Lecture #1
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Chapter 6~
A Tour of the Cell
Nucleus
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Genetic material...
•chromatin
•chromosomes
•nucleolus: rRNA;
ribosome synthesis
Protein synthesis (mRNA)
Double membrane envelope
with pores
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Pores designed to allow RNA to
exit the nucleus
Ribosomes
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Manufacture Protein – complete the protein structure not
finished in the nucleus; addition of amino acids
Free •cytosol; •protein function in cell
Bound •endoplasmic reticulum; •membranes, organelles,
and export
Endomembrane system, I
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Endoplasmic reticulum (ER)
Continuous with nuclear envelope
Rough ER
•with ribosomes;
•synthesis of secretory
proteins (glycoproteins),
membrane production
Smooth ER
•no ribosomes;
•synthesis of lipids,
•metabolism of
carbohydrates;
•detoxification of drugs and
poisons
Endomembrane system, II
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Golgi apparatus
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ER products are modified, stored, and then shipped
Cisternae: flattened membranous sacs
trans face (shipping) & cis face (receiving)
Transport vesicles
Endomembrane system, III
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Lysosomes
•sac of hydrolytic
enzymes; digestion of
macromolecules
Phagocytosis –
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the intake of particulate
matter into the cell
Autophagy: recycle cell’s
own organic material
Tay-Sachs disease
–
lipid-digestion disorder
which causes the brain to
become congested with
lipids; lipids are not broken
down
Endomembrane system, IV
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Vacuoles
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membrane-bound sacs
(larger than vesicles)
Found in plant cells
Used for Storage
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Food (phagocytosis)
Contractile (pump excess
water)
Central (storage in plants)
tonoplast membrane
separates the cytosol from
cell sap
Other membranous organelles, I
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Mitochondria
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quantity in cell correlated
with metabolic activity
cellular respiration
double membranous
(phospholipid)
cristae/matrix
intermembrane space
contain own DNA
believed to originate through
symbiosis
Endosymbiosis Theory
Other membranous organelles, II
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Chloroplast
•type of plastid; •double membranous; •thylakoids
(flattened disks); •grana (stacked thylakoids);
•stroma; •own DNA
Peroxisomes
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Single membrane
Produce hydrogen
peroxide in cells
Metabolism of fatty
acids; detoxification of
alcohol (liver)
Hydrogen peroxide
then converted to
water
The Cytoskeleton I
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Fibrous network in cytoplasm
Support, cell motility, biochemical
regulation
Microtubules:
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Microfilaments :
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thickest
tubulin protein
shape, support, transport, chromosome
separation
thinnest
actin protein filaments
motility, cell division, shape
Intermediate filaments:
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middle diameter
keratin
shape, nucleus anchorage
Actin and Keratin Filaments
The Cytoskeleton II
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Cell motility:
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Changes in the cell location
Limited movements of parts
of the cell
All membrane bound
organelles are bound to
the cytoskeleton.
Movement of vesicles,
peroxisomes, lysosomes,
etc. all occurs through the
cytoskeleton
Centrosomes/centrioles
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Centrosome: region near nucleus
Centrioles: 9 sets of triplet microtubules in a ring;
used in cell replication; only in animal cells
Cilia/flagella
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Locomotive appendages
Ultrastructure: “9+2”
•9 doublets of microtubules
in a ring
•2 single microtubules in
center
•connected by radial spokes
•anchored by basal body
•dynein protein
Cytology: science/study of cells
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Light microscopy •resolving power~ measure of clarity
Electron microscopy
•TEM~ electron beam to study cell ultrastructure
•SEM~ electron beam to study cell surfaces
Cell fractionation~ cell separation; organelle study
Ultracentrifuges~ cell fractionation; 130,000 rpm
Cell Types: Prokaryotic
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Nucleoid: DNA
concentration
No organelles with
membranes
Ribosomes: protein
synthesis
Plasma membrane (all
cells); semi-permeable
Cytoplasm/cytosol (all
cells)
Cell size
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As cell size increases, the surface area to volume
ratio decreases
Rates of chemical exchange may then be
inadequate for cell size
Cell size, therefore, remains small
Cell surfaces & junctions
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Cell wall:
•not in animal cells
•protection, shape,
regulation
Plant cell:
•primary cell wall produced first
•middle lamella of pectin
(polysaccharide); holds
cells together
•some plants, a secondary
cell
wall; strong
durable matrix;
wood
(between plasma
membrane and primary
wall)
Extracellular matrix (ECM)
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Glycoproteins:
• proteins covalently bonded to
carbohydrate
Collagen (50% of protein in human
body)
•embedded in proteoglycan
(another glycoprotein-95%
carbohydrate)
Fibronectins
•bind to receptor proteins in plasma
membrane called integrins
(cell communication?)
Intracellular junctions
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PLANTS:
Plasmodesmata:
cell wall perforations; water and
solute passage in plants
ANIMALS:
Tight junctions ~ fusion of
neighboring cells; prevents
leakage between cells
Desmosomes ~ riveted,
anchoring junction; strong
sheets of cells
Gap junctions ~ cytoplasmic
channels; allows passage of
materials or current between
cells
Cell Signaling I
Cells use the intracellular junctions to
communicate with each other
 Signal Transduction
 Stimulus used to send signals
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Mechanical: physical touch of one cell to
another
Chemical: use of ions such as Ca2+
Electrical: used in nerve cell communications
Signal Hypothesis
Cell Signaling II
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Three stages:
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Reception: the cell’s detection of a signal from outside
the cell, usually binding of protein to a receptor on the
membrane surface
Transduction: converts the initial signal to a form than
can bring about a specific cellular response
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Response: the specific desired result
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Often relay molecules and second messengers are used
Many possibilities including rearrangement of the cytoskeleton
Amplification can occur to make the signal
stronger within the cell