cell structure and function - del mar...
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Cell Structure and Function
Chapter 4 Part 2
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4.7 Visual Summary of Eukaryotic Cells
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Fig. 4-15a, p. 63
CELL WALL Protects, structurally
supports cell
CHLOROPLAST Specializes in
photosynthesis
CENTRAL VACUOLE Increases cell surface area; stores metabolic wastes
NUCLEUSnuclear envelope
Keeps DNA separated from cytoplasm; makes ribosome subunits; controls access to DNA
DNA in nucleoplasmCYTOSKELETON microtubules
Structurally supports, imparts
shape to cell; moves cell and its components
microfilaments RIBOSOMESintermediate filaments (not shown)
(attached to rough ER and free in cytoplasm) Sites of protein synthesis
ROUGH ERMITOCHONDRION Modifies proteins made by
ribosomes attached to itEnergy powerhouse; produces many ATP
by aerobic respiration SMOOTH ER
PLASMODESMACommunication
junction between adjoining cells
Makes lipids, breaks down carbohydrates and fats, inactivates toxins
GOLGI BODY Finishes, sorts, ships lipids, enzymes, and membrane and secreted proteins
LYSOSOME-LIKE VESICLEDigests, recycles materials
a Typical plant cell components.
PLASMA MEMBRANE Selectively controls the kinds and
amounts of substances moving into and out of cell; helps maintain
cytoplasmic volume, composition
nucleolus
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4.7 Visual Summary of Eukaryotic Cells
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Fig. 4-15b, p. 63
NUCLEUS
Keeps DNA
separated from
cytoplasm; makes
ribosome subunits;
controls access to
DNA
nuclear
envelope
nucleolus
DNA in
nucleoplasm
CYTOSKELETON
microtubules
Structurally
supports,
imparts shape
to cell; moves
cell and its
components
microfilaments RIBOSOMES
(attached to rough ER
and free in cytoplasm)
Sites of protein synthesis
intermediate
filaments
ROUGH ER Modifies
proteins made by
ribosomes attached to it
MITOCHONDRION
Energy powerhouse;
produces many ATP
by aerobic respiration
SMOOTH ER
Makes lipids, breaks
down carbohydrates and
fats, inactivates toxins
CENTRIOLES
Special centers that
produce and organize
microtubules
GOLGI BODYPLASMA MEMBRANE
Selectively controls the
kinds and amounts of
substances moving into
and out of cell; helps
maintain cytoplasmic
volume, composition
Finishes, sorts, ships
lipids, enzymes, and
membrane and
secreted proteins
LYSOSOME
Digests, recycles
materials
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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
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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
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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
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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
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Chromosome Condensation
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p. 65
one chromosome
(one unduplicated
DNA molecule)
one chromosome
(one duplicated DNA
molecule, partially
condensed)
one chromosome
(one duplicated DNA
molecule, completely
condensed)
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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
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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
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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
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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
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The Endomembrane System
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The Endomembrane System
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The Endomembrane System
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Fig. 4-18a, p. 66
nucleus
rough ER
smooth ER
Golgi body
vesicles
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Fig. 4-18b, p. 66
protein
RNA
C Vesicles
Vesicles that bud from the
rough ER carry some of
the new proteins to Golgi
bodies. Other proteins
migrate through the
interior of the rough ER,
and end up in the smooth
ER.
ribosome attached to ER
vesicle budding from ER
B Rough ER
Some of the RNA in
the cytoplasm is
translated into
polypeptide chains
by ribosomes
attached to the
rough ER. The
chains enter the
rough ER, where
they are modified
into final form.
A Nucleus
Inside the nucleus, DNA instructions
for making proteins are transcribed
into RNA, which moves through
nuclear pores into the cytoplasm.
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Fig. 4-18c, p. 67
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.
protein in smooth ER
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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
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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
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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
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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
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Mitochondrion
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Fig. 4-20, p. 69
outer membrane
outer
compartment
inner membrane
inner compartment
0.5 µm
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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
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The Chloroplast
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Fig. 4-21, p. 69
two outer
membranes
stroma
thylakoids
(inner membrane
system folded into
flattened disks)
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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
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4.12 Cell Surface Specializations
A wall or other protective covering often
intervenes between a cell’s plasma membrane
and the surroundings
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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
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Plant Cell Walls
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Fig. 4-22a, p. 70
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Fig. 4-22a, p. 70
middle
lamella
plasma
membraneA Plant cell secretions
form the middle lamella,
a layer that cements
adjoining cells together.
cytoplasm
primary
cell wall
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Fig. 4-22b, p. 70
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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
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Fig. 4-22c, p. 70
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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
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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.
Fig. 4-22, p. 70
middle
lamella
plasma
membrane
A Plant cell secretions form the middle lamella, a layer that cements adjoining cells together.
cytoplasm
primary
cell wall
pipeline
made of
abutting
cell walls
plasmodesma
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.secondary
cell wall
(added in
layers)
primary
cell wall
Stepped Art
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Plant Cuticle
Cuticle
• A waxy covering that protects exposed surfaces
and limits water loss
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Fig. 4-23, p. 71
thick, waxy
cuticle at
leaf surface
cell of leaf
epidermis
photosynthetic
cell inside leaf
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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
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ECM
A bone cell surrounded by extracellular matrix
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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
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Cell Junctions in Animal Tissues
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Fig. 4-25, p. 71
free surface of
epithelial tissue
different kinds of
tight junctions
gap junction
basement membrane
(extracellular matrix)
adhering junction
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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
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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
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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
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Components of the
Cytoskeleton
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Fig. 4-26 (a-c), p. 72
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Fig. 4-26a, p. 72
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Fig. 4-26a, p. 72
tubulin subunit
25 nm
Microtubule
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Fig. 4-26b, p. 72
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Fig. 4-26b, p. 72
actin subunit
6–7 nm
Microfilament
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Fig. 4-26c, p. 72
one
polypeptide
chain
Intermediate filament
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Fig. 4-26d, p. 72
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Fig. 4-26, p. 72
one
polypeptide
chain
Intermediate filament
actin
subunit
6–7 nm
Microfilament
tubulin
subunit
25 nm
Microtubule
Stepped Art
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Motor Proteins
Motor proteins
• Accessory proteins that move molecules through
cells on tracks of microtubules and microfilaments
• Energized by ATP
• Example: kinesins
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Motor Proteins: Kinesin
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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
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Moving Cells
Flagellum of the human sperm, and pseudopods
of a predatory amoeba
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Fig. 4-28a, p. 73
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Fig. 4-28b, p. 73
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Eukaryotic Flagella
and Cilia
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Fig. 4-29a, p. 73
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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.
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Fig. 4-29b, p. 73
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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. Phosphate-
group 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
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Fig. 4-29c, p. 73
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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:
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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
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Summary: Components of
Prokaryotic and Eukaryotic Cells