Download Chapter 4

Chapter 4
Cell Structure and
Function
Including some materials
from lectures by
Gregory Ahearn
University of North Florida
Ammended by
John Crocker
Copyright © 2009 Pearson Education, Inc..
What Is the Cell Theory?
 Tenets of Modern Cell Theory
• Every living organism is made of one or more
cells
• The smallest organisms are made of single
cells while multicellular organisms are made
of many cells
• All cells arise from pre-existing cells
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4.1 What Features Are Shared By All Cells?

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Cells are the smallest unit of life.
Cells are enclosed by a plasma membrane.
Cells use DNA as a hereditary blueprint.
Cells contain cytoplasm, which is all the
material inside the plasma membrane and
outside the DNA-containing region.
 Cells obtain energy and nutrients from their
environment.
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Copyright © 2009 Pearson Education Inc.
4.1 What Features Are Shared By All Cells?
 Cell function limits cell size.
• Most cells are small (1 to 100 um in diameter)
• Cells need to exchange nutrients and wastes
with the environment
• No part of the cell can be far away from the
external environment.
• Diffusion of molecules across cell membranes
limits the diameter of cells.
• As cells get bigger, their nutrient and waste
elimination needs grow faster than the
membrane area to accommodate them.
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4.1 What Features Are Shared By All Cells?
 The volume of cytoplasm grows faster than the
plasma membrane area.
Fig. 4-2
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tallest trees
10 m
1m
10 cm
1 cm
adult human
visible with unaided
human eye
 Relative sizes
Diameter
100 m
chicken egg
frog embryo
100 m
10 m
1 m
Units of measurement:
1 meter (m) = 39.37 inches
1 centimeter (cm) = 1/100 m
1 millimeter (mm) = 1/1,000 m
1 micrometer (m) = 1/1,000,000 m
1 nanometer (nm) = 1/1,000,000,000 m
10 nm
1 nm
0.1 nm
visible with
special electron
microscopes
100 nm
most eukaryotic cells
visible with conventional
electron microscope
visible with
light microscope
1 mm
mitochondrion
most bacteria
virus
proteins
diameter of DNA double helix
atoms
Fig. 4-1
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All Cells Share Common Features
 A plasma membrane encloses all cells and
regulates material flow
 Cytoplasm is the fluid interior where a cell’s
metabolic reactions occur
• May contain organelles
• Fluid portion (cytosol) contains water, salts,
and organic molecules
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Copyright © 2009 Pearson Education Inc.
All Cells Share Common Features
 All cells use DNA (deoxyribonucleic acid) as
a hereditary blueprint
 All cells use RNA (ribonucleic acid) to copy
DNA to make proteins
 All cells obtain energy and nutrients from the
environment
 All cells use common building blocks to
build the molecules of life
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Some Cell Types Have Cell Walls

Cell walls are stiff coatings on outer
surfaces of bacteria, plants, fungi, and
some protists
•
•
Composed of polysaccharides like cellulose
or chitin
Support and protect fragile cells and are
usually porous
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Cell Walls

Cell walls in plants may have multiple layers
•
•
•
Primary cell walls in plants are outermost
Secondary cell walls are innermost
Cell walls of adjacent cells joined by middle
lamellae
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4.2 How Do Prokaryotic And Eukaryotic
Cells Differ?
 There are two kinds of cells.
• Prokaryotic cells
• Are found only in two groups of single-celled
organisms—the bacteria and archaea
• Eukaryotic cells
• Are structurally more complex cells
• Possess a membrane-enclosed nucleus
• Probably arose from prokaryotic cells
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There Are Two Basic Cell Types
 Prokaryotic
• Before nucleus
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4.7 What Are The Features Of Prokaryotic
Cells?
 Prokaryotic cells are much smaller than
eukaryotic cells (< 5 µm long)
 Are very reproductively successful and so
are more abundant
 Have a simple internal structure
 Surrounded by a stiff cell wall, which
provides shape and protection
 Can take the shape of rods, spheres, or
helices
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Prokaryotic Cells
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No nuclear membrane or membrane-bound
organelles are present
Some have internal membranes used to
capture light
Cytoplasm contains ribosomes used for
protein synthesis
Cytoplasm may contain food granules
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Copyright © 2009 Pearson Education Inc.
Prokaryotic Cells
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Single, circular chromosome of DNA
•
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Chromosome found coiled in an area called
the nucleoid
Small rings of DNA (plasmids) are located
in the cytoplasm
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Prokaryotic Cells
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Some bacteria are propelled by flagella
Infectious bacteria may have
polysaccharide adhesive capsules and
slime layers on their surfaces
Pili and fimbriae are protein projections
in some bacteria that further enhance
adhesion
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Copyright © 2009 Pearson Education Inc.
There Are Two Basic Cell Types
 Eukaryotic
• True nucleus
• Includes Protist, Fungi, Plant, and
Animal cells
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4.3 What Are The Main Features Of
Eukaryotic Cells?
 Eukaryotic cells are > 10 µm long
 The cytoskeleton provides shape and
organization
 A variety of membrane-enclosed organelles
perform specific functions
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Major Features
 Nucleus: contains DNA
 Mitochondria: produce energy
 Endoplasmic reticulum: synthesizes
membrane components and lipids
 Golgi apparatus: molecule sorting center
 Lysosomes: digest cellular membranes or
defective organelles
 Microtubules: make up the cytoskeleton
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Major Features
 A generalized animal cell
flagellum
cytoplasm
rough endoplasmic
reticulum
ribosome
lysosome
nuclear pore
chromatin (DNA)
nucleus
nucleolus
nuclear envelope
centriole
intermediate
filaments
plasma
membrane
Golgi
apparatus
vesicle
microtubules
free ribosome
smooth
endoplasmic
reticulum
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vesicle
mitochondrion
Fig. 4-3
Major Features
 Animal and plant cells differ with regards to
cell walls, chloroplasts, plastids, central
vacuoles, and centrioles
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Major Features
 A generalized plant cell
microtubules
(part of cytoskeleton)
mitochondrion
chloroplast
central
vacuole
Golgi
apparatus
plasmodesma
smooth
endoplasmic
reticulum
vesicle
cell wall
rough
endoplasmic
reticulum
plasma
membrane
nucleolus
nuclear pore
chromatin
nuclear
envelope
intermediate
filaments
nucleus
ribosomes
free ribosome
Fig. 4-4
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4.4 What Role Does The Nucleus Play?
 The nucleus is the largest organelle
in the cell.
• It is bounded by a nuclear envelope.
• It contains granular-looking chromatin.
• It contains the nucleolus.
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The Nucleus
 The nuclear envelope separates
chromosomes from cytoplasm
• Envelope is a double membrane with
nuclear pores for transport
• Some smaller materials can move through
the pores, while others, such as DNA, are
excluded.
• Outer membrane is studded with ribosomes
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The Nucleus
 The nucleus
nuclear
envelope
nucleolus
nuclear
pores
nucleus
nuclear
pores
chromatin
(a) Structure of the nucleus
(b) Yeast cell
Fig. 4-5
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Copyright © 2009 Pearson Education Inc.
The Nucleus
 The nucleus contains DNA in various
configurations
• Compacted chromosomes (during cell
division)
• Diffuse chromatin (as DNA directs reactions
through an RNA intermediate by coding for
proteins)
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The Nucleus
 Darker area within the nucleus called the
nucleolus
• Functions as the site of ribosome synthesis
• Ribosomes synthesize proteins
• Ribosomes are composed of RNA and
proteins
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The Nucleus
 Ribosome components are made at the
nucleolus.
• The nucleolus contains DNA, RNA, proteins,
and ribosomes in various stages of
construction.
• This is the site where components of
ribosomes are constructed.
• Ribosome components leave the nucleus and
are assembled in the cytoplasm.
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4.5 What Roles Do Membranes Play In
Eukaryotic Cells?
 The plasma membrane isolates the cell, and
alternately, helps it interact with its
environment.
• The phospholipid bilayer contains globular
proteins that regulate the transport of
molecules into and out of the cell.
• Plant, fungi, and some protist cells also have a
cell wall outside the plasma membrane, which
acts as a protective coating.
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System of Membranes
 The endoplasmic reticulum (ER) forms a
series of enclosed, interconnected channels
within cell
• There are two forms of ER:
• Rough endoplasmic reticulum: is studded
with ribosomes
• Smooth endoplasmic reticulum: has no
ribosomes
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System of Membranes
 Smooth ER has no ribosomes
• Contains enzymes that detoxify drugs (in liver
cells)
• Synthesizes phospholipids and cholesterol.
• Together with rough ER are the sites of new
membrane synthesis for the cell.
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System of Membranes
 Rough ER is studded with ribosomes on
outside
• Produces proteins and phospholipids destined
for other membranes or for secretion (export)
• Together with rough ER are the sites of new
membrane synthesis for the cell.
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System of Membranes
 Vesicles are membranous sacs that
transport substances among the separate
regions of the membrane system
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System of Membranes
 The Golgi Apparatus is a set of stacked
flattened sacs
• Receive proteins from ER (via transport
vesicles) and sorts them by destination
• Modify some molecules (e.g. proteins to
glycoproteins)
• Package material into vesicles for transport
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Copyright © 2009 Pearson Education Inc.
System of Membranes
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Three fates of substances made in the
membrane system:
1. Secreted proteins made in RER, travel
through Golgi, then are exported through
plasma membrane
– The following figure illustrates this process
for antibodies
– Antibodies are proteins produced by white
blood cells to inactivate foreign diseasecausing agents
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Copyright © 2009 Pearson Education Inc.
System of Membranes
2. Digestive proteins made in RER, travel
through Golgi, and are packaged as
lysosomes for use in cell
• Lysosomes fuse with food vacuoles and
digest food into basic nutrients
• In the cytoplasm, they digest defective
organelles or pieces of membrane into
component parts that can be recycled.
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Copyright © 2009 Pearson Education Inc.
System of Membranes
3. Membrane proteins and lipids made in
ER, travel through Golgi, and replenish
or enlarge organelle and plasma
membranes
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4.6 What Other Structures Play Key Roles
In Eurkaryotic Cells?
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Vacuoles
Mitochondria
Chloroplasts
Plastids
Cytoskeleton
Cilia and flagella
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Vacuoles
 Fluid-filled sacs with a single membrane
 Functions of vacuoles
• Contractile vacuoles in freshwater organisms
used to collect and pump water out
• Many plant cells have a large central vacuole.
• Plant central vacuoles used in several ways
• Maintain water balance
• Store hazardous wastes, nutrients, or
pigments
• Provide turgor pressure on cytoplasm to
keep cells rigid
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Copyright © 2009 Pearson Education Inc.
Mitochondria Extract Food Energy
 Mitochondria are round, oval, or tubular
sacs of double-membranes
• Inner membrane is folded into cristae
• Intermembrane compartment lies between
inner and outer membranes
• Matrix space within inner membrane
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Copyright © 2009 Pearson Education Inc.
Mitochondria Extract Food Energy
 Function as the “powerhouses of the cell”
• Mitochondria extract energy from food
molecules
• Extracted energy is stored in high-energy
bonds of ATP
• Energy extraction process involves anaerobic
and aerobic reactions
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Mitochondria Extract Food Energy
 Mitochondria may be remnants of free-living
prokaryotes (endosymbiotic hypothesis)
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Chloroplasts
 Chloroplasts are specialized organelles
surrounded by a double membrane
• Outer membrane
• Inner membrane encloses the stroma space
• Stacked hollow membranous sacs
(grana) within stroma are called
thylakoids
• The thylakoid membranes contain
chlorophyll and other pigments that
capture sunlight and with CO2 and water
make sugar and O2 (photosynthesis)
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Copyright © 2009 Pearson Education Inc.
Plants Use Plastids for Storage
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Plastids found only in plants and
photosynthetic protists
Surrounded by a double membrane
Functions
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•
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Storage for photosynthetic products like
starch
Storage of pigment molecules giving color
to ripe fruit
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Copyright © 2009 Pearson Education Inc.
Cytoskeleton
 The cytoskeleton provides shape, support,
and movement.
• All organelles in the cell do not float about the
cytoplasm, but instead, are attached to a
network of protein fibers called the
cytoskeleton.
 Several type of protein fibers make up the
cytoskeleton.
• Microfilaments: thin fibers
• Intermediate filaments: medium-sized fibers
• Microtubules: thick fibers
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Cytoskeleton
plasma
membrane
microfilaments
mitochondrion
microtubules (red)
intermediate
filaments
ribosomes
endoplasmic
reticulum
microtubule
nucleus
vesicle
microfilaments (blue)
(a) Components of the cytoskeleton
(b) Cell with stained cytoskeleton
Fig. 4-9
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Cilia and Flagella
 Cilia and flagella are extensions of the
plasma membrane
 Cilia and flagella are composed of
microtubules in a “9+2” arrangement
formed by centrioles which become
membrane-anchored structures called basal
bodies
 Cilia are short (10-25 µm) and numerous
while flagella are long (50-75 µm) but few in
any cell
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Cilia and Flagella
 Long pairs of microtubules slide along each
other (using ATP) causing movement of cilia
and flagella
 Functions
• Cilia or flagella may be used to move cell
about
• Cilia may be used to create currents of moving
fluid in their environment
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4.6 What Other Structures Play Key Roles
In Eurkaryotic Cells?
 Cilia provide force parallel to the plasma
membrane, which can be described as a
“rowing” motion.
propulsion of fluid
power stroke
plasma membrane
return stroke
cilia lining
the trachea
(a) Cilium
Fig. 4-10a
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4.6 What Other Structures Play Key Roles
In Eurkaryotic Cells?
 Flagella provide a force perpendicular to plasma
membrane, like the engine on a motorboat.
direction of locomotion
propulsion of fluid
continuous propulsion
flagellum
of human
sperm
(b) Flagellum
Fig. 4-10b
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Evolution of
Membrane-Enclosed Organelles
 The first eukaryotes (cells that possess
membrane-bound organelles) appeared
about 1.7 billion years ago
 Several organelles (mitochondria,
chloroplasts, centrioles) may have arisen
when primitive cells engulfed certain types of
bacteria (the endosymbiont hypothesis)
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Evolution of Mitochondria
 Anaerobic, predatory prokaryotic cell
engulfs an aerobic bacterium that it failed
to digest
 Predatory cell and bacterium gradually
enter into a symbiotic relationship
 Descendants of engulfed bacterium evolve
into mitochondria
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Copyright © 2009 Pearson Education Inc.
Evolution of Chloroplasts
 Mitochondria-containing predatory
prokaryotic cell engulf a photosynthetic
bacterium
 Predatory cell and bacterium gradually
enter into a symbiotic relationship
 Descendants of engulfed bacterium evolve
into chloroplasts
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Copyright © 2009 Pearson Education Inc.
Evidence for Endosymbionts
 Many biochemical features are shared by
eukaryotic organelles and living bacteria
 Mitochondria, chloroplasts, and centrioles
contain their own supply of DNA
 Living intermediates (modern cells that
host bacterial endosymbionts)
• Pelomyxa palustris harbors aerobic bacteria
• Paramecium harbors photosynthetic bacteria
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Copyright © 2009 Pearson Education Inc.