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Chapter 6
A Tour of the Cell
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
You should now be able to:
1. Distinguish between the following pairs of
terms: 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
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5. Describe the structure of a plant cell wall
6. Describe the structure and roles of the
extracellular matrix in animal cells
7. Describe the intercellular junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview: The Fundamental Units of Life
• All organisms are made of cells- cell theory
• The cell is the simplest collection of matter
that can live
• 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
10 m
1m
Human height
Length of some
nerve and
muscle cells
0.1 m
Chicken egg
1 cm
Microscopy
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
• 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
Fig. 6-4
TECHNIQUE
(a) Scanning electron
microscopy (SEM)
RESULTS
Cilia
1 µm
(b) Transmission electron Longitudinal Cross section
section of
of cilium
microscopy (TEM)
1 µm
cilium
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
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Comparing Prokaryotic and Eukaryotic Cells
• Basic features of all cells:
– Plasma membrane
– Semifluid substance called cytosol
– Chromosomes (carry genes)
– Ribosomes (make proteins)
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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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-6
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 µm
(a) A typical
rod-shaped
bacterium
Flagella
(b) A thin section
through the
bacterium
Bacillus
coagulans (TEM)
• 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
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
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
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Fig. 6-10
Nucleus
1 µm
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Pore
complex
Surface of
nuclear envelope
Rough ER
Ribosome
1 µm
0.25 µm
Close-up of nuclear
envelope
Pore complexes (TEM)
Nuclear lamina (TEM)
• 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
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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
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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
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
Functions of Smooth ER
• The smooth ER
– Synthesizes lipids
– Metabolizes carbohydrates
– Detoxifies poison
– Stores calcium
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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
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
• Some types of cell can engulf another cell by
phagocytosis; this forms a food vacuole
• A lysosome fuses with the food vacuole and
digests the molecules
• Lysosomes also use enzymes to recycle the
cell’s own organelles and macromolecules, a
process called autophagy
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-14a
Nucleus
1 µm
Lysosome
Lysosome
Digestive
enzymes
Plasma
membrane
Digestion
Food vacuole
(a) Phagocytosis
Fig. 6-14b
Vesicle containing
two damaged organelles
1 µm
Mitochondrion
fragment
Peroxisome
fragment
Lysosome
Peroxisome
Vesicle
(b) Autophagy
Mitochondrion
Digestion
Vacuoles- A plant cell or fungal cell may have one or several
vacuoles
• Food vacuoles are formed by phagocytosis
• Contractile vacuoles, found in many
freshwater protists, pump excess water out of
cells
• Central vacuoles, found in many mature plant
cells, hold organic compounds and water
Video: Paramecium Vacuole
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Fig. 6-15
Central vacuole
Cytosol
Nucleus
Central
vacuole
Cell wall
Chloroplast
5 µm
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. 6-16-3
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
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• 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
Fig. 6-17
Mitochondria: Chemical Energy Conversion
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-18
Chloroplast structure includes:
Thylakoids, membranous sacs, stacked to form a granum
Stroma, the internal fluid
Ribosomes
Stroma
Inner and outer
membranes
Granum
Thylakoid
1 µm
Fig. 6-20
Cytoskeleton is composed of three types of molecular
structures:
Microtubules
Microfilaments
Intermediate filaments
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
Microtubules
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
Fig. 6-23
Direction of swimming
(a) Motion of flagella
Microtubules- Cilia and Flagella
5 µm
Direction of organism’s movement
Power stroke Recovery stroke
(b) Motion of cilia
15 µm
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. 6-25b
ATP
Cross-linking proteins
inside outer doublets
Anchorage
in cell
(b) Effect of cross-linking proteins
1
3
2
(c) Wavelike motion
Fig. 6-26
Microvillus
Plasma membrane
Microfilaments (actin
filaments)
Intermediate filaments
0.25 µm
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
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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
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. 6-30a
Collagen
Proteoglycan
complex
EXTRACELLULAR FLUID
Fibronectin
Integrins
Plasma
membrane
Microfilaments
CYTOPLASM
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
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-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