Match the appropriate lettered protein with the structure of function indicated by the numbered items that follow.

(A)    Desmin
(B)    Ankyrin
(C)    Profilin
(D)    Dynein
(E)    Fragmin
(F)    Actin
(G)    ? –actinin
(H)    Myosin
(I)    Keratin
(J)    Kinesin
(K)    Integrin
(L)    Tubulin
(M)    Fibronectin
(N)    Spectrin

195.    This protein binds tightly to actin monomers, reducing their ability to polymerize into microfilaments.

196.    Interaction with this integral membrane protein is one means by which components of the cytoskeleton are linked to the plasma membrane.

197.    This only is an ATPase that helps move membrane-bound organelles from the perinclear cytoplasm of cells such as neurons to the ends of cytoplasmic extinctions.

198.    Founds only in red blood cells, this proteins plays a mayor role in determining the shape and dispensability of normal red blood cells.

199.    Hereditary spherocytosis involves the failure of this cytoplasmic protein to link spectrin to the plasma membrane.

200.    It is found as heterodimers, with a total MW ? 110,000 that bind GTP and GDP.

201.    This extracellular proteins is though to affect the cytoskeleton via binding to transmembrane proteins.

202.     In nemaline myopathy, this protein is overproduced and accumulates in rod-like arrays adjacent to Z-disks.

ANSWER AND TUTORIAL ON ITEMS 195-202

The answers are: 195-C; 196-K; 197-J; 198-N; 199-B; 200-L; 201-M; 202-G. With the exception of integrin (K) and fibronectin (M) all the proteins in this extended matching set are cytoplasmic components that are either part of, or interact with, the cytoskeleton. Desmin (A) is the subunit of most intermediate filaments in muscle cells, while keratin (I) is the primary component of intermediate filament in epithelial cells. Ankyrin (B) links the protein spectrin (N), founds only in red blood cells, to the inner surface of the red blood cell membrane. Spectrin is though to be important for maintaining the shape of red blood cells. Ankyrinis lacking in patients with hereditary spherocytosis. Profilin (C), found in many cells, can bind actin monomers, thus removing them from the polymerization-competent pool and causing microfilaments to desasemble.

Glosolin, another actin binding proteins, reduces the tendency of microfilaments to be transiently cross-linked into gel-forming arrays. Fragmin (E) is one member of a family of proteins that can bind to microfilaments and cause them to be broken into shorter filaments, thus “fragmenting” them. Actin (F) and myosin (H) are found not only in muscle cells but also in most non-muscle cells, where they play roles in cell motility and in stabilizing cell shape. The protein ? –actinin (G), involved in the attachment of actin filaments to the Z-line in skeletal muscle, and overproduced in nemaline myopathy, may also play a role in some non-muscle cells attaching microfilaments to specific patches of the plasma membrane. Kinesins (J) ATPases, smaller than and distinct from myosins and dyneins (D), that cause movement of membrane limited vesicles along microtubules, usually away from the cytocenter and out toward the periphery of the cell.

Intergrins (K) are a class of integral membrane proteins that have specific domains exposed both at the cytoplasmic side if the membrane and at the intracellular face. As such, they can serve as transmembrane linkers allowing information related to extracellular conditions to affect the way cytoskeletal components are arranged. Fibronectin (M) is a large extracellular protein (whish can interact with specific intergrins) that provides directional clues to certain motile cells. Tubulins (L) are the major components of the microtubules founds in cilia and flagella, as well as throughout the cytoplasm of many cell types. Tubulins are hetorodimers of ? and ? subunits; the subunits have MW ? 55,000, so the tubulin dimmer a MW ? 110,000. Microtubules form by the polymerization of tubulins dimmers. The dimmers bind two molecules of guanine nucleotide, whit most dimmers constraining one molecule of GTP and one of GDP. GTP is spit to yield GDP during the polymerization process. Video Eyepiece Cameras Video Zoom Inspection microscopes