Exam 4 - Myosins and Muscle slides Flashcards Preview

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Flashcards in Exam 4 - Myosins and Muscle slides Deck (46):

How many subgroups of myosin's are there?



What does Myosin I do?

Ubiquitous cellular protein for vesicle transport, step size = 10 nm, monomeric. Isoforms in mircrovilli.


What does Myosin II do?

Aka conventional myosin, dimer with two light chains for each heavy chain (essential light chain and regulatory light chain on neck region). Produces muscle contraction (smooth muscle cells and sarcomeres of striated muscle).
- Also has alpha-helical coiled coil


What does Myosin IV do?

Monomeric, has a single IQ motif and tail that lacks any could-coil forming sequence.


What does Myosin V do?

1. Dimeric myosin with a 36 nm step size, six light chains for each heavy chain => vesicle transport.
2. Walks towards barbed end (+ end)
3. Vesicle movement from center of cell to periphery.
4. May act as a dynamic tether, retaining vesicles and organelles in the actin-rich periphery of cells.


What does Myosin VI do?

Dimeric, together with Myosin IX which are monomers so far the only minus end directed motors -> vesicle transport from cell periphery to center.
- Associates with clathrin coated pits/vesicles at the plasma membrane -> transport of endocytotic vesicles into the cell.
- "unconventional myosin"


What does Myosin VIII do?

Plant-specific myosin involved in cell division.


Myosin II leads to what formation?

Thick filament formation


What is RLC and ELC?

RLC = Regulatory light chain = Calmodulin
ELC = essential light chain


What do Rab GTPases do?

Ras family member of monomeric GTPases: regulate manny steps of membrane traffic including vesicle formation and vesicle movement along actin.


What does phosphorylation of the tail domain do?

Causes the myosin to release its cargo


What is melanophilin?

Carrier protein and Rab effector protein.


What are muscles derived from?

Contractile tissue of animals, derived from the mesodermal layer of embryonic germ cells.


What are the three types of muscle?

1. Skeletal Muscle
2. Cardiac Muscle
3. Smooth muscle
1 and 2 are striated muscles


What are some examples of smooth muscle tissue?

Non-striated muscle: blood vessels, urinary bladder, uterus, gastrointestinal tract, respiratory tract


What does smooth muscle tissue contain?

Actin, myosin (class II), and tropomyosin. No troponin (replaced by calmodulin, calponin, caldesmon and others)


Smooth muscle containing tissue tend to demonstrate what better than striated muscle?

Greater elasticity and function within a larger length-tension curve than striated muscle.


How are contractions controlled in smooth muscle tissue?

May be spontaneous, controlled by pacemaker cells (e.g. in gut), or can be induced by a number of agents (e.g. hormones, drugs, neurotransmitters) particularly from the autonomic nervous system.


In striated muscle, which bands move when contracted vs relax?

Sarcomere, Z-line, H-Band, I-Band


In striated muscle, which bands remain in place when contracted vs relaxed?

A-Band and M-Band


Cardiac muscle is under control of what?

Autonomic nervous system


Cardiac muscle forms the striated muscle known as:

Heart tissue


Cardiac muscle is adapted to be?

Highly resistant to fatigue: it has a large number of mitochondria (ATP-synthesis), enabling continuous aerobic respiration via oxidative phosphorylation.


What does the cardiac muscle contain?

Numerous myoglobins (oxygen-storing pigment) and good blood supply, which provides nutrients and oxygen.


What does the cardiac muscle require?

Extracellular calcium ions for contraction (unlike skeletal muscle where Ca++ is provided from the ER via channels upon activation).


Cardiac muscle has large what?

Very large T-tubules (ER-like invaginations that allow depolarization of the membrane to quickly penetrate to the interior of the cell).


How is skeletal muscle controlled?

Somatic nervous system = voluntarily controlled


How many skeletal muscles are there in the human body?

About 640.


Skeletal muscles are usually attached to bones by what?

Bundles of collagen fibers (tendons)


What is skeletal muscle composed of?

Myocytes (muscle cells) that contain myofibrils.


The plasma membrane of myocytes is known as what? The cytoplasm?

Sarcolemma, the cytoplasm known as the sarcoplasm (contains the myofibrils).


What surrounds the myofibrils and what does it do?

The sarcoplasmic reticulum (instead of ER) surrounds the myofibrils and holds a reserve of the calcium ions needed to cause a muscle contraction.


What transmits an action potential in skeletal muscle?

Enlarged "sacs" of sarcoplasmic reticulum (terminal cysternae) are connected by T-tubules that transmit an action potential leading to Ca++ release and troponin activation.


What are the two major types of skeletal muscle fibers?

Type I: Slow twitching type
Type II: Fast twitching type
Muscles may be a mix of both types, depending on their tasks.


What are the two subtypes of skeletal muscle fibers?

Type IIA: Semi-fast twitchers
Type IIB: Fast twitchers


What is true for a beef tenderloin?

It contains large amounts of myosin II.


In striated muscle, where are the plus and minus ends located?

Plus end of actin filament located near Z-line. Minus end located near H zone.


What is troponin made of?

Troponin C, I, and T


Where is troponin located?

Skeletal and cardiac muscle, but absent in smooth muscle (replaced by calponin and other component)


What does troponin do?

Regulates myosin-actin interactions in sarcomeres via tropomyosin. Ca++ dependent: action potential from nerves opens channels in sarcoplasm.


What is tropomyosin made of?

Coiled-coil complex made of four alpha-helical chains, named A-D.


Where is tropomyosin located?

Smooth, skeletal, and cardiac muscle.


What does tropomyosin do?

Regulates myosin-actin interactions in sarcomeres together with troponin (in the absence of Ca++ troponin-T blocks the myosin binding site on the thin filament).


Certain tropomyosins are known to cause what?

Allergies (e.g. from shrimp mollusks => seafood allergies)


What is titin and where is it found?

Large abundant protein of striated muscle.
1. Flexible protein made out of 244 modules which unfold under tension, and refold when relaxed.
2. Largest known protein with the largest numbers of eons (363) and the longest single exon known (17,106 bp).
3. Human variant consists of 34,350 residues ~ 3.8MDa (CHNOS)
4. Connects between the Z-line and the M-line of the thick filaments, thereby maintaining their position (A-band) between Z-lines (hence, a single titin molecule spans half of the sarcomere length).


What is Nebulin and where?

1. Large abundant protein of striated muscle.
2. 600-900 kDa protein localized to the I-band of the sarcomeres in skeletal muslce.
3. Nebulette (in cardiac muscle) = ~107 kDa
4. Connects along ~200 actin monomers along the thin filament => considered the sarcoplasmic ruler defining the length of the sarcomeres.