A&P Lecture 1.10: Mitochondria

This is an in depth  explanation of Mitochondria as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE 1.10

MITOCHONDRIA

All cells in the body, with the exception of mature red blood cells, have from a hundred to a few thousand organelles called mitochondria (singular, mitochondrion ). Mitochondria serve as sites for the production of most of the energy of cells

Mitochondria vary in size and shape, but all have the same basic structure.. Each mitochondrion is surrounded by an inner and outer membrane, separated by a narrow intermembranous space. The outer mitochondrial membrane is smooth, but the inner membrane is characterized by many folds, called cristae, which project like shelves into the central area (or matrix ) of the mitochondrion. The cristae and the matrix compartmentalize the space within the mitochondrion and have different roles in the generation of cellular energy.

Mitochondria can migrate through the cytoplasm of a cell and are able to reproduce themselves. Indeed, mitochondria contain their own DNA. All of the mitochondria in a person’s body are derived from those inherited from the mother’s fertilized egg cell. Thus, all of a person’s mitochondrial genes are inherited from the mother. Mitochondrial DNA is more primitive (consisting of a circular, relatively small, doublestranded

molecule) than that found within the cell nucleus. For this and other reasons, many scientists believe that mitochondria evolved from separate organisms, related to bacteria, that invaded the ancestors of animal cells and remained in a state of symbiosis. This symbiosis might not always benefit the host; for example, mitochondria produce superoxide radicals that can provoke an oxidative stress and some scientists believe that accumulations of mutations in mitochondrial DNA may contribute to aging. Mutations in mitochondrial DNA occur at a rate at least ten times faster than in nuclear DNA (probably due to the superoxide radicals),

and there are more than 150 mutations of mitochondrial DNA presently known to contribute to different human diseases. However, genes in nuclear DNA code for 99% of mitochondrial proteins (mitochondrial DNA contains only 37 genes), and so many mitochondrial diseases are produced by mutations in nuclear DNA.

Neurons obtain energy solely from aerobic cell respiration, which occurs in mitochondria. Thus, mitochondrial fission (division) and transport over long distances is particularly important in neurons, where axons can be up to l meter in length. Mitochondria can also fuse together, which may help to repair those damaged by “reactive oxygen species” generated within mitochondria.