Download Cell Size

Chapter 4
A Tour of the Cell
Cytology: science/study of
cells
• 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
• Nucleoid: DNA
concentration
• No organelles with
membranes
• Ribosomes: protein
synthesis
• Plasma membrane (all
cells); semi-permeable
• Cytoplasm/cytosol (all
cells)
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
Range of Cell Size
Cell Fractionation
Nucleus
• Genetic material...
•chromatin
•chromosomes
•nucleolus: rRNA;
ribosome synthesis
• Double membrane envelope
with pores
• Protein synthesis (mRNA)
Ribosomes
• Protein manufacture
• Free - cytosol, proteins function in cell
• Bound - endoplasmic reticulum, membranes,
organelles, and export
Compartmentalization
• Increases internal
surface area
• Sometimes enzymes
are incorporated into
the membrane.
• Provide localized
environmental areas.
• Sequester reactions
(hydrolytic enzymes in
lysosomes)
The Endomembrane System
• Membranes may be
interrelated directly or
indirectly via vesicles.
• Membranes are dynamic
structures.
•
•
•
•
•
•
Nuclear Envelope
Endoplasmic Reticulum
Golgi Apparatus
Lysosomes
Vacuoles
Plasma membrane (not
actually a member of the
system, but related to it).
1. Endoplasmic Reticulum (ER)
Continuous with nuclear envelope
• Smooth ER
•no ribosomes
•synthesis of lipids
•metabolism of carbohydrates
•detoxification of drugs and
poisons
Stores Ca2+ ions
• Rough ER
•with ribosomes;
•synthesis of secretory proteins
(glycoproteins), membrane
production
Rough ER Ribosomes
1. Rough ER ribosomes
synthesize secretory proteins
2. Growing polypeptide is
threaded through the ER
membrane into the lumen or
cisternal space
3. Protein folds into its native
conformation
4. Local enzymes catalyze
covalent bondingmodifications
5. Protein departs in a transport
vesicle
2. Golgi Apparatus
•
•
•
•
ER products are modified, stored, and then shipped
Cisternae: flattened membranous sacs
trans face (shipping) & cis face (receiving)
Transport vesicles
3. Lysosomes
•
•
•
•
•
Sac of hydrolytic enzymes; digestion of macromolecules
Phagocytosis
Autophagy: recycle cell’s own organic material
Tay-Sachs disease - lipid-digestion disorder
Apoptosis
4.Vacuoles
• Membrane-bound sacs
(larger than vesicles)
• Food vacuole
(phagocytosis)
• Contractile (pump
excess water)
• Central vacuole
(storage in plants)
• Tonoplast (membrane)
Relationships Among Endomembranes
Other Membranous Organelles
• Not part of endomembrane system
• Peroxisomes
• Mitochondria
• Chloroplasts
Peroxisomes
• Single membrane
• Produce hydrogen
peroxide in cells
• Metabolism of fatty
acids; detoxification of
alcohol (liver)
• Hydrogen peroxide
produced, then
converted to water –
action of catalase.
Mitochondria
• quantity in cell correlated
with metabolic activity;
• cellular respiration;
• double membranous
(phospholipid);
• cristae/matrix;
• intermembrane space;
• contain own DNA
• bacterial origin
Chloroplasts
• type of plastid;
• thylakoids (flattened disks)
• stroma;
• double membranous;
• grana (stacked thylakoids);
• own DNA
The Cytoskeleton
•
•
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
Tubulin in endothelial cell
Motor Molecules and the
Cytoskeleton
a. motor molecules on one
microtubule ‘grab’ and
slide past another
microtubule.
b. motor molecules attach to
receptors on organelles
such as vesicles, enabling
them to ‘walk’ along the
microtubule
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
a. ls. cilium
b. cs cilium, showing 9+2 arrangement
c. cs basal body, anchors the cilium to the cell – third
microtubule incorporated (centriole) central 2 lost
How Dynein ‘walking’ Moves
Cilia and Flagella
The dynein arms of one
doublet grip the adjacent
doublet.
Powered by ATP
Microfilaments
and Motility
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
Plamodesmata in a thin plant section
Intercellular Junctions in Animals
The Lives of a Cell
Harvard Animation
• http://aimediaserver.com/studiodaily/videop
layer/?src=harvard/harvard.swf&width=640
&height=520
Narrated version
Assignment
http://www.bu.edu/histology/m/t_electr.htm
Choose 4 images to draw and label