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Question

Difficulty: HardKingdom Fungi: Moulds, Yeasts, and Mushrooms

Which of the following represents the correct chronological sequence of events during asexual reproduction by budding in the unicellular yeast *Saccharomyces*?

  1. 1Localized enzymatic softening of the chitinous cell wall and outward bulging of the mother cell membrane.
  2. 2Mitotic division of the mother cell nucleus and migration of one daughter nucleus into the expanding bud.
  3. 3Deposition of a chitinous primary septum at the narrow neck region separating the mother and daughter cells.
  4. 4Enzymatic cleavage of the septal wall layers, releasing the independent daughter cell and leaving a permanent bud scar.

Answer

The correct sequence begins with localized softening of the chitin cell wall to form a bud bulge, followed by mitotic nuclear division and migration into the bud, deposition of a chitinous septum across the bud neck, and finally enzymatic cleavage leading to daughter cell separation and bud scar formation.
In *Saccharomyces*, budding progresses in a strict order: localized enzymatic softening of the chitin cell wall permits bud emergence, after which mitotic nuclear division sends one daughter nucleus into the bud. Next, a chitinous septum is synthesized across the bud neck to seal both compartments, and finally, enzymatic cleavage breaks the septum to release the daughter cell and form a bud scar.

Step-by-Step Solution

1
Identify the initial cellular event initiating yeast budding.
Specific enzymes weaken the rigid cell wall at a designated bud site, allowing turgor pressure to push out a small cytoplasmic bulge.
Bud formation requires localized structural weakening of the cell wall before cellular contents can expand outward.
2
Trace the movement and division of genetic material.
The parent nucleus undergoes mitosis, elongating through the bud neck so that one daughter nucleus enters the growing bud while the other remains in the parent cell.
Asexual budding ensures genetic continuity through exact mitotic segregation.
3
Determine how the cytoplasm of the two cells is partitioned.
Chitin synthases deposit a primary chitin septum across the narrow bud neck between the mother and daughter cell membranes.
Septum synthesis creates a secure physical partition prior to actual detachment.
4
Identify the concluding event resulting in autonomous yeast cells.
Chitinases and glucanases hydrolyze the outer wall layers of the septum, freeing the daughter yeast cell and leaving a chitin-rich bud scar on the mother cell wall.
Enzymatic separation completes the division cycle while leaving a permanent structural marker on the parent cell.

Key Concept

Asexual Reproduction by Budding in Saccharomyces Yeast
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Topics

Kingdom Fungi: Moulds, Yeasts, and Mushrooms

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