Transcript Cells: Chapt. 5 & Chapt. 4: Pgs. 70-75

Cells & Organelles
A Dr.
Production
Two Basic Types of Cells
• Pro karyotes:
– prounounced: pro-carry-oats
• Eu karyotes
– 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
Single linear chromosome
Contain the domains;
1. True (Eu)bacteria &
2. Archaebacteria
1. True Bacteria = Eubacteria
• Majority of bacteria
• Examples include: E. coli,
Lactobacillus (yogurt),
Lyme disease
Eubacteria
•Peptido glycan cell
walls (carbos & AA)
•Separated into
Gram + and - forms
 Gram
positive
Gram
negative
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, wellorganized mitotic process
Liver Cell 9,400x
Eukaryotes
• Larger more complex
cells that make up most
familiar life forms:
plants, animals, fungi,
protists
• Surrounded by a cell
membrane made of lipids
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
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
• Surface 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
• Cytosol: 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…
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
in the form of chromatin
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..
Plastids
Synthesize
carbohydrates
• Leucoplasts: white
in roots and tubers
• Chromoplasts:
rainbow accessory
pigments
• Chloroplasts:
green in leaves
and stems
Chloroplasts
• Found in plants and some
protists. Responsible for
capturing sunlight and
converting it to food =
photosynthesis.
• Surrounded by 2
membranes
• And…contain DNA
Ribosomes
• Size ~20nm
• Made of two subunits
(large and small)
• Composed of RNA and
over 30 proteins
• Come in two sizes…80S
(40s + 60s) and 70S (30s
+ 50s)
• 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
• Outer surface of ER may be
smooth (SER): synthesizes
secretes, stores, carbs, lipids
and non pps
• Or Rough (RER):
synthesizes pp for excretion
• 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 glycoproteins and glycolipids
• Also, makes vesicles
to release stuff from
cell
ER to Golgi network/Endo
membrane system
Membrane Flow through Golgi
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 apoptosis
Vacuoles
• Formed by the
pinching of the cell
membrane
• Very little or no
inner structure
• Stores various items
Peroxisomes/Microbodies
• Large vesicles
containing oxidative
enzymes which
transfer H from
substrates to O
• Contains catalase that
changes H2O2 to H2O
• In plants responsible
for photorespiration
and converting fat to
sugar during
germination
Cytoskeleton
• Composed of 3 filamentous
proteins:
Microtubules
Microfilaments
Intermediate filaments
• All produce a complex
network of structural fibers
within cell
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
Function in:
- division of cells
(formation of spindle
fibers)
- some aspects of shape
- many cell movements
(flagella and cilia)
- “transport” system
within cell
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)
• 9+2 vs 9x3 arrangement
Protist Movement
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)
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
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
Flagella (flagellum)
• Motile structure of many eukaryotic cells; long,
hair-like projection
- e.g., tail of sperm
• Core composed of 9 + 2 array of microtubules
that arise from a basal body apparatus
– Flagellated E. coli
Cilia (cilium)
• Motile or sensory structure in
eukaryotes composed of 9 + 2
array of microtubules
• Usually numerous short, hairlike projections along outside
of cell
• Found in many Protista and in
lining of lungs
– Stentor feeding
– Paramecium rotating
Possible Origins of Eukaryotic Cells
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
Support for this Theory:
• Eg. of this type of symbiosis are found today. Sponges harbor photosyn.
algae within their tissues, allowing them to photosynthesize.
• The organelles (chloroplasts and mitochondria) resemble bacteria in size
and structure.
• These organelles each contain a small amount of DNA but lack a nuclear
membrane.
• Each has the capability of self-replication. They reproduce by binary
fission.
• They make their own proteins.
• During protein synthesis, these organelles use the same control codes and
initial amino acid as prokaryotes.
• They contain and make their own ribosomes, which resemble
prokaryote’s.
• The enzymes that replicate DNA and RNA (polymerases) of the
organelles are similar to those in prokaryotes but different from those of
eukaryotes.
• The organelles have a double membrane that might be derived from a
prokaryote’s plasma membrane and the membrane of a vesicle.
Resources
• Rediscovering Biology Animation Guide
• Cell Signaling and Cell Cycle Animations