Muscle

Question 1

Titin

Answer 1

Elastic protein that connects myosin to Z-disk. Spring-like action keeps myosin centered in sarcomere

Question 2

Nebulin

Answer 2

Inelastic protein attached to Z-disk, and parallels actin

Question 3

Myomesin

Answer 3

Myosin binding protein that holds myosin filaments in register at M-line

Question 4

C protein

Answer 4

Myosin binding protein with function similar to myomesin

Question 5

Alpha-actinin

Answer 5

Bundles actin filaments into parallel arrays.

Anchors actin filaments to Z-disk

Question 6

Desmin

Answer 6

Intermediate filament that helps bind myofibrils to each other. Encircles Z-disk. Interlinked by plectin protein

Question 7

Dystrophin

Answer 7

Actin binding protein. It may anchor muscle membrane proteins to actin

Question 8

Duchenne muscular dystrophy patients

Answer 8

Lack dystrophin

Question 9

What regulates in vivo polymerization of actin?

Answer 9

Thymosin 𝝱-4 & profilin

Question 10

What does the A band contain?

Answer 10

Thick myofilaments & thin myofilaments

Question 11

What does the I band contain?

Answer 11

Thin myofilaments (attached to Z disk)

Question 12

What does the H band contain?

Answer 12

Myosin (no heads) & creatine kinase

Question 13

What does creatine kinase do?

Answer 13

Catalyzes:

ADP + phosphocreatine –> ATP

Question 14

What is the M line?

Answer 14

Region of myomesin linking with myosin

Question 15

What is the Z disk?

Answer 15

Attachment region of thin filaments. It contains 𝝰-actinin

Question 16

What does tropomyosin do?

Answer 16

Binds 3 troponin peptides, Tn-T, Tn-I, and Tn-C

Question 17

What does Tn-T do?

Answer 17

Binds Tn complex to tropomyosin

Question 18

What does Tn-I do?

Answer 18

Inhibits binding of actin to myosin, with help of tropomyosin

Question 19

What does Tn-C do?

Answer 19

When Ca ions bind Tn-C, it releases the Tn-I-tropomyosin inhibition of the actin activation of myosin ATPase

Question 20

What is tropomyosin?

Answer 20

Protein dimer (35K MW) that lies in grooves of actin helix

Question 21

What does plectin do?

Answer 21

Interlinks filaments of desmin

Question 22

What is 𝝰𝝱-crystallin?

Answer 22

A heat-shock protein that protects desmin from stress-induced damage

Question 23

Sarcoglycanopathies (limb-girdle muscular dystrophies)

Answer 23

Mutations in genes for sarcoglycans causes defective assembly of sarcoglycans. This disrupts the interaction with other proteins & association of sarcolemma with the ECM

Question 24

Cardiac muscle cell

Answer 24

Single, centrally located nucleus

Question 25

What makes cardiac muscle fibers unique?

Answer 25

Their composition of several cardiac muscle cells joined end-to-end by intercalated disks

Question 26

What comprises intercalated disks?

Answer 26

A transverse portion–containing fasciae adherens (actin filament anchor site) and macula adherens (desmosomes)–that binds adjacent cells together, and a lateral portion (gap junctions) that ionically couples adjacent cells

Question 27

What three changes manifest in cardiocytes following a myocardial infarction?

Answer 27

• eosinophilic cytoplasm
• pyknotic nuclei (condensed chromatin)
• inflammatory cells infiltrate after 3 days

Question 28

What characterizes smooth muscle cells?

Answer 28

Spindle shape, but may branch
Single, central, oval nucleus, w/1 or more nucleoli
Surrounded by basal lamina, may secrete collagen & elastin
Does not have sarcomeres

Question 29

Where are single smooth muscle cells found?

Answer 29

These myoepithelial cells of ectodermal origin are found: around sweat, salivary, mammary & lacrimal glands

Question 30

Where is smooth muscle of mesodermal origin found?

Answer 30

In circulatory, digestive, respiratory & reproductive tracts

Question 31

Where is smooth muscle of ectodermal origin found?

Answer 31

In the iris & cilliary body of the eye

Question 32

What comprises the functional equivalent of a Z disk in smooth muscle?

Answer 32

Membrane associated & cytoplasmic dense bodies that contain 𝝰-actinin