5.18
Centrioles and Centrosomes
Most animal cells comprise a pair of centrioles together called a centrosome. The cell duplicates its centrosome and contains two centrosomes side-by-…
Centrioles are barrel-shaped structures located near the nucleus.
Each centriole is composed of nine sets of triplet microtubules. It is about 0.5 micrometers long and 0.2 micrometers in diameter.
In animal cells, two centrioles are positioned at a right angle and linked by interconnecting fibers.
The centrosome, the principal microtubule-organizing center in animal cells, is made of two interconnected centrioles and a surrounding protein mass called the pericentriolar material.
The centrosome replicates before cell division and forms the two poles of the mitotic spindle. During anaphase- the fourth phase of mitosis, the spindle fibers originating from the centrosome participate in chromatid separation.
As a part of the cytoskeleton, the centrosome also regulates the movement and position of the nucleus and other subcellular organelles.
Centrioles have additional roles in some cells, including acting as the basal bodies for specialized structures such as cilia and flagella which aid cell motility.
View the full transcript and gain access to JoVE Core videos
Q1: What is the structure of a centriole?
A centriole is a barrel-shaped structure composed of nine sets of triplet microtubules. Each centriole measures approximately 0.5 micrometers long and 0.2 micrometers in diameter. In animal cells, two centrioles are positioned at right angles to each other and linked by interconnecting fibers, forming the centrosome.
Q2: What is the role of the centrosome in cell division?
The centrosome, composed of two interconnected centrioles and surrounding pericentriolar material, serves as the principal microtubule-organizing center. It replicates before cell division and forms the two poles of the mitotic spindle. During anaphase, spindle fibers originating from the centrosome participate in separating sister chromatids to opposite ends of the cell.
Q3: How do centrosomes organize the mitotic spindle during prophase?
During prophase, the duplicated centrosomes move to opposite sides of the cell. Microtubules extend from each centrosome toward the other end, forming the mitotic spindle. As centrosomes migrate apart, they establish the two poles that organize and direct microtubule growth throughout cell division.
Q4: What functions do centrioles have beyond cell division?
Centrioles act as basal bodies for specialized structures such as cilia and flagella, which aid cell motility. As part of the cytoskeleton, centrosomes also regulate the movement and position of the nucleus and other subcellular organelles, contributing to overall cellular organization and function.
Q5: How do kinetochores connect sister chromatids to the mitotic spindle?
The kinetochore is a protein structure located on the centromere that serves as the attachment point between the mitotic spindle and sister chromatids. During metaphase, microtubules attach to kinetochores, positioning sister chromatids along the metaphase plate. These microtubules then shorten during anaphase to pull chromosomes toward opposite poles.
Q6: Why do plant cells lack centrosomes?
Unlike animal cells, plant cells do not have centrosomes or basal bodies. Instead, plants use alternative mechanisms to nucleate the assembly of microtubules and organize their cytoskeleton. This represents a key difference in cell diversity between plant and animal cell types.
Q7: What happens to the metaphase plate during anaphase?
During anaphase, sister chromatids separate from one another, forming individual chromosomes. The metaphase plate, which is the plane through the center of the spindle where chromatids were aligned, dissolves as chromosomes are pulled to opposite ends of the cell by their kinetochores over a few minutes.