Cytoskeleton, Cell Walls, & ECM

Slide show modified from:http://www.explorebiology.com

Cytoskeleton –network of fibers extending throughout the cytoplasm

MICROTUBULES FUNCTIONStructural support and cell movement

~ Move chromosomes during cell division

» Centrioles & spindle fibers

~ tracks guide motor proteins» Motor proteins: dynein & myosin

~ cell motility» Cilia & flagella

MICROTUBULESTracks guide motor proteins to destination

(Motor proteins: dynein & myosin)

ATP

Vesicle

Receptor formotor protein

Motor protein(ATP powered)

Microtubuleof cytoskeleton

SEE MOTORPROTEINS inACTION

http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/movies/kinesin.dcr

http://python.rice.edu/~kolomeisky/transport.htm

EXAMPLES• Vesicles containing neurotransmitters migrate to tips of nerve cells• Vesicles move to Golgi along cytoskeletal tracks• Cytoplasmic streaming

Cilia and Flagella

– Are locomotor appendages– Extensions of cytoskeleton

Examples: Many unicellular protists move with flagellaSome plant reproductive cells have flagellaCilia in oviducts move egg toward uterusCilia lining windpipe sweep mucous out of

lungsFlagellum in sperm cells(Prokaryotic flagella don’t have microtubules)

Cilia and flagella share a common ultrastructure

(b)

Outer microtubuledoublet

Dynein arms

Centralmicrotubule

Outer doublets cross-linkingproteins inside

Radialspoke

Plasmamembrane

Microtubules

Plasmamembrane

Basal body

0.5 µm

0.1 µm

0.1 µm

Cross section of basal body

Triplet

CILIUM (many, short) oar-like movement; cell moves perpendicular to axis of cilium

FLAGELLUM (few, long) whip-like movement; cell moves in same direction as axis of flagellum

http://web.jjay.cuny.edu/~acarpi/NSC/13-cells.htmhttp://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

MICROFILAMENTSMake up contractile apparatus of muscle

– Contain the motor protein myosin in addition to actin

Actin filament

Myosin filament

Myosin motors in muscle cell contraction. (a)

Muscle cell

Myosin arm

Amoeboid movement– Actin filaments constantly form & dissolve making

cytoplasm liquid or stiff during movement

Cortex (outer cytoplasm):gel with actin network

Inner cytoplasm: sol with actin subunits

Extendingpseudopodium

http://www.nextftp.com/jissen/ameba.gif

Cytoplasmic streaming– Speeds distribution of materials

Nonmovingcytoplasm (gel)

Chloroplast

Streamingcytoplasm(sol)

Parallel actinfilaments Cell wall

http://www.daviddarling.info/images/cytoplasmic_streaming.gif

NUCLEAR LAMINA

Cell Walls of PlantsProtectionMaintain shapeAlso found in Prokaryotes, fungi, and some protistsComposition varies with species/cell type

Basic design:Microfibrils of polysaccharide cellulose embedded in matrix of other polysaccharides

(like steel reinforced concrete)

Plant cell wall StructurePRIMARY CELL WALLMIDDLE LAMELLA- ~ between primary cell walls of adjacent cells ~ made of sticky polysaccharides (pectins) ~ glues cells togetherSECONDARY 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 JUNCTIONSMembranes of neighboring cells and pressed together & bound by proteinsForms continuous seal to prevent leakage of extracellular fluid across layer of cells

DESMOSOMES (anchoring junctions)Act like “rivets” to fasten cells together into strong sheetsIntermediate proteins (keratin) anchor desmosomes in cytoplasm

GAP JUNCTIONS (communicating junctions)Channels connect to adjacent cellsSpecial membrane proteins surround poreNecessary for communication between cells in heart muscle and animal embryos

The Cell: A Living Unit Greater Than the Sum of Its Parts

• Cells rely on the integration of structures and organelles in order to function

5 µ

m

Figure 6.32