Exam 4 - Myosins and Muscle slides

Question 1

How many subgroups of myosin’s are there?

Answer 1

18

Question 2

What does Myosin I do?

Answer 2

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

Question 3

What does Myosin II do?

Answer 3

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

Question 4

What does Myosin IV do?

Answer 4

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

Question 5

What does Myosin V do?

Answer 5

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.

Question 6

What does Myosin VI do?

Answer 6

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”

Question 7

What does Myosin VIII do?

Answer 7

Plant-specific myosin involved in cell division.

Question 8

Myosin II leads to what formation?

Answer 8

Thick filament formation

Question 9

What is RLC and ELC?

Answer 9

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

Question 10

What do Rab GTPases do?

Answer 10

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

Question 11

What does phosphorylation of the tail domain do?

Answer 11

Causes the myosin to release its cargo

Question 12

What is melanophilin?

Answer 12

Carrier protein and Rab effector protein.

Question 13

What are muscles derived from?

Answer 13

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

Question 14

What are the three types of muscle?

Answer 14

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

Question 15

What are some examples of smooth muscle tissue?

Answer 15

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

Question 16

What does smooth muscle tissue contain?

Answer 16

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

Question 17

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

Answer 17

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

Question 18

How are contractions controlled in smooth muscle tissue?

Answer 18

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.

Question 19

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

Answer 19

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

Question 20

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

Answer 20

A-Band and M-Band

Question 21

Cardiac muscle is under control of what?

Answer 21

Autonomic nervous system

Question 22

Cardiac muscle forms the striated muscle known as:

Answer 22

Heart tissue

Question 23

Cardiac muscle is adapted to be?

Answer 23

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

Question 24

What does the cardiac muscle contain?

Answer 24

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

Question 25

What does the cardiac muscle require?

Answer 25

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

Question 26

Cardiac muscle has large what?

Answer 26

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

Question 27

How is skeletal muscle controlled?

Answer 27

Somatic nervous system = voluntarily controlled

Question 28

How many skeletal muscles are there in the human body?

Answer 28

About 640.

Question 29

Skeletal muscles are usually attached to bones by what?

Answer 29

Bundles of collagen fibers (tendons)

Question 30

What is skeletal muscle composed of?

Answer 30

Myocytes (muscle cells) that contain myofibrils.

Question 31

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

Answer 31

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

Question 32

What surrounds the myofibrils and what does it do?

Answer 32

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

Question 33

What transmits an action potential in skeletal muscle?

Answer 33

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

Question 34

What are the two major types of skeletal muscle fibers?

Answer 34

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

Question 35

What are the two subtypes of skeletal muscle fibers?

Answer 35

Type IIA: Semi-fast twitchers

Type IIB: Fast twitchers

Question 36

What is true for a beef tenderloin?

Answer 36

It contains large amounts of myosin II.

Question 37

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

Answer 37

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

Question 38

What is troponin made of?

Answer 38

Troponin C, I, and T

Question 39

Where is troponin located?

Answer 39

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

Question 40

What does troponin do?

Answer 40

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

Question 41

What is tropomyosin made of?

Answer 41

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

Question 42

Where is tropomyosin located?

Answer 42

Smooth, skeletal, and cardiac muscle.

Question 43

What does tropomyosin do?

Answer 43

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).

Question 44

Certain tropomyosins are known to cause what?

Answer 44

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

Question 45

What is titin and where is it found?

Answer 45

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).

Question 46

What is Nebulin and where?

Answer 46

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.