CELL & MOLECULAR BIOLOGY HOMEWORK #9 ANSWER THE FOLLOWING: 1. Compare the actin binding proteins: formin, Arp2/3, cofilin, profilin, fimbrin, α-actinin, spectrin. Address the following questions

as applicable: In what part of the actin cytoskeleton do these proteins bind and, if known, to what specifically do they bind? What activity or action are they involved in?

2. Compare the structure of fimbrin, α-actinin, filamin and spectrin

Actin binding protein Size* Binds as: Composed of: Distance b/w ABDs* Fimbrin

α-actinin

Filamin

Spectrin

* Make your best guess, using relative terms (e.g. small, long, etc.)

COMPLETE THE FOLLOWING THREE TABLES:

Table 1. Selected Functions of the Cytoskeleton In the appropriate boxes either check the cytoskeletal element(s) involved or write the name of the structure. Note: not every box of the table will be filled.

Activity/Function Microfilaments Intermediate Filaments Microtubules Network below the surface of plasma

membrane that functions in support

Attachment to substratum

Attachment to adjacent cells

Support or movement of cell surface protrusions

General support & integration of the 3 cytoskeletal filaments

Polarity of nerve cell fibers (axons vs. dendrites)

Transportation of organelles & vesicles

Flagella & cilia

Spindle fibers of mitosis

Contractile ring of cytokinesis in animals

Table 2. Match the transmembrane protein to its primary function Transmembrane Protein Function: anchoring of… 1. cadherins a. the cell cortex to the plasma membrane 2. integrins b. cells to extracellular matrix 3. glycophorin c. cells to adjacent cells

Table 3. Specialized Regions of Cell Contacts Most cells of a multicellular organism must form intimate contacts with adjacent cells and often with extracellular matrix. Both cell surface proteins and specialized regions of the plasma membrane allow the cells to form stable or transient interacations. There are numerous types of specialized regions that form such junctions. Consider the junctions listed in the table below and fill in the boxes appropriately. Note: some of the boxes will be blank. Also, define the terms in the footnotes below the table.

Junction Cytoskeletal Attachment Transmembrane pro. Extracellular binding site Intracell. binding site(s) Cell-Matrix Contacts Focal Adhesions

Hemidesmosome

Cell-Cell Contacts Tight junctions

Adherens Junction

Desmosome

Gap junctions

Plasmodesmata

Adhesion belt: Junctional complex: