Transcript Motor proteins: dynein & myosin

Slide show modified from:
http://www.explorebiology.com
Cytoskeleton, Cell Walls,
& ECM
Cytoskeleton –
network of fibers extending throughout
the cytoplasm
MICROTUBULES FUNCTION
Structural support and cell movement
~ Move chromosomes during cell division
» Centrioles & spindle fibers
~ tracks guide motor proteins
» Motor proteins: dynein & myosin
~ cell motility
» Cilia & flagella
http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/movies/kinesin.dcr
MICROTUBULES
Tracks guide motor proteins to destination
(Motor proteins: dynein & myosin)
Vesicle
Receptor for
motor protein
ATP
Motor protein
(ATP powered)
Microtubule
of cytoskeleton
SEE MOTOR
PROTEINS in
ACTION
EXAMPLES
• Vesicles containing neurotransmitters migrate to tips of nerve cells
• Vesicles move to Golgi along cytoskeletal tracks
• Cytoplasmic streaming
http://python.rice.edu/~kolomeisky/transport.htm
Cilia and Flagella
– Are locomotor appendages
– Extensions of cytoskeleton
Examples:
Many unicellular protists move with flagella
Some plant reproductive cells have flagella
Cilia in oviducts move egg toward uterus
Cilia lining windpipe sweep mucous out of lungs
Flagellum in sperm cells
(Prokaryotic flagella don’t have microtubules)
Cilia and flagella share a common ultrastructure
Outer microtubule
doublet
0.1 µm
Dynein arms
Central
microtubule
Outer doublets
cross-linking
proteins inside
Microtubules
Radial
spoke
Plasma
membrane
Basal body
(b)
0.5 µm
0.1 µm
Triplet
Cross section of basal body
Plasma
membrane
FLAGELLUM (few, long) whip-like movement;
cell moves in same direction as axis of flagellum
CILIUM (many, short) oar-like movement;
cell moves perpendicular to axis of cilium
http://web.jjay.cuny.edu/~acarpi/NSC/13-cells.htm
http://www.sk.lung.ca/content.cfm?edit_realword=hwbreathe
MICROFILAMENTS
• STRUCTURE
– Thinnest class of fibers
– Twisted double chain of actin subunits
~ 7 nm in diameter
• FUNCTION
– Crosslinks with microtubules (cell shape)
– Muscle cells:
Actin filaments interact with myosin motor proteins to
create muscle contraction
– Amoeboid movement
– Cytoplasmic streaming
MICROFILAMENTS
Make up contractile apparatus of muscle
– Contain the motor protein myosin in addition
to actin
Muscle cell
Actin filament
Myosin filament
Myosin arm
(a) Myosin motors in muscle cell contraction.
Amoeboid movement
– Actin filaments constantly form & dissolve making
cytoplasm liquid or stiff during movement
Cortex (outer cytoplasm):
gel with actin network
http://www.nextftp.com/jissen/ameba.gif
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
Cytoplasmic streaming
http://www.daviddarling.info/images/cytoplasmic_streaming.gif
– Speeds distribution of materials
Nonmoving
cytoplasm (gel)
Chloroplast
Streaming
cytoplasm
(sol)
Parallel actin
filaments
Cell wall
NUCLEAR LAMINA
Cell Walls of Plants
Protection
Maintain shape
Also found in Prokaryotes, fungi, and some protists
Composition varies with species/cell type
Basic design:
Microfibrils of polysaccharide cellulose
embedded in matrix of other
polysaccharides
(like steel reinforced concrete)
Plant cell wall Structure
PRIMARY CELL WALL
MIDDLE LAMELLA~ between primary cell walls of adjacent cells
~ made of sticky polysaccharides (pectins)
~ glues cells together
SECONDARY CELL WALL
~ built when cell stops growing
~ between plasma membrane and 1° cell wall
Unify plant into one living continum
Types of intercellular junctions in animals
TIGHT JUNCTIONS
Membranes of neighboring cells and pressed together & bound by proteins
Forms continuous seal to prevent leakage of extracellular fluid across
layer of cells
DESMOSOMES (anchoring junctions)
Act like “rivets” to fasten cells together into strong sheets
Intermediate proteins (keratin) anchor desmosomes in cytoplasm
GAP JUNCTIONS (communicating junctions)
Channels connect to adjacent cells
Special membrane proteins surround pore
Necessary for communication between cells in heart muscle and animal
embryos
The Cell: A Living Unit Greater Than
the Sum of Its Parts
5 µm
• Cells rely on the integration of structures
and organelles in order to function
Figure 6.32