Transcript Table of Contents

Cells: The Basic Units of Life:
Prokaryotes
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Cells: The Basic Units of Life
• The Cell: The Basic Unit of Life
• Prokaryotic cells
• Microscopy techniques
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The Cell: The Basic Unit of Life
Shared characteristics of life:
 Grow and develop.
 Reproduce themselves using the hereditary material
DNA.
 Capture energy from their environment.
 Sense their environment and respond to it
 Evolve
 Show a high level of organization (complex)
Life can be defined as an organized genetic unit capable of
metabolism, reproduction, and evolution.
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The Cell: The Basic Unit of Life
• Life requires a structural compartment separate
from the external environment in which
macromolecules can perform unique functions in a
relatively constant internal environment.
• These “living compartments” are cells.
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What is Life?
• Current living organisms are divided into five
kingdoms
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The Cell: The Basic Unit of Life
• Current living organisms can be divided into five kingdoms
• Cells show two organizational patterns:
 Prokaryotes
 Eukaryotes
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Three Domains
All cells (Prokaryotes and Eukaryotes) have certain
characteristics in common:
 They have DNA that encodes polypeptides.
 They produce polypeptides by transcription and
translation and use the same genetic code.
 They replicate their DNA semiconservatively.
 They have plasma membranes and ribosomes.
 They use sugar as energy source.
• Prokaryotes have inhabited earth for billions of
years
 Prokaryotes are the oldest life-forms and
remain the most numerous and widespread
organisms
Colorized SEM 650 
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Earth harbors huge amount invisible bacteria, PROKARYOTES
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General Biology of the Prokaryotes
• Prokaryotes are found in every conceivable
habitat on the planet.
 They live at extremely hot temperatures.
 They can survive extreme alkalinity and saltiness.
 Some survive in the presence of oxygen, while
others survive without it.
 Some live at the bottom of the sea.
 Some live in rocks more than 2 km into Earth’s solid
crust.
 Many are not yet identified and described
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Heat and
acid-loving
Archaea
inside a volcanic
vent on the
Island of Kyushu
Japan
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Some Would Call It Hell; Archaea Call It Home
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Salt-loving
Archaea
easily visible
because of their
carotenoids
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Extreme Halophiles
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Spain’s Rio TintoA river of pH 2
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Earth or Ancient Mars?
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Earth harbors huge amount invisible bacteria, PROKARYOTES
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• Most prokaryotes are unicellular, although some species
form colonies
• Most prokaryotic cells are 0.5–5 µm, much smaller than the
10–100 µm of many eukaryotic cells
• Prokaryotic cells have a variety of shapes
• The three most common shapes are spheres (cocci), rods
(bacilli), and spirals
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Prokaryotic cells have a variety of shapes
spheres (cocci), rods (bacilli), and spirals (Spirochetes)
1 m
(a) Spherical (cocci)
2 m
(b) Rod-shaped (bacilli)
5 m
(c) Spiral
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A Prokaryotic Cell
Features shared by all prokaryotic cells:
• All have a plasma membrane and very simple internal organization.
• The cytoplasm (the plasma-membrane enclosed region) consists of the
nucleoid, ribosomes, and a liquid portion called the cytosol.
• The region called the nucleoid is where DNA is concentrated.
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Cell-Surface Structures
• One of the most important features of nearly all prokaryotic
cells is their cell wall, which maintains cell shape, provides
physical protection, and prevents the cell from bursting in a
hypotonic environment
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Cell-Surface Structures
Cell surface features of prokaryotic cells:
 A cell wall just outside the plasma membrane.
 Some bacteria have another membrane outside the cell
wall, a polysaccharide-rich phospholipid membrane.
 Some prokaryotes have an outermost slimy layer made
of polysaccharides and referred to as a capsule.
 Many antibiotics target peptidoglycan and damage
bacterial cell walls
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Cell-Surface Structures
Cell wall features of prokaryotic cells:
Carbohydrate portion
of lipopolysaccharide
Outer
membrane
Cell
wall Peptidoglycan
layer
Plasma membrane
Protein
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The cell wall
Bacteria are often covered by a sticky capsule that
protects cells from drying and from the immune system
and help them adhere to substrate
 The capsule thickness can be changed by the
bacterium
Colorized TEM 70,000 

Capsule
Streptococcus attached to a tonsil cell
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Cell-Surface Structures
Bacterial cell walls contain peptidoglycan, a network of sugar
polymers cross-linked by polypeptides
peptidoglycan:
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The Gram stain
 Scientists can classify many bacterial species into two
groups based on cell wall composition, Gram-positive
and Gram-negative
Lipopolysaccharide
Cell wall
Peptidoglycan
layer
Cell wall
Outer
membrane
Peptidoglycan
layer
Plasma membrane
Plasma membrane
Protein
Protein
Grampositive
bacteria
Gramnegative
bacteria
20 m
(a) Gram-positive. Gram-positive bacteria have
a cell wall with a large amount of peptidoglycan
that traps the violet dye in the cytoplasm. The
alcohol rinse does not remove the violet dye,
which masks the added red dye.
(b)
Gram-negative. Gram-negative bacteria have less
peptidoglycan, and it is located in a layer between the
plasma membrane and an outer membrane. The
violet dye is easily rinsed from the cytoplasm, and the
cell appears pink or red after the red dye is added.
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Prokaryotic Cells
• Some bacteria have flagella, locomotory structures
shaped like a corkscrew turning at10-20,000 rpm.
• Some bacteria have pili, threadlike structures that help
bacteria adhere to one another during mating or to other
cells for food and protection.
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motility
• Most motile bacteria propel themselves by flagella that are
structurally and functionally different from eukaryotic flagella
• In a heterogeneous environment, many bacteria exhibit
taxis, the ability to move toward or away from certain stimuli
Flagellum
Filament
50 nm
Cell wall
Hook
Basal apparatus
Plasma
membrane
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Some prokaryotes have specialized membranes
• Memebrane invaginations are found in some bacteria
and are important for metabolism (primarily for
photosynthesis and respiration)
0.2 m
1 m
Respiratory
membrane
Thylakoid
membranes
(a) Aerobic prokaryote
(b) Photosynthetic prokaryote
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Prokaryotic Cell Division
• Prokaryotes divide by fission.
 Most prokaryotes have one circular chromosome.
 As DNA replicates, each of the two resulting DNA
molecules attaches to the plasma membrane.
 As the cell grows, new plasma membrane is added
between the attachment points, and the DNA
molecules are moved apart.
 Cytokinesis separates the one cell into two, each
with a complete chromosome.
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Prokaryotic Cell Division
Bacteria divide
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The Bacteria endospores
• When a key nutrient becomes scarce, some produce endospores, which
are heat-resistant resting structures.
 The bacterium replicates its DNA and encapsulates one copy in a
tough cell wall, thickened with peptidoglycan and covered with a
spore coat.
 The parent cell then breaks down, releasing the endospore.
 Some endospores can be reactivated after more than a thousand
years of dormancy.
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Conjugation and Plasmids
• Conjugation is the process where genetic material
is transferred between bacterial cells
• Sex pili allow cells to connect and pull together for
DNA transfer
Sex pilus
1 µm
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Conjugation and Plasmids
• A piece of DNA called the F factor is required for
the production of sex pili
• The F factor can exist as a separate circular piece
of DNA called a plasmid or as DNA within the
bacterial chromosome
• During conjugation plasmid or chromosomal DNA
can be transferred
F plasmid
Bacterial chromosome
F+ cell
F+ cell
Mating
bridge
F– cell
Bacterial
chromosome
(a) Conjugation and transfer of an F plasmid
F+ cell
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Nutritional and metabolic adaptations
• Phototrophs obtain energy from light
• Chemotrophs obtain energy from chemicals
• Autotrophs require CO2 as a carbon source
• Heterotrophs require an organic nutrient to make
organic compounds
• These factors can be combined to give the four
major modes of nutrition: photoautotrophy,
chemoautotrophy, photoheterotrophy, and
chemoheterotrophy
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Nutritional and metabolic adaptations
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Nutritional and metabolic adaptations
• In some prokaryotic species, metabolic
cooperation occurs in surface-coating colonies
called biofilms
Extremophile microbial community in the Richmond Mine
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Prokaryotes are important
Prokaryotes are beneficial:
• Milk products, fixation of nitrogen, oil
contamination…
Prokaryotes are harmful:
• Human infectious disease and death
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General Biology of the Prokaryotes
Wash your hands with chlorinated-lime
solution
Ignaz Semmelweis (1818 - 1865)
Hungarian physician called also the “savior of mothers”, who discovered in 1847 that the
incidence of puerperal fever could be drastically reduced by practicing hand washing
standards in obstetrical clinics.
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The founders of medical bacteriology
Louis Pasteur (1822-1895)
Food preservation
Vaccines (anthrax, cholera, rabies)
Germ theory of disease offered a theoretical
explanation for Semmelweis’ findings
Robert Koch (1843-1920)
Germ theory of disease
Bacterial isolation
(Mycobacterium tuberculosis)
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The founders of medical bacteriology
Fleming
1881-1955
Discovery of the enzyme lysozyme and the antibiotic
substance penicillin (1928).
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The Bacteria
• Mycoplasmas lack cell walls, are the smallest bacteria
(some have a diameter of 0.2 µm), and have the least
amount of DNA.
• They may have the minimum amount of DNA necessary
to code for the essential properties of a living cell.
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Cells are tiny
• Cell size is limited by the surface area-to-volume ratio.
• The surface of a cell is the area that interfaces with the cell’s
environment. The volume of a cell is a measure of the space inside a
cell.
• The microscopic size of most cells ensures a sufficient surface area
across which nutrients and wastes can move to service the cell volume
10 m
30 m
A small cell has a
greater ratio of
surface area to
volume
Than a large
cell of the same
shape
30 m 10 m
Surface area
of one large cube
 5,400 m2
Total surface area
of 27 small cubes
 16,200 m2
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The Scale of Life
• Because most cells are tiny, with diameters in the range of 1
to 100 m, microscopes are needed to visualize them.
• With normal human vision the smallest objects that can be
resolved (i.e., distinguished from one another) are about 200
m (0.2 mm) in size.
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The Scale of Life
• Light microscopes use glass lenses to focus visible light and
typically have a resolving power of 0.2 m.
• Electron microscopes have magnets to focus an electron beam.
The wavelength of the electron beam is far shorter than that of
light, and the resulting image resolution is far greater (about 0.5
nm).
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Minimum resolved
by electron microscopy
nm
Minimum resolved
by light microscopy
nm
Minimum resolved
by unaided eye
mm
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Largest cells
Some cells are large and long…
200 m
Ovum (egg)
35 - 160 µm
Megakaryocyte Multi-nuclear cells in the
bone marrow and lungs -producing platelates
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Largest cells
The longest cells in the human body
Cells of the sciatic nerve are the
largest cells in the body
Go from the toes to the spine - over
a meter long.
BUT are very thin and are
supported by other cells
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The first observations
Robert Hooke - an English micoscopist (1635-1703)
“Little rooms”-cellulae
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The first observations
Anton van Leeuwenhoek - a Dutch microscopist (1632-1723)
“Tiny “animalcules” in rainwater and other liquids
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Modern light microscopy
• Light microscopy can be used to visualize live and killed
(fixed cells).
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Light waves
Intensity
Light travels in waves
Different wavelength = different color
Visible spectrum of human eye: 380 to 750 nm
Wavelength
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Light waves and interference
Intensity
Interference between light waves
Wavelength
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Phase-Contrast Light Microscopy
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Cells are transparent
Contrast: relative differences of intensities of objects
within the field
• Contrast is generated by:
Absorption of light (color, stains)
Diffraction - scattering of light
Refraction - bending of light between two mediums
Different optical devices take advantage of these
features of light to produce contrast
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Light Microscopy
LM 1,000
Light image of Euglena
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Light Microscopy
Microtome is used to make thin sections
Stains are used to improve contrast
Histological section of
urine-collecting ducts of
the kidney stained with
Hematoxylin and eosin
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Phase-Contrast Light Microscopy
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Light waves and interference
Intensity
Interference between light waves
Wavelength
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Phase-Contrast Light Microscopy
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Phase-Contrast Light Microscopy
Bright-field
Phase-contrast
Nomarski differential
Interference-contrast
(DIC)
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Computer aided image processing
Image processing
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Fluorescence microscopy
Multiple-fluorescent labeling of cells (following fixation) can help
identify specific cellular components
Human cells stained for
DNA (blue dye)
Cytoskeleton (Red)
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Indirect immunolabeling
Specific labeling of cellular components using
antibodies
Fluorescent probe
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Fluorescence microscopy
Fluorescent dyes
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Fluorescence microscopy
Phenomenon of fluorescence
Fluorescence
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Fluorescence microscopy
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Fluorescence microscopy
A natural substance in the cell (or a fluorescent dye that binds
to a specific component in the cell) is stimulated by a beam
of light with a specific wavelength, and a longer wavelength
fluorescent light is observed
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Fluorescence microscopy
Human skin cells stained for
DNA (blue dye) and intermediate filaments (green labeled antibody)
Multiple-fluorescent labeling of cells (following fixation)
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Measuring Ca2+ concentrations in the cytoplasm of living cells
Fura-ester
Fura-ester
Esterase
Ca concentration in the cytoplasm
of resting cells is 10-7 M. Many
hormones or other stimuli cause a
rise in cytosolic Ca to ~ 10-6 M
Ca levels in the cell can be
monitored by using Fura which
fluoresce when it binds Ca
Fura
Ca
Fura-Ca
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Ca++ concentrations in living cells after fertilization
Time-lapse fluorescence imaging
Time-lapse fluorescence imaging
Real-time changes in the local concentration of Ca 2+ in sea urchin egg following fertilization.
Increased Ca concentration triggers the fusion of small vesicles with the plasma membrane,
causing changes in the cell surface that prevent penetration of additional sperm, and prompts
development.
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Green fluorescent protein (GFP)
• Isolated from the jellyfish Aequorea victoria
• GFP and its variants can be expressed in many types of
cells.
• These proteins provide a unique reporter system for
monitoring cellular dynamics
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Light Microscopy-resolution
• The Resolving power of a microscope depends on both
the condenser and the lens
• Light microscopes can distinguish objects separated by
0.2 m (200nm) apart (= resolution).
Wavelength
(within visible light)
Resolution
(smaller is better)
D=
0.61 x l
N x sina
Refractive index
(medium, Water/oil)
D=200 nm
Minimum resolved
by light microscopy
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Transmission electron microscope-TEM
• A Beam of electrons is focused on the
object by magnets. Objects appear darker if
they absorb the electrons. If the electrons
pass through, they are detected on a
fluorescent screen.
• practical resolution: ~0.1nm.
• Magnifications of 350,000 times can be
routinely obtained for many materials,
whilst in special circumstances, atoms can
be imaged at magnifications greater than
15 million times
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Transmission electron microscope-TEM
• A Beam of electrons is focused on the
object by magnets. Objects appear darker if
they absorb the electrons. If the electrons
pass through, they are detected on a
fluorescent screen.
• practical resolution: ~0.1nm.
• Magnifications of 350,000 times can be
routinely obtained for many materials,
whilst in special circumstances, atoms can
be imaged at magnifications greater than
15 million times
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Sample preparation TEM
• Fixation: the tissue is cut into small cubes and plunged into
fixing solution (glutaraldehyde) that covalently cross-links and
immobilizes proteins.
• Staining of membranes lipids and certain macromolecules
with osmium tetroxide (metal).
• Dehydration
• Plastic embedding
• Sectioning
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TEM micrograph of cell’s organelles and of a mitochondrion
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Localization of the enzyme catalase in peroxisomes
Specific macromolecules can be visualized by immunogold
electron microscopy
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Scanning Electron Microscope
Images of surfaces can be obtained by scanning electron
microscopy (SEM)
Three dimensional appearance
Resolution not very high (10 nm); effective mag x20,000
Stereocilia projecting from a hair
cell in the inner ear of a bullfrog
• Sperm attaches itself to the egg
(X3000)
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Scanning Electron Microscope
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Scanning Electron Microscope
Damage to the sensory cells of the cochlea caused by noise or
drug exposure which result in a loss of hearing