Exam review continues; see Dr. K-I-A

Letís get the AIDS $$$$$$ coming in, please!

Other Business???

And at this time of the semester, a comforting word from Dr. K-I-AÖ.
 
 
 
 

Tropomyosin

64,000 MW

Long, filamentous molecule

Covers myosin binding sites on actin units of thin filaments

Troponin

TnC

Ca⁺⁺ binding subunit

Related to calmodulin

TnI (Inhibitory)

Inhibits muscle contraction as Troponin sits on tropomyosin

TnT

Binds to tropomyosin
 
 

Contractions

Isometric

Isotonic

Step 1 in Muscle Contraction
(see Fig 23-18)

Myosin has ADP and Pi bound to it in the high energy configuration

In the presence of Ca⁺⁺, myosin in this configuration binds actin of thin filaments

Called a Cross Bridge (x bridge)

The Pi is released
 
 

Step 2 in Muscle Contraction
(see Fig 23-18)

ADP is released from myosin and headpiece changes angle

Called the Power Stroke

Muscle shortens
 
 

Step 3 in Muscle Contraction
(see Fig 23-18)

ATP replaces ADP

Myosin releases from actin

Note: without ATP ---> the myosins remain attached tot he thin filaments

rigor mortis
 
 

Step 4 in Muscle Contraction
(see Fig 23-18)

ATP on myosin is hydrolyzed

Results in ADP and Pi bound to myosin

Myosin headpiece is now in the high energy, cocked position

Regulation of Contraction

Release and Sequestration of Ca⁺⁺ by the sarcoplasmic reticulum
 
 

Can we put the whole thing together?

Excitation contraction coupling
 
 
 
 

NOTE: The following graph has the correct y axis. Be sure to note this change in this figure as presneted in lecture.

Features of Striated Muscle

Striated pattern

Large tension

Narrow range of lengths

Rapid onset and cessation of contraction

Thin filament regulation of excitation

Features of Cardiac Muscle

Striated Pattern

Large tension

Narrow range of lengths

Coordinated contraction & relaxation

Prolonged contraction

Thin filament regulation of excitation

Features of Smooth Muscle

No striations

Little tension

Slow onset and relaxation

Works over wide range of lengths

Thick filament regulation of excitation
 
 

Smooth Muscle Length ? Tension Cureve

Relaxation of Smooth Muscle

MLC Phosphatase

Inactivated by Ca⁺⁺ - calmodulin