Myosin Flashcards
Do microtubules havae fast/slow turnover?
Fast (except for stable nuerons)
Some functions of microtubules
…
What structures do all myosins have in common?
- Ne terminal head domains (bind to actin and exhibit ATPase activity)
- variable sized taild omain that dictates specific interactions of myosin with other proteins
- some type of associated light chain
What are “conventional myosin” and where are they formed?
Myosin II
Form thick filaments and involved n actin-myosin sliding contraction
In msucle but foudn in non-muscle cells as well
What are unconventional myosins? What are their funciton?
DO NOT FORM FILAMENTS
not involved iwth muscle conrcations
invovled in other cell movements
Transprot of membrane vesicles along filament, phagocytosis, extenion of cell processes
Is ATPase activity and actin binding function of myosin head domain conserved for various myosin isotypes>
YES!
What 2 funcitons fo myosin head domains are conserved in myosin head domains
- ATPase
2. Actin-binding function
What is myosin broken down to with treatment with proteoylytic enzmes?
- LMM - lght meromyosin
2. HMM- heavy meromyosin
What is LMM composed of
Light meromyosin
Tail myosin
What is HMM composed of?
Heavy meromyosin
S1 fragment + S2 FragmentHEAD Piece with ATPase activity and actin binding activity
What does HMM breakdown to with further Tx
S1 fragment- myosin heads + actin binding portion
- S2- rod like fragment
What are S1 fragments used for? What direction do arrowheads point?
To demonstrate polarity of actin filaments
Arrowheads piont to the (-) slow gorwing ends while barbed ends are at teh (+) ends for the microfilaments
What is a bare zone
Free of mysoin head dominates this area = all tails
Describe Myosin Polarity-
Bipolor!
Myosin molecules (~300) aggregate together by means of tial region- heads on the outside
Describe Myosin II filaments in non-muscle
Much smaller (15-20 molecules) but have similar bipolar arrangements
What are lenght of skeletal muscle cell? Width
Lenght- 2-3 cm long
Width- 100 nm wide
What ar the four classes of muscle cells in mammals
Heart muscle, Smooth muscle, Myoepithelial cell, Skeletal muscle fiber
Skeletal muscles
multinucleated cell
cells form via fusion of myoblasts; once fomred they are generally non-mitotic
Heart msucle
only have one nucleaus per cell
Smooth muscle
do not appear straited- foudn in regions like eigstiv tract or around arteries and veins
Myoepithelial cells- non stirated
ecotdermally dericed (unlike other muslce ells) serve to expel fluids (saliva, sweat, milke) from glandular tissue
Diameter or myofibril
1-2 um
myofibirls comprised of long repeated chains of tiny contracile units- called sarcomeres
What direction (minus or plus) end of actin near Z lines?
Plus ends are towards Z lines!
Minus ends are towards M lines
A bands are anisotropic
I bands are isotropic
yeeeppp
What is Titin?
associated with mysoin thick filaments
How far does titin extend? What are its characterisitcs?
Z–> M line
Elastic changes lenght as sarcomere contracts and rleaxes
What are nebulin?
Assocaited with actin fibers
same lenth as thin filmants
What is Cap Z
Anchors (+) end of actin to Z-line
What does Z-disc contain?
alpha actinin and IF (Desmin)
What is polarity of Myosin fibers?
Same relative poslarity-
Myosin heads have + ends and tails are -
M yosin heads oeprate with low processivity sot hey don’t hodl each other back
What percent of cycelt time is Myosin Head bound to Actin?
5% of cycle time
Does myosin walk towards (+) or (-) ends of actin
Positive end of actin, close to Z line
What is the complex of the Troponin complex or 3 polypeptides
- T- tropoyosin binding
- I: Inhibitory
- Calcium-biding
What happens with I-T complex undar increase in Clacium
calcium binds to Troponin C–> Troponin I rleases Actin
what is tropomyosin?
elongated molecule that binds along groove of actin helix
What is Hypertorphic Cardiomyopathy
Mutations in genes encoding contractile proteins
death in young atheletes
]Familial,
genes including myosin llight cahins, myosin heavy chains, cardiac troponin or tropomyosin
In SM and non-muscle cells, Myosin II is activitated yb? Why? What enzyme is in charge of it?
Phophorylation–> in order to form filaments
MLCK (myoskin Light chain knase)
What phosphorylates Mysoin II?
MLCK enzyme
Wht happens when Myosin II in non-muscle is phosphorylated?
Releases Myosin Tail from Sticky Patch in Myosin Head –> Tails assemble into short, bipolar thick filaments
Thickness of MII in non-msucle vs skeletal muscle
Thinner b/c 15-20 moleucls vs hudnreds
In SM,
1) Actin: mysoin ration vs in sk musclte
2) ATPase activity
In SM , Act:Myosin ratio higher
ATPase activity lower in smooth muslce
What attaches thin filaments (actin) to cell membrane in SM?
Dense bodies with alpha actinin
INtracellular scaffolding of IF- DESMIN
Thin is interdigiteded between thick filaments`
What is the contractile ring made up of ( funciton sduring cytokineses)
Actin-Myosin II in non muscles that pinch daughter cells
end of mitosis during cytokineses
What are two unconventional Myosin Examples? Function? How theyre differnt form Myosin II
Myosin I
Myosin V
Smaller tale domains
Assocated with structures such as membrane vesicles and organelles
Myosin I
One headed motor head moves along atin
Tails carry cargo in microvilli
Myosin I is invovled in moving membrane vesicles along the central core of MF in teh microvilllus
Myosin V
forms dimers and functions as 2-headed motor
Myosin V reads the polarity of actin filaments and tranpsorts cargo bound to its tal piece (IF) towards teh plus ends of actin filaments
TOWARDS PLUS END
Waht is the fucntion of Intermediate Filaments?
Major structural elemetns that provide mechanism support and structure to cells
Do they have fast/slow turnover?
SLOOWWWWW! long-lived (like hair, hails, insoluble)
Involved in cell motiliy?
No
Are there a lot or a little>
A lot
abundant in some cells far more than MTs or MF
Soluble/Insoluble
Insoluble
Diameter
10-11 nm
What are four types of IF
Nuclear
Vimentin-like
Epithelial
Axonal
Which ones of the IFs are OBLIGATORY HETERPOLYMERS
Epthelial
Axoanl
What are the components polypeptides of nuclear IF
laminins A, B,C
found in nuclear lana (all nucleated cells)
What are component polypeptides of vimentin-like
- Vimentin
(manycells of mesenchymal orgiin, fibroblast, lymphosyte, endothelial cells)
2 .Desmin (ONLY in muscle)
3.Glila fibrilaly acidic protein
(glila cells (astrocytes an some Schwann cells)
- Peripherin- some neurons
What are components of epithelial polypeptides
Type I Keratins (acidic)
Type II kertains (basic)
in epithelial cells and their derivatives
What are components of Axonal Componetn polypeptides
Neurofilament proteins (NF-L- NF-M and NF-H_
Are type I kertains acidic of basic?
Acidic (heteropolymer)
Are tyep II kertains acidic or basic?
Basic (heteropolyemr
what is conserved in all IFs
Conserved core domain
Central rod domain
DIfferent heads and tials
Chaaracteristic of rod domain
Dimer coiled cords
Tetramers formed by anti parallel aggregation of 2 coil-coiled dimers –> rope
What are protofilaments?
Tetramers taht aggregateend to end
Assocaite alterally, forming final IF that is 10-11 nm thick
How any IF proteins molecules present
32 IF protein molecules
Where are keratins located?
Intracellulary in epi cells layer of skin at specialized cell-cell jucntions called spot desmosomes
IFs are also foudn as HEMIDESMOSMES where epithelial cells make connections with ECM
also present EXTRACEULLARY as keratinziedlayer of skin as well as in specialized derivatives of epithelal cells hair and nails
what are tonofilaments?
looping kertain IFs in hemidesmosomes and desmins
What is EBS?
Epidermolysis bullosa Simpex (EBS)
aut dominant disase invovling mutaiotn of kertain gene in teh Basl skin layer
Bio finding of EBS
Aberrant kertain filametns and disrupted keratin
What happens with mechanical stress in EBS
an lead to ruptur of basal epithelial cells –> blistering and sloughign off of skin
Why is EBS dangerous?
Rapid loss of fluids when skin isn’t intact
What are neruofilament fucntions?
Major proteins in neurons
stabilize cell shape, long axonal region
Stable trasnit for year sbefore they reach end of axon
when are NF modified
Post translationsioanlly (in axons, very phosphooryalated)
What makes NF different from other IFs
Cross bridges
What does GFAP expression lead to?
increase in Reactive Astrocyte and fomrs of cellular scar after injuries to CNS
Where are GFAPs located?
Mature Astrocytes (supporting cells in brain)
Injury –> hypertrophyin CNS
Where are primary brain turmos primarily dervied?
Astrocytes
What makes Nuclear Lamins different from other Intermediate Fibers?
1) Longer central rod domain
(central rod domain is the same in all IFs)
2) Also, they have a Nuclear import signal –> enables poteins to be directed from Cytosol (translated)–> nucleus (
3) Form a sheetlike lattice, differnt from the IF networks of other ptoeins
Regulated by phosphorylation/dephosphorylation evens that are synchronized to events of mitosis (nuclear evelope dissoltuion and refomraiton in prophase and telophase)
What regualtes assembly of lamins
phos/dephos synchronized to mitosis
Structure of lamin
Sheetlike lattice, large central rod
