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Dr. Darryl Kropf
[email protected] (cell biology in subject line)
Office 203 G S. Biology
What is a “Cell?”
I took a good clear piece of cork,
and with a Pen-knife sharpen’d as
keen as a Razor, I cut a piece of it
off… then, examining it with a
Microscope, me thought I could
perceive it to appear a little
porous…
Robert Hooke
1655
Hook named the porous
structures he saw (the walls of
the cork cells) cellulae because
they reminded him of monk’s
cells in a monastery…
The “Cell Theory” of life…
1.
All organisms are composed of cells;
2.
Cells only arise from other cells.
3.
The cell is the smallest structural unit of all life
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So what is life?
FM Harold - “The Way of The Cell”
Complex organization
Metabolism
Reproduce
Adapt to environment
ECB Highly organized
Homeostasis
(constant internal environment)
Reproduce
Grow and develop
Take energy from environment
Respond to stimuli
Adapt to environment
“Autopoietic systems capable of evolution by natural selection”
(autopoietic - capable of making themselves)
Cells come in a variety of sizes and shapes…
Biologists classify cells into three domains
Domain Archaebacteria:
Archaebacteria. Mostly anaerobic;
extreme halophiles, thermophiles,
methanogens.
= Prokarya (prokaryotes)
Domain Eubacteria:
“before nucleus”
Eubacteria. With peptidoglycan wall.
Cyanobacteria, soil bacteria, nitrogen-fixing
bacteria, coliform bacteria Ex: E. coli .
Domain Eukarya (eukaryotes) “true nucleus”:
Fungi. Ex: Yeasts, mushrooms.
Plants. Ex: algae, Arabidopsis thaliana.
Animals. Ex: worms, flies, frogs, Homo sapiens .
Aveolates. Dinoflagellates etc.
Stramenopiles. Brown algae etc.
Rhodophytes. Red algae
Other protists. Additional 50+ lineages
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Evolution of life on Earth
ECB Fig.1-29
Are viruses alive? A comparison of
viruses, prokaryotes, and eukaryotes…
Size
Viruses
Prokaryotes
Eukaryotes
~50-500 nm
~0.3-5 um
> 5 um
ECB figure 1-25
Influenza virus
E. coli
ECB figure 1-25
Human
lymphocytes
Are viruses living cells? NO!
ECB figure 1-25
Influenza virus
E. Coli
ECB figure 1-25
Human
lymphocytes
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Microscopy
Most early discoveries were made by looking at
cells and organisms, and microscopes remain one of
the most useful tools of the cell biologist
Sizes of cells and molecules
First consider light microscopy
ECB 1-6
A modern light microscope
(ECB panel 1-1)
Detector
Occular
Objective
Specimen
Condensor
Light source
Magnification = M objective x M occular
Resolution - ability to discriminate two points close together
Best resolution with a light microscope is about 0.2 µm
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Cells can be viewed unstained or stained
unstained
stained
Brightfield
Phase contrast
cell wall stain on plant root tip
Differential interference contrast (DIC)
Immunofluorescence microscopy allows the subcellular
localization of specific proteins (ECB Panel 1-1)
Fix cells with aldehydes or
alcohols…
Bind antibodies (Y) to cytoskeletal
protein (i.e.: anti-tubulin)…
Bind fluorescently-labeled
*
“secondary” antibody ( )…
Cells stained with anti-TB (green) and anticentrosome antibodies (red)
Examine with epifluorescence
microscope…
Nowdays, a laser scanning confocal microscope is most often used
For smaller objects (<200nm) need electron microscopes
e- source
50KeV to 2 MeV
Condensor
Specimen
Objective
Projector
Detector
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Transmission electron microscopy resolves
cellular details as small as 1-2 nm
e- source
50KeV to 2 MeV
Condensor
Specimen
Objective
Projector
Detector
Scanning electron microscopy reveals
details of cell surface topography…
Stereocilia on a hair cell in the inner ear.
Bar = 1 µm. ECB panel 1-1.
Cell anatomy
Prokaryotes (no organelles)
versus
Eukaryotes (many organelles)
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Anatomy of a prokaryote: Escherichia coli…
Outer membrane
Periplasmic space
Inner (plasma) membrane
Nucleoid
(packaged DNA)
Cytoplasm
ECB figure 1-25
Anatomy of a
eukaryote (animal) cell:
Anatomy of an
animal (epithelial) cell:
The plasma membrane…
(Also in prokarotes)
The Nucleus…
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DNA content of nucleus does NOT correlate
with organismal complexity
ECB 1-40
Anatomy of an
animal (epithelial) cell:
The Nucleus…
Nucleoli
Anatomy of an
animal (epithelial) cell:
The Endoplasmic
Reticulum (ER)…
Smooth ER (SER) plays a role in
lipid synthesis and metabolism.
Rough ER (RER) is studded with
ribosomes making secretory or
membrane proteins.
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Anatomy of an
animal (epithelial) cell:
(Also in prokarotes)
Anatomy of an
animal (epithelial) cell:
The Golgi apparatus…
Anatomy of an
animal (epithelial) cell:
Mitochondria…
Ribosomes…
ECB Fig. 1-19
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Anatomy of an
animal (epithelial) cell:
The “Cytoskeleton”…
Microfilaments
Microtubules
Intermediate filaments
Anatomy of plant cell:
Nucleus
Mitochondrion
Anatomy of plant cell:
Plant cells have most of the
organelles and structures
found in animal cells,
including a nucleus, RER and
SER, mitochondria,
cytoskeleton, etc. However,
a number of features
distinguish plant and animal
cells…
The Vacuole…
Much of a plant cell’s volume is
filled by a membrane-bounded
vacuole, with only a peripheral
shell of cytoplasm.
Vacuole
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Cell wall
Outside the plasma membrane
Anatomy of plant cell:
Chloroplasts…
Chloroplasts are the photosynthetic
organelles of plant cells.
Biologists classify cells into
three domains
How did this complexity arise… how did cells evolve?
How did life on earth begin?
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A “year” of Earth’s history…
1 January: The Earth formed 4.5-4.6 billion
years ago (bya), by accretion of material from
the solar nebula.
For 800 million years, Earth was subjected to
bombardment by asteroid-sized meteors.
Conditions were incompatible with life.
4 March: By 3.8 bya, bombardment had
slowed, and the Earth had cooled to
temperatures “compatable” with life (<100 o
C?). No atmospheric O 2 ; high CO2, CH 4, NH 3
and H2. Pre-biotic synthesis of biopolymers…
Earth’s early environment was harsh…
Hot!
Electric!
Wet…
Reducing (no O 2)
•
H2
•
CH4
•
NH3
•
CO2
Organic compounds synthesized in “Miller-Urey” experiment:
Hydrogen cyanide
Glycine
Sugars
Formic acid
Alanine
Purines
Acetic acid
Other amino acids
Pyrimidines
Urea
proteins
RNA/DNA
Evolution of cells: From RNA to protein to DNA…
membrane
ECB Fig. 7-42
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A “year” of Earth’s history…
1 January: The Earth formed 4.6 billion
years ago (bya), by accretion of material from
the solar nebula.
For 800 million years, Earth was subjected to
bombardment by asteroid-sized meteors.
Conditions were incompatible with life.
4 March: By 3.8 bya, bombardment had
slowed, and the Earth had cooled to
temperatures “compatable” with life (<100 o
C?). No atmospheric O 2 ; high CO2, CH 4, NH 3
and H2. Pre-biotic synthesis of biopolymers…
20 March: The first cells are thought to
have “evolved” by 3.6 bya. These primitive
cells were probably similar in many respects
to modern archaebacteria…
28 March - 21 April: The oldest fossil
evidence of life dates to 3.5-3.2 bya. These
“microfossils” bear striking similarities to
modern cyanobacteria (blue-green algae),
suggesting that photosynthesis had already
been “invented.”
A “year” of Earth’s history…
7 May: Between 3.5-3.0 bya, prokaryotes
invented a new photosynthetic pathway that
used H 2O as an electron donor and generated
O2 as a byproduct.
For the next 1-1.5 billion years, O 2 generated
biotically was sequestered by Fe in the
Earth’s oceans and crust.
17 July: The first “nucleated” eukaryotic
cells are thought to have evolved from their
archaebacterial ancestors about 2.1 bya. The
oldest eukaryotic fossils date to 1.8 bya.
A “year” of Earth’s history…
7 May: Between 3.5-3.0 bya, prokaryotes
invented a new photosynthetic pathway that
used H 2O as an electron donor and generated
O2 as a byproduct.
For the next 1-1.5 billion years, O 2 generated
biotically was sequestered by Fe in the
Earth’s oceans and crust.
17 July: The first “nucleated” eukaryotic
cells are thought to have evolved from their
archaebacterial ancestors about 2.1 bya. The
oldest eukaryotic fossils date to 1.8 bya.
25 July: O2 buildup in Earth’s atmosphere;
prokaryotes invent “aerobic” metabolic
pathways, including respiration.
10 August: Mitochondria evolve from an
endosymbiotic relationship between respiring
prokaryotes and a primitive anaerobic
eukaryote about 2-1.8 bya.
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A “year” of Earth’s history…
26 August – 3 September: Chloroplasts
evolve from an endosymbiotic relationship
between a photosynthetic bacteria and a
respiring eukaryote… about 1.6-1.5 bya.
A “year” of Earth’s history…
26 August – 3 September: Chloroplasts
evolve from an endosymbiotic relationship
between a photosynthetic bacteria and a
respiring eukaryote… about 1.6-1.5 bya.
13 November: The first metazoans
(multicellular animals) appear about 0.6 bya
(metazoan fossils are found in pre-Cambrian
deposits dating to 580 mya).
Explosive radiation of eukaryotic lineages
A “year” of Earth’s history…
29 November: Plants and arthropods “invade”
the Earth’s land masses about 400 mya.
4 December: The earliest fossils of reptiles
date to approx. 340 mya
7 December: The earliest fossils of seed
plants (ancestors of modern gymnosperms and
angiosperms) date to about 300 mya.
14-15 December: The first dinosaurs and
(placental) mammals appear about 220 mya.
Birds appear about 200 mya
26 December: Primates appear about 65 mya.
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A “year” of Earth’s history…
Dec 31 - New Years Eve
4 PM: Evidence of bipedal hominids
(A. afarensis from 4.2 mya shown)
dates to ~4-5 mya.
8 PM: The genus Homo (H. habilis )
dates to about 2 mya (H. erectus
from 1.6 mya shown)…
11:40 PM: Homo sapiens sapiens
appears about 200,000 years ago.
11:58 PM: Cave art in the Perigord
of France dates to 20,000 years ago.
11:59:53 PM: Fremont artwork in
the Colorado basin dates from 1,000
years ago.
11:59:57 PM: Columbus “discovers”
the new world 500 years ago.
11:59:59 PM: Pioneers settle the
Utah territory in 1847.
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