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CHAPTER 4
A Tour of the Cell
THE MICROSCOPIC WORLD OF CELLS
• Cells are the building blocks of all life
• Cells must be tiny for materials to move in and
out of them fast enough to meet the cell’s
metabolic needs
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• Organisms are either:
– Single-celled (unicellular), such as most bacteria
and protists
– Multi-celled (multi-cellular), such as plants,
animals, and most fungi
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Leeuwenhoek
What is he
known for?
Developed the
first microscope.
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This is Leeuwenhoek’s
first microscope.
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Englishman
Robert Hooke
First to use
the word:
“Cells.”
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Unfortunately, he was
looking at cork cells
which aren’t living
structures but the remains
of living cells
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Robert Brown
in 1833,
Scottish
Scientist who
discovered
the nucleus
of cells
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Matthias Schleiden Theodor Schwann
“First to see
plant cells”
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“First to see
animal cells”
“The Cell Theory”
•All living things are
made of cells
•Cells are the basic
units of structure
and function in
living things
•All cells come from
Rudolph Virchow preexisting cells
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Microscopes as Windows to Cells
• The light microscope is used by many scientists
– Light passes
through the
specimen
– Lenses enlarge,
or magnify, the
image
(a) Light micrograph (LM) of a white blood cell
(stained purple) surrounded by red blood cells
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• The electron microscope (EM) uses a beam of
electrons
– It has a higher resolving power than the light
microscope
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• The electron
microscope can
magnify up to
100,000X
Human height
Length of some
nerve and
muscle cells
Chicken
egg
Frog
eggs
– Such power
reveals the
diverse parts
within a cell
Plant and
animal
cells
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
Proteins
Lipids
Small
molecules
Atoms
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SEM
• The scanning electron
microscope (SEM) is used
to study the detailed
architecture of the
surface of a cell
(b) Scanning electron micrograph (SEM) of cilia (above)
And a white blood cell
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TEM
• The transmission electron microscope (TEM) is useful
for exploring the internal structure of a cell
(c) Transmission electron micrograph (TEM) of a white blood cell & cilial
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The Two Major Categories of Cells
• The countless cells on earth fall into two
categories
– Prokaryotic cells
– Eukaryotic cells
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• Prokaryotic and eukaryotic cells differ in several
respects
Prokaryotic cell
Nucleoid region
Eukaryotic cell
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Nucleus
Organelles
• Prokaryotic cells
– Are smaller than eukaryotic cells
– Lack internal structures surrounded by
membranes
– Lack a nucleus
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Prokaryotic
flagella
Nucleoid region (DNA)
Ribosomes
Plasma
membrane
Cell wall
Capsule
Pili
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A Generic Animal Cell
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• An idealized plant cell
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Structure and Function of the Nucleus
• The nucleus is bordered by a double membrane
called the nuclear envelope
– It contains chromatin -a DNA-protein structure
– It contains a nucleolus - which produces
ribosomal parts
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Ribosomes
• Ribosomes build all the cell’s proteins
– Are not membrane bound
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How DNA Controls the Cell
• DNA controls the
cell by transferring
its coded
information into
RNA
– The information in
the RNA is used to
make proteins
DNA
1 Synthesis of
mRNA in the
nucleus
Nucleus
Cytoplasm
2 Movement of
mRNA into
cytoplasm via
nuclear pore
3 Synthesis of
protein in the
cytoplasm
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mRNA
mRNA
Ribosome
Protein
THE ENDOMEMBRANE SYSTEM:
MANUFACTURING AND DISTRIBUTING
CELLULAR PRODUCTS
• Many of the membranous organelles in the cell
belong to the endomembrane system
– Endoplasmic reticulum - rough and smooth
– Golgi Apparatus
– Lysosomes
– Vacuoles
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The Endoplasmic Reticulum
• The endoplasmic
reticulum (ER)
Nuclear
envelope
– Greek for
‘network within
a cell’
– Produces an
enormous variety
of molecules
– Is composed of
smooth and
rough ER
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Ribosomes
Rough ER
Smooth ER
Rough ER
• The “roughness” of the rough ER is due to
ribosomes that stud the outside of the ER
membrane
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• The functions of the rough ER include
– Producing proteins
– Producing new membrane
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• After the
rough ER
synthesizes a
molecule it
packages the
molecule
into
transport
vesicles
1
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Smooth ER
• The smooth ER lacks
the surface
ribosomes of ER
• Produces lipids,
including steroids
and sex hormones
• Regulates sugar
• Detoxifies drugs
• Stores calcium
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The Golgi Apparatus
• The Golgi apparatus
– Works in partnership with the ER
– Refines, stores, and distributes the products of cells
Transport
vesicle
from ER
“Receiving” side of
Golgi apparatus
Golgi apparatus
New vesicle forming
Transport vesicle
from the Golgi
“Shipping” side of
Golgi apparatus
Plasma membrane
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Lysosomes
• A lysosome is a membrane-enclosed sac
– Greek for ‘breakdown body’
– It contains digestive enzymes
• Isolated by membrane
– The enzymes break down
• Macromolecules
• Old organelles
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• Lysosomes have several
types of digestive
functions
• They exit the Golgi
apparatus
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– They fuse
with food
vacuoles to
digest the
food
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– They fuse with
old organelles
to recycle parts
– Digest bacteria
in white blood
cells
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Vacuoles
• Vacuoles are membranous sacs
– Two types are the contractile vacuoles of protists
and the central vacuoles of plants
Central
vacuole
Contractile
vacuoles
(a) Contractile vacuoles in a protist
(b) Central vacuole in a plant cell
Figure 4.15
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CHLOROPLASTS AND MITOCHONDRIA:
ENERGY CONVERSION
• Cells require a constant energy supply to do all
the work of life
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CHLOROPLASTS
• Chloroplasts are
the sites of
photosynthesis,
the conversion
of light energy
to chemical
energy
Figure 4.17
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Inner and outer
membranes of
envelope
Granum
Space between
membranes
Stroma (fluid in
chloroplast)
Mitochondria
• Mitochondria are the sites of cellular respiration,
which involves the production of ATP from food
molecules
Outer
membrane
Inner
membrane
Cristae
Matrix
Space between
membranes
Figure 4.18
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THE CYTOSKELETON:
CELL SHAPE AND MOVEMENT
• The cytoskeleton is an infrastructure of the cell
consisting of a network of fibers
– Microfilaments - small threads
– Intermediate filaments - ropelike
– Microtubules - small tubes
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Maintaining Cell Shape
• One function of
the cytoskeleton
– Provide
mechanical
support to
the cell and
maintain its
shape
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Figure4.9x
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• The cytoskeleton can
change the shape of a cell
– This allows cells like
amoebae to move
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Cilia and Flagella
• Cilia and flagella are motile appendages
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• Flagella propel the cell
in a whip-like motion
• Cilia move in a
coordinated back-andforth motion
Figure 4.20A, B
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• Some cilia or flagella
extend from nonmoving
cells
– The human windpipe is
lined with cilia
– Smoking damages the
cilia
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CELL SURFACES:
PROTECTION, SUPPORT, AND CELL-CELL
INTERACTIONS
• Most cells secrete materials that are external to
the plasma membrane
• This extra cellular matrix
– Regulates
– Protects
– Supports
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