-gel transformations drive cytoplasmic
streaming
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cyclosis in Elodea
http://viewpure.com/PFtzs_cUddI
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
• cell wall
– an extracellular structure that distinguishes plant
cells from animal cells
– Prokaryotes, fungi, and some protists also have
cell walls
– 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
– 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
– covered by an elaborate extracellular matrix
(ECM)
– made up of glycoproteins such as collagen,
proteoglycans, and fibronectin
• bind to receptor proteins in the plasma
membrane called integrins
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-30
Collagen
Proteoglycan
complex
EXTRACELLULAR FLUID
Polysaccharide
molecule
Carbohydrates
Fibronectin
Core
protein
Integrins
Proteoglycan
molecule
Plasma
membrane
Proteoglycan complex
Microfilaments
CYTOPLASM
Fig. 6-30a
Collagen
Proteoglycan
complex
EXTRACELLULAR FLUID
Fibronectin
Integrins
Plasma
membrane
Microfilaments
CYTOPLASM
Fig. 6-30b
Polysaccharide
molecule
Carbohydrates
Core
protein
Proteoglycan
molecule
Proteoglycan complex
• Functions of the Extracellular matrix (ECM):
– Support
– Adhesion
– Movement
– Regulation
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
– channels that perforate plant cell walls
– 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
• Desmosomes
– (anchoring junctions) fasten cells together into
strong sheets
• Gap junctions
– (communicating junctions) provide cytoplasmic
channels between adjacent cells
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
Intermediate
filaments
Desmosome
Gap
junctions
Space
between
cells
Plasma membranes
of adjacent cells
Extracellular
matrix
Fig. 6-32b
Tight junction
0.5 µm
Fig. 6-32c
Desmosome
1 µm
Fig. 6-32d
Gap junction
0.1 µm
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
Fig. 6-33
Fig. 6-UN1
Cell Component
Concept 6.3
The eukaryotic cell’s genetic
instructions are housed in
the nucleus and carried out
by the ribosomes
Structure
Surrounded by nuclear
envelope (double membrane)
perforated by nuclear pores.
The nuclear envelope is
continuous with the
endoplasmic reticulum (ER).
Nucleus
Function
Houses chromosomes, made of
chromatin (DNA, the genetic
material, and proteins); contains
nucleoli, where ribosomal
subunits are made. Pores
regulate entry and exit of
materials.
(ER)
Two subunits made of riboProtein synthesis
somal RNA and proteins; can be
free in cytosol or bound to ER
Ribosome
Concept 6.4
The endomembrane system
regulates protein traffic and
performs metabolic functions
in the cell
Concept 6.5
Mitochondria and chloroplasts change energy from
one form to another
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
Golgi apparatus
Stacks of flattened
membranous
sacs; has polarity
(cis and trans
faces)
Modification of proteins, carbohydrates on proteins, and phospholipids; synthesis of many
polysaccharides; sorting of Golgi
products, which are then
released in vesicles.
Lysosome
Membranous sac of hydrolytic
enzymes (in animal cells)
Vacuole
Large membrane-bounded
vesicle in plants
Digestion, storage, waste
disposal, water balance, cell
growth, and protection
Mitochondrion
Bounded by double
membrane;
inner membrane has
infoldings (cristae)
Cellular respiration
Endoplasmic reticulum
(Nuclear
envelope)
Chloroplast
Peroxisome
Rough ER: Aids in synthesis of
secretory and other proteins from
bound ribosomes; adds
carbohydrates to glycoproteins;
produces new membrane
Breakdown of ingested substances,
cell macromolecules, and damaged
organelles for recycling
Typically two membranes
Photosynthesis
around fluid stroma, which
contains membranous thylakoids
stacked into grana (in plants)
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
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
You should now be able to:
1. Distinguish between the following pairs of
terms: magnification and resolution;
prokaryotic and eukaryotic cell; free and
bound ribosomes; smooth and rough ER
2. Describe the structure and function of the
components of the endomembrane system
3. Briefly explain the role of mitochondria,
chloroplasts, and peroxisomes
4. Describe the functions of the cytoskeleton
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
5. Compare the structure and functions of
microtubules, microfilaments, and
intermediate filaments
6. Explain how the ultrastructure of cilia and
flagella relate to their functions
7. Describe the structure of a plant cell wall
8. Describe the structure and roles of the
extracellular matrix in animal cells
9. Describe four different intercellular junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
How might cells from various parts of
the body differ in the number and types
of cellular organelles they contain due
to their specific function?
• stomach cell
– rough ER for secretion
• muscle cell
– mitochondria for ATP
• liver storage cell
– vacuoles for storage
• Liver detoxification cell
– peroxisomes and smooth ER to break down toxins
• Adipose cell
– vacuoles for storage
• white blood cell
– lysosomes to break down engulfed pathogens
• mesophyll cell—plant leaf cell
– chloroplasts for photosynthesis
• potato cell
– vacuoles for starch storage
Recycling
• Cells are wonderful at recycling!
– the endomembrane system
• cycles phospholipids
– lysosomes, peroxisomes and the smooth ER
• break down macromolecules to component parts and
reassemble them
– the cytoskeleton
• constant flow of assembling and de-assembling
subunits
Why are cells so efficient at recycling?
• Limited resources
• limited energy
• efficiency