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Cytoskeleton: Structure, Function, and Types - Cell Biology Lecture Notes, Schemes and Mind Maps of Cell Biology

Université Badji MokhtarCell Biology

A comprehensive overview of the cytoskeleton, a dynamic network of protein filaments essential for cell structure, shape, and movement. It delves into the three main types of cytoskeletal filaments: microfilaments, intermediate filaments, and microtubules, explaining their composition, structure, and roles in cellular processes. The document also highlights the importance of the cytoskeleton in maintaining cell shape, facilitating organelle movement, and enabling cell motility.

Typology: Schemes and Mind Maps

2023/2024

Available from 01/11/2025

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Cell Biology
Badji Mokhtar University
Introduction:
All cells have a support network of biological protein polymers: thin filaments, sometimes referred
to as fibers or tubules.
They are classified into three categories: microfilaments, intermediate filaments and microtubules.
• The cytoskeleton is located in:
Cell periphery, in the cytoplasm and nucleoplasm
• The cytoskeleton is a dynamic system that assembles and constantly disassembling requiring
Energy ( GTP and ATP)
1. Microfilaments :
These are extremely fine filaments (7nm in diameter) made up of a protein called actin. Each actin
filament is made up of two strands of subunits arranged in rosary beads, twisted together like a
rope. These globular subunits are stabilized by calcium ions and associated with ATP molecules that
supply the energy required for the contractile mechanism.
• Example:
In striated muscle cells, actin filaments associated with fibers consisting of
another protein called myosin.
Contraction occurs when actin and myosin filaments slide along each other, powered by the energy
released by the associated ATP molecules.
• Cells that are not considered contractile also contain globular actin subunits (Actin G) that
rapidly assemble into microfilaments (Actin F) and then dissociate, providing the cell with a
dynamic structural network.
Cytoskeleton
2024/2025
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Download Cytoskeleton: Structure, Function, and Types - Cell Biology Lecture Notes and more Schemes and Mind Maps Cell Biology in PDF only on Docsity!

Introduction:

All cells have a support network of biological protein polymers : thin filaments , sometimes referred to as fibers or tubules. They are classified into three categories : microfilaments, intermediate filaments and microtubules.

  • The cytoskeleton is located in: Cell periphery , in the cytoplasm and nucleoplasm
  • The cytoskeleton is a dynamic system that assembles and constantly disassembling requiring Energy ( GTP and ATP)

1. Microfilaments :

These are extremely fine filaments ( 7nm in diameter ) made up of a protein called actin. Each actin filament is made up of two strands of subunits arranged in rosary beads, twisted together like a rope. These globular subunits are stabilized by calcium ions and associated with ATP molecules that supply the energy required for the contractile mechanism.

  • Example: In striated muscle cells, actin filaments associated with fibers consisting o f another protein called myosin. Contraction occurs when actin and myosin filaments slide along each other, powered by the energy released by the associated ATP molecules.
  • Cells that are not considered contractile also contain globular actin subunits ( Actin G ) that rapidly assemble into microfilaments ( Actin F ) and then dissociate , providing the cell with a dynamic structural network.
  • Beneath the plasma membrane, actin, in association with various transmembrane proteins and binding proteins (especially filamin ), forms a solid support network called the " cell cortex ", protecting cells from deformation while allowing them to adapt to morphological changes.

2. Intermediate filaments :

  • As their name suggests, these filaments are intermediate in size between microfilaments and microtubules ( 10 - 15 nm in diameter ). Their role is purely structural and fundamental : they are not involved in cell motility.
  • These protein filaments join together to form larger filaments and link intracellular structures to each other and to plasma membrane proteins, forming a resistant framework for cells and tissues.

3. Microtubules:

  • They are much larger than microfilaments ( 24 nm in diameter ), and like them, are made up of globular protein subunits capable of associating and dissociating easily to prevent alterations in cell shape and organelle position.
  • Microtubules originate in a specialized organizing center, the centriole. Microtubule subunits are of two types : Alpha and Beta tubulin , and polymerize to form a hollow tubule. A cross- section shows 13 tubulin molecules arranged in a circular pattern.
  • Microtubule-associated proteins (MAPs ) act as " caps " on the extended ends of microtubules. (called also motor proteins) Two binding proteins , Dynein and Kynesin ( which can move along the tubules towards or away from the cell center, respectively ) can attach to membrane-bound organelles (such as vesicles and mitochondria ), allowing them to move inside the cytoplasm along the "rails". The function of the spindle during cell division is a classic example of this mechanism.