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Transcript
Cells & Organelles
A Dr.
Production
Two Basic Types of Cells
• Pro karyotes:
– prounounced: pro-carry-oats
• Eu karyotes
– Proun: you-carry-oats
Organization of Domains
Evolution of the 3 Domains
Development of the Cell Theory
• Hooke (1665) named the cell
• Schwann (1800’s) states:
-all animals are made of cells
• Pasteur (1859) disproved idea of spontaneous
generation
– living things arise from nonliving matter
• Modern cell theory emerged
-All organisms composed of cells and cell products.
-Cell is the simplest structural and functional unit of life.
-Organism’s structure and functions are due to the
activities of its cells.
-Cells come only from preexisting cells.
-Cells of all species have many fundamental similarities.
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
2. Archaebacteria
• Live in extreme
environments: high
salt, high temps
• Different cell wall
• Very different
membrane lipids
• Unusual nucleic acid
sequence
Archaea = Extremophiles
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, etherlinked membrane lipids, etc.). And, these
prokaryotes exhibit unique structural or
biochemical attributes which adapt them to their
particular habitats.
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).
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,
protists
• Surrounded by a cell
membrane made of
lipids
Cell Size
• Human cell size
– most from 10 - 15 µm in
diameter
• egg cells (very large)100 µm
diameter
• nerve cell (very long) at 1
meter long
• Limitations on cell size
– cell growth increases
volume faster than surface
area
• nutrient absorption and
waste removal utilize surface
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
• 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
Cell Surface Area
and Volume
Why can’t cells be
infinitely large?
Cell Radius
(R)
5 µm
50 µm
Surface Area
(4πr2)
Volume
(4/3πr3)
Surface Area
to Volume Ratio
314 µm2 31,400 µm2
3
524 µm3 524,000 µm
0.6
0.0006
Cell Shape and Function
The Eukaryotic Cell: Components
• 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 secretion
• 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
glyco-lipids
• Also, makes vesicles
to release stuff
from cell
ER to Golgi network/
Endomembrane system
Membrane Flow through Golgi
• 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 (TaySachs disease)
• Or may self-destruct
cell such as in
apoptosis
Lysosomes
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:
• Involved in cell shape,
mitosis (spindle fibers),
flagellar movement,
organelle movement
(“transport” system within
cell)
• Long, rigid, hollow tubes
~25nm wide
• Composed of a and ß tubulin
(small globular proteins)
• 9+2 vs 9x3 arrangement
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,
hair-like projections along
outside of cell
• Found in many Protista
and in lining of lungs
– Stentor feeding
– Paramecium rotating
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
Possible Origins of Eukaryotic Cells
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
Molecular Movies
Apoptosis Animation
Bacterial Animations