Lecture Notes on Myofibrils, Actin, and Myosin Filaments

Introduction to Myofibrils

• Myofibrils have distinct zones characterized by light and dark areas.
  • Light areas: Thin filaments (Actin filaments)
  • Dark areas: Thick filaments (Myosin filaments)

Actin Filament Composition

• Actin Filament Structure
  • Comprised of globular proteins known as actin.
  • Globular proteins are spherical or ball-shaped.
  • Actin filament: Long structure formed by globular actin proteins joining together.
  • Bonds such as covalent bonds are involved in forming the filament.
• Additional Components of Actin Filament
  • Troponin
    • Protein molecule that acts as a calcium ion receptor.
    • Detailed function to be covered in future lectures.
  • Tropomyosin
    • Fibrous, linear-shaped protein.
    • Covers actin filament to prevent attachment with myosin heads.

Exam Tips

• To describe an actin filament:
  • Mention it is a thin filament.
  • Composed of actin proteins, troponin, and tropomyosin.

Introduction to Myosin Filament

• Structure
  • Thick filament held together by the M line.
  • Myosin filament has extensions described as many arms or heads.
  • These extensions are referred to as myosin heads.
• Orientation
  • Myosin heads face away from the M line.
  • Connection with actin filaments during muscle contraction will be discussed in future lectures.

Enzymatic Function of Myosin Heads

• Myosin heads can act as enzymes by:
  • Receiving ATP molecules.
  • Hydrolyzing ATP into ADP and phosphate.
  • Function as ATPase, an enzyme that hydrolyzes ATP.

Teaching Strategy

• Concepts are introduced in small, digestible chunks to avoid overwhelming students.
• Future videos will elaborate on connections between actin and myosin filaments and their roles in muscle contraction.