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CELLS
The Fundamental Units of Life
Cell Theory
1. All organisms are composed of 1 or more
cells.
2. The cell is the basic living unit, providing
organization for all organisms.
3. All cells arise from preexisting cells.
Cells Are Small
• Most are too small to be
seen with the unaided
eye…so Microscopes are
used.
• A Light Microscope uses
visible light shone through
glass lenses.
• A “thin section” of
specimen is required.
• van Leeuwenhoek
Principles of Microscopy
•
•
•
•
LIGHT
REFRACTION
MAGNIFICATION
RESOLUTION
MAGNIFICATION
• Image size exceeds real size.
• Achieved with convex lenses.
• There are limits…
…involving the nature
of light.
• First, you need enough
light to penetrate the thin
specimen.
RESOLUTION
• Next, you need light of
appropriate wavelength…or
RESOLUTION is
compromised.
• A measure of clarity – of
focus.
• Minimum distance between
two points that allow the
points to be distinguishable.
• Light microscopy not very
useful below 0.2um.
RESOLUTION
Electron Microscopy
• Uses e- rather than light.
• Electrons have a much
shorter wavelength.
• SEM = Scanning
Electron Microscopy
• TEM = Transmission
Electron Microscopy
Electron Microscopy
Cells!
ALL CELLS
• Plasma Membrane (Cell Membrane)
– Separate the contents of the cell from the
environment.
• Cytoplasm (Cytosol)
– Semi-fluid contents of the cell
– Lots of “floaties”
• Nucleus “area”
– Location of DNA
CELLS
• Eukaryotic Cells (animals, plants, fungi, protists)
– Complex & relatively large.
– Membrane-bound nucleus & organelles.
– 80-S Ribosomes.
• Prokaryotic Cells (archaea, bacteria)
– Simple & relatively small.
– NO Membrane-bound nucleus & organelles.
– 70-S Ribosomes.
CELLS
PROKARYOTIC
EUKARYOTIC
EUKARYOTIC CELLS
Organelles = “little organs”
(not really)
Membrane-bound
ORGANELLES
• Nucleus
– Isolates the DNA & provides access to its
hereditary information.
– The “control center” of the cell (Transcription).
Nucleus
1. Nuclear Envelope (a double membrane)
with Pores.
2. Nucleolus
•
•
•
rRNA
Proteins
Ribosomes
3. Nucleoplasm
with Chromatin/Chromosomes.
Ribosomes
•
•
•
•
Not true organelles, more “structures”.
Protein factories.
2 sub-units.
Free (in cytosol/cytoplasm), more for
intracellular activities.
• Bound (on E.R.), often for extracellular
activities (secretion) & packaging within
certain organelles.
Endomembrane System
• Synthesis of Proteins & their transport into
membranes and/or organelles.
• Packaging of Proteins for transport out of
the cell (secretion) or to other areas of the
cell.
• Modification of Proteins.
• Transport of lipids, lipoproteins,
glycoproteins, etc.
Endomembrane System
1. Endoplasmic Reticulum (E.R.)
– Rough E.R.
– Smooth E.R.
2. Golgi Apparatus
3. Vesicles
– Lysosomes
(also, nuclear envelope, vacuoles, and plasma membrane)
Endoplasmic Reticulum
• Network of interconnected membranes
(continuous with the nuclear envelope).
• Flattened or tubular Cisternae.
Rough E.R.
• The site of protein synthesis, particularly
secretory proteins.
• Initial modification of proteins.
– Especially, formation of Glycoproteins.
• Formation (budding) of Transport Vesicles.
• Formation of NEW Membrane =
Phospholipid Synthesis
Smooth E.R.
• Modification of Proteins.
• Formation of Lipids, detoxification.
– Lipid-derived hormones (steroids) are
synthesized, including sex hormones
(testosterone, etc.) in certain glands.
– Solubilization of toxins (drugs, alcohol,
caffeine, etc. ) in liver cells.
– Calcium ion storage & release in muscle cells.
Golgi Apparatus
• Modification, storage,
sorting, & shipping of ERproduced molecules (esp.
for secretion).
• Addition of non-protein
portions to protein
molecules.
Golgi Apparatus
• Stacks of cisternae, with cis & trans faces.
– Cis – receiving (takes in vesicles).
– Trans – sending (gives rise to vesicles).
Lysosomes
• Specific vesicles carrying digestive enzymes
– hydrolytic (proteolytic) enzymes.
• Animal Cells.
• Digestion of food brought in by phagocytosis.
Lysosomes
• Digestion and recycling of old & damaged
organelles within the cell: Autophagy.
Endomembrane System
Vacuoles
• Large vesicles with particular functions.
– Food Vacuoles.
– Contractile Vacuoles.
– Central Vacuole w/ tonoplast in Plant Cells.
•Storage.
•Dissolved Solutes.
•Dumping Ground.
•Protection.
•Shape.
Mitochondrion
• Surrounded by a double membrane – an
envelope.
Outer
Membrane
Inner
membrane
(Cristae)
Matrix
Mitochondrion
• Site of cellular respiration = energy
production.
Carbohydrates
ATP
• Not part of endomembrane system.
• Have their own DNA, RNA, Proteins, and
Ribosomes (70-S).
• Grow and reproduce independently.
• Animals, Plants, Fungi, Protists.
Chloroplast
• Surrounded by a double membrane – an
envelope.
Outer
Membrane
Inner Membrane
(Grana composed of
stacked Thylakoids)
Stroma
Chloroplast
• Site of Photosynthesis = acquisition of
chemical energy from sunlight.
Sunlight + CO2
Carbohydrates
• A plastid (not part of endomembrane
system).
• Have their own DNA, RNA, Proteins, and
Ribosomes (70-S).
• Grow and reproduce independently.
• Plants, Protists.
Peroxisomes
• Odd vesicles that carry Hydrogen to
Oxygen, forming Hydrogen Peroxide
(H2O2).
• Used to break down larger molecules.
• Detoxify alcohol in Liver Cells.
Cytoskeleton
• Fiber-like structures that lend organization.
• Support (providing a scaffolding onto which
organelles & vesicles can be organized).
• Shape (maintain particular shape depending
on the cell’s location and/or function).
• Transport of materials around or out of the
cell.
• Motility of the whole cell from one location to
another.
Cytoskeleton
Microtubules
Microfilaments Intermediate
Filaments
Keratin
Subunits
Tubulin
Actin
Keratin
Cytoskeleton
• Permanent
– Flagella
– Cilia
– Muscle Contraction
– Scaffolding & Shape
Maintenance
Cytoskeleton
• Transient
– Spindle Fibers
– Transport filaments
Cell Wall
• OUTSIDE the Cell Membrane (technically,
outside the cell!)
• Various proteins & glycoproteins in
Prokaryotes.
• Cellulose in Plants.
• Chitin in Fungi.
Eukaryotic Cell
Endosymbiont Theory
Onion Cells