BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

V. CYTOLOGY. THE CONCEPT OF THE CELL

Structure of the Plant Cell

Mitochondria

Cell/35.html">Mitochondria are cytoplasmic double-membrane Organelles that serve as centers for intracellular oxidation. They contain Enzymes of the di- and tricarboxylic acid cycles, the Electron Transport Chain, and Oxidative Phosphorylation.

They can be spherical, cylindrical, or branched in shape. A mitochondrion typically has a diameter of 0.5–1.5 μm and a length of up to 6 μm. Young Cells in the ROOT apex of maize contain about 200 mitochondria, whereas cells in the absorbing zone contain around 2,500. In contrast, cells of Chlorella and Yeast contain only a single branched mitochondrion.

A mitochondrion is enclosed by a double-membrane envelope surrounding a finely granular matrix with a high protein content. The outer membrane is approximately 6 nm thick, has a smooth surface, and features a high lipid content. It is freely permeable to low-molecular-weight compounds and certain Proteins.

The inner membrane (6 nm thick) forms numerous folds or infoldings known as cristae. In higher plants, mitochondrial cristae originate with a narrow neck and terminate in a bulb or plate. An intermembrane space, 6–8 nm wide, is located between the outer and inner membranes and extends inside the cristae. The matrix-facing surface of the inner membrane features rod-like particles consisting of a short stalk and a spherical HEAD. These structures contain the enzyme ATPase, which catalyzes the synthesis of ATP from ADP and orthophosphate. The components of The electron transport chain are embedded within the inner membrane. Furthermore, the inner membrane acts as a barrier to many ions and possesses specific transmembrane transport systems.

The mitochondrial matrix contains Two Types of particles—Ribosomes and calcium granules—as well as fibrillar particles known as nucleoids. The calcium granules consist primarily of calcium phosphate. The fibrillar material of the nucleoids contains DNA which, unlike chromosomal cells, is not bound to histone proteins. Mitochondrial DNA contains 15,000 to 75,000 Base Pairs and can encode The Biosynthesis of 15–80 low-molecular-weight proteins, each consisting of about 300 amino acid residues; consequently, the majority of mitochondrial proteins are encoded by nuclear DNA. The matrix also contains all the enzymes of The Tricarboxylic Acid Cycle, with the exception of succinate dehydrogenase, which is embedded in the crista membrane.

New mitochondria are formed by division. This process begins when the inner membranes invaginate, dividing the matrix into two parts enclosed by the outer membrane. Subsequently, the outer membranes constrict and separate, resulting in two independent mitochondria. Evolutionary studies suggest that mitochondria originated from Prokaryotic Cells, most likely Bacteria.