Centromeres - Structure, Functions and Types of Centromeres

What are Centromeres?

Centromeres can be defined as the compressed region or a part of elongated chromosomes. It is the specialized DNA sequence in the chromosomes that links or holds together the pair of sister chromatids. The centromeres are also involved in separating the chromosome into a short arm (p) and a long arm (q). 

As per the name, centromeres are not located exactly in the centre but is located at the end of chromosomes. This organelle is also referred to as the chromosome’s arms as they are present on either side of the centromere.

Structure of Centromeres

Structure of Centromeres

According to the examination of centromeres under the light microscope, it is generally believed that the main component of the centromere is the kinetochore, and DNA associated proteins. Centromeres are densely packed with the heterogeneous domain capped by the trilaminar kinetochore. The DNA of the centromeres is normally in a heterochromatin state, and are required during the process of the cohesin complex. This mediates and coordinates with the sister chromatid cohesion after DNA replication and separation during anaphase.

Functions of Centromeres

  1. The centromeres are the point of attachment of the kinetochore. The main functions include the attachment of sister chromatids, and it is the site for attachment of spindle fibre.
  2. Centromeres help in the proper alignment and segregation of the chromosomes during the process of cell division in eukaryotic cells.
  3. Centromeres play an important part in the production of a new cell. When the chromosomes are copied, these centromere serves as a binding site for the two replicated chromosomes, which are known as sister chromatids.
  4. Centromeres are also involved in the sister chromatid adhesion and separation, chromosome movement, microtubule attachment, the establishment of heterochromatin and mitotic checkpoint control. 
  5. Centromeres also function as sophisticated signal processing centres, which are involved in the regulation of  cell cycle progression.

Types of Centromeres

Broadly speaking, there are two main types of centromeres.

Point Centromeres

These are centromeres where the mitotic spindle fibres are attracted to specific sequences of DNA. In this case, the cell proteins bind to these particular DNA sequences and form the foundation for the binding of the mitotic spindle fibres.

Regional Centromeres

Humans and most eukaryotic cells use regional centromeres.

These centromeres are determined during the mitotic spindle binding by a combination of characteristics working together to signal the location of a centromere and not by a precise sequence of DNA.

There are other types of centromere and this classification is mainly based on the location of the centromere on the chromosomes, which includes – Metacentric, Submetacentric, Acrocentric, and Telocentric.

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