The key difference between centromere and kinetochore is that centromere is the region of the chromosome that holds two sister chromatids together after the replication of chromosome while kinetochore is the disc-shaped protein complex of the chromosome that allows spindle fibers to attach during the cell division.
Inheritance of genetic information depends on the proper segregation of chromosomes in the process of mitosis and meiosis. Mitosis is the production of genetically identical daughter cells, while meiosis is the production of daughter cells which contain one pair of each chromosome that was present in the parental cell. Furthermore, the chromosome segregation is an extremely accurate process. Its microstructure and shape are very important for the segregation process. Also, this process totally depends on the integrity of microtubules. The sites of attachment of microtubules, therefore, should have certain specific properties. Centromere and kinetochore are two regions of the chromosomes that play a major role during the cell division. The main aim of this article is to highlight the difference between centromere and kinetochore.
CONTENTS
1. Overview and Key Difference
2. What is Centromere
3. What is Kinetochore
4. Similarities Between Centromere and Kinetochore
5. Side by Side Comparison – Centromere vs Kinetochore in Tabular Form
6. Summary
What is Centromere?
A centromere is a highly constricted region on a chromosome that holds two sister chromatids together in a chromosome. It also allows spindle fibers to attach to it during the process of mitosis and meiosis. These special regions contain non-histone proteins that protect them from endonuclease digestion and they are free of nucleosomes. The major role of the centromere is to provide sites for kinetochores.
Figure 01: Centromere
In eukaryotes, the sizes of the centromeres vary, but all have the same function. Most eukaryotes have monocentric centromeres, where the centromere-kinetochore complex forms at a single point on the chromosome except in some nematodes. Unlike in unicellular organisms, centromeres of multicellular organisms exist embedded within the constructive centric heterochromatin. Centromere has highly specialized repetitive DNA sequences. Furthermore, it only binds with a unique set of proteins. These regions, therefore, chemically differ from the rest of the chromosome.
What is Kinetochore?
Kinetochore is a disc-shaped protein complex present in the centromere region of a chromosome which is in the mitotic or meiotic division. Each chromosome has a kinetochore. The functions of these complexes are to bind microtubules of the spindle bundle and depolarize them during the cell division. Many animal cells contain disc-like kinetochores with three distinct layers that form on one side of each chromatid. The inner layer of the kinetochore is associated with the centromere while the outer layer interacts with microtubules. The function of the middle layer is unknown. The number of bound microtubules to a kinetochore varies with the species. For example, human kinetochore binds approximately with 15 microtubules whereas kinetochore of Saccharomyces binds with only one microtubule.
Figure 02: Kinetochore
In certain organisms like protozoa, some fungi, and insects, kinetochores cannot be visualized as proteins disintegrate during preparation. Unattached kinetochores have extending-fibers that contain many proteins known as corona. These coronas help to capture microtubules during the cell division. The microtubules associated with kinetochores have long lives, while those in the rest of the spindle have very short lives.
What are the Similarities Between Centromere and Kinetochore?
- Both centromere and kinetochore are present in the chromosomes.
- They are extremely important for cell division.
- And, they are visualized during the cell division.
What is the Difference Between Centromere and Kinetochore?
A centromere is a constricted region found on a chromosome with highly specialized, repetitive DNA sequences. Whereas, kinetochore is a disc-shaped protein complex found in the centromere region of the chromosome. So, this is the key difference between centromere and kinetochore. Furthermore, a significant difference between centromere and kinetochore is that centromeres are clearly visible under the light microscope as a constricted region on the condensed chromosome while kinetochores can only be seen with the aid of an electric microscope. Also, unlike in centromeres, there are three different layers in the kinetochore. Hence, this is also a difference between centromere and kinetochore.
Moreover, a further difference between centromere and kinetochore is that the kinetochore has corona while no such structures are found in centromeres. Besides, the centromeres cannot bind with the microtubules. Only the kinetochores that are associated with centromeres have the ability to bind microtubules. Therefore, we can consider this also as a difference between centromere and kinetochore.
Below infographic summarizes the difference between centromere and kinetochore.
Summary – Centromere vs Kinetochore
A centromere is a constriction point in a chromosome. It has highly condensed chromatin around the histone proteins. It holds two sister chromatids of a chromosome together. On the other hand, kinetochore is a protein complex assembled around the centromere of the chromosome. It provides sites for the attachment of microtubules during the cell division. Both centromere and kinetochore ensure the correct division and separation of chromosomes and chromatids during the cell division. Thus, this is the summary of the difference between centromere and kinetochore.
Reference:
1. “Kinetochore.” Wikipedia, Wikimedia Foundation, 22 Feb. 2019, Available here.
2. “Centromere – Definition and Structure.” Study.com, Available here.
Image Courtesy:
1. “Figure 10 02 03” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “Chromosome cohesion – en” By Dawn08 – Own work (CC BY-SA 3.0) via Commons Wikimedia