Cell Types and Subcellular Structures Lecture

Course: 4BBY1030 Cell Biology & Neuroscience
Instructor: Dr. Clemens Kiecker
Date: October 2024

Learning Outcomes

By the end of the lecture, students should be able to:

• Explain the terms microfilament, intermediate filament, and microtubule.
• Describe the structure and polymerization of actin and the function of myosin.
• Discuss the properties of tubulin and microtubules and how tubulin polymerizes.
• Explain the role of the cytoskeleton in maintaining cell structure, shape, and motility.
• Understand the role of motor proteins (kinesin and dynein) in organelle transport and their ATP dependence.

Cytoskeleton Overview

• Classes of cytoskeleton:
  • Microfilaments (actin)
  • Intermediate filaments
  • Microtubules

Actin and Microfilaments

• Actin:
  • Present in all eukaryotic cells.
  • Found in structures like microvilli, smooth muscle cells, etc.
  • Organized in bundles or networks, defining cell shape and structure.
  • Involved in exerting force, cell movement, and division.
• Actin Structures:
  • Stress fibres, lamellipodia, and filopodia in motile cells.

Actin Molecule

• Most abundant in eukaryotic cells (375 amino acids, 55 kDa monomer).
• Binds ATP/ADP, with mutations causing disorders like muscular dystrophy.

Actin Polymerization

• G-actin polymerizes into F-actin (microfilaments).
• Features treadmilling where molecules migrate from the barbed to pointed end.
• Regulated by ~60 actin-binding proteins.

Actomyosin in Muscle Contraction

• Actomyosin filaments in muscle fibers facilitate contraction via sarcomeres.

Intermediate Filaments

• Provide stability and cohesion, supporting against mechanical stress.
• Keratin: Mutations can cause epidermolysis bullosa.
• Nuclear Lamins: Important for structural support in the nucleus.

Microtubules

• Main component of the mitotic spindle, originating in MTOCs like the centrosome.
• Substrate for organelle transport and major component of cellular cilia.
• Stability regulated by microtubule-associated proteins.

Drugs Affecting Microtubules

• Colchicine: Inhibits formation, used for gout treatment.
• Nocodazole: Synthetic, used in cancer chemotherapy.
• Taxol: Stabilizes microtubules, used in cancer treatment.
• Vinblastine: Inhibits formation, used in chemotherapy.

Motor Proteins

• Kinesin: Moves towards microtubule plus end, using ATP.
• Dynein: Moves towards minus end, involved in axonal transport and cilia movement.
• No motor proteins act on intermediate filaments.

Ciliary Function

• Dynein helps cilia beat, important for functions like mucus removal and sperm motility.
• Mutations can lead to disorders such as Bardet-Biedl Syndrome.

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