Main Difference – Centrosome vs Centromere
Centrosome and centromere are two components involved in the division of a cell. A centrosome is an organelle which is made up of microtubules. It nucleates all the microtubules inside a cell in order to form the spindle apparatus during the prophase of cell division. The centromere is a region of DNA which is highly constricted to form a tiny area holding the two sister chromatids together during the cell division. The main difference between centrosome and centromere is that a centrosome is a cylindrical structure which forms the spindle apparatus by controlling cell’s microtubules where the centromere is a DNA region which holds the two sister chromatids together during the cell division.
This article explores,
1. What is Centrosome
– Structure, Function, Location, Characteristics
2. What is Centromere
– Structure, Function, Positions, Characteristics
3. What is the difference between Centrosome and Centromere
What is a Centrosome
A centrosome is an organelle which serves as the organizing center of all microtubules in an animal cell. It assembles microtubules into a spindle during the cell division. Centrosomes are only evolved in the metazoan lineage of eukaryotes. Thus, plant and fungal cells lack centrosomes. Plant cell spindle is formed independently, without the control of centrosomes.
Structure of Centrosome
A centrosome is composed of two centrioles, arranged in an orthogonal manner. The two centrioles are surrounded by pericentriolar material (PCM). The PCM is an amorphous mass anchoring microtubules by microtubule nucleation. The anchoring microtubule types are γ-tubulina, ninei, and pericentrin. A centriole is made up of nine triplet microtubules assembled in a cylinder like cartwheel structure. Centrin, cenexin and tektin are the types of microtubules which are arranged in this cylindrical structure to form the centrioles.
Figure 1: Centrosome Structure
Function of Centrosome
The centrosome is usually attached to the plasma membrane. During the prophase of the cell division, centrosome duplicates to from two centrosomes and these two centrosomes move to the opposite poles of the cell. After the degradation of the nuclear membrane, each centrosome nucleates their microtubules in order to form the spindle apparatus. The spindle microtubules are later attached to the centromeres of each chromosome in the cell. Contractions of the spindle microtubules let the chromosomes to segregate into opposite poles of the cell, creating two new daughter cells.
Other than the formation of the spindle apparatus, the mother centrosome makes flagellum and cilia of a non-dividing cell.
What is Centromere
The centromere is the central region of the chromosome which consists of highly constricted DNA. It holds the two sister chromatids together. Cohesin protein complexes are present between the two sister chromatids, linking the two copies of the replicated chromosome.
Structure of Centromere
Centric heterochromatin is the highly constricted form of DNA found in the centromere. It is flanked by pericentric heterochromatin. The major role of the centromere is to provide a site in the middle of a chromosome for the binding of microtubules via the kinetochores. Kinetochores are protein complexes, assembled on the centromere of the chromosome. Spindle microtubules are bound to the kinetochores. Two types of centromeres can be identified within chromosomes: point centromeres and regional centrosomes. Point centromeres bind with specific proteins to form centromeres. Though the formation of centromere prefers a unique DNA sequence to form the centromere, regional centromeres also can be formed on the other DNA sequences. The structure of a chromosome, bearing a centromere is shown in figure 2.
Figure 2: Duplicated Chromosome Structure
1 – Sister chromatid, 2 – Centromere, 3 – Short/p arm, 4 – Long/q arm
Positions of Centromeres
The chromosome is divided into two arms by the presence a centromere at the approximate middle of a chromosome. The two arms are long arm, which is known as q arm, and short arm, which is known as the p arm. Depending on the centromere position on chromosomes, they can be divided into four main types: metacentric chromosomes, submetacentric chromosomes, acrocentric chromosomes and telocentric chromosomes. Metacentric chromosomes consist of equal lengths in both p and q arms. In submetacentric chromosomes, p and q arms are fairly unequal in lengths. In acrocentric chromosomes, q arm is longer than the p arm. In telocentric chromosomes, the centromere is located at the terminal end of the chromosome.
Depending on the number of centromeres present on a chromosome, two types of organisms can be identified: monocentric organisms and holocentric organisms. Organisms with a single centromere per one chromosome are known as monocentric organisms. Holocentric organisms consist of more than one centromere per one chromosome.
Difference Between Centrosome and Centromere
Structure
Centrosome: A centrosome is an organelle consisting of two centrioles.
Centromere: A centromere is a highly constricted region on the chromosome.
Composition
Centrosome: The centrosome is made up of microtubules, centrin, cenexin and tektin.
Centromere: The centromere is made up of centric heterochromatin.
Function
Centrosome: Centrosomes anchor spindle microtubules in order to form the spindle apparatus during the cell division.
Centromere: Centromeres hold two sister chromatids together in a replicated chromosome.
Presence
Centrosome: Centrosomes are present only in metazoans.
Centromere: Centromeres are present in all eukaryotes.
Conclusion
Both centrosome and centromere are involved in cell division. A centrosome is made up of protein microtubules like centrin, cenexin and tektin. It is a cylindrical structure, assembling the microtubules in order to form the spindle apparatus in metazoans. The centromere is a constricted region of DNA in the form of centric heterochromatin. It holds the two sister chromatids together and provides sites for the attachment of spindle microtubules during the chromosomal segregation. Therefore, the main difference between centrosome and centromere is their structure and function.
Reference:
1. “Centrosome.” Wikipedia. Wikimedia Foundation, 06 Mar. 2017. Web. 12 Mar. 2017.
2.”Centromere.” Wikipedia. Wikimedia Foundation, 06 Mar. 2017. Web. 12 Mar. 2017.
Image Courtesy:
1. “Centrosome (borderless version)-en” By Kelvinsong – Own work (CC BY 3.0) via Commons Wikimedia
2.”Chromosome” – derivative work: Tryphon (talk)Chromosome-upright.png: Original version: Magnus Manske (CC BY-SA 3.0) via Commons Wikimedia
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