Sliding Filament Theory

 

Study Questions on the Sliding Filament Theory:

1.     According to the sliding filament theory, when a muscle cell contracts, the _THICK__ filaments slide past the _THIN____ filaments and the __SARCOMERE__ shortens.

 

 

2. List the six most important chemicals involved in muscle contraction.

 a. Myosin        b. Actin            c. Tropomyosin          d. Troponin        e. ATP        f. Ca2+

 

 

 

 

3. Where is myosin found in skeletal muscle cells?

a. in the thin filaments

b. in the thick filaments

c. in the sarcoplasmic reticulum

d. in the terminal cisternae

e. in the T tubules

 

4. What two important binding sites are found on the cross bridges (heads) of myosin?

 a. ATP        b. Actin

 

 

5. What three protein molecules are the thin filaments made of?

 

 Actin, Troponin, and Tropomyosin

 

6.     Actin contains binding sites for __myosin_____________.

 

 

 

7.     What is the function of tropomyosin?

 

     Covers binding sites on actin filaments in inactive (non-contracting) muscle.

 

8. What is the function of troponin?

 

 Binds Ca2+ and drags the tropomyosin away from the myosin binidng sites.

 

9. Identify the parts of the thin filament below.

       A. Actin        B. Tropomyosin        C. Troponin

 

10. What causes the tropomyosin to move away from the myosin binding sites on the actin?

 

  The binding of Ca2+ to a subunit of troponin

 

 

11. What causes the release of calcium ions into the cytosol from the terminal cisternae?

 

  A nerve impulse (action potential) that causes depolarization of the sarcolemma. 

 

12. What causes the myosin binding sites on actin to be exposed?

 

 Movement of tropomyosin following binding of Ca2+ to troponin.

 

13. What causes the tropomyosin to cover back over the actin binding sites?

 

 Pumping of Ca2+ from the sarcoplasm back into the sarcoplasmic reticulum.

 

14. What is required to move the calcium ions from the cytosol back into the sarcoplasmic reticulum?

 

 Ca2+ pumps in the sarcoplasmic reticulum that use the energy of ATP to carry out active transport.

 

15. After a sarcomere has contracted fully and the calcium ion concentration within the cytosol decreases, what happens within the sarcomere?

 

 The sarcomere lengthens due to the elasticity of the muscle and attached connective tissues.  (Remember, this is passive; muscles can only SHORTEN with force).