Week 5 Muscles 2

Question 1

What is the contractile unit of myofibrils?

Answer 1

Actin and myosin2 (aka the myofilaments)

Question 2

Sarcomere

Answer 2

Basic contractile unit defined by the Z line, an actin and myosin array

Question 3

Why is the nucleus typically pushed off to the side in a muscle cell?

Answer 3

Because the actin and myosin myofilaments take up so much room in the muscle cell

Question 4

What is the reservoir for calcium in myofibrils?

Answer 4

Sarcoplasmic reticulum

Question 5

Where is the sarcoplasmic reticulum (sER) in relation to myofilaments (actin/myosin)?

Answer 5

Right next and intertwined. Intimately related*

Question 6

A band

Answer 6

Thick (myosin) and thin (actin) filaments

Question 7

H zone

Answer 7

Subdivision of A band where there is ONLY thick myosin

Question 8

I band

Answer 8

Thin (actin) only, lighter area

Question 9

A band

Answer 9

Actin and myosin area of overlap (thin and thick band). Does not shrink during contraction

Question 10

How do you remember Actin is thin?

Answer 10

actIN thIN = I band

Question 11

What is the Z-line

Answer 11

Defines border of sarcomere, is where the actin MEETS in I band

Question 12

When skeletal muscle contracts what happens to H zone and I band?

Answer 12

They get smaller

Question 13

Thin filaments contain what regulatory proteins? What do they do?

Answer 13

Troponin and tropomyosin. Regulate interaction between the actin and myosin

Question 14

What anchor actin filaments to the z-line?

Answer 14

Alpha-actinin protein

Question 15

What type of myosin is found in skeletal muscle?

Answer 15

Myosin 2

Question 16

Myosins are a family of ______ proteins

Answer 16

Motor

Question 17

Myosins are ________ enzymes

Answer 17

ATPase

Question 18

What is the moving part of muscle contraction?

Answer 18

Myosin

Question 19

Tropomyosin

Answer 19

Laterally associated with actin (looks like it wraps around it). CONTRACTILE force

Question 20

Troponin

Answer 20

Complex of 3 subunits. Acts to inhibit tropomyosin, but is sensitive to Ca. Therefore, with Ca present, there is no inhibition

Question 21

Tropomodulin

Answer 21

Small actin binding protein that “caps” the end of actin near the H band in the middle

Question 22

Nebulin

Answer 22

Large inelastic protein, acts as stabilizer of the actin filaments, safety net to keep actin filaments from disassembling

Question 23

Titin

Answer 23

Prevents excessive stretch and helps restore the sarcomere length

Question 24

Dystrophin

Answer 24

Links the ECM protein laminin to the actin filaments within the myofibril

Question 25

Desmin

Answer 25

Intermediate filament protein, maintains a lattice supporting the sarcomere and links myofibrils throughout the muscle fascicle ***anchors sarcomere to sarcolemma”

Question 26

What is the plasma membrane called in muscle?

Answer 26

Sarcolemma

Question 27

Myosin in unbent configuration

Answer 27

looks bent myosin is holding actin, no ATP

Question 28

Myosin in “bent” configuration

Answer 28

looks straight ATP binds to myosin head, myosin released actin

Question 29

What is “recovery stroke”?

Answer 29

When myosin resumes resting unbent configuration with ATP hydrolysis, attaches to actin again but weakly

Question 30

What is the “power stroke”?

Answer 30

With release of inorganic phosphate to allow strong bonding of myosin to actin again, this allows myosin filaments to slide relative to actin

Question 31

Recap of contraction

Answer 31

Ca release, relieves inhibition of tropomyosin by troponin, myosin head binds to actin in unbent, ATP binds to myosin to change it to bent shape and move down to next actin binding site, hydrolysis released inorganic phosphate to trigger contraction step