Question 1

What is a centrosome and what role does it play in cell division?

Accepted Answer

A centrosome is the main microtubule organizing center in eukaryotic cells. It consists of two centrioles surrounded by a pericentriolar matrix and plays a vital role in forming the mitotic spindle, a bipolar arrangement of microtubules that separates sister chromatids during cell division. The two spindle poles are formed by two oppositely placed centrosomes.

Question 2

When does centrosome duplication occur during the cell cycle?

Accepted Answer

Centrosome duplication begins in early G1 phase when separase disengages the two centrioles. Daughter centrioles start growing at a right angle to each parent centriole near S phase onset and elongate through G2. By the time the cell reaches mitosis, it has two centrosomes, each containing a pair of centrioles and pericentriolar matrix.

Question 3

What proteins regulate centrosome duplication in the cell cycle?

Accepted Answer

The G1/S-cyclin dependent kinase complex, consisting of cyclin E and Cdk2 in animal cells, triggers centrosome duplication and cell cycle entry. Plk-4, a polo-like protein kinase, is an important regulator for centriole biogenesis in humans. These proteins ensure centrosome duplication occurs only once per cell cycle.

Question 4

How does centrosome duplication resemble chromosome duplication?

Accepted Answer

Both centrosomes and chromosomes duplicate only once per cell cycle through a semiconservative process where a new copy is produced from a pre-existing parent copy. After cell division, one copy of each is equally distributed to each daughter cell. This parallel regulation ensures proper inheritance of both genetic material and microtubule organizing capacity.

Question 5

What happens to centrosomes at the beginning of mitosis?

Accepted Answer

At mitosis onset, the centrosome splits in two through a process called centrosome disjunction. The two resulting centrosomes move apart, with microtubule motor proteins facilitating their separation. Both centrosomes then nucleate microtubules, primarily at the mother centriole, collectively forming the mitotic spindle and assembly dynein kinesin and microtubules.

Question 6

What is the structure of a centriole within a centrosome?

Accepted Answer

Each centriole consists of nine sets of three microtubules held together by proteins. The two centrioles are positioned at right angles to each other and surrounded by a shapeless protein cloud called the pericentriolar matrix. This organized structure enables the centrosome to function as the primary microtubule organizing center.

Question 7

How can excessive centrosome duplication lead to disease?

Accepted Answer

Excessive centrosome duplication impairs mitotic spindle assembly and causes chromosomes to segregate improperly, leading to chromosomal abnormalities. These errors are implicated in multiple diseases, notably cancer. Tumor suppressor proteins and oncogenes are linked to detrimental changes in tumor cell centrosomes, making them attractive treatment targets.

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