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Cellular and Molecular Biology

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Organelles: Autophagy and Cellular Lifespan

CELLS-LPO$EJ

It has been experimentally demonstrated that during periods of starvation, cells grown in culture will use lysosomes to engulf and break down non-essential organelles or other large macromolecules through a process known as autophagy. This degradation releases basic molecular building blocks that the cell can use to support its metabolism.

Interestingly, researchers observed that cell cultures subjected to repeated periods of starvation actually survived longer than cells that were cultured in a nutritionally-rich growth medium. Similarly, when tested at the organismal level, researchers found mice that were fed a diet with periodic calorie-restriction lived significantly longer than mice that were fed a full-calorie diet.

Based on your knowledge of cell biology, which of the following statements is MOST consistent with these experimental results?

A

In addition to breaking down organelles and other large macromolecules, autophagy is also used to degrade extracellular pathogens that are engulfed and internalized by the cell. The increased levels of autophagy help these cells better fight off potential infections and live longer.

B

In addition to breaking down organelles, activation of autophagy also results in the degradation of telomeres at the ends of chromosomes. This protects the chromosomes from the enzyme telomerase, preserving the genetic information and allowing the cells to remain viable for more cell divisions.

C

The activation of autophagy in the cell breaks down organelles and other large macromolecules, including those that are potentially defective or harmful in some way. When the period of starvation ends, the organelles and macromolecules are rebuilt, restoring their function. Repeated cycles of degradation help clear out damaged cellular components and restore their function, extending the life of the cell.

D

The activation of autophagy in the cell results in the degradation of peroxisomes. These organelles contain highly toxic substances derived from oxygen. In the absence of peroxisomes, the damaging effects of peroxisome-associated molecules are reduced, allowing the cell to live longer.