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Cell Structure and Function
Chapter 4 Part 2
4.7 Visual Summary of Eukaryotic Cells
CELL WALL
Protects, structurally
supports cell
CYTOSKELETON
Structurally
supports, imparts
shape to cell;
moves cell and
its components
microtubules
microfilaments
intermediate
filaments
(not shown)
MITOCHONDRION
Energy powerhouse;
produces many ATP
by aerobic respiration
PLASMODESMA
Communication
junction between
adjoining cells
PLASMA MEMBRANE
Selectively controls the kinds and
amounts of substances moving into
and out of cell; helps maintain
cytoplasmic volume, composition
CHLOROPLAST CENTRAL VACUOLE
Specializes in Increases cell surface area;
photosynthesis stores metabolic wastes
NUCLEUS
Keeps DNA separated
from cytoplasm;
makes ribosome
subunits; controls
access to DNA
nuclear
envelope
nucleolus
DNA in
nucleoplasm
RIBOSOMES
(attached to rough ER and
free in cytoplasm) Sites of
protein synthesis
ROUGH ER
Modifies proteins made by
ribosomes attached to it
SMOOTH ER
Makes lipids, breaks down
carbohydrates and fats,
inactivates toxins
GOLGI BODY
Finishes, sorts, ships
lipids, enzymes, and
membrane and secreted
proteins
LYSOSOME-LIKE
VESICLE
Digests, recycles
materials
a Typical plant cell components.
Fig. 4-15a, p. 63
4.7 Visual Summary of Eukaryotic Cells
CYTOSKELETON
Structurally
supports,
microtubules
imparts shape
microfilaments
to cell; moves
intermediate
cell and its
filaments
components
MITOCHONDRION
Energy powerhouse;
produces many ATP
by aerobic respiration
nuclear
envelope
nucleolus
DNA in
nucleoplasm
NUCLEUS
Keeps DNA
separated from
cytoplasm; makes
ribosome subunits;
controls access to
DNA
RIBOSOMES
(attached to rough ER
and free in cytoplasm)
Sites of protein synthesis
ROUGH ER Modifies
proteins made by
ribosomes attached to it
CENTRIOLES
Special centers that
produce and organize
microtubules
SMOOTH ER
Makes lipids, breaks
down carbohydrates and
fats, inactivates toxins
PLASMA MEMBRANE
Selectively controls the
kinds and amounts of
substances moving into
and out of cell; helps
maintain cytoplasmic
volume, composition
GOLGI BODY
Finishes, sorts, ships
lipids, enzymes, and
membrane and
secreted proteins
LYSOSOME
Digests, recycles
materials
Fig. 4-15b, p. 63
Animation: Common eukaryotic
organelles
4.8 The Nucleus
 The nucleus keeps eukaryotic DNA away from
potentially damaging reactions in the cytoplasm
 The nuclear envelope controls when DNA is
accessed
The Nuclear Envelope
 Nuclear envelope
• Two lipid bilayers pressed together as a single
membrane surrounding the nucleus
• Outer bilayer is continuous with the ER
• Nuclear pores allow certain substances to pass
through the membrane
The Nucleoplasm and Nucleolus
 Nucleoplasm
• Viscous fluid inside the nuclear envelope, similar
to cytoplasm
 Nucleolus
• A dense region in the nucleus where subunits of
ribosomes are assembled from proteins and RNA
The Chromosomes
 Chromatin
• All DNA and its associated proteins in the nucleus
 Chromosome
• A single DNA molecule with its attached proteins
• During cell division, chromosomes condense and
become visible in micrographs
• Human body cells have 46 chromosomes
Chromosome Condensation
one chromosome
(one unduplicated
DNA molecule)
one chromosome
(one duplicated DNA
molecule, partially
condensed)
one chromosome
(one duplicated DNA
molecule, completely
condensed)
p. 65
4.9 The Endomembrane System
 Endomembrane system
• A series of interacting organelles between the
nucleus and the plasma membrane
• Makes lipids, enzymes, and proteins for secretion
or insertion into cell membranes
• Other specialized cell functions
The Endoplasmic Reticulum
 Endoplasmic reticulum (ER)
• An extension of the nuclear envelope that forms a
continuous, folded compartment
 Two kinds of endoplasmic reticulum
• Rough ER (with ribosomes) folds polypeptides
into their tertiary form
• Smooth ER (no ribosomes) makes lipids, breaks
down carbohydrates and lipids, detoxifies poisons
Vesicles
 Vesicles
• Small, membrane-enclosed saclike organelles
that store or transport substances
 Peroxisomes
• Vesicles containing enzymes that break down
hydrogen peroxide, alcohol, and other toxins
 Vacuoles
• Vesicles for waste disposal
Golgi Bodies and Lysosomes
 Golgi body
• A folded membrane containing enzymes that
finish polypeptides and lipids delivered by the ER
• Packages finished products in vesicles that carry
them to the plasma membrane or to lysosomes
 Lysosomes
• Vesicles containing enzymes that fuse with
vacuoles and digest waste materials
The Endomembrane System
The Endomembrane System
The Endomembrane System
nucleus
rough ER
smooth ER
Golgi body
vesicles
Fig. 4-18a, p. 66
A Nucleus
Inside the nucleus, DNA instructions
for making proteins are transcribed
into RNA, which moves through
nuclear pores into the cytoplasm.
protein
RNA
C Vesicles
B Rough ER
Vesicles that bud from the
Some of the RNA in
rough ER carry some of
the cytoplasm is
the new proteins to Golgi
translated into
bodies. Other proteins
polypeptide chains
migrate through the
by ribosomes
interior of the rough ER,
attached to the
and end up in the smooth
rough ER. The
ER.
chains enter the
rough ER, where
ribosome
vesicle budding
they are modified
attached to ER from ER
into final form.
Fig. 4-18b, p. 66
protein in smooth ER
D Smooth ER
Some proteins
from the rough
ER are packaged
into new vesicles
and shipped to
the Golgi. Others
become enzymes
of the ER, which
assemble lipids or
inactivate toxins.
E Golgi body
Proteins
arriving in
vesicles from
the ER are
modified into
final form and
sorted. New
vesicles carry
them to the
plasma
membrane
or to
lysosomes.
F Plasma membrane
Golgi vesicles fuse with
the plasma membrane.
Lipids and proteins of a
vesicle’s membrane fuse
with the plasma
membrane, and the
vesicle’s contents are
released to the exterior
of the cell.
Fig. 4-18c, p. 67
Animation: The endomembrane system
4.10 Lysosome Malfunction
 When lysosomes do not work properly, some
cellular materials are not properly recycled,
which can have devastating results
 Different kinds of molecules are broken down by
different lysosomal enzymes
• One lysosomal enzyme breaks down
gangliosides, a kind of lipid
Tay Sachs Disease
 In Tay Sachs disease, a genetic mutation alters
the lysosomal enzyme that breaks down
gangliosides, which accumulate in nerve cells
• Affected children usually die by age five
4.11 Other Organelles
 Eukaryotic cells make most of their ATP in
mitochondria
 Plastids function in storage and photosynthesis
in plants and some types of algae
Mitochondria
 Mitochondrion
• Eukaryotic organelle that makes the energy
molecule ATP through aerobic respiration
• Contains two membranes, forming inner and
outer compartments; buildup of hydrogen ions in
the outer compartment drives ATP synthesis
• Has its own DNA and ribosomes
• Resembles bacteria; may have evolved through
endosymbiosis
Mitochondrion
outer membrane
outer
compartment
inner compartment
inner membrane
0.5 µm
Fig. 4-20, p. 69
Plastids
 Plastids
• Organelles that function in photosynthesis or
storage in plants and algae; includes
chromoplasts, amyloplasts, and chloroplasts
 Chloroplasts
• Plastids specialized for photosynthesis
• Resemble photosynthetic bacteria; may have
evolved by endosymbiosis
The Chloroplast
two outer
membranes
stroma
thylakoids
(inner membrane
system folded into
flattened disks)
Fig. 4-21, p. 69
Animation: Structure of a chloroplast
The Central Vacuole
 Central vacuole
• A plant organelle that occupies 50 to 90 percent
of a cell’s interior
• Stores amino acids, sugars, ions, wastes, toxins
• Fluid pressure keeps plant cells firm
4.12 Cell Surface Specializations
 A wall or other protective covering often
intervenes between a cell’s plasma membrane
and the surroundings
Eukaryotic Cell Walls
 Animal cells do not have walls, but plant cells
and many protist and fungal cells do
 Primary cell wall
• A thin, pliable wall formed by secretion of
cellulose into the coating around young plant cells
 Secondary cell wall
• A strong wall composed of lignin, formed in
some plant stems and roots after maturity
Plant Cell Walls
Fig. 4-22a, p. 70
A Plant cell secretions
form the middle lamella,
a layer that cements
adjoining cells together.
middle
lamella
plasma
membrane
cytoplasm
primary
cell wall
Fig. 4-22a, p. 70
Fig. 4-22b, p. 70
B In many plant tissues, cells
also secrete materials that are
deposited in layers on the inner
surface of their primary wall.
These layers strengthen the
wall and maintain its shape.
They remain after the
cells die, and become
part of pipelines
that carry water
through the
plant.
secondary
cell wall
(added in
layers)
primary
cell wall
pipeline
made of
abutting
cell walls
Fig. 4-22b, p. 70
Fig. 4-22c, p. 70
middle lamella
C Plasmodesmata are
channels across the cell
walls and the plasma
membranes of living cells
that are pressed against
one another in tissues.
plasmodesma
middle lamella
Fig. 4-22c, p. 70
A Plant cell secretions form the middle lamella, a layer that cements adjoining cells together.
middle
lamella
B In many plant
tissues, cells also
secrete materials that
are deposited in
layers on the inner
surface of their
primary wall. These
layers strengthen the
wall and maintain its
shape. They remain
after the cells die, and
become part of
pipelines that carry
water through the
plant.
primary
cell wall
plasma
membrane
cytoplasm
middle lamella
C Plasmodesmata are
channels across the
cell walls and the
plasma membranes
of living cells that are
pressed against one
another in tissues.
primary
cell wall
secondary
cell wall
(added in
layers)
plasmodesma
middle lamella
pipeline
made of
abutting
cell walls
Stepped Art
Fig. 4-22, p. 70
Animation: Plant cell walls
Plant Cuticle
 Cuticle
• A waxy covering that protects exposed surfaces
and limits water loss
thick, waxy
cuticle at
leaf surface
cell of leaf
epidermis
photosynthetic
cell inside leaf
Fig. 4-23, p. 71
Matrixes Between Animal Cells
 Extracellular matrix (ECM)
• A nonliving, complex mixture of fibrous proteins
and polysaccharides secreted by and surrounding
cells; structure and function varies with the type
of tissue
• Example: Bone is mostly ECM, composed of
collagen (fibrous protein) and hardened by
mineral deposits
ECM
 A bone cell surrounded by extracellular matrix
Cell Junctions
 Cell junctions allow cells to interact with each
other and the environment
 In plants, plasmodesmata extend through cell
walls to connect the cytoplasm of two cells
 Animals have three types of cell junctions: tight
junctions, adhering junctions, gap junctions
Cell Junctions in Animal Tissues
free surface of
epithelial tissue
different kinds of
tight junctions
gap junction
basement membrane
(extracellular matrix)
adhering junction
Fig. 4-25, p. 71
Animation: Animal cell junctions
4.6-4.12 Key Concepts:
Eukaryotic Cells
 Cells of protists, plants, fungi, and animals are
eukaryotic; they have a nucleus and other
membrane-enclosed compartments
 They differ in internal parts and surface
specializations
4.13 The Dynamic Cytoskeleton
 Eukaryotic cells have an extensive and dynamic
internal framework called a cytoskeleton
 Cytoskeleton
• An interconnected system of many protein
filaments – some permanent, some temporary
• Parts of the cytoskeleton reinforce, organize, and
move cell structures, or even a whole cell
Components of the Cytoskeleton
 Microtubules
• Long, hollow cylinders made of tubulin
• Form dynamic scaffolding for cell processes
 Microfilaments
• Consist mainly of the globular protein actin
• Make up the cell cortex
 Intermediate filaments
• Maintain cell and tissue structures
Components of the
Cytoskeleton
Fig. 4-26 (a-c), p. 72
Fig. 4-26a, p. 72
tubulin subunit
25 nm
Microtubule
Fig. 4-26a, p. 72
Fig. 4-26b, p. 72
actin subunit
6–7 nm
Microfilament
Fig. 4-26b, p. 72
one
polypeptide
chain
Intermediate filament
Fig. 4-26c, p. 72
Fig. 4-26d, p. 72
tubulin
subunit
25 nm
Microtubule
actin
subunit
one
polypeptide
chain
Intermediate filament
6–7 nm
Microfilament
Stepped Art
Fig. 4-26, p. 72
Motor Proteins
 Motor proteins
• Accessory proteins that move molecules through
cells on tracks of microtubules and microfilaments
• Energized by ATP
• Example: kinesins
Motor Proteins: Kinesin
Animation: Motor proteins
Cilia, Flagella, and False Feet
 Eukaryotic flagella and cilia
• Whiplike structures formed from microtubules
organized into 9 + 2 arrays
• Grow from a centriole which remains in the
cytoplasm as a basal body
 Psueudopods
• “False feet” used by amoebas and other
eukaryotic cells to move or engulf prey
Moving Cells
 Flagellum of the human sperm, and pseudopods
of a predatory amoeba
Fig. 4-28a, p. 73
Fig. 4-28b, p. 73
Eukaryotic Flagella
and Cilia
Fig. 4-29a, p. 73
protein
spokes
pair of microtubules
in a central sheath
pair of
microtubules
plasma
membrane
dynein arms
A Sketch and micrograph of one
eukaryotic flagellum, cross-section.
Like a cilium, it contains a 9+2 array:
a ring of nine pairs of microtubules
plus one pair at its core. Stabilizing
spokes and linking elements that
connect to the microtubules keep
them aligned in this radial pattern.
Fig. 4-29a, p. 73
Fig. 4-29b, p. 73
B Projecting from each pair
of microtubules in the outer
ring are “arms” of dynein, a
motor protein that has
ATPase activity. Phosphategroup transfers from ATP
cause the dynein arms to
repeatedly bind the adjacent
pair of microtubules, bend,
and then disengage. The
dynein arms “walk” along the
microtubules. Their motion
causes adjacent microtubule
pairs to slide past one
another
basal body, a microtubule
organizing center that
gives rise to the 9+2 array
and then remains beneath
it, inside the cytoplasm
Fig. 4-29b, p. 73
Fig. 4-29c, p. 73
C Short, sliding strokes occur in a
coordinated sequence around the
ring, down the length of each
microtubule pair. The flagellum
bends as the array inside bends:
Fig. 4-29c, p. 73
Animation: Flagella structure
4.13 Key Concepts:
A Look at the Cytoskeleton
 Diverse protein filaments reinforce a cell’s shape
and keep its parts organized
 As some filaments lengthen and shorten, they
move cell structures or the whole cell
Summary: Components of
Prokaryotic and Eukaryotic Cells
Animation: Nuclear envelope
Video: E. coli in food
Video: Cilia and flagella protozoans