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Cells:
Chapt. 4
Two Basic Types of Cells
• Prokaryotes:
– prounounced: pro-carry-oats
• Eukaryotes
– Proun: you-carry-oats
A. Prokaryotes
Small, simple cells (relative to eukaryotes)
Size: about 1 µm (1 micron)
No internal membrane-bounded organelles
No nucleus
Simple cell division
Contain the;
1. true bacteria &
2. archaebacteria
1. True Bacteria = Eubacteria
• Majority of bacteria
• Examples include: E. coli,
Lactobacillus (yoghurt),
Lyme disease
Eubacteria
•Peptidoglycan cell
walls (carbos & AA)
•Separated into
Gram + and - forms
Text pg. 58
Bacteria in the Environment
example:
Iron
utilizing
Baceria
A
B
A) An acid hot spring in Yellowstone is rich in iron and sulfur.
B) A black smoker chimney in the deep sea emits iron sulfides
at very high temperatures (270 to 380 degrees C).
2. Archaebacteria
• Live in extreme
environments: high
salt, high temps
• Different cell wall
• Very different
membrane lipids
• Unusual nucleic acid
sequence
Archaea types:
Based on their physiology, Archae can be organized into
three types:
•
•
•
Methanogens (prokaryotes that produce methane);
Extreme halophiles (prokaryotes that live at very
high concentrations of salt (NaCl);
Extreme (hyper) thermophiles (prokaryotes that live
at very high temperatures).
All archaea have features that distinguish them from
Bacteria (i.e., no murein in cell wall, ether-linked
membrane lipids, etc.). And, these prokaryotes exhibit
unique structural or biochemical attributes which adapt
them to their particular habitats.
B. Eukaryotes
• Bigger cells: 10-100 µm
• True nucleus
• Membrane-bounded
structures inside. Called
organelles
• Divide by a complex,
well-organized mitotic
process
Liver Cell 9,400x
Eukaryotes
• Larger more complex
cells that make up
most familiar life
forms: plants, animals,
fungi, algae
• Surrounded by a cell
membrane made of
lipids
• Text pg 60-61
The Cell Theory
• Cells first observed by R. Hooke 1665
• Named for the Monk prayer cells
• Cell Theory states that;
1. All life is composed of cells
2. Cells are the basic units of life
3. Cells arise from already existing cells
Cells are typically Small
Typical cell size
•Text pg. 56
Why are Cells Small?
• Cells must exchange gases & other
molecules with environment…
• Nutrients in, Wastes out
• As size increases, the rate of diffusion
exchange slows down….
• This is due to the ratio of surface area to
volume
Surface Area to Volume
• Cell surface area is important in taking in
nutrients
• Sfc area increases as the square of cell
diameter
• But… entire cell volume needs to be fed
• And, cell volume increases as the cube of
cell diameter
Consider 2 Cells...
Surface Area to Volume
Cell Radius
(R)
5 µm
50 µm
Surface Area
(4πr2)
Volume
3
(4/3πr )
Surface Area
to Volume Ratio
314 µm2 31,400 µm2
3
524 µm3 524,000 µm
0.6
0.06
The Eukaryotic Cell:
Components
• Outer cell membrane
composed of lipids
and proteins
• Cytoplasm: interior
region. Composed of
water & dissolved
chemicals…a gel
• Numerous
organelles….
Organelles
• Specialized structures
within eukaryotic cells that
perform different
functions...
• Analogous to small plastic
bags within a larger plastic
bag.
• Perform functions such as :
– protein production (insulin,
lactase…)
– Carbohydrates, lipids…
• Text pg 60-61
Organelles of Note:
The Nucleus
• Contains the genetic
material (DNA), controls
protein synthesis.
DNA --> RNA --> Protein
• Surrounded by a double
membrane with pores
• Contains the chromosomes
= fibers of coiled DNA &
protein
• Text pg. 62
Chromosomes
All Chromosomes
from a single cell
One chromosome
Pulled apart
A single chromosome
Showing the amount
of DNA within
Mitochondria
• Generate cellular energy in the
form of ATP molecules
• ATP is generated by the
systematic breakdown of glucose
= cell respiration
• Also, surrounded by 2 membrane
layers
• Contain their own DNA!
• A typical liver cell may have
1,700 mitoch.
• All your mitoch. come from
your mother..
• Text pg. 68
Chloroplasts
• Found in plants, algae and
some bacteria.
Responsible for capturing
sunlight and converting it
to food = photosynthesis.
• Surrounded by 2
membranes
• And…contain DNA
• Text pg. 69
Ribosomes
• Size ~20nm
• Made of two subunits
(large and small)
• Composed of RNA
and over 30 proteins
• Come in two
sizes…80S and 70S
• S units =
Sedimentation speed
Ribosomes
• DNA --> RNA --> Protein
• The RNA to Protein step
(termed translation) is
done on cytoplasmic
protein/RNA particles
termed ribosomes.
• Contain the protein
synthesis machinery
• Ribosomes bind to RNA
and produce protein.
Endoplasmic Reticulum = ER
• Cytoplasm is packed w.
membrane system which move
molecules about the cell and to
outside
• An internal cellular subway
system
• Outer sfc of ER may be
smooth (SER)
• Or Rough (RER)
• ER functions in lipid and
protein synthesis and transport
Golgi Complex
• Stacks of
membranes…
• Involved in modifying
proteins and lipids into
final form…
– Adds the sugars to
make glyco-proteins
and glyco-lipids
• Also, makes vesicles
to release stuff from
cell
• Text pg. 66-67
ER to Golgi network
Lysosomes
• important in breaking
down bacteria and old cell
components
• contains many digestive
enzymes
• The ‘garbage disposal’ or
‘recycling unit’ of a cell
• Malfunctioning lysosomes
result in some diseases
(Tay-Sachs disease)
• Or may self-destruct cell
such as in asbestosis
• Text pg 67
Cytoskeleton
• Composed of 3 filamentous
proteins:
Microtubules
Microfilaments
Intermediate filaments
• All produce a complex
network of structural fibers
within cell
• Text pgs. 72-76
The specimen is human lung cell double-stained to
expose microtubules and actin microfilaments using a
mixture of FITC and rhodamine-phalloidin. Photo taken
with an Olympus microscope.
Microtubules
• Universal in eukaryotes
• Involved in cell shape,
mitosis, flagellar
movement, organelle
movement
• Long, rigid, hollow tubes
~25nm wide
• Composed of a and ß
tubulin (small globular
proteins)
• Text pg. 72
http://www.cytochemistry.net/Cell-biology/
Microfilaments
• Thin filaments (7nm
diam.) made of the
globular protein actin.
• Actin filaments form a
helical structure
• Involved in cell movement
(contraction, crawling, cell
extensions)
• Text pg. 72
Intermediate filaments
• Fibers ~10nm diam.
• Very stable, heterogeneous
group
• Examples:
Lamins: hold nucleus shape
Keratin: in epithelial cells
Vimentin: gives structure to
connective tissue
Neurofilaments: in nerve
cells
Text pg. 72
Image of Lamins which reside in the
nucleus just under the nuclear envelope
Cell Motility:
Flagella & Cilia
• Both cilia & flagella
are constructed the
same
• In cross section:
9+2 arrangement of
microtubules (MT)
• MTs slide against
each other to
produce movement
• Text p 74
Human Sperm: TOTO-3 iodide for DNA (blue) and
Nile red for membrane lipid (red)
How Flagella Move a Cell
Possible Origins of Eukaryotic Cells
• Text pg 70
Infolding of outer membranes
Uptake of prokaryotes
Endosymbiosis
• Theory that eukaryotic cells arose from an
early prokaryote (1) engulfing a second,
smaller prokaryote (2)
• The internalized #2 was not digested but
became a symbiote.
• Today’s mitochondria & chloroplasts may
have arisen this way
• Text pg. 70
Evidence for Endosymbiosis
• Double membrane around both organelles
• Both organelles have their own DNA
• Both organelles have smaller (70S)
ribosomes…
• Both organelles divide by simple fission