Part Four: Myosin & Actin Filaments of the Sarcomere

Question 1

Name parts “E” and “F.”

(Note: This filament is simplified in this diagram. In real life it is

much thicker with many more “E” structures.)

Answer 1

E= myosin head F= myosin filament

Question 2

Structure “D” is named after its chain of protein “beads” called actin.

What is “A” in the diagram (light area on bead structure)?

What happens at “A” during a muscle contraction?

Answer 2

A= active site (on actin) The active site is like a “sticky

spot” on actin that the myosin head attaches to during a

contraction.

Question 3

Name parts “B” through “D.”

Answer 3

B= troponin C= tropomyosin D= actin filament (The actin

filament contains actin, troponin, and tropomyosin.)

Question 4

The proteins “B” and “C” have control over whether the myosin heads

are attached to actin or not. Name “C” and tell its role in this job.

Answer 4

Tropomyosin (“C”) helps control when myosin can attach to actin

in muscle because it covers the active sites on the actin

filament.

Question 5

Calcium that is released from the sarcoplasmic reticulum attaches to

protein “B” to begin a muscle contraction. What does this calcium

cause to happen that allows the muscle contraction to start?

Answer 5

The calcium released from the sarcoplasmic reticulum (SR)

sticks/binds to troponin (“B”). Troponin is like a limp “hand”

holding onto tropomyosin. When calcium binds to troponin, it

pulls tropomyosin off of the active sites. Once the active sites

are uncovered, the myosin heads can now attach to the active

sites on actin to begin a muscle contraction.