1. 4
A Tour of the Cell

2. 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
Makes up 80% of plant cell
Enclosed by membrane called tonoplast
Many storage functions for plants
Certain vacuoles in plants and fungi carry out enzymatic hydrolysis like lysosomes
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3. Central vacuole Cytosol Central vacuole Nucleus Cell wall Chloroplast
Figure 4.14
Central vacuole
Cytosol
Central
vacuole
Nucleus
Figure 4.14 The plant cell vacuole
Cell wall
Chloroplast
5 mm
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4. Peroxisomes: Oxidation
Figure 4.19
Peroxisomes: Oxidation
Specialized metabolic compartments bounded by a single membrane
Peroxisome
Mitochon-
drion
Figure 4.19 A peroxisome
Chloroplasts
1 mm
Found in all eukaryotes
Peroxisomes produce hydrogen peroxide and then convert it to water & oxygen
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5. Concept 4.5: Mitochondria and chloroplasts change energy from one form to another
Mitochondria: Sites of cellular respiration, a metabolic process that uses oxygen to generate ATP
Chloroplasts: found in plants and algae, are the sites of photosynthesis
Endosymbiont theory
A bacteria may have merged with an engulfed heterotrophic bacteria to become a eukaryotic cell with a mitochondrion
A bacteria may have merged with a photosynthetic prokaryote, becoming the ancestor of cells that contain chloroplasts
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6. Nonphotosynthetic eukaryote
Figure 4.16
Endoplasmic
reticulum
Nucleus
Nuclear
envelope
Engulfing of oxygen-
using nonphotosynthetic
prokaryote, which,
becomes a mitochondrion
Ancestor of
eukaryotic cells (host cell)
Mitochondrion
Engulfing of
photosynthetic
prokaryote
Chloroplast
At least
one cell
Mitochondrion
Figure 4.16 The endosymbiont theory of the origins of mitochondria and chloroplasts in eukaryotic cells
Nonphotosynthetic
eukaryote
Photosynthetic eukaryote
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7. Mitochondria: Chemical Energy Conversion
Found in all eukaryotic cells
“Powerhouses of cells”; break down food and release energy and oxygen
They have a smooth outer membrane and a folded inner membrane called cristae
Cristae & mitochondrial matrix (compartment enclosed by cristae): where all of cellular respiration (CR) takes place
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8. Outer membrane DNA Inner membrane Cristae Matrix
Figure 4.17
Mitochondrion
10 mm
Intermembrane space
Mitochondria
Outer
membrane
DNA
Inner
membrane
Free
ribosomes
in the
mitochondrial
matrix
Mitochondrial
DNA
Cristae
Matrix
Nuclear DNA
Figure 4.17 The mitochondrion, site of cellular respiration
0.1 mm
(a) Diagram and TEM of mitochondrion
(b) Network of mitochondria in
Euglena (LM)
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9. Chloroplasts: Capture of Light Energy
Found in plant eukaryotes only
Chlorophyll-containing organelle which is the site of photosynthesis (PS)
Chloroplasts are found in leaves and other green organs of plants and in algae
Thylakoid membranes: flattened membraneous sacs; a stack is called a grana
Where chlorophyll is found
Site of Light Reactions of PS
Stroma: fluid outside of thylakoid membranes
Where Calvin Cycle of PS takes place
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10. (a) Diagram and TEM of chloroplast
Figure 4.18
Chloroplast
Stroma
Ribosomes
50 mm
Inner and outer
membranes
Granum
Figure 4.18 The chloroplast, site of photosynthesis
Chloroplasts
(red)
DNA
Thylakoid
Intermembrane space
1 mm
(a) Diagram and TEM of chloroplast
(b) Chloroplasts in an algal
cell
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11. Concept 4.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cell
Found in all eukaryotes
Network of fibers extending throughout the cytoplasm
Forms the framework for support and movement
Constructed of 3 types of protein fibers;
Microtubules: thickest
Intermediate filaments
Microfilaments (actin filaments): thinnest
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12. Video: Organelle Transport
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13. (a) Motor proteins “walkˮ vesicles along cytoskeletal fibers.
Figure 4.21
Vesicle
ATP
Receptor for
motor protein
Motor protein
(ATP powered)
Microtubule
of cytoskeleton
(a) Motor proteins “walkˮ vesicles along
cytoskeletal fibers.
0.25 mm
Microtubule
Vesicles
Figure 4.21 Motor proteins and the cytoskeleton
(b) Two vesicles move toward the tip of a nerve
cell extension called an axon (SEM)
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14. Figure 4.T01 The structure and function of the cytoskeleton
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15. Intermediate Filaments 5 mm Fibrous proteins coiled into cables
Figure 4.T01-3
Intermediate Filaments
5 mm
Fibrous proteins coiled into cables
8–12 nm
One of several different proteins
(such as keratins)
Maintenance of cell shape; anchor-
age of nucleus and certain other
organelles; formation of nuclear
lamina
Figure 4.T01-3 The structure and function of the cytoskeleton (part 3: intermediate filaments)
Keratin proteins
Fibrous subunit (keratins
coiled together)
8–12 nm
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16. Microtubules
Microtubules: hollow rods constructed from globular protein dimers called tubulin
Functions of microtubules
Shape and support the cell
Guide movement of organelles
Separate chromosomes during cell division
Make up centrosomes, centrioles, cilia and flagella
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17. Centrosomes, Centrioles, Cilia & Flagella
In animal cells, microtubules grow out from a centrosome near the nucleus
The centrosome is a “microtubule-organizing center” (MTOC)
The centrosome has a pair of centrioles, each with 9 triplets of microtubules arranged in a ring
Cilia and flagella: in animal cells only; locomotor organelles
Cilia: short, many, work like oars, back and forth motion
Flagella: long, one or a few, whip–like motion
Both are extensions of the PM with a core of microtubules arranged in a 9+2 pattern
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18. Centrosome Microtubule Centrioles Figure 4.22
Figure 4.22 Centrosome containing a pair of centrioles
Centrioles
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19. (a) Longitudinal section of motile cilium
Figure 4.23
Plasma
membrane
Outer microtubule
doublet
0.1 mm
Motor proteins
(dyneins)
Central
microtubule
Radial spoke
Microtubules
Cross-linking
protein between
outer doublets
(b) Cross section
of motile cilium
Plasma
membrane
Basal body
0.1 mm
0.5 mm
Figure 4.23 Structure of a flagellum or motile cilium
Triplet
(a) Longitudinal section
of motile cilium
(c) Cross section
of basal body
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20. Microfilaments (Actin Filaments)
Microfilaments : thin solid rods, built from molecules of actin strands wound into a helix
Functions:
Bear tension, resisting pulling forces within the cell
Bundles make up the core of microvilli of intestinal cells
Muscle contraction (muscles need the proteins actin and myosin)
Localized contraction of cells: called cytoplasmic streaming
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21. Microfilaments (actin filaments) Plasma membrane 0.25 mm Microvillus
Figure 4.24
Microfilaments
(actin filaments)
Plasma membrane
0.25 mm
Microvillus
Figure 4.24 A structural role of microfilaments
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22. Intermediate Filaments
Intermediate filaments: more permanent than microtubules or microfilaments
Found in the cells of some animals, including vertebrates
Made of keratin proteins supercoiled into thicker cables
Functions:
For bearing tension and framework
Reinforce cell shape
Fix organelle positions
Line interior of nuclear envelope
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23. Cell Walls of Plants
Cell wall: extracellular structure that distinguishes plant cells from animal cells
Protects the plant cell, maintains its shape, and prevents excessive uptake of water
In bacteria (prokaryotes): made of peptidoglycan (sugary-protein)
In plants (eukaryotes): made of polysaccharide cellulose
In fungi (eukaryotes): made of polysaccharide chitin
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24. Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata
Figure 4.25
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
Plasmodesmata
Secondary
cell wall
Figure 4.25 Plant cell walls
Primary
cell wall
Middle
lamella
1 mm
© 2016 Pearson Education, Inc.

25. The Extracellular Matrix (ECM) of Animal Cells
Figure 4.26
The Extracellular Matrix (ECM) of Animal Cells
Animal cells lack cell walls but are covered by an elaborate ECM
A proteoglycan complex:
Collagen
EXTRACELLULAR FLUID
Polysaccharide
molecule
Carbo-
hydrates
Fibronectin
Core
protein
Plasma
membrane
Proteoglycan
molecule
Figure 4.26 Extracellular matrix (ECM) of an animal cell
Micro-
filaments
CYTOPLASM
Integrins
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.
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26. Intercellular Junctions in Animals
Animal cells have 3 main types of cell junctions
Tight junctions: Continuous belts that hold cells tightly together
Desmosomes: rivets cells into strong sheets
Gap junctions: communicating junction in animals: allows material transport from one cell to another
Intercellular Junction in Plants
Plasmodesmata: channels that make holes in plant cell walls to allow communication between plant cells
Similar to gap junctions in animals
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27. Tight junctions prevent fluid from moving across a layer of cells.
Figure 4.27
Tight junctions prevent
fluid from moving
across a layer of cells.
Tight junction
TEM
0.5 mm
Tight junction
Intermediate
filaments
Desmosome
TEM
Gap
junction
1 mm
Figure 4.27 Exploring cell junctions in animal tissues
Ions or small
molecules
Extracellular
matrix
TEM
Plasma membranes
of adjacent cells
Space
between cells
0.1 mm
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28. envelope (double membrane) perforated by nuclear pores;
Figure 4.UN03
Cell Component
Structure
Function
Surrounded by nuclear
envelope (double membrane)
perforated by nuclear pores;
nuclear envelope continuous
with endoplasmic
reticulum (ER)
Houses chromosomes, which
are made of chromatin
(DNA and proteins); contains
nucleoli, where ribosomal
subunits are made; pores
regulate entry and exit of
materials
Nucleus
(ER)
Ribosome
Two subunits made of
ribosomal RNA and proteins;
can be free in cytosol or
bound to ER
Protein synthesis
Figure 4.UN03 Summary of key concepts: nucleus and ribosomes
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29. Endoplasmic reticulum Extensive network of membrane-bounded tubules
Figure 4.UN04
Cell Component
Structure
Function
Endoplasmic reticulum
Extensive network of
membrane-bounded tubules
and sacs; membrane
separates lumen from
cytosol; continuous with
nuclear envelope
Smooth ER: synthesis of lipids,
metabolism of carbohydrates,
Ca2+ storage, detoxification of
drugs and poisons
(Nuclear
envelope)
Rough ER: aids in synthesis of
secretory and other proteins
from bound ribosomes; adds
carbohydrates to proteins to
make glycoproteins; produces
new membrane
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
Figure 4.UN04 Summary of key concepts: endomembrane system
Lysosome
Membranous sac of hydrolytic
enzymes (in animal cells)
Breakdown of ingested
substances, cell
macromolecules, and damaged
organelles for recycling
Vacuole
Large membrane-bounded
vesicle
Digestion, storage, waste
disposal, water balance, plant
cell growth and protection
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30. Bounded by double membrane; inner membrane has infoldings (cristae)
Figure 4.UN05
Cell Component
Structure
Function
Mitochondrion
Bounded by double membrane;
inner membrane has infoldings
(cristae)
Cellular respiration
Chloroplast
Typically two membranes around
fluid stroma, which contains
thylakoids stacked into grana (in
cells of photosynthetic eukaryotes,
including plants)
Photosynthesis
Peroxisome
Specialized metabolic compartment
bounded by a single membrane
Contains enzymes that transfer
hydrogen atoms from certain
molecules to oxygen, producing
hydrogen peroxide (H2O2) as a
by-product; H2O2 is converted to
water by another enzyme
Figure 4.UN05 Summary of key concepts: mitochondria and chloroplasts
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