19.1:
Mitochondria
The primary function of mitochondria in eukaryotic cells is to convert energy from oxygen and nutrients via oxidative phosphorylation into ATP, a usable form of cellular energy.
A mitochondrion can occur as a single organelle or may be fused to one another, forming a complex mitochondrial network. The complexity of these networks increases with an increase in the cell's ATP demand.
Moreover, the mitochondria per cell vary widely depending on the energy demand of different kinds of cells. For example, neutrophils contain very few mitochondria, whereas cardiac muscle cells have about five thousand mitochondria per cell.
In addition to the production of energy molecules, mitochondria are also involved in the biosynthesis of macromolecules such as nucleic acids, proteins, and lipids.
For example, the mitochondrial ribosome generates polypeptide chains that can fold and become functional protein centers of the electron chain complexes.
Additionally, mitochondria produce reactive oxygen species or ROS that can trigger cell damage and death.
To prevent this ROS-induced damage to the healthy cells, the enzymatic antioxidant systems of mitochondria neutralize excessive ROS, thus, protecting the normal cells from any damage.
19.1:
Mitochondria
Mitochondria are eukaryotic cellular organelles that are known to produce energy through a process called oxidative phosphorylation. Besides their primary function, mitochondria are involved in various cellular processes, including cell growth, differentiation, signaling, metabolism, and senescence. Age-related changes cause a decline in mitochondrial quality and integrity due to increased mitochondrial mutations and oxidative damage. Thus, aging can severely impact mitochondrial functions, leading to abnormal cell processes.
Mitochondria are known for their structural plasticity and undergo fission or fusion depending on specific cellular processes. For instance, mitochondrial fission is associated with mitophagy, a regulatory process that specifically removes damaged mitochondria, thus maintaining tissue homeostasis. However, aging can cause loss or mutation in proteins involved in mitochondrial fission. This eventually impairs mitophagy, a condition often correlated with several age-related diseases such as Alzheimer's disease, Parkinson's disease, cardiomyopathies, and cancer.
In another critical function, mitochondria associates with the cytoskeleton to facilitate their own mobility. It is a crucial factor that enables the distribution of mitochondria across cytoplasms in cells with a complex structure such as neurons. However, in aging cells, the cytoskeleton can become unstable, decreasing the mitochondrial movement and leading to abnormal neuronal functions.
Energy production through respiration is the fundamental function of the mitochondria. The mitochondrial respiratory chains generate superoxide radicals as a toxic byproduct. The mitochondrial antioxidant system typically neutralizes these radicals. However, the aging mitochondria have decreased antioxidant capacity and cannot combat the oxidative stress from the superoxide radicals. This results in the accumulation of reactive oxygen species in the cell that eventually cause cell death.
Suggested Reading
- Seo, Arnold Y., Anna-Maria Joseph, Debapriya Dutta, Judy CY Hwang, John P. Aris, and Christiaan Leeuwenburgh. "New insights into the role of mitochondria in aging: mitochondrial dynamics and more." Journal of cell science 123, no. 15 (2010): 2533-2542.
- Sun, Nuo, Richard J. Youle, and Toren Finkel. "The mitochondrial basis of aging." Molecular cell 61, no. 5 (2016): 654-666.