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Chapter 6 Notes
A Tour Of the Cell
Microscopy
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Light Microscope (EM)
- visible light is passed through the specimen and then
through glass lenses
Electron Microscope (EM)
-focuses a beam of electrons through the specimen or
onto its surface
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Scanning Electron Microscope (SEM)
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-useful for detailed study of the topography of a specimen
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Transmission Electron Microscope (TEM)
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-used to study the internal structure of cells
Cells
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Eukaryotic cells have internal membranes that
compartmentalize their functions
Cells are the basic structural and functional units of
every organism
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There are two types of cells:
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-Prokaryotic cells: Domains Bacteria and Archaea
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-Eukaryotic cells: Protists, Fungi, Animals and
Plants
Comparing Prokaryotic and Eukaryotic Cells
• All cells have several basic features in common
– They are enclosed by a plasma membrane
• Functions as a selective barrier
• Allows sufficient passage of nutrients
and waste
-Inside all cells is a semifluid, jelly-like substance called
cytosol, in which subcellular components are
suspended
-All cells contain chromosomes, which carry genes in the
form of DNA
-All cells have ribosomes, tiny complexes that make
proteins according to instructions from the genes
• Prokaryotic cells
– Do not contain a nucleus
– Have their DNA located in a region called
the nucleiod
• Eukaryotic cells
–Contain a true nucleus, enclosed by a membranous
nuclear envelope
–Are generally quite a bit bigger than prokaryotic cells
A Panoramic View of the Eukaryotic Cell
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Eukaryotic cells
–Have extensive and elaborately arranged internal membranes,
which form organelles
– Larger than prokaryotic cells
– complex internal structure with membranous and
non-membranous organelles
• membranous: nucleus, endoplasmic reticulum, Golgi
apparatus,mitochondria, lysosomes and peroxisomes
• non-membranous: ribosomes, microtubules, centrioles,
flagella and cytoskeleton
Plant and animal cells have most of the same organelles
The Nucleus: Information Central
The nucleus contains most of the genes in the
eukaryotic cell
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The nucleus houses chromosomes, which are made
of chromatin (DNA and proteins)
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The nuclear envelope
– Encloses the nucleus, separating its contents
from the cytoplasm
-Nuclear envelope is a double membrane
-also contains nucleoli, where ribosomal subunits
are made
Ribosomes: Protein Factories
• Ribosomes
–Are particles made of ribosomal RNA and protein
– Site of protein synthesis
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Build proteins in two cytoplasmic locales:
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-Free Ribosomes-suspended in the cytosol
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-Bound Ribosomes-attached to the outside of the
endoplasmic reticulum or nuclear envelope
Bound and free ribosomes are structurally identical,
and ribosomes can alternate between two roles
Endomembrane System
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The endomembrane system regulates protein
traffic and performs metabolic functions in the cell
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The endomembrane system includes:
– Endoplasmic reticulum (ER)
– Golgi apparatus
– Lysosomes
– Vacuoles
– (plasma membrane)
Endoplasmic Reticulum: Biosynthetic Factory
•The ER membrane is continuous with the nuclear envelope
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There are two distinct regions of ER
-which lack ribosomes
-with attached ribosomes
Two regions of ER:
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The smooth ER-outer surface lacks ribosomes appears smooth
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Synthesizes lipids
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Metabolizes carbohydrates
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Stores calcium
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Detoxifies poison
The rough ER-studded with ribosomes appears rough
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Aids in synthesis of secretory and other proteins to make glycoproteins; produces new
membrane
Golgi Apparatus: Shipping and Receiving Center
• After leaving the ER, many transport vesicles travel to the Golgi
Apparatus
The Golgi apparatus
• Golgi apparatus finishes, sorts and ships cell
products transported in vesicles from ER
– consists of flattened membranous sacs called cisternae
–Receives many of the transport vesicles produced in the rough
ER
- Modifies some of the products of the rough ER
-Synthesis of many polysaccharides
Lysosomes: Digestive Compartments
• A lysosome
– Is a membranous sac of hydrolytic enzymes
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Lysosomes contain enzymes to digest food
and wastes
– defective lysosomes cause fatal diseases
• Lysosomes carry out intracellular digestion by
– phagocytosis
– autophagy
Vacuoles:Diverse Maintenance Compartments
• Vacuoles function in general cell
maintenance
– a plant or fungal cell may have one or several
vacuoles
– food vacuoles are formed by phagocytosis
– contractile vacuoles pump excess water out of
protist
• Central vacuoles are found in plant cells
– hold reserves of important organic compounds
and water
Mitochondria and Chloroplasts
• Mitochondria and chloroplasts have similarities with
bacteria
– Enveloped by a double membrane
– Contain free ribosomes and circular DNA
molecules
– Grow and reproduce somewhat independently in
cells
Mitochondria
• Mitochondria:
– found in all eukaryotic cells, except anaerobic
protozoans
– surrounded by double membrane
• a smooth outer membrane
• an inner membrane folded into cristae
– site of cellular respiration
Chloroplasts: Capture of Light Energy
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Typically two membranes around fluid stroma, which
contains thylakoids stacked into grana
Chloroplasts are specialized members of a
family of closely related plant organelles called
plastids
– contain chlorophyll
– found in plants and algae
– site of photosynthesis
• convert solar energy to chemical energy (sugars are
made)
Peroxisomes: Oxidation
• Peroxisomes
- specialized metabolic compartment bounded by a
single membrane
– i.e. breaks down fatty acids, breaks down toxins
• detoxify blood toxins in liver and kidneys
Ex. Alcohol
-Produce hydrogen peroxide as a by-product and
convert it to water
The Cytoskeleton
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Network of fibers that organizes structures and activities in
the cell.
Functions in the structural support for the cell and in
motility and signal transmission
Cell motility generally requires the interaction of the
cytoskeleton with motor proteins
• Components of the Cytoskeleton:
–microfilaments:rods of globular proteins
– intermediate filaments: ropelike strands of fibrous proteins
– intermediate filaments: hollow tubes of globular proteins
Centrosomes and Centrioles
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In animal cells, microtubles grow out of a
centrosome.
A centrosome is a region that is often
located near the nucleus and is
considered a “microtuble-organizing
center”
Cilia and Flagella
Cilia and flagella
– function to move whole cell
– are locomotor appendages of some cells
• Cilia and flagella share a common ultrastructure
– structure consists of 9 microtubule doublets
arranged around central pair (9+2)
• Movement of cilia and flagella occurs when
arms consisting of the protein dynein move
the microtubule doublets past each other
Microfilaments (Actin Filaments)
• Microfilaments are built from molecules of the
protein actin
– microfilaments cause contraction of muscle
cells
– they also function in amoeboid movement,
cytoplasmic streaming and support for cellular
projections
Intermediate Filaments
– support cell shape
– fix organelles in plac
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Extracellular Components
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Plant cell walls
– Are made of cellulose fibers embedded in other
polysaccharides and protein
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Animal cells
– Lack cell walls
– Are covered by an extracellular matrix, ECM
Tight Junctions, Desmosomes, and Gap Junctions
in Animal Cells
• In animals, there are three types of intercellular
junctions
– Tight junctions
– Desmosomes
– Gap junctions