Cytoskeleton

Overview of the Lecture

  • Introduction to the Cytoskeleton

    • Cute lecture award for its engaging content.

    • Reminder about upcoming seminars:

    • Microbiologist BEP Austin on Monday.

    • Entomologist at EB seminar on Tuesday.

  • Important Exam Information

    • Exam Two: Scheduled for one week from today.

    • Last lecture covering material for Exam Two.

    • Additional lecture on nuclei included for the first time.

    • No answer key for practice questions provided by Notion.

    • Dr. Dalton and the presenter will create a study tool to assist in organizing material.

    • Emphasis on detail and blended concepts across lectures.

Major Functions of the Cytoskeleton

  • Key points to understand by the end of the lecture:

    1. Major functions of the cytoskeleton.

    2. Building blocks of the cytoskeleton.

    3. Unique shared and distinct features of cytoskeletal components.

    4. Interaction between "rails" (cytoskeletal filaments) and "engines" (motor proteins).

  • The cytoskeleton addresses four primary issues:

    1. Maintaining cell shape.

      • Prevents cell collapse, provides internal structure.

    2. Cell motility.

      • Facilitates movement of the cell itself.

    3. Cargo transport within cells.

      • Moves cellular components efficiently.

    4. Cell division.

      • Organizes and aids in the division process.

The Structure and Components of the Cytoskeleton

Major Building Blocks

  • Main Components (Rails):

    • Microfilaments (Actin Filaments): Smallest type of filament.

    • Microtubules: Largest, made of tubulin.

    • Intermediate Filaments: Intermediate in size, variable in composition (e.g., keratin, vimentin).

  • Engines:

    • Kinesin

    • Dynein

    • Myosin

  • Prokaryotical Presence:

    • Prokaryotes have simpler cytoskeletal structures than eukaryotes.

    • Eukaryotic cytoskeleton is more similar to archaea than bacteria due to evolutionary history.

Types of Filaments

Microfilaments (Actin Filaments)

  • Structure: Double-stranded, helical formation.

  • Components: Made of globular (G-actin) monomers that polymerize into filamentous (F-actin).

  • Functions:

    • Serve as tracks for myosin.

    • Involved in amoeboid movement, where they polymerize at the leading edge of the cell (lamellipodium).

  • Special characteristics of actin polymerization:

    • ATP binding and hydrolysis is crucial for growing filaments.

    • Plus end (fast growth) vs. minus end (slow growth) - Not a charge designation.

Microtubules

  • Structure: Hollow tubes made of heterodimers of alpha and beta tubulin, larger than actin filaments.

  • Functions:

    • Serve as tracks for kinesin and dynein.

    • Arrange in a nine plus two formation for cilia and flagella.

  • Polymerization dynamics involve GTP binding for microtubule growth.

  • Two types of dynamics:

    1. Treadmilling

    2. Dynamic instability—sensing available tubulin in the cell.

Motor Proteins (Engines of Cytoskeleton)

Kinesin

  • General Movement:

    • Moves from minus to plus on microtubules.

    • Structure:

    • Composed of two motor heads and a cargo-binding tail.

    • Steps in an ATP-dependent manner.

  • Mechanics of movement:

    1. Binding: One head attaches to the microtubule.

    2. Conformational Change: ATP binding changes the neck linker, swinging the next head forward.

    3. Release: ATP hydrolysis leads to release of ADP and repositioning for the next step.

Dynein

  • General Movement:

    • Moves from plus to minus along microtubules, opposite to kinesin.

  • Structure and Movement:

    • Similar structural mechanics as kinesin (two heads, cargo-binding mechanisms) but opposite directionality.

Myosin

  • General Movement:

    • Moves along microfilaments, typically from minus to plus.

  • Dynamics:

    • Different myosin types exhibit directionality, some may move in opposite directions.

Cytoskeleton in Health and Disease

  • Viruses co-opting cytoskeleton:

    • Use actin filaments to move within and between cells (example: COVID transmission).

Conclusion and Upcoming Topics

  • Summary of the roles of cytoskeleton in movement, shape maintenance, and transport.

  • Next lecture: Exploration of cellular waste management processes.