Mitochondria definition, Function, Structure

Mitochondria Definition

Mitochondria are structures specific to the cells of animals, plants, and fungi. They act as batteries, powering the various functions of the cell and the organism as a whole. Although mitochondria are an integral part of the cell, evidence suggests that they evolved from primitive bacteria.

Mitochondria definition, Function, Structure

What are mitochondria?

Numerous small, spherical, club-shaped, filamentous, granular, and rod-shaped structures are found in the cytoplasm of eukaryotic cells, which are called mitochondria.

Mitochondria were discovered by Kolliker and the name Mitochondria was given by Benda (1897).

Mitochondria Occurrence

All living organisms are constructed with a fundamental brick: cell. In some cases, a single cell constitutes the entire organism. Cells contain genetic substances (DNA and RNA), and they carry out essential functions, such as metabolism and protein synthesis. Cells are also capable of self-replication. However, the level of organization within cells of different organisms varies. Based on these differences, organisms are divided into two groups: eukaryotes and prokaryotes.

Mitochondria definition, Function, Structure

Plants, animals, and fungi are all eukaryotes and are highly ordered cells. Their genetic material is packaged into a central nucleus. They also have specialized cellular components called organelles, each of which performs a specific function. Organizations such as mitochondria, the Rough Endoplasmic Reticulum, and Golgi work respectively to generate energy, synthesizing proteins, and package proteins for transport to different parts of the cell and beyond. The nucleus, as well as most eukaryotic organelles, are bound by membranes that regulate the entry and exit of proteins and enzymes and other cellular material from the organelle.

Prokaryotes, on the other hand, are single-celled organisms such as bacteria and archaea. Prokaryotic cells are less structured than eukaryotic cells. They have no nucleus; Instead, their genetic material is free-floating within the cell. They also lack many membrane-bound organisms found in eukaryotic cells. Thus, prokaryotes have no mitochondria.

Mitochondria Structure

In a 1981 review of the history of mitochondria in the Journal of Cell Biology, authors Lars Ernster and Gottfried Schutz note that the first true observation of mitochondria was made in 1890 by Richard Altman. While Altman called them “bioblasts”, his present, blind. A descriptive name was given by Karl Benda in 1898, based on his observations of developing sperm. “Mitochondria” derives from two Greek words: “mitos” which means thread, and “chondros” means granule. As described by Karen Hales, a professor of biology at Davidson College in Nature Education, these organs move and fuse together continuously to form chains and then diverge.

Mitochondria definition, Function, Structure

Individual mitochondria are capsule-shaped, consisting of an outer membrane and a flowing inner membrane, which resemble protruding fingers. The shape of these membranes is called the placenta and works to increase the overall surface area of ​​the membrane. When compared to cristae, the outer membrane is more porous and less selective as to which materials it allows inside. The matrix is ​​the central part of the organelle and is surrounded by cristae. It contains enzymes and DNA. Mitochondria are unlike most organelles (with the exception of plant chloroplasts), in which they have their own set of DNA and genes that encode proteins.

Plant mitochondria were first observed by Friedrich Meaves in 1904, as noted by Ernster and Shutz (Journal of Cell Biology, 1981). While plant and animal mitochondria do not differ in their basic structure, their genome is quite different, said Dan Sloan, an assistant professor at the University of Colorado. They differ in size and structure.

According to Sloan, the genome of most flowering plants is approximately 100,000 base pairs in size and can be as large as 10 million base pairs. In contrast, the mammalian genome is approximately 15,000 to 16,000 base pairs in size. Furthermore, while the animal mitochondrial genome has a simple spherical configuration, Sloan stated that the plant mitochondrial genome, although represented as circular, may take an alternative form. “Their actual structure is not well understood [within the plant] in vivo. They can be complex branching molecules,” he said.

Mitochondria definition, Function, Structure

Mitochondria Function

The main function of mitochondria is to metabolize or decompose carbohydrates and fatty acids to generate energy. Eukaryotic cells use energy in the form of a chemical molecule called ATP (adenosine triphosphate

  1. All foods in mitochondria are oxidized, so mitochondria are also called the powerhouse of the cell.
  2. During mating, yolk platelets are produced by mitochondria.
  3. The mitochondrial ring is formed at the time of spermatogenesis by mitochondria.
  4. The energy generated by mitochondria is in the form of ATP (adenosine triphosphate) and is formed by mixing inorganic phosphate and adenosine diphosphate (ADP).
  5. In mitochondria, CO_ {2} and water are formed by the formation of energy as well as oxidation. In the Christie of mitochondria, the electron access mechanism is completed.

ATP generation occurs within the mitochondrial matrix, although there are early stages of carbohydrate (glucose) metabolism outside the organelle. According to Geoffrey Cooper in “The Cell: A Molecular Approach 2 Ed” (Sinuar Associates, 2000), glucose is first converted to pyruvate and then transported into the matrix. Fatty acid, on the other hand, enters the mitochondria.

ATP is produced through three linked stages. First, pyruvate and fatty acids are converted into a molecule known as acetyl-COA, using enzymes present in the matrix. It then becomes the starting material for a second chemical reaction known as the citric acid cycle or the Krebs cycle. This step produces carbon dioxide and two additional molecules, NADH and FADH2, which are rich in electrons. Two molecules move to the inner mitochondrial membrane and begin the third phase: oxidative phosphorylation. In this final chemical reaction, NADH and FADH2 donate their electrons to oxygen, which leads to suitable conditions for the formation of ATP.

A secondary function of mitochondria is to synthesize proteins for their own use. They work independently and perform transcription of DNA to RNA, and translation of RNA to amino acids (building blocks of proteins) without using any component of the cell. However, here too, there are differences within eukaryotes. The sequence of the three DNA nucleotides U-A-G (uracil-adenine-guanine) is an instruction for translation into the eukaryotic nucleus.

According to the authors of “Molecular Cell Biology 4th Ed” (WH Freeman, 2000), while this sequence also inhibits translation in plant mitochondria, it encodes the amino acid tryptophan in mitochondria of mammals, fruit flies, and yeast. Does. Furthermore, RNA tapes that originate from mitochondrial genes are processed differently in plants than in animals. Sloan told LiveScience, “Plant mitochondria have to undergo a lot of modifications for those genes to be functional.” For example, in plants, individual nucleotides of RNA transcripts are edited before translation or protein synthesis occurs. In addition, introns, or fractions of mitochondrial RNA that do not carry out instructions for protein synthesis, are excluded.

Origins of mitochondria: The Endosymbiont Theory

In her 1967 paper, “The Origin of Mating Cell”, published in the Journal of Theoretical Biology, scientist Lynn Margulis proposed a theory to explain how eukaryotic cells formed with their organelles. She suggested that mitochondria and plant chloroplasts were once free-living prokaryotic cells that were swallowed by a primitive eukaryotic host cell.

Margulis’s hypothesis is now known as the “Endosymbian theory”. Dennis Searcy, Emeritus Professor at the University of Massachusetts Amherst, explained it this way: “Two cells started living together, some type of substrate or metabolite [products of metabolism, such as ATP]. The association became mandatory so that now, the host cell could no longer live separately. “

Even at the time when Margulis proposed it, versions of the endosymbiont theory already existed, some dating back to 1910 and 1915. “While these ideas are not new, in this paper they have been synthesized in such a way as to be consistent with recent data on the biochemistry and cytology of subcellular organisms,” she wrote in her paper. By Michael Gray According to a 2012 article on mitochondrial development at Cold Spring Harbor Perspectives in Biology, Margulis based his hypothesis on two key pieces of evidence. First, mitochondria have their own DNA. Second, any resource of eukaryotic cells Without using, organisms are able to translate the messages encoded in their genes into proteins.

Genome sequencing and analysis of mitochondrial DNA has established that Margulis was correct about the origin of mitochondria. The lineage of organelle has been traced back to a primitive bacterial ancestor known as alphaproteobacteria (α-proteobacteria).

Despite confirmation of mitochondria’s bacterial heritability, research on endosymbiont theory continues. Sloan told LiveScience, “One of the biggest questions right now is, ‘Who is the host cell?” As Gray noted in his article, the question is whether the eukaryotic cells originated after mitochondria were produced (as envisaged in endosymbiont theory) or mitochondria and host cells simultaneously, at the same time.

Mitochondria definition, Function, Structure

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Mitochondria definition, Function, Structure

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