(45-46) Cell junctions and Cystoskeleton

Tissue are made of — and organ are made of —

cells of the same type; arrangement of tissues of different types together

3 primary functional categories of cell junctions

adhering, impermeable, communicating

Adhering junctions

desmosomes. Junctions which hold two cells together. Made of intermediate and/or micro filaments

2 types of desmosome

spot and belt

Spot desmosome

adhering junction. In areas of high shear force. Series of intermediate filaments (like keratin) in one cells connects to another series of intermediate filaments of another cell with intermediate filaments

t/f spot desmosomes are found in the skin (explain answer)

true; there may be high shear force on the skin

Belt desmosome

adhering junction. Series of actin microfilaments in two connecting cells with intermediate filaments that tie them together. Uses both microfilaments and intermediate filaments

t/f two cells held together via only desmosomes are tightly packed against one another, so no fluid may move between them

false

Impermeable junctions

tight junctions. Holds cells together tightly so that fluid or other materials may not move between the cells. One transmembrane protein of one cell connects to another transmembrane protein of the other cell

t/f desmosomes and tight junctions may be found throughout the surface of the cell

true

Communicating junctions

gap junctions. Important to cell communication. 6 connexin proteins form to make one connexon on each cell surface which then connect to form the communicating junction.

Connexin

proteins that when 6 are formed together creates a single connexon

Connexon

formed from 6 connexin. Connect to another connexon of another cell to form a gap junction

communicating/gap junction create a — and — connection between two cells, unlike desmosomes or tight junctions

chemical and electrical

In what organ is gap junctions especially important and why?

heart, because all of the cell must act in unison to pump properly

What may be exchanged through a gap junction

fluids, cytoplasm, small molecules

Desmosomes are made of — and/or —, tight junctions are made of —, and gap junctions are made of —

micro and/or intermediate filaments ; transmembrane proteins; a series of six conexin proteins which make up a connexon in each cell

Cytoskeleton

structure in a cell formed from microtubules, microfilaments, and intermediate filaments (all of which are made of proteins)

Microtubules

found in all eukaryotic cells. Tubular in appearance. Diameter of 25 nm. Length may vary from microns to 100s of nm. Usually found within the cytoplasm of the cell (not within organelles). Made of alpha and beta tubulin dimers which form into a slinky like shape.

The cross section of a microtubule is a circle of — monomers.

13

— % of microtubules is tubulin and –% is other proteins

85; 10-15

Tubulin

protein which primarily makes up microtubules. Alpha and beta versions are 55 kilodaltons each.

MAPs

microtubule associate proteins. Makes up 10-15% of microtubule

How do microtubules grow? How do they shorten?

tubulin dimers are added to one end of a microtubule and they may be removed from the other end. These ends are constant (ie you can only ever add to one end of a microtubule)

How may a microtubule push or pull on the plasma membrane

by shortening or growing

How do microtubules assist in cell movement?

pushing and pulling on the cell membrane from within the cell

Microtubules are involved in both the movement of the — and —

cell and organelle or molecules within the cell

Cilia and Flagella

made of microtubules. Involved in movement of a cell or fluid around the cell. Cross section looks like 9 pairs of microtubules with one pair in the middle (20 total microtubules) connected to one another and to the pair in the center (looks like spokes on a wheel)

Difference in function of cilia and flagella

flagella are often involved in movement of the cell whereas cilia moves fluid around a cell.

How do cilia and fagella move?

they consume lots of ATP to slide against each other and produce a beating motion.

Microfilaments (structure)

composed of actin monomers linked together in a long chain twisted with another actin chain. 6-7 nm in diameter. May form at one end and grow at the other like microtubules. More closely associated with the plasma membrane.

Microfilaments function

important to endocytotic vesicle movement. Important for cytoplasmic streaming. May push or pull on the plasma membrane (like microtubules).

How do microfilaments control cytoplasmic streaming?

if they are all parallel, the cytoplasm may easily move between the filaments (right) or they may be used to block movement when placed erratically (left)

Cytoplasmic streaming

movement of cytoplasm from one area to another area of the cell.

Actin

monomer of microfilaments. Forms into a chain which wraps with another actin chain to form a microfilament

Intermediate filaments

9-10 nm in diameter. Neither tubulin or actin. May be made of many different proteins (ie keratin or desmin). Specific to certain cell types. Usually functions outside of the cell.

Keratin

intermediate filament found in skin and finger nails

Desmin

intermediate filament found in muscle cells