A Tour of
the Cell
Cytology: science/study of cells
• Light microscopy
• resolving power: measure of clarity
• Electron microscopy
• TEM (transmission): electron beam to study cell ultrastructure
• SEM (scanning): electron beam to study cell surfaces
• Cell fractionation: cell separation; organelle study
• Ultracentrifuges: cell fractionation; 130,000 rpm
Cell Types: Prokaryotic
• Nucleoid region: DNA
concentration
• No organelles with
membranes
• Ribosomes: protein
synthesis
• Plasma membrane (all
cells); semi-permeable
• Cytoplasm/cytosol (all
cells)
Prokaryote vs. eukaryote
• Prokaryote
• Less complex (generally
bacteria)
• Has plasma membrane
• May have cell wall
• May have some
photosynthetic
material
• Does not have membrane
bound organelles
• DNA is not bound
(circular)
• Has ribosomes (not
attached to ER)
• Have proteins and
enzymes
• Have mitochondria
• Eukaryote
• More complicated
• Has membrane bound
organelles
• DNA is stored in the
nucleus of the cell
• Double helix
• Bound to histone
proteins
• Ribosomes are
attached to rough ER
• Make proteins and
enzymes
Cell size
• 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
Composite Animal Cell
Nuclear envelope
Lysosome
Plasma
membrane
Composite Animal Cell
Next quiz
•For the quiz, you MUST know
the parts of the cell for both
the plant and animal cell
•See pp. 100-101 in your text
Nucleus
• Genetic material...
• chromatin
• chromosomes
• nucleolus: rRNA;
ribosome synthesis
• Double membrane
envelope with pores
• Protein synthesis (mRNA)
Nucleolus
• Located within the nucleus
• Primarily responsible for the production of
ribosomes
• The different subunits are created within
the nucleolus and then transported out of
the nucleolus to be assemble along the
endoplasmic reticulum (ER)
• This makes this portion of the ER the rough
ER
Ribosomes
• Protein manufacturing
• Free
• cytosol;
• protein function in cell
• Bound
• endoplasmic reticulum;
• membranes, organelles
Endomembrane system, I
• Endoplasmic reticulum (ER)
• Continuous with nuclear envelope
• Smooth ER
•no ribosomes;
•synthesis of lipids,
•metabolism of carbohydrates;
•detoxification of drugs and
poisons
• Rough ER
•with ribosomes;
•synthesis of secretory
proteins (glycoproteins),
membrane production
Endomembrane system, II
• Golgi apparatus
•ER products are modified, stored, and then shipped
• Cisternae: flattened membranous sacs
• trans face (shipping) & cis face (receiving)
• Transport vesicles
Endomembrane system, III
• Lysosomes
• sac of hydrolytic
enzymes; digestion
of macromolecules
• Phagocytosis
• Autophagy: recycle
cell’s own organic
material
• Tay-Sachs disease:
lipid-digestion
disorder
Endomembrane system, IV
• Vacuoles
• membrane-bound
sacs (larger than
vesicles)
• Food (phagocytosis)
• Contractile (pump
excess water)
• Central (storage in
plants)
Other membranous organelles
• Mitochondria
• quantity in cell
correlated with
metabolic activity;
• cellular respiration;
• double membranous
(phospholipid);
• cristae/matrix;
• intermembrane space
• contain own DNA
Other membranous organelles
• Chloroplast
•
•
•
•
•
•
type of plastid;
double membranous;
thylakoids (flattened disks);
grana (stacked thylakoids);
stroma;
own DNA
Peroxisomes
• Single membrane
• Produce hydrogen
peroxide in cells
• Metabolism of fatty
acids; detoxification of
alcohol (liver)
• Hydrogen peroxide
then converted to
water
The Cytoskeleton end here
• Fibrous network in cytoplasm
• Support, cell motility, biochemical
regulation
• Microtubules:
• thickest;
• tubulin protein;
• shape, support, transport,
chromosome separation
• Microfilaments :
• thinnest;
• actin protein filaments;
• motility, cell division, shape
• Intermediate filaments:
• middle diameter;
• keratin;
• shape, nucleus anchorage
Centrosomes/centrioles
• Centrosome: region near nucleus
• Centrioles: 9 sets of triplet microtubules in a
ring; used in cell replication; only in animal cells
Cilia/flagella
• 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
Review – plant vs. animal
• Animal
• Pretty much
there are no
additional
organelles in an
animal cell
compared to a
plant cell
• Plant
• Primarily has 3
extra structures
• Plastids/
chloroplasts
• Cell wall
• Central
vacuole
Cell surfaces & junctions
• 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)
• 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
• 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