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Chapter 4
A Tour of the Cell
PowerPoint® Lectures for
Campbell Essential Biology, Fourth Edition
– Eric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third Edition
– Eric Simon, Jane Reece, and Jean Dickey
Lectures by Chris C. Romero, updated by Edward J. Zalisko
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Biology and Society:
Drugs That Target Bacterial Cells
• Antibiotics were first isolated from mold in 1928.
• The widespread use of antibiotics drastically decreased deaths
from bacterial infections.
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Figure 4.00
Colorized TEM
• Most antibiotics kill bacteria while minimally harming the human
host by binding to structures found only on bacterial cells.
• Some antibiotics bind to the bacterial ribosome, leaving human
ribosomes unaffected.
• Other antibiotics target enzymes found only in the bacterial cells.
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THE MICROSCOPIC WORLD OF CELLS
• Organisms are either
– Single-celled, such as most prokaryotes and protists or
– Multicelled, such as plants, animals, and most fungi
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Microscopes as Windows on the World of Cells
• Light microscopes can be used to explore the structures and
functions of cells.
• When scientists examine a specimen on a microscope slide
– Light passes through the specimen
– Lenses enlarge, or magnify, the image
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LM
Light Micrograph (LM)
(for viewing living cells)
Light micrograph of a protist, Paramecium
Figure 4.1a
Colorized SEM
Scanning Electron Micrograph (SEM)
(for viewing surface features)
Scanning electron micrograph of Paramecium
Figure 4.1b
Colorized TEM
Transmission Electron Micrograph (TEM)
(for viewing internal structures)
Transmission electron micrograph of Paramecium
Figure 4.1c
• Magnification is an increase in the specimen’s apparent size.
• Resolving power is the ability of an optical instrument to show
two objects as separate.
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• Cells were first described in 1665 by Robert Hooke.
• The accumulation of scientific evidence led to the cell theory.
– All living things are composed of cells.
– All cells come from other cells.
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• The electron microscope (EM) uses a beam of electrons, which
results in better resolving power than the light microscope.
• Two kinds of electron microscopes reveal different parts of cells.
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• Scanning electron microscopes examine cell surfaces.
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• Transmission electron microscopes (TEM) are useful for
internal details of cells.
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• The electron microscope can
– Magnify up to 100,000 times
– Distinguish between objects 0.2 nanometers apart
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Figure 4.2
10 m
1m
Length of some
nerve and
muscle cells
10 cm
Chicken egg
Unaided eye
Human height
1 cm
Frog eggs
Plant and
animal cells
10 mm
1 mm
100 nm
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
10 nm
Electron microscope
100 mm
Light microscope
1 mm
Proteins
Lipids
1 nm
0.1 nm
Small molecules
Atoms
Figure 4.3
The Two Major Categories of Cells
• The countless cells on earth fall into two categories:
– Prokaryotic cells — Bacteria and Archaea
– Eukaryotic cells — plants, fungi, and animals
• All cells have several basic features.
– They are all bound by a thin plasma membrane.
– All cells have DNA and ribosomes, tiny structures that build proteins.
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• Prokaryotic and eukaryotic cells have important differences.
• Prokaryotic cells are older than eukaryotic cells.
– Prokaryotes appeared about 3.5 billion years ago.
– Eukaryotes appeared about 2.1 billion years ago.
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• Prokaryotes
– Are smaller than eukaryotic cells
– Lack internal structures surrounded by membranes
– Lack a nucleus
– Have a rigid cell wall
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• Eukaryotes
– Only eukaryotic cells have organelles, membrane-bound structures that
perform specific functions.
– The most important organelle is the nucleus, which houses most of a
eukaryotic cell’s DNA.
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Plasma membrane
(encloses cytoplasm)
Cell wall (provides
Rigidity)
Capsule (sticky
coating)
Colorized TEM
Prokaryotic
flagellum
(for propulsion)
Ribosomes
(synthesize
proteins)
Nucleoid
(contains DNA)
Pili (attachment structures)
Figure 4.4
Plasma membrane
(encloses cytoplasm)
Cell wall (provides rigidity)
Capsule (sticky coating)
Prokaryotic
flagellum
(for propulsion)
Ribosomes
(synthesize
proteins)
Nucleoid
(contains DNA)
Pili (attachment structures)
Figure 4.4a
Figure 4.4b
Colorized TEM
An Overview of Eukaryotic Cells
• Eukaryotic cells are fundamentally similar.
• The region between the nucleus and plasma membrane is the
cytoplasm.
• The cytoplasm consists of various organelles suspended in fluid.
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• Unlike animal cells, plant cells have
– Protective cell walls
– Chloroplasts, which convert light energy to the chemical energy of food
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Ribosomes
Cytoskeleton
Centriole
Lysosome
Not in most
plant cells
Flagellum
Plasma
membrane
Nucleus
Mitochondrion
Rough
endoplasmic
reticulum (ER)
Golgi
apparatus
Idealized animal cell
Smooth
endoplasmic
reticulum (ER)
Figure 4.5a
Cytoskeleton
Central
vacuole
Cell wall
Chloroplast
Mitochondrion
Nucleus
Not in
animal cells
Rough endoplasmic
reticulum (ER)
Ribosomes
Plasma
membrane
Smooth
endoplasmic
reticulum (ER)
Channels between
cells
Golgi apparatus
Idealized plant cell
Figure 4.5b
MEMBRANE STRUCTURE
• The plasma membrane separates the living cell from its nonliving
surroundings.
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The Plasma Membrane: A Fluid Mosaic of
Lipids and Proteins
• The membranes of cells are composed mostly of
– Lipids
– Proteins
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• The lipids belong to a special category called phospholipids.
• Phospholipids form a two-layered membrane, the phospholipid
bilayer.
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Outside of cell
Hydrophilic
head
Hydrophobic
tail
Phospholipid
Cytoplasm (inside of cell)
(a) Phospholipid bilayer of membrane
Figure 4.6a
Outside of cell
Proteins
Hydrophilic
region of
protein
Phospholipid
bilayer
Hydrophilic
head
Hydrophobic
tail
Hydrophobic
regions of
protein
Cytoplasm (inside of cell)
(b) Fluid mosaic model of membrane
Figure 4.6b
• Most membranes have specific proteins embedded in the
phospholipid bilayer.
• These proteins help regulate traffic across the membrane and
perform other functions.
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• The plasma membrane is a fluid mosaic:
– Fluid because molecules can move freely past one another
– A mosaic because of the diversity of proteins in the membrane
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The Process of Science:
What Makes a Superbug?
• Observation: Bacteria use a protein called PSM to disable human
immune cells by forming holes in the plasma membrane.
• Question: Does PSM play a role in MRSA infections?
• Hypothesis: MRSA bacteria lacking the ability to produce PSM
would be less deadly than normal MRSA strains.
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• Experiment: Researchers infected
– Seven mice with normal MRSA
– Eight mice with MRSA that does not produce PSM
• Results:
– All seven mice infected with normal MRSA died.
– Five of the eight mice infected with MRSA that does not produce PSM
survived.
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• Conclusions:
– MRSA strains appear to use the membrane-destroying PSM protein, but
– Factors other than PSM protein contributed to the death of mice
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Colorized SEM
MRSA bacterium
producing PSM
proteins
Methicillin-resistant
Staphylococcus aureus (MRSA)
PSM proteins
forming hole
in human
immune cell
plasma
membrane
PSM
protein
Plasma
membrane
Pore
Cell bursting,
losing its
contents
through
the pores
Figure 4.7-3
Cell Surfaces
• Plant cells have rigid cell walls surrounding the membrane.
• Plant cell walls
– Are made of cellulose
– Protect the cells
– Maintain cell shape
– Keep the cells from absorbing too much water
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• Animal cells
– Lack cell walls
– Have an extracellular matrix, which
–
Helps hold cells together in tissues
–
Protects and supports them
• The surfaces of most animal cells contain cell junctions,
structures that connect to other cells.
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THE NUCLEUS AND RIBOSOMES:
GENETIC CONTROL OF THE CELL
• The nucleus is the chief executive of the cell.
– Genes in the nucleus store information necessary to produce proteins.
– Proteins do most of the work of the cell.
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Structure and Function of the Nucleus
• The nucleus is bordered by a double membrane called the nuclear
envelope.
• Pores in the envelope allow materials to move between the
nucleus and cytoplasm.
• The nucleus contains a nucleolus where ribosomes are made.
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Nuclear
envelope
Nucleolus
Pore
TEM
Chromatin
TEM
Ribosomes
Surface of nuclear envelope
Nuclear pores
Figure 4.8
• Stored in the nucleus are long DNA molecules and associated
proteins that form fibers called chromatin.
• Each long chromatin fiber constitutes one chromosome.
• The number of chromosomes in a cell depends on the species.
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DNA molecule
Proteins
Chromatin
fiber
Chromosome
Figure 4.9
Ribosomes
• Ribosomes are responsible for protein synthesis.
• Ribosome components are made in the nucleolus but assembled in
the cytoplasm.
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Ribosome
mRNA
Protein
Figure 4.10
• Ribosomes may assemble proteins:
– Suspended in the fluid of the cytoplasm or
– Attached to the outside of an organelle called the endoplasmic reticulum
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TEM
Ribosomes in
cytoplasm
Ribosomes attached
to endoplasmic
reticulum
Figure 4.11
How DNA Directs Protein Production
• DNA directs protein production by transferring its coded
information into messenger RNA (mRNA).
• Messenger RNA exits the nucleus through pores in the nuclear
envelope.
• A ribosome moves along the mRNA translating the genetic
message into a protein with a specific amino acid sequence.
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DNA
Synthesis of
mRNA in the
nucleus
mRNA
Nucleus
Cytoplasm
Movement of
mRNA into
cytoplasm
via
nuclear pore
Synthesis of
protein in the
cytoplasm
mRNA
Ribosome
Protein
Figure 4.12-3
THE ENDOMEMBRANE SYSTEM:
MANUFACTURING AND DISTRIBUTING
CELLULAR PRODUCTS
• Many membranous organelles forming the endomembrane
system in a cell are interconnected either
– Directly or
– Through the transfer of membrane segments between them
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The Endoplasmic Reticulum
• The endoplasmic reticulum (ER) is one of the main
manufacturing facilities in a cell.
• The ER
– Produces an enormous variety of molecules
– Is composed of smooth and rough ER
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Nuclear
envelope
Ribosomes
TEM
Rough ER
Smooth ER
Ribosomes
Figure 4.13
Rough ER
• The “rough” in the rough ER is due to ribosomes that stud the
outside of the ER membrane.
• These ribosomes produce membrane proteins and secretory
proteins.
• After the rough ER synthesizes a molecule, it packages the
molecule into transport vesicles.
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Proteins are
often modified in
the ER.
Secretory
proteins depart in
transport vesicles.
Ribosome
Vesicles bud off
from the ER.
Transport
vesicle
Protein
A ribosome
links amino acids
into a
polypeptide.
Rough ER
Polypeptide
Figure 4.14
Smooth ER
• The smooth ER
– Lacks surface ribosomes
– Produces lipids, including steroids
– Helps liver cells detoxify circulating drugs
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The Golgi Apparatus
• The Golgi apparatus
– Works in partnership with the ER
– Receives, refines, stores, and distributes chemical products of the cell
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Transport vesicle
from rough ER
“Receiving” side of
Golgi apparatus
New
vesicle
forming
Transport
vesicle
from the
Golgi
“Shipping” side of
Golgi apparatus
Plasma
membrane
Figure 4.15a
Colorized SEM
“Receiving” side of Golgi apparatus
New vesicle forming
Figure 4.15b
Lysosomes
• A lysosome is a sac of digestive enzymes found in animal cells.
• Enzymes in a lysosome can break down large molecules such as
– Proteins
– Polysaccharides
– Fats
– Nucleic acids
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• Lysosomes have several types of digestive functions.
– Many cells engulf nutrients in tiny cytoplasmic sacs called food vacuoles.
– These food vacuoles fuse with lysosomes, exposing food to enzymes to
digest the food.
– Small molecules from digestion leave the lysosome and nourish the cell.
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Plasma membrane
Digestive enzymes
Lysosome
Lysosome
Digestion
Food vacuole
Vesicle containing
damaged organelle
(a) Lysosome digesting food
Digestion
(b) Lysosome breaking down the molecules of damaged
organelles
Organelle fragment
Vesicle containing two
damaged organelles
TEM
Organelle fragment
Figure 4.16
• Lysosomes can also
– Destroy harmful bacteria
– Break down damaged organelles
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Vacuoles
• Vacuoles are membranous sacs that bud from the
– ER
– Golgi
– Plasma membrane
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• Contractile vacuoles of protists pump out excess water in the cell.
• Central vacuoles of plants
– Store nutrients
– Absorb water
– May contain pigments or poisons
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TEM
Vacuole filling with water
TEM
Vacuole contracting
(a) Contractile vacuole in Paramecium
Figure 4.17a
Colorized TEM
Central vacuole
(b) Central vacuole in a plant cell
Figure 4.17b
• To review, the endomembrane system interconnects the
– Nuclear envelope
– ER
– Golgi
– Lysosomes
– Vacuoles
– Plasma membrane
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Golgi
apparatus
Rough ER
Transport
vesicle
Transport vesicles
carry enzymes and
other proteins from
the rough ER to the
Golgi for processing.
Transport
vesicle
Plasma
membrane
Secretory
protein
Some products
are secreted
from the cell.
Vacuole
Lysosomes carrying
digestive enzymes can
Lysosome fuse with other vesicles.
Vacuoles store some
cell products.
Figure 4.18a
Golgi apparatus
New vesicle forming
TEM
Transport vesicle from
the Golgi
Figure 4.18b
CHLOROPLASTS AND MITOCHONDRIA:
ENERGY CONVERSION
• Cells require a constant energy supply to perform the work of life.
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Chloroplasts
• Most of the living world runs on the energy provided by
photosynthesis.
• Photosynthesis is the conversion of light energy from the sun to
the chemical energy of sugar.
• Chloroplasts are the organelles that perform photosynthesis.
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• Chloroplasts have three major compartments:
– The space between the two membranes
– The stroma, a thick fluid within the chloroplast
– The space within grana, the structures that trap light energy and convert
it to chemical energy
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Inner and outer
membranes
Space between
membranes
Granum
TEM
Stroma (fluid in chloroplast)
Figure 4.19
Mitochondria
• Mitochondria are the sites of cellular respiration, which produce
ATP from the energy of food molecules.
• Mitochondria are found in almost all eukaryotic cells.
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• An envelope of two membranes encloses the mitochondrion.
These consist of
– An outer smooth membrane
– An inner membrane that has numerous infoldings called cristae
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TEM
Outer
membrane
Inner
membrane
Cristae
Matrix
Space between
membranes
Figure 4.20
• Mitochondria and chloroplasts contain their own DNA, which
encodes some of their proteins.
• This DNA is evidence that mitochondria and chloroplasts evolved
from free-living prokaryotes in the distant past.
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THE CYTOSKELETON: CELL SHAPE AND
MOVEMENT
• The cytoskeleton is a network of fibers extending throughout the
cytoplasm.
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Maintaining Cell Shape
• The cytoskeleton
– Provides mechanical support to the cell
– Maintains its shape
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• The cytoskeleton contains several types of fibers made from
different proteins:
– Microtubules
–
Are straight and hollow
–
Guide the movement of organelles and chromosomes
– Intermediate filaments and microfilaments are thinner and solid.
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LM
(a) Microtubules
in the cytoskeleton
LM
(b) Microtubules
and movement
Figure 4.21
• The cytoskeleton is dynamic.
• Changes in the cytoskeleton contribute to the amoeboid motion of
an Amoeba.
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Cilia and Flagella
• Cilia and flagella aid in movement.
– Flagella propel the cell in a whiplike motion.
– Cilia move in a coordinated back-and-forth motion.
– Cilia and flagella have the same basic architecture.
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Colorized SEM
(a) Flagellum of a human sperm cell
Colorized SEM
Colorized SEM
(b) Cilia on a protist
(c) Cilia lining the
respiratory tract
Figure 4.22
• Cilia may extend from nonmoving cells.
• On cells lining the human trachea, cilia help sweep mucus out of
the lungs.
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Evolution Connection:
The Evolution of Antibiotic Resistance
• Many antibiotics disrupt cellular structures of invading
microorganisms.
• Introduced in the 1940s, penicillin worked well against such
infections.
• But over time, bacteria that were resistant to antibiotics were
favored.
• The widespread use and abuse of antibiotics continues to favor
bacteria that resist antibiotics.
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