Cmcb-Myosins And Intermediate Filaments

Front 1

What is the function of Myosin?
What is their basic structure?

Back 1

Myosin are the actin motor protons that cause actin to move or slide.

They have N terminal head domain with atphase activity, variable tail lengths ( depend on function of myosin) and light chains.

Front 2

What are two types of myosin?

Back 2

conventional Myosin II - makes thick filaments, actin-myosin movement, mostly in muscle cells

unconventional myosin - they don't form filaments and not involved in muscle contraction. Transport vesicles across along actin filaments, etc.

Front 3

describe the structure of myosin II molecule

Back 3

HMM vs LMM

HMM: involves two mysoin heads and atphase activity
-breaks into S1 - one head. They point towards the -end (pointed end), demonstrating polarity.


LMM - tail
-breaks into S2 - small components of the tail.

Conserved Core Motor domain!

Front 4

Explain the structure of the myosin II thick filament

Back 4

They are bipolar.
Tails make up the thick core. Heads point outwards.
Central bare zone in the middle is only made up of tails.

Front 5

What are 4 types of contracile cells that use Myosin II? are they nucleated? striated?

Back 5

1. skeletal muscles
-multinucleated + striate

2. Cardiac muscle
-mononucleated + striated

3. Smooth muscle
- nonsriated

4. myoepithelial cells
-ectoderm derived
-not striated

Front 6

Describe the structure of the skeletal muscle

Back 6

Skeletal muscles-->myofibrils-->sarcomeres-->thick+thin filaments

Z disc - attachment sites for + end of filaments (CapZ anchors the actin filaments to this)

M line - in the middle, it attaches the two myosin filaments go ether.

Dark band - myosin thick filament

Light band - actin filament

titin - follows the mysoin filament - elastic -allows for contracitility

-nebulin - follows actin

-troponin/tropomyosin - on the actin.

Thick filaments reverses polarity in the middle.
Thin filaments exhibit opposite polairities at the 2 ends of sarcomere

Front 7

How do muscles contract?

Back 7

1. attach - short lived - myosin is bound tightly to actin in rigor.

2. Released - ATP binds to myosin head - myosin is released from actin, slight conformation

3. Cocked - ATP clamps onto myosin - big conformational change. ATP is hydrolyzed. ADP and pI remain tightly bound.

4. Force generating - head binds to actin, power stroke
5. at end of cycle, head is bound to actin again in original conformation but different location.

***many oars (myosin) that row the boat
myosin walks along actin filament

Front 8

What two proteins regulate muscle contraction? and how?

Back 8

Tropomyosin and Tropnin are on actin filaments.

Tropomysoin blocks the mysoin binding site on Actin. When there is Ca+ (muscle contraction), Ca+ binds to Troponin which moves Tropomyosin to a new site. This allows for myosin binding.

Front 9

What is familial hypertrophic cardiomyopathy? What is it caused by?

Back 9

mutations in genes encoding contractile proteins (myosin) causing enlarged heart.

Front 10

What is needed to form mysoin II filaments in smooth muscles or nonmuscle cells?

Back 10

MLCK phosphorylates light chains to change conformation. it exposes actin binding sites.

Front 11

What is the arrangment of filaments in smooth muscle?

Back 11

A network is formed around the cell. Alpha actinin and othe rproteins bind the network to the cell membrane.

Front 12

What happens during cytokinesis?

Back 12

Actin and Myosin II form a contractile ring that pinches off the two cells.

Front 13

There are two main unconventional myosins.
What are they and what do they do?

Back 13

1. Myosin I - small tails, one head. Head walks along the actin filament towards the + end, carrying cargo on tail. Happens in Microvilli for secretion.

2. Myosin V - bigger, has two heads. Holds cargo with tail and heads walks along actin towards + end.

Front 14

What are some characteristics of intermediate filaments?

Back 14

They are very stable, structural support.
Not involved in cell motility
long lived.

Front 15

What are 4 types of intermediate filaments? What makes up those filaments and where are they found?

Back 15

1. nuclear - heteropolmymerss
-Laminin - Nuclear lamina

2. vimentin - homopolymers
-desmin - muscle
-GFAP - glial cells
Periphrin - some neurons

3. Epithelial - heteropolymers
-Keratin - epithelial cells and hair and nails

4. Axonal - heteropolymers
-neurofilaments - neurons

Front 16

What is the structure of intermediate filament?

Back 16

All have highly conserved central rod domain. variety in head and tail.

Central rod domain - alpha helix, etc
-dimers, tetramers, 8 tetramers = 32 IF.
-tetramers aggregate end to end creating protofilaments.

Front 17

Where are keratins present intracelulary and extracelular?

Back 17

intracel - desmosomes and hemidesmosomes

extracel - hair and nails

Front 18

Do intermediate filments work with adapter proteins?

Back 18

yes. need adaptor proteins to attach IF to membrane.

Front 19

Describe neurofilaments

Back 19

They are found in neurons and are extremely stable since axons of neurons are stable.

They also create cross bridges to other filaments -no other filaments do this

Front 20

GFAP

Back 20

found in astrocytes in the CNS. Expression increases after injury to CNS, creating a scar. Tumor cells also express a marker.

Front 21

Nuclear lamins

Back 21

Form the nuclear lamina in the nucleus.
different in that longer rod and have nuclear import signal and form sheet like lattice.

regulated by phosphorylation and dephos thats linked with mitosis

Very dynamic-breaking down building up
-present in all nucleated cells.

Front 22

cell type, tumor type of:
1 - Keratin
2-Vimentin
3-desmin
4-GFAP
5-Neurofilament

Whats so special about vimentin

Back 22

1-epithelia - carcinoma
2-mesechymally derived cells - many tumors
***Vimentin is not diagnostic unless just itself shows up.

3-Muscle - muscle sarcoma
4-astrocytes - gliomas
5-neurons - neuroblastomas