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Cilia and Flagella

Figs 22-6 through 22-8

   

Myosins & Actin-Based Cell Motility
 

Myosins

Type 2:  forms filaments (bipolar or bidirectional) and is found in muscle cells

Types I and V bind membranes

Involved in vesicle transport and other membrane-associated motility
 

Muscle Myosin

Rod-shaped protein, 510,000 MW

Six subunits

2 heavy chains

4 light chains (2 pairs)

Actin binding site

ATPase activity

Forms bi-directional filaments

 

Muscles:

     

Structure - Function

Striated

Large amounts of tension, rapid contraction speeds, narrow range of contraction

Subtypes
 
 

Muscles:in vertebrates

Structure - Function
 
 

Cardiac

Large tension, prolonged coordinated contraction, narrow range of lengths

 
 

Smooth

Slow onset and speed of contraction, low tension, prolonged contractions, wide range of lengths

   

Striated Muscle Terminology

I Band - thin filaments

A Band - thick filaments

Titin - flexible protein, connects tick filaments to Z line

Z line - site of thin filament attachment via a actinin & CapZ

Striated Muscle Terminology

Sarcomere - Z line to Z line

H Zone - in A band; thick filaments only

M Line

holds thick filaments in register

Contains myomesin

   

During contraction:

I bandsand H Zones decrease in length

A bands remain the same length
 

   

Conclusion???
 

   

Thin Filament proteins

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
 

     

Depletion of ATP?

Rigor mortis

Length ? Tension Experiment

Results can be predicted from the structure of the muscle fiber