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Chapter 6
A Tour of the Cell
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Importance of Cells
Cell Theory:
1. All organisms are composed of one or
more cells
2. Cells are the smallest living things
3. Cells arise only by division of a
previously existing cell
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Cell Size
1. Cell size
–
from a few micrometers to several centimeters
2. Most cells are small because larger cells do not function
efficiently
3. It is advantageous to have a large surface-to-volume ratio
– Smaller sizes have greater Surface for volume
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• A smaller cell
– Has a higher surface to volume ratio, which
facilitates the exchange of materials into and
out of the cell
Surface area increases while
total volume remains constant
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
12
6
Figure 6.7
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• Cell structure is correlated to cellular function
Figure 6.1
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10 µm
Visualizing Cells
Unaided eye
• Different types of microscopes
– Can be used to visualize different sized
cellular structures
10 m
0.1 m
Human height
Length of some
nerve and
muscle cells
Chicken egg
1 cm
Light microscope
1m
10 µ m
1µm
100 nm
Most plant
and Animal
cells
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
10 nm
Ribosomes
Proteins
1 nm
Lipids
Small molecules
Figure 6.2
0.1 nm
Atoms
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Electron microscope
100 µm
Electron microscope
Frog egg
1 mm
Measurements
1 centimeter (cm) = 102 meter (m) = 0.4 inch
1 millimeter (mm) = 10–3 m
1 micrometer (µm) = 10–3 mm = 10–6 m
1 nanometer (nm) = 10–3 mm = 10–9 m
– 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).
(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
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(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
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Electron Microscopes
• 1. 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)
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Electron Microscopes
2. 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)
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Cross section
of cilium
1 µm
Types of Cells
Two types:
1. Prokaryotic – NO NUCLEUS
2. Eukaryotic - NUCLEUS
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Common features
Prokaryotic & Eukaryotic Cells share:
1. Bound by plasma membrane
2. Contain cytosol – semifluid substance where
organelles found
3. Have ribosomes
4. Contain chromosomes
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Prokaryotes
Eukaryotes
1.
Contain a membrane bound nucleus
No membrane bound NUCLEUS
DNA is found is specialized region of the
cytoplasm called NUCLEOID region
Includes nucleoplasm, DNA, & DNA
associated enzymes
2. No membrane bound ORGANELLES
Many membrane organelles
Sub cellular structure that contains
components which have SPECIFIC functions
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Prokaryotes
Eukaryotes
3. Size – very small (.2 to 50 micrometers)
Size – much larger (100 micrometers)
4. DNA is present as a SINGLE CIRCULAR
MOLECULE (called genophore)
Multiple molecules of LINEAR DNA (called
chromosomes)
5. No HISTONE proteins
DNA organized around HISTONE proteins
6. Reproduce by BINARY FISSION
Reproduce by MITOSIS
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Prokaryotes
Eukaryotes
7. No cholesterol in plasma membrane (less
stable)
Cholesterol to stabilize
8. 70 S ribosomes (refers to mass)
80 S ribosomes
9. Cell wall of PEPTIDOGLYCAN
No Peptidoglycan
May have no cell wall
If cell wall (composed of cellulose or chitin)
10. Bacteria & Archaea
Protista (primitive)
Fungi, Plantae, Animalia
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Prokaryotes
•
1. Plasma Membrane
•
2. Ribosomes
•
3. Cytoplasm
•
4. Cell wall of peptidoglycan
•
5. Some have flagella (for movement)
•
6. Pili (small hair-like appendages found on surface of bacteria)
•
Aid in ADHERANCE
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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
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
Figure 6.6 A, B
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(b) A thin section through the
bacterium Bacillus coagulans
(TEM)
Eukaryotic sub cell structures
1. NUCLEUS
a.
Surrounded by a double membrane called NUCLEAR
MEMBRANE or Nuclear envelope
Studded with nuclear PORES (mRNA exit here)
b. Nucleolus – dark staining region within the nucleus
* site for ribosome assembly
c. DNA - usually in the for of chromatin (with histone
proteins) - DNA in this state is uncondensed
Chromosomes – condensed DNA only visualized during
MITOSIS (cell division that makes exact copies)
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• The nuclear envelope
– Encloses the nucleus, separating its contents
from the cytoplasm
Nucleus
1 µm
Nucleolus
Chromatin
Nucleus
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Pore
complex
Rough ER
Surface of nuclear
envelope.
1 µm
Ribosome
0.25 µm
Close-up of
nuclear
envelope
Figure 6.10
Pore complexes (TEM).
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Nuclear lamina (TEM).
Eukaryotic Sub Structures
d.
Enzymes that interact w/DNA (transcription & DNA
replication)
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2.
Endoplasmic Reticulum (ER)
a. Huge collection of membrane bound “tubes” that
snake throughout the cytoplasm
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• The ER membrane
– Is continuous with the nuclear envelope
Smooth ER
Rough ER
Nuclear
envelope
ER lumen
Cisternae
Ribosomes
Transitional ER
Transport vesicle
Smooth ER
Rough ER 200 µm
Figure 6.12
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b. Types of ER
1. Rough ER
covered with Ribosomes (little circles)
Main site for protein synthesis
Newly made proteins are pushed into the
LUMEN (opening or empty center region or the
Rough ER)
carry out initial modifications of newly
manufactured protein
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2. Smooth ER
No Ribosomes – looks exactly like rough ER w/o ribo
site for synthesis of lipids & carbohydrates
site for toxin inactivation
ex. Alcohol dehydrogenase
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3. Ribosomes
a. Composed of ribosomal RNA and protein
2 Sub units (large and small)
b. Carry out protein synthesis (aka protein
factories)
c. Two types
1. Free ribosomes – located in cytosol
(proteins will function within cytosol)
2. Bound ribosomes - located on Rough ER
(proteins will be packaged for insertion into
membranes, packaging within organelles)
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– Carry out protein synthesis
Ribosomes
ER
Cytosol
Endoplasmic reticulum (ER)
Free ribosomes
Bound ribosomes
Large
subunit
0.5 µm
TEM showing ER and ribosomes
Figure 6.11
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Small
subunit
Diagram of a ribosome
4.
Golgi (complex, body, appartus)
a. stack of flattened membrane sacs called cisternae
completes all modifications to newly made
macromolecules
b. * Packages molecules into vessicles & places a
molecular address onto package
*Sends vessicle to ultimate destination (w/in cell or to be
secreted)
c. Two faces
1. cis face – incoming/receiving
2. trans face - shipping
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• Functions of the Golgi apparatus
Golgi
apparatus
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
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)
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0.1 0 µm
TEM of Golgi apparatus
5.
Lysosomes (membranous sacs)
Contain hydrolytic enzymes that “digest” macromolecules
Recycle of “worn out” cell components
Apoptosis – cell suicide in cells infected w/viruses or
transformed into cancer
Can arise from “budding” off the Golgi apparatus
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• 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
Food vacuole
Figure 6.14 A
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(a) Phagocytosis: lysosome digesting food
• Autophagy
Lysosome containing
two damaged organelles
1µm
Mitochondrion
fragment
Peroxisome
fragment
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
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• 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
Smooth ER
cis Golgi
Nuclear envelop
3
Golgi pinches off transport
Vesicles and other vesicles
that give rise to lysosomes and
Vacuoles
Plasma
membrane
trans Golgi
4
Lysosome available
for fusion with another
vesicle for digestion
Figure 6.16
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5 Transport vesicle carries 6
proteins to plasma
membrane for secretion
Plasma membrane expands
by fusion of vesicles; proteins
are secreted from cell
6.
Peroxisomes (type of vessicle)
Contains collection of enzymes that inactivate toxic byproducts
of oxygen presence
ex. Catalase
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Peroxisomes: Oxidation
• Peroxisomes
– Produce hydrogen peroxide and convert it to
water
Chloroplast
Peroxisome
Mitochondrion
Figure 6.19
1 µm
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7.
Vacuoles – they are like your garage and often look like balloons!
Found in plant or fungal cells
Three types:
1. Food Vacuole – form by phagocytosis
2. Contractile Vacuole – pump out excess water (freshwater protists)
3. Central Vacuole – found in PLANTS
hold reserves of important organic molecules
can contain by-products or pigments
can also be protection – hold poisonous compounds
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• A animal cell
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
Figure 6.9
Mitochondrion
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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
Peroxisome
Plasma membrane
Chloroplast
Cell wall
Plasmodesmata
Wall of adjacent cell
Figure 6.9
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In plant cells but not animal cells:
Chloroplasts
Central vacuole and tonoplast
Cell wall
Plasmodesmata
8.
Mitochondria – Powerhouse of the cell
a.
Location for aerobic respiration (cellular respiration)
Use oxygen to produce ATP
Three parts: inner membrane, outer membrane, matrix
1.
Krebs cycle occurs in matrix
biochem reactions that converts energy into usable
forms for the cell
1.
Electron Transport system in the inner membrane
last biochemical step in production of ATP
*oxygen is the FINAL ELECTRON RECEPTOR
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• 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
Figure 6.17
Mitochondrial
DNA
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100 µm
• Mitochrondria
–
Have their own DNA (circular and single stranded)
–
Replicate INDEPENDENTLY of the cell
–
Endosymbiotic theory – scientists think mitochrondria and
chloroplasts were once a cell and then engulfed by
eukaryotes about a billion years ago
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9.
Chloroplasts
Found only in plants ( also in a few protists)
Site for photosynthesis
Parts:
Stroma – light independent rxns occur
Grana – composed of thylakoid membrane
light dependent rxns occur here via electron
transport chain
Contain own DNA, reproduce independently
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• Chloroplasts
– Are found in leaves and other green organs of
plants and in algae
Chloroplast
Ribosomes
Stroma
Chloroplast
DNA
Inner and outer
membranes
Granum
1 µm
Figure 6.18
Thylakoid
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• The cytoskeleton
– Is a network of fibers extending throughout the
cytoplasm
Microtubule
Figure 6.20
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0.25 µm
Microfilaments
10. Cyotskeleton – the FRAMEWORK
collection of proteins fibers that confer shape & mvmt to
the cell
Parts:
1. Microtublules
fat hollow polymers of the protein TUBULIN
*main support of cell & form cilia & flagella
*can function as “tracks” along which other subcellular
structures can be transported
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•
Parts:
2.
Intermediate filaments
Composed of strong proteins like KERRATIN
Functions to hold other cytoskeletal components together
(like rope)
Found in large quantities in nucleoplasm
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Parts:
3. Microfilaments
Composed of polymers of the protein ACTIN
Usually involved in movement
Found under plasma membrane
Cell shape, muscle movement
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• There are three main types of fibers that make
up the cytoskeleton
Table 6.1
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• Microfilaments that function in cellular motility
– Contain the protein myosin in addition to actin
Muscle cell
Actin filament
Myosin filament
Myosin arm
Figure 6.27 A
(a) Myosin motors in muscle cell contraction.
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– Is involved in cell motility, which utilizes motor
proteins
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
Figure 6.21 A, B
(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.)
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Centrosomes and Centrioles
• The centrosome
– Is considered to be a “microtubule-organizing
center”
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– Contains a pair of centrioles
Centrosome
Microtubule
Centrioles
0.25 µm
Figure 6.22
Longitudinal section
of one centriole
Microtubules
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Cross section
of the other centriole
Cilia and Flagella
11. Cilia (short and many)
Flagella (few & long)
– Contain specialized arrangements of
microtubules
– Are locomotor appendages of some cells
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• Flagella beating pattern
(a) Motion of flagella. A flagellum
usually undulates, its snakelike
motion driving a cell in the same
direction as the axis of the
flagellum. Propulsion of a human
sperm cell is an example of
flagellatelocomotion (LM).
Direction of swimming
Figure 6.23 A
1 µm
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• Ciliary motion
(b) Motion of cilia. Cilia have a backand-forth motion that moves the
cell in a direction perpendicular
to the axis of the cilium. A dense
nap of cilia, beating at a rate of
about 40 to 60 strokes a second,
covers this Colpidium, a
freshwater protozoan (SEM).
Figure 6.23 B
15 µm
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• Cilia and flagella share a common
ultrastructure (9 + 2 arrangement)
Outer microtubule
doublet
Dynein arms
0.1 µm
Central
microtubule
Outer doublets
cross-linking
proteins inside
Microtubules
Radial
spoke
Plasma
membrane
Basal body
(b)
0.5 µm
(a)
0.1 µm
Triplet
(c)
Figure 6.24 A-C
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Cross section of basal body
Plasma
membrane
• The protein dynein
– Is responsible for the bending movement of
cilia and flagella
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
relative to each other.
Figure 6.25 A
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ATP
Outer doublets
cross-linking
proteins
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
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1
3
2
(c) Localized, synchronized activation of many dynein arms
probably causes a bend to begin at the base of the Cilium or
flagellum and move outward toward the tip. Many successive
bends, such as the ones shown here to the left and right,
result in a wavelike motion. In this diagram, the two central
microtubules and the cross-linking proteins are not shown.
Figure 6.25 C
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• Cytoplasmic streaming
– Is another form of locomotion created by
microfilaments
Nonmoving
cytoplasm (gel)
Chloroplast
Streaming
cytoplasm
(sol)
Parallel actin
filaments
Figure 6.27 C
(b) Cytoplasmic streaming in plant cells
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Cell wall
Extracellular
Extracellular components and connections
between cells help coordinate cellular activities
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Cell Walls of Plants
• The cell wall
– Is an extracellular structure of plant cells that
distinguishes them from animal cells
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• 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
Cytosol
Plasma membrane
Plant cell walls
Figure 6.28
Plasmodesmata
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The Extracellular Matrix (ECM) of Animal Cells
• Animal cells
– Lack cell walls
– Are covered by an elaborate matrix, the ECM
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• The ECM
– Is made up of glycoproteins and other
macromolecules
EXTRACELLULAR FLUID
Collagen
A proteoglycan
complex
Polysaccharide
molecule
Carbohydrates
Core
protein
Fibronectin
Plasma
membrane
Integrin
Integrins
Microfilaments
Figure 6.29
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CYTOPLASM
Proteoglycan
molecule
• Functions of the ECM include
– Support
– Adhesion
– Movement
– Regulation
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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
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Plasma membranes
Animals: Tight Junctions, Desmosomes, and Gap Junctions
• In animals, there are three types of intercellular
junctions
– Tight junctions
– Desmosomes
– Gap junctions
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• Types of intercellular junctions in animals
TIGHT JUNCTIONS
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
At tight junctions, the membranes of
neighboring cells are very tightly pressed
against each other, bound together by
specific proteins (purple). Forming continuous seals around the cells, tight junctions
prevent leakage of extracellular fluid across
A layer of epithelial cells.
DESMOSOMES
Desmosomes (also called anchoring
junctions) function like rivets, fastening cells
Together into strong sheets. Intermediate
Filaments made of sturdy keratin proteins
Anchor desmosomes in the cytoplasm.
Tight junctions
Intermediate
filaments
Desmosome
Gap
junctions
Space
between Plasma membranes
cells
of adjacent cells
1 µm
Extracellular
matrix
Gap junction
Figure 6.31
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0.1 µm
GAP JUNCTIONS
Gap junctions (also called communicating
junctions) provide cytoplasmic channels from
one cell to an adjacent cell. Gap junctions
consist of special membrane proteins that
surround a pore through which ions, sugars,
amino acids, and other small molecules may
pass. Gap junctions are necessary for communication between cells in many types of tissues,
including heart muscle and animal embryos.
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
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• 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
Hydrophobic
region
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.
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Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane