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Lecture 16 Ch 9 Cytoskeleton II Intermediate Filaments and Microfilaments

Terms in this set (22)

Intermediate filaments are fibrous proteins that terminate in globular domains.

+ There are 5 different families:
- Acidic keratin
- Basic keratin
- Vimentin and others
- Neurofilaments
- Lamins

o Differences:
They are different because they have diverse amino acid sequences (difference sin primary structure).

o Similarities:
- Central, rod shaped, alpha helical domain of similar length flanked on each side by globular domains of variable size.
- Thus, they have similar tertiary structure, that is fibrous in nature. Dimers and tetramers of fibrous proteins (long and extended)
- They have the same polar shape, being an extended fibrous protein, there is an N and C terminus with globular domains (not a globular protein) - Specificity- of what bind to the intermediated filaments is based on N and C globular domains sticking outwards from the long fiber. Which allows intermediate filaments to hook to something (Other IF's, microtubules, actin microfilaments). A molecule that can do that connection role is Plectin.
- Intermediate filament resist the force of stretching. They don't tare when they are pulled on because they are strong, fibrous proteins. (VERY STRONG)
- There are more than 70 genes (divided into 5 classes)

When two monomers wrap around one another to form a dimer, they do so in a polar way so if your asked, "Is the intermediate polar?", well the monomer is polar, and the dimer is polar, but the polarity disappears when a tetramer (two dimers aligned) is made. When two dimers align together, they align in an antiparallel fashion, thus the two ends look identical and it is no longer a polar molecule. These tetramers will align to make a basic unit of intermediate filaments, but they are non-polar so full length of IF is nonpolar. And one-unit link of filament will join with other links of filaments to form full intermediate filament. When they do, IFs are generally 10 nm in diameter (smaller than microtubules but larger than microfilaments).
1) They can help cell break in cytokinesis, help with hearing, encourage muscle contractions, and help with organelle migration. Its structure is that of a globular helix protein with a growing + barbed end and a shrinking - pointed end. In order for the barbed end to grow, the proteins serve as ATPase and have ATP bind to them and hydrolyze ADP. This structure allows proteins to walk along them for cell transport, for them to grow out to help with hearing, to grow out and then pull together for cytokinesis, and also pull together for muscle contraction.

Functional Structural:
- Ex: linen of small of intestine, because it increases surface are due to the need of absorptions. Villi that make linen intestine is near cell surface made out of microfilaments.
- Cell cortex: just under the plasma membrane providing support for the plasma membrane.
- Focal Adhesions: connect ECM àintegrin àactin. ANCHORING

Movement, Dynamic
-Axonal outgrowth: Leading edge is made of microfilaments
-Vesicle transport path
-Stereocilia of cochlear hair cells that convert sound waves to signal
-Facilitates neural crest cell migration during embryonic development as well as immunocyte motility in inflammation - filopodia
-Muscle Contraction:

Microfilaments are the main driver in non-flagellar, non-ciliary cell locomotion. HOWEVER, THE COOPERATION OF CYTOSKELETAL ELEMENTS OVERALL HELP!!!

Actin microfilament have an inextensible helicalform that is considered to be flexible. Suh helical filament has a plus(barbed) end, and a negative - minus(pointed)end. New actin monomers are added to the barbed (+) end 10x faster than the (-) end. However, Before the actin monomer is even incorporated into a filament, the actin monomer must be bound to a molecule of ATP. (ATP hydrolyzed to ADP at some time point after it is incorporated into the end of a growing. After ADP-actin is released from the polymer, ADP/ATP exchange must occur before reincorporation possible.) actin protein is considered to be an ATPase because hydrolysis ATP to ADP. S1 Myosinis what surrounds such actin filament.