Table of Contents
- Kinetochore Structure – Understanding the Structure and Function
- Kinetochore Structure – Regions of Kinetochore
- Frequently Asked Questions about Kinetochore Structure
Kinetochore Structure – Understanding the Structure and Function
Kinetochores are large protein assemblies that help in chromosome segregation during cell division in eukaryotes. It is present in the centromere of the chromosome and attaches the chromosome to the spindles of the microtubules. In order to assemble a functional kinetochore, the size of chromosomes vary from species to species. In humans, the size of chromosome segments can range from 45 to 248 million base pairs (bps).
Kinetochores consist of different types of proteins. When we look at the simplest kinetochore, it is made up of more than 19 different proteins including histone. Some other proteins are dynein and kinesin. During mitosis, the chromosomes move with the help of forces generated by these two proteins.
Since it is present in the centromere, note that one centromere contains only one kinetochore complex in it. When talking about structure, it has two regions, i.e., the inner kinetochore and the outer kinetochore as well as a fibrous corona. Observing a kinetochore is only possible with the help of an electron microscope because of its limited visibility under different conditions and circumstances.
Kinetochore Structure – Regions of Kinetochore
The earlier studies of kinetochore (of vertebrates) in electron microscopy revealed that kinetochore is a trilaminar structure. It is approximately 20 nanometres (nm) wide and 80 nm deep. It has three different regions – an inner and outer layer, and a fibrous corona. All of them have different roles to play during cell division (separation of sister chromatids). Every chromatid has its own kinetochore.
Inner Region of Kinetochore Structure
While closely examining the kinetochore structure, you will find that the inner layer is connected with the centromere. It is in close proximity to the centromeric DNA. The inner layer contains nucleosomes made up of histones (CENP-A to be particular) which substitutes the H-3. It holds the two sister chromatids together.
Outer Region of Kinetochore Structure
The outer layer is connected to the microtubules. As described earlier for kinetochore, it interacts with the spindle microtubule; it is the outer part to be specific. In vertebrates, it has about 20 different sites for binding kinetochore to microtubules.
Fibrous Corona
This is an expanded mesh like structure which is formed on the outer layer of the kinetochore structure. The fibrous corona helps to regulate the microtubule and outer layer attachment. It is made up of a network of temporary and permanent proteins and is formed on unattached kinetochores.
The location and organisation of these regions helps equally in cell division. They play an equally important role in mitosis and meiosis.
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