The number and morphology of mitochondria vary between cells, tissues and species. Proteomic characterization of mitochondrial proteins has revealed that they are highly dynamic, changing during development and in response to external conditions.
This complexity suggests that the complex machinery for establishing mitochondria must be highly coordinated. This article will explore the various levels at which this coordination occurs.
What are they?
Mitochondria are the organelles that convert energy in the cells of all plants, animals, and fungi. They are often referred to as the “powerhouses” of the cell and are crucial for most cellular processes, including cell growth, protein production, metabolite regulation, and reproduction.
They are a complex structure consisting of two distinct membranes that form a small intermembrane space between them. Both the inner and outer membranes contain highly specialized proteins. The mitochondrial DNA is located within the intermembrane space.
Both the outer and inner membranes contain channels and pores that allow the passage of ions and certain molecules. The inner membrane is convoluted into many folds called cristae, which increase its surface area and therefore increases the efficiency of ATP production. The cristae also act like a sieve, allowing only certain molecules to pass into the matrix. The matrix contains numerous enzymatic reactions that are responsible for mass energy production.
These proteins pass electrons along a chain that ends in the creation of ATP. This process is known as the “redox” reaction, and it is one of the most important cellular reactions. In order for the redox reaction to work, it must occur in the correct environment. In the matrix, the proteins are surrounded by a complex network of mitochondrial DNA that provides the necessary information for proper reactions to take place.
It is important to note that the redox reaction in the inner mitochondrial membrane generates superoxide radicals, which are very toxic. To counteract this, the matrix contains enzymes that scavenge and eliminate these reactive molecules. Mitochondria are also involved in the oxidation of various lipids to form fatty acids, which is an important part of energy production.
Mitochondria are a fascinating part of the eukaryotic cell. They are a testament to the great power that can come from symbiotic relationships between different organisms. They have an inner membrane that contains proteins similar to those of prokaryotic cells and their own circular genome, although most of the genes for mitochondrial functions are encoded in the cell nucleus. Their role in converting energy has been critical for the evolution of larger and more complicated cells, and they are responsible for much of what makes us human.
What are their functions?
The purpose of mitochondria, as of any other organelle, is to produce energy. They convert broken-down nutrients within the cell to adenosine triphosphate (ATP), which powers other cellular processes such as growth, repair, and reactivity to environmental changes. Without ATP, cells would not be able to survive and would die.
While ATP production is one of the most critical functions of mitochondria, they also provide several other benefits for plants. For example, they help store calcium, and play roles in the cell’s metabolism, apoptosis (controlled cell death), and abiotic stress responses. In addition, they also act as a backup to the chloroplasts in photosynthesis, and they are important for the growth of plant tissue.
These organelles are shaped like long tubes or small spheres, and they are separated from the rest of the cytoplasm by two membranes. The outer membrane is porous and allows ions and small, uncharged molecules to pass freely through it, while the inner membrane is tightly asymmetrical, forming invaginations known as cristae. These are designed to fit more mitochondrial membrane into a smaller space, so that more energy-producing reactions can take place simultaneously.
Inside the inner mitochondrial membrane, proteins tethered to DNA form complexes that carry electrons in a chain reaction that ultimately produces ATP. In order for the tethered protein to pass through the inner mitochondrial membrane, a signal sequence on its surface recognizes a receptor protein on the opposite side of the membrane and sticks to it. The receptor protein then hands off the tethered protein to a translocator protein, which guides it past both the inner and outer mitochondrial membranes into the matrix.
The exact mechanism of mitochondrial control is not fully understood, but a few key insights are emerging. For example, the fact that many of the same genes that control mitochondrial function are found in both the nucleus and mitochondria suggests that there are common, highly conserved regulatory mechanisms that oversee mitochondrial gene expression. And the presence of intermembrane spaces between mitochondria suggests that signals from the outside of the mitochondria may also impact gene expression, as well as the binding of tethered proteins to their respective targets.
How do they make them?
Scientists have learned a lot about mitochondria in recent years. They have discovered that they produce the energy needed to power cells; they also help with blood clotting, muscle contraction, and cell growth. Mitochondria have small chromosomes, so their DNA is separate from that of the nucleus. Mitochondria and chromosomes are inherited from the mother, so people with a different mother have a distinct mitochondrial genome.
In general, the number of mitochondria in a cell correlates with how active that cell is. However, there are some exceptions to this rule. For example, in cancerous tumors, there are often many more mitochondria than normal cells. Researchers have attributed this to the fact that cancerous cells require a great deal of energy.
Mitochondria are made in a structure called the chloroplast. This is a specialized plant organelle that transforms light energy into chemical energy through photosynthesis. The process of photosynthesis has several steps, including absorbing carbon dioxide and water from the air, producing food for the plant by splitting molecules, and releasing oxygen into the atmosphere. The food produced in the chloroplast is used to drive cellular processes, like cellular respiration, which generates ATP for all the cell’s needs.
The mitochondria in a cell are separated by an inner and outer membrane. In between the two membranes is a space called the matrix that contains enzymes that perform oxidative phosphorylation. In order for the enzymes in the matrix to work, they must have access to oxygen. The inner membrane is folded into cristae, which increase the surface area and allow oxygen to access the matrix.
Researchers have been able to identify the proteins that make up mitochondrial membranes. They have also been able to determine how these proteins are able to transport substances across the membrane. This is done through a system of tethering and channeling. A signal sequence at the tip of a protein recognizes a specific receptor protein on another protein inside the mitochondria and sticks to it. The tethered protein is then “handed off” to a translocator protein that channels the unfolded protein past both the inner and outer mitochondrial membranes.
How do they die?
The mitochondria is a membrane-bound organelle found in the cytoplasm of all eukaryotic cells (cells with clearly defined nuclei). It is known as the powerhouse of the cell because it is responsible for converting glucose and other fuels into energy in the form of adenosine triphosphate (ATP). Despite their common name, mitochondria are not involved in cellular respiration alone. They also store calcium for cell signaling, generate heat and play a role in various other metabolic functions.
The organelle consists of two semi-permeable membranes with an intermembrane space between them. The inner membrane is highly folded, forming structures called cristae where the machinery for generating ATP is located. The cristae are also where mitochondrial DNA is present and where ribosomes for protein synthesis reside.
During cellular respiration, the enzyme complexes that produce ATP pass electrons across the inner mitochondrial membrane in an electrochemical gradient called a proton gradient. This creates a potential difference of electric charge, or voltage, that drives hydrogen out of the matrix space into the intermembrane space. Once in the intermembrane space, the hydrogen combines with carbon dioxide to form water and molecular oxygen. This enables the enzyme complexes to generate ATP from ADP.
In plants, the process is known as photosynthesis, in which light energy from sunlight is used to convert organic molecules into energy. Plant chloroplasts are the primary site of photosynthesis.
Mitochondria and chloroplasts have similar functions, but their mechanisms are fundamentally different. Whereas mitochondria use fuels such as glucose and fats to generate adenosine triphosphate, allowing cells to grow and reproduce, chloroplasts use molecular oxygen to synthesize organic nutrients from simple molecules such as carbon dioxide and water.
Mitochondria are oblong in shape and range in size from 1 to 10 micrometers. They are distributed throughout the cytoplasm in numbers that directly correlate to their metabolic activity level. Time-lapse studies of living cells have shown that the mitochondria move rapidly and are packed into long traveling chains or clusters, tightly packed into relatively stable groups, and in a variety of other formations, depending on their metabolic requirements. This mobility is linked to the fact that they are transported along the cytoplasmic microtubule network with motor proteins, probably in tandem with other organelles and based on a mutual recognition of specific motor protein binding sites.