The key difference between actin filaments and microtubules is that actin filaments are the smallest type of filamentous proteins made from actin while microtubules are the largest type of filamentous proteins made from tubulin.
The cytoskeleton is the skeleton of the cell and is responsible for giving structure and support to the cell. It is an important component of the cytosol of the cytoplasm. In animal cells, the cytoskeleton is made up of three main proteins: microfilaments, microtubules and intermediate filaments.
CONTENTS
1. Overview and Key Difference
2. What are Actin Filaments
3. What are Microtubules
4. Similarities Between Actin Filaments and Microtubules
5. Side by Side Comparison – Actin Filaments vs Microtubules in Tabular Form
6. Summary
What are Actin Filaments?
Actin filaments, also known as microfilaments, are the narrowest protein filaments found in the cytoskeleton. They are made of a protein called actin. Their diameter is about 6 nm. They are arranged like long spiral chains. Moreover, actin filaments have two structurally different ends, which are plus and minus ends. Actin filaments slide along another type of filaments called myosin in muscle cells. Therefore, in muscle cells, both actin filaments and myosin form sarcomeres, which are important for muscle contraction.
Figure 01: Actin Filaments
In addition to its role in muscle contraction, actin filaments also serve several important functions in the cell. In animal cell division, a ring made of actin and myosin pinches the cell apart to generate two new daughter cells. Moreover, a network of actin filaments located beneath the cell cortex provides shape and structure to the cell.
What are Microtubules?
Microtubules are the largest protein filaments found in the cytoskeleton. They are made of a protein called tubulin. Tubulin proteins have two subunits as alpha-tubulin and beta-tubulin. These protein subunits string together and form long protofilaments. Thirteen protofilaments come closer and arrange to form a hollow straw-like structure, which is a microtubule. Their diameter is about 25 nm. Microtubules can grow and shrink by the addition or removal of tubulin proteins. Two ends of the microtubule are known as the plus end and minus end.
Figure 02: Microtubules
Basically, microtubules provide strength to the cell. Apart from that, microtubules help the cell resisting compression forces. Moreover, they assemble into a structure called spindle during the cell division.
What are the Similarities Between Actin Filaments and Microtubules?
- Actin filaments and microtubules are two of the three main cytoskeletal components.
- They are made up of filamentous proteins.
- They participate in providing mechanical support to the cell.
- Both actin filaments and microtubules have plus and minus ends, so both actin filaments and microtubules are polar.
- They can grow and shrink quickly by the addition or removal of monomer proteins.
What is the Difference Between Actin Filaments and Microtubules?
Actin filaments and microtubules are two types of protein fibres found in the cytoskeleton. Actin filaments are the smallest filaments made up of actin proteins. Microtubules are the largest filaments made up of tubulin proteins. So, this is the key difference between actin filaments and microtubules. Moreover, actin filaments are thin and flexible, while microtubules are thick and stiff. Furthermore, actin filaments are solid rods, while microtubules are hollow straw-like tubes.
The below infographic shows more comparisons related to the difference between actin filaments and microtubules.
Summary – Actin Filaments vs Microtubules
The cytoskeleton of a cell consists of microtubules, actin filaments, and intermediate filaments. Microtubules are the largest of the three types of cytoskeletal fibres. They are made up of tubulin protein filaments. In contrast, actin filaments are the smallest, and they are made up of actin protein filaments. Actin filaments have a two-stranded lattice, and they are thin and flexible protein filaments. Microtubules have a hollow, thirteen-stranded lattice and they are thicker and much stiffer. Thus, this is the summary of the difference between actin filaments and microtubules.
Reference:
1. “Microtubules, Filaments | Learn Science At Scitable”. Nature.Com, 2020, Available here.
2. “The Cytoskeleton (Article) | Khan Academy”. Khan Academy, 2020, Available here.
Image Courtesy:
1. “MEF microfilaments” By Y tambe – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Tubulin Infographic” By PKS615 – Own work (CC BY-SA 4.0) via Commons Wikimedia