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CHAPTER 4
A Tour of the Cell
PowerPoint® Lectures for
Essential Biology, Third Edition
– Neil Campbell, Jane Reece, and Eric Simon
Essential Biology with Physiology, Second Edition
– Neil Campbell, Jane Reece, and Eric Simon
Lectures by Chris C. Romero
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Biology and Society:
Cells That Cure
• During a heart attack,
– Heart muscle cells die because they are starved
for oxygen.
• Unfortunately, these kinds of cells do not
regenerate.
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• In recent years, a new treatment called “cell
therapy” has emerged.
• In this procedure, cells are taken from other parts
of the body
– And delivered to the ailing heart, facilitating
healing.
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Figure 4.1
The Microscopic World of Cells
• Organisms are either:
– Single-celled, such as
most bacteria and
protists
– Multicelled, such as
plants, animals, and
most fungi
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The Microscopic World of Cells
•
The human body is made up of trillions of cells many of which are
specialized
–
Muscle cells, Nerve cells, & blood cells…
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• Cells were first discovered in 1665 by Robert
Hooke.
• The accumulation of scientific evidence led to the
cell theory.
– All living things are composed of cells.
– All cells are formed from previously existing
cells.
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Microscopes provide windows to the world of the
cell
The light microscope enables us to see the
overall shape and structure of a cell
Image seen by viewer
Eyepiece
Ocular
lens
Objective lens
Specimen
Condenser lens
Light source
Figure 4.1A
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Microscopes as a Window on the World of Cells
• The light microscope is used by many scientists.
– Light passes through the specimen.
– Lenses enlarge, or magnify, the image.
• Magnification
– Is an increase in the specimen’s apparent size.
• Resolving power
– Is the ability of an optical instrument to show two
objects as being separate.
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• The electron microscope (EM) uses a beam of
electrons.
– It has a higher resolving power than the light
microscope.
• The electron microscope can magnify up to
100,000X.
– Such power reveals the diverse parts within a cell.
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Microscopes as a Window on the World of Cells
• The scanning electron
microscope (SEM) is used
to study the detailed
architecture of the surface
of a cell.
• Produces a 3D image
• Used to study cell
surfaces
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Microscopes as a Window on the World of Cells
• The transmission electron
microscope (TEM) is
useful for exploring the
internal structure of a cell.
• An electron beam is
aimed through a thin
section.
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The Two Major Categories of Cells
• The countless cells on earth fall into two
categories:
– Prokaryotic cells
– Eukaryotic cells
• Both cells
– Are surrounded by a plasma membrane
– Consist of cytoplasm and organelles and contain
DNA
• Prokaryotic and eukaryotic cells differ in several
respects.
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Figure 4.4
Most cells are
10-100
micrometers in
size
Cell size and
shape relate to
function
Figure 4.2
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Natural laws limit cell size
The lower limit of cell size is determined by the
fact that a cell must be large enough to house the
parts it needs to survive and reproduce
The maximum size of a cell is limited by the
amount of surface needed to obtain nutrients
from the environment and dispose of wastes.
• The ratio of surface are to volume imposes limits
on cell size
• Muscle and nerve cells can be very long because
they are thin and have more surface area compared
to volume
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A small cell has a greater ratio of surface area to
volume than a large cell of the same shape
30 µm
Figure 4.3
10 µm
Surface area
of one large cube
= 5,400 µm2
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Total surface area
of 27 small cubes
= 16,200 µm2
• Prokaryotic cells
– Are smaller than eukaryotic cells.
– Lack internal structures surrounded by
membranes.
– Lack a nucleus.
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A prokaryotic cell is enclosed by a plasma
membrane and is usually encased in a rigid cell
wall
• The cell wall
may be covered
by a sticky
capsule
Prokaryotic
flagella
Nucleoid Region (DNA)
Capsule
Cell wall
• Inside the cell
are its DNA and
other parts
Plasma
membrane
Ribosome
Pili
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Figure 4.4
Structures of Prokaryotic Cells
Nucleoid region – area where DNA is coiled in
the cytoplasm. DNA is in direct contact with the
rest of the cell
Plasmid – smaller circular DNA molecules
Ribosomes – where proteins are made
Plasma membrane – encloses the cytoplasm of
the prokaryotic cell
Cell wall – rigid, composed of lipids,
carbohydrates and protein. Protects the cell and
maintains its shape
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Cell Wall components
determine if bacteria is
classified as
•gram positive (+)
• or gram negative
• In general more toxic and
resistant to antibiotics
http://www.bio.upenn.edu/computing/media/Instructional.Stain.Gram.php
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Structures of the Prokaryotic Cell
Capsule – sticky outer coat that surrounds some
prokaryotes. Protects the cell surface. Helps
bacteria attach to surfaces
Pili – short surface projections found in some
prokaryotes. Helps attach bacteria to surfaces
Flagella – long whiplike extensions found in some
prokaryotes. Propel cell through liquid
environments
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The Role of Bacteria in the Nitrogen Cycle
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Eukaryotic cells are partitioned into functional
compartments
All other life forms are made up of one or more
eukaryotic cells
These are larger and more complex than
prokaryotic cells
Eukaryotes are distinguished by the presence of
a true nucleus
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A Panoramic View of Eukaryotic Cells
• An idealized animal cell
Cytoplasmic Streaming
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Figure 4.6b
The Plasma Membrane
Would this organelle/ structure also be found in prokaryotes?
If so, are there any important differences in structure or function?
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The Plasma Membrane:
A Fluid Mosaic of Lipids and Proteins
• The plasma membrane separates the living cell
from its nonliving surroundings.
• The membranes of cells are composed mostly of:
– Lipids
– Proteins
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The plasma membrane
• The lipids belong to a special category called
phospholipids.
• Phospholipids form a two-layered membrane, the
phospholipid bilayer.
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The plasma membrane
• Most membranes have
specific proteins
embedded in the
phospholipid bilayer.
• Membranes also contain
cholesterol wedged
between the
phospholipids.
• Carbohydrates are found
on the external surface
attached to phospholipids
or protein.
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• Membrane phospholipids and proteins can drift
about in the plane of the membrane.
• This behavior leads to the description of a
membrane as a fluid mosaic:
– Molecules can move freely within the membrane.
– A diversity of proteins exists within the
membrane.
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Cell Surfaces
• Most cells secrete materials for coats of one kind or
another
– That are external to the plasma membrane.
• These extracellular coats help protect and support
cells
– And facilitate interactions between cellular
neighbors in tissues.
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• Animal cells have an
extracellular matrix,
– Which helps hold cells
together in tissues and
protects and supports
them.
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The Cell Wall
Would this organelle/
structure also be found
in prokaryotes?
If so, are there any
important differences
in structure or
function?
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• Plant cells have cell walls,
– Which help protect the cells, maintain their shape,
and keep the cells from absorbing too much water.
– Made of Cellulose and other components in plant
cells
– Prokaryotes’ cell wall performs the same function,
though it is composed of different organic molecules
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• Cell Junctions
– “Tunnels” that
Connects the cytoplasm
of one plant cell with
the cytoplasm of
another plant cell, thus
allowing small
substances to move
from cell to cell.
– There are other types of
junctions, but that is for
Advanced bio I
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Ex: cell Junctions
The Nucleus
Would this organelle/
structure also be found in
prokaryotes?
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The Nucleolus
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Figure 4.8
The Nucleus and Ribosomes:
Genetic Control of the Cell
• The nucleus is the manager of the cell
– Genes in the nucleus store information necessary
to produce proteins which direct the cell’s
activities
• It is usually the largest organelle.
• It contains chromatin (DNA)
• The nucleus is separated from the cytoplasm by the
nuclear envelope.
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Structure and Function of the Nucleolus
• The nucleolus is found within the nucleus
– It is a mass of fibers and granules
– It is where ribosomes are made
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Ribosomes
Would this organelle/ structure also be found in prokaryotes?
If so, are there any important differences in structure or
function?
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Ribosomes
• Ribosomes are
responsible for protein
synthesis.
• DNA controls the cell by
transferring its coded
information into RNA.
– The information in
the RNA is used by
ribosomes to make
proteins.
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The Endomembrane System: Manufacturing and
Distributing Cellular Products
The endomembrane system is a collection of
membranous organelles
• These organelles manufacture and distribute cell
products
• The endomembrane system divides the cell into
compartments
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Figure 4.10
The Endoplasmic Reticulum
• The endoplasmic reticulum (ER)
– Produces an enormous variety of molecules.
– Is composed of smooth and rough ER.
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Rough Endoplasmic Reticulum
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Rough ER makes membrane and proteins
• The “roughness” of the rough ER is due to
ribosomes that stud the outside of the ER
membrane.
• The functions of the rough ER include:
– Producing two types of membrane proteins
– Producing new membrane
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Rough Endoplasmic REticulum
• After the rough ER synthesizes a molecule, it
packages the molecule into transport vesicles.
Transport vesicle
buds off
4
Ribosome
Sugar
chain
1
3
Secretory
(glyco-) protein
inside transport
vesicle
Glycoprotein
2
Polypeptide
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ROUGH ER
Smooth Endoplasmic Reticulum
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Smooth ER
• Continuous with the rough ER
• Lacks the surface ribosomes of ER
• Produces lipids, including steroids.
–
For example how cells in your ovaries or testes produce steroid based
sex hormones like estrogen and testosterone
• In some cells, it regulates carbohydrate metabolism
•
In liver cells breaks down toxins and drugs
–
Antibiotics, barbiturates, alcohol
• In other cells- especially muscle cells it stores calcium
ions.
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The Golgi Complex
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Figure 4.12
The Golgi Apparatus
• The Golgi apparatus
– Works in partnership with the ER.
– It consists of stacks of membranous sacs
– Refines, stores, and distributes the chemical
products of cells.
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Vesicles
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Lysosomes
• A lysosome is a
membrane-enclosed sac.
– It contains digestive
enzymes.
– The enzymes break
down
macromolecules.
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Figure 4.13a
Figure 4.13b
• Lysosomes have several types of digestive
functions.
– They fuse with food vacuoles to digest the
food.
– They break down damaged organelles.
Lysosome Formation
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Connection: Abnormal lysosomes can cause fatal
diseases
Lysosomal storage diseases are hereditary
• They interfere with other cellular functions
• Examples: Pompe’s disease, Tay-Sachs disease
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Vacuoles
• Vacuoles are membranous sacs.
– Two types are the contractile vacuoles of protists and the
central vacuoles of plants.
Paramecium Vacuole
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The Central Vacuole
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Vacuoles function in the general maintenance of the
cell
Plant cells contain
a large central
vacuole
• The vacuole
absorbs water,
stores vital
chemicals,
stores waste
products
Central
vacuole
Nucleus
Figure 4.13A
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Protists may have contractile vacuoles
• These pump out excess water
Nucleus
Contractile
vacuoles
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Figure 4.13B
Figure 4.15
Chloroplasts and Mitochondria:
Energy Conversion
• Cells require a constant energy supply to do all the
work of life.
• This function is carried out by the chloroplasts and
the mitochondria
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Chloroplasts
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Chloroplasts
• Chloroplasts are found in
plants and some protists.
• Chloroplasts are the sites
of photosynthesis, the
conversion of light energy
to chemical energy in
sugars.
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Mitochondria
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Mitochondria
• Mitochondria are the sites
of cellular respiration,
which involves the
production of ATP from
food molecules.
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• Mitochondria and chloroplasts share another
feature unique among eukaryotic organelles.
– They contain their own DNA.
• The existence of separate “mini-genomes” is
believed to be evidence that
– Mitochondria and chloroplasts evolved from
free-living prokaryotes in the distant past.
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Cytoskeleton
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The Cytoskeleton:
Cell Shape and Movement
• The cytoskeleton is an
infrastructure of the cell
consisting of a network of
fibers.
• One function of the
cytoskeleton is to provide
mechanical support to the
cell and maintain its
shape.
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The Cytoskeleton
• The cytoskeleton can
change the shape of a cell.
• This allows cells like
amoebae to move.
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Flagella
Would this organelle/
structure also be found
in prokaryotes?
If so, are there any
important differences in
structure or function?
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Cilia and Flagella
• Cilia and flagella are
motile appendages.
• Flagella propel the cell in
a whiplike motion.
• Cilia move in a
coordinated back-andforth motion.
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Cilia and Flagella
• Some cilia or flagella
extend from nonmoving
cells.
• The human windpipe is
lined with cilia.
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Evolution Connection:
The Origin of Membranes
• Phospholipids were
probably among the
organic molecules on the
early Earth.
• When mixed with water,
phospholipids
spontaneously form
membranes.
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