The Lysosomes Are membranous particles located between mitochondria and microsomes that contain a wide range of digestive enzymes (approximately 50) primarily used for digestion and removal of excessive or worn organelles, food particles and viruses or bacteria.
Using a more colloquial term, it could be said that lysosomes are like the stomach of the cell.
The lysosomes are surrounded by a membrane composed of phospholipids that separate the interior of the lysosomes from the external medium of the membrane. Phospholipids are the same cell molecules that form the cell membrane that surrounds the whole cell. Lysosomes range in size from 0.1 to 1.2 microns.
Specific functions include:
- The digestion of macromolecules from phagocytosis, endocytosis and autophagy.
- Digestion of bacteria and other waste materials.
- The repair of the damage to the plasma membrane acting as a membrane patch.
- And apoptosis.
They are often referred to as"suicide pockets"because of their role in autolysis.
Discovery of lysosomes
Lysosomes were discovered by the Belgian biochemist and biochemist Christian René de Duve In the fifties. De Duve obtained a part of the Nobel Prize in Medicine in 1974 for his discovery of lysosomes and other organelles known as peroxisomes.
De Duve discovered the lysosomes using biochemical methods and using electron microscopy. This basic finding has led to the current compression of several inherited disorders caused by defective lysosomal proteins, including Tay-Sach disease and the Gaucher disease .
Types
Recent research suggests that there are two types of lysosomes: secretory and conventional lysosomes.
Secretory lysosomes
Secretory lysosomes are found, but not exclusively, in different cells of the immune system, such as T lymphocytes, derived from the hematopoietic cell line.
Secretory lysosomes are a combination of conventional lysosomes and secretory granules. They differ from the conventional lysosomes in that they contain the particular secretory product of the cell in which they reside.
T lymphocytes, for example, contain secretory products (perforin and granzymes) that can attack both infected and tumor cells.
"Secretory lysosome"combi cells also contain hydrolases, membrane proteins and have the pH-regulating facility of conventional lysosomes. This regulatory function maintains an acidic environment in which the secretory products are kept in an inactive form.
Mature secretory lysosomes move within the cytoplasm to the plasma membrane. Here they stand in standby mode with powerful secretions of inactive but ready"warheads".
When the T lymphocyte cell is perfectly focused on the target cell, secretion is"triggered"and environmental and chemical changes, including pH, activate secretions before blocking the target.
All this is done with precise control of the location and time not only to maximize the effect on the target, but also to minimize collateral damage to neighboring friendly cells.
Genetically controlled disorders of secretory lysosomes can lead to altered platelet synthesis, a type of immunodeficiency and hypopigmentation.
Conventional lysosomes
Lysosomes reside in the cell as reusable organelles and, when cell division occurs, each daughter cell receives a series of lysosomes. It is thought that the deposit of chemicals in the lysosome can be"refilled"by the supplies of the Golgi apparatus .
The chemicals are manufactured in the endoplasmic reticulum, modified in the Golgi apparatus and transported to the lysosomes in the vesicles. The modification in the Golgi apparatus includes a"targeting"at a molecular level which ensures that the vesicle is delivered to a lysosome and not to the plasma membrane or elsewhere.
The"tag"is returned to the Golgi apparatus for reuse. Material from 3 different sources requires disassembly and recycling. The substrates of two of these sources enter the cell from the outside and the third originates from within.
From outside the cell, the process of endocytosis, including pinocytosis, admits small particles and liquids through the formation, in the plasma membrane, of small cavities coated with proteins. These seal to form vesicles coated with proteins.
Each vesicle becomes an"early endosome"and then a"late endosome." Also from outside the cell, phagocytosis (cell feed) brings relatively large particles (usually 250 nm in size), including bacteria and cell debris.
Phagocytosis can be carried out by"ordinary cells", but is mainly performed by macrophages that can contain up to 1,000 lysosomes per cell. The resulting structure of phagocytosis is called phagosome. From inside the cell, autophagosomes are responsible for the elimination of organelles, such as mitochondria and ribosomes.
Functions of lysosomes
The main functions of lysosomes are:
Intracellular digestion
The word lysosome derives from"smooth"(lytic or digestive), and"soma"(body). Pinocytic vacuoles, formed as a result of the absorption of the fluid substance into cellular or phagocytic vacuoles (formed by the absorption of solid particles in the cell), transport the protein material to the lysosomal region.
These proteins could undergo digestion within the cell as a result of endocytosis. Endocytosis includes the processes of phagocytosis, pinocytosis and micropinocytosis.
Phagocytosis and pinocytosis are active mechanisms in which the cell needs energy for its functioning. During phagocytosis by leukocytes, oxygen uptake, glucose uptake and glycogen decomposition increase significantly.
In endocytosis the contraction of microfilaments of actin and myosin present in the peripheral cytoplasm occurs. This causes the plasma membrane to invaginate and form the endocytic vacuole. Ingested particles enclosed in membranes derived from the plasma membrane and forming vacuoles are sometimes cellular phagosomes.
After the entry of a large particle or body into the cell by endocytosis and the formation of a phagosome, the membranes of the phagosome and a lysosome can be fused to form a single large vacuole.
Within this vacuole the lysosomal enzymes begin the process of digestion of the foreign material. Initially the lysosome, known as the primary lysosome, contains the enzyme complex in an inactive state, but after fusion with the phagosome it produces a secondary lysosome with a different morphology and active enzymes.
After enzymatic digestion, the digested material diffuses into the hyaloplasm of the cell. Some materials may remain in the enlarged lysosome vacuole. This remaining vacuole is the residual body, since it contains the residue of the digestive process.
During starvation as well, lysosomes digest stored food materials, ie proteins, lipids and glycogen from the cytoplasm and provide the energy required by the cell. The digestion of proteins usually ends at the level of the dipeptide, which can pass through the membrane and then be digested into the amino acids.
Digestion of intracellular substances or autophagy
Many cellular components, such as mitochondria, are constantly removed from the cell by the lysosomal system. The cytoplasmic organelles are surrounded by membranes of smooth endoplasmic reticulum, forming vacuoles, then the lysosomal enzymes are discharged into autophagic vacuoles and the organelles are digested.
Autophagy is a general property of eukaryotic cells. These are related to the renewal of cellular components.
Digestion of mitochondria or other cellular structures provides a source of energy for these cells. After digestion of the cellular structure, autophagic vacuoles can become residual bodies.
They have a role in metamorphosis
Recently, the role of the lysosome has been discovered in the metamorphosis of the frog. The disappearance of the tail of the tadpole larvae of the frog is due to the lysosomal activity (action of the cathepsins present in the lysosomes).
They help in the synthesis of proteins
Scientists Novikoff and Essner (1960) have suggested the possible role of lysosomes in protein synthesis. In the liver and pancreas of some birds, lysosomes appear to be more active and developed showing this a possible relationship with cellular metabolism.
They help fertilization
During fertilization, the sperm head secrete some lysosomal enzymes that aid in the penetration of the spermatozoa into the yolk layer of the egg.
The acrosome contains protease and hyaluronidase and abundant acid phosphatase. The hyaluronidase disperses in the cells around the oocyte and the protease digests the zona pellucida making a channel through which the spermatic nucleus penetrates.
Has a role in osteogenesis
It has been argued that the formation of bone cells and also their destruction depends on the lysosomal activity. Similarly, cell aging and parthenogenetic development are related to the activity of lysosomes.
Osteoclasts (multinucleated cells) that remove bone, do so by releasing lysosomal enzymes that degrade the organic matrix. This process is activated by parathyroid hormone.
Malfunction of lysosomes
A malfunction of the lysosomes can lead to diseases. For example, when glycogen absorbed by lysosomes is not digested, Pompe disease .
The ruptures of lysosomes in skin cells exposed to direct sunlight lead to pathological changes after sunburn. The enzymes released by these lysosomes destroy the cells of the epidermis, causing blisters and then a detachment of a layer of epidermis occurs.
Autolysis of cartilage and bone tissue
Excess vitamin A causes cell poisoning. It disrupts the lysosomal membrane, causing the release of enzymes in the cell and producing autolysis in the cartilage and bone tissue.
Lysosomal diseases
Gaucher Diseases Types I, II and III
Gaucher disease is the most common type of lysosomal storage disorder. Researchers have identified three different types of Gaucher disease based on absence (type I) or presence and extent of (types II and III) neurological complications.
Most affected individuals have type I, being able to experience bruises, chronic fatigue and an abnormally enlarged liver and / or spleen (hepatosplenomegaly).
Type II Gaucher disease occurs in neonates and infants, and is characterized by neurological complications that may include involuntary muscle spasms, difficulty swallowing, and loss of previously acquired motor skills.
Gaucher disease type III appears during the first decade of life. Neurological complications may include mental deterioration, inability to coordinate voluntary movements, and muscle spasms of the arms, legs or whole body.
Types of Niemann-Pick A / B, C1 and C2 disease
Niemann-Pick disease consists of a group of hereditary disorders related to the metabolism of fats. Some features common to all types include enlargement of the liver and spleen. Children with Niemann-Pick disease, types A or C, also experience progressive loss of motor skills, eating difficulties, progressive learning difficulties, and Convulsions .
Fabry disease
Symptoms of Fabry's disease Usually begin during early childhood or adolescence, but may not become apparent until the second or third decade of life.
Early symptoms include episodes of severe burning pain in the hands and feet. Other early signs may include a decrease in sweat production, discomfort when warm temperatures are experienced, and a rash that turns reddish to dark blue, especially in the area between the hips and knees.
Glycogen storage disease II (Pompe disease)
Pompe disease has a late onset form. Patients with the infantile form are most severely affected. Although these babies usually appear normal at birth, the disease occurs within the first two to three months with rapidly progressive muscle weakness, decreased muscle tone (hypotonia), and a type of heart disease known as hypertrophic cardiomyopathy.
Feeding problems and breathing difficulties are common. The juvenile / adult form presents between the first and seventh decades as a progressively slow muscle weakness or with symptoms of respiratory failure.
Gangliosidosis Type I (Tay Sachs disease)
There are two main forms of Tay Sachs disease: the classic or infantile form and the late onset form.
In individuals with Tay Sachs infantile disease, symptoms usually appear for the first time between three and five months of age. These may include feeding problems, general weakness (lethargy), and an exaggerated jerk reflex in response to loud and sudden noises. Motor delays and mental deterioration are progressive.
In individuals with the late onset form, symptoms may appear at any time from adolescence to age 30. The infant form often progresses rapidly, resulting in significant mental and physical impairment.
A characteristic symptom of Tay Sachs disease, which occurs in 90 percent of cases, is the development of red spots on the back of the eyes. The symptoms of late-onset Tay Sachs disease vary widely from case to case. This disorder progresses much more slowly than the infantile form.
Gangliosidosis type II (Sandhoff disease)
The first symptoms of Sandhoff's disease usually begin between three and six months of age. The disease is clinically indistinguishable from Type I gangliosidosis.
Metachromatic leukodystrophy
The first signs and symptoms can be vague and gradual, so this disorder is difficult to diagnose. Instability when walking is often the first symptom observed.
Occasionally, the earliest symptom is delayed development or deterioration in school performance. Over time, symptoms may include Spasticity Marked seizures, and profound mental retardation.
Mucopolysaccharide storage diseases (Hurler's disease and variants, type A, B, C, D, Morquio Types A and B, diseases of Maroteaux-Lamy and Sly)
These diseases are caused by alterations in the normal decomposition of complex carbohydrates known as mucopolysaccharides. These diseases have certain characteristics in common, including deformities of the bones and joints that interfere with mobility and often cause osteoarthritis, especially of large, weight bearing joints.
All of these diseases, except Sanfilippo's disease, interfere with growth, causing short stature.
Schindler's Disease Types I and II
Schindler's disease type I is the classic form, which appears for the first time during childhood. Affected individuals appear to develop normally until they are one year old, when they begin to lose previously acquired skills that require the coordination of physical and mental activities.
Schindler Type II is the form of appearance in adults. Symptoms may include the development of clusters of warts-like discolorations on the skin, the permanent widening of blood vessel clusters that cause reddening of the skin on affected areas, relative thickening of facial features and mild intellectual impairment.
Batten Disease
The Batten's disease Is the juvenile form of a group of progressive neurological disorders known as neuronal ceroid lipofuscinosis. It is characterized by the accumulation of a fatty substance in the brain, as well as in the tissue that does not contain nerve cells.
Batten disease is marked by rapidly progressive vision failure (optic atrophy) and neurological disorders, which can begin before age eight. It occurs mainly in families of Scandinavian descent in Northern Europe and the disorder affects the brain and can cause deterioration of the intellect and neurological functions.
Affected Population
As a group, it is believed that lysosomal storage diseases have an estimated frequency of approximately one in 5,000 live births. Although individual diseases are rare, the group as a whole affects many people around the world.
Some diseases have a higher incidence in certain populations. For example, Gaucher and Tay-Sachs diseases are more prevalent among the Ashkenazi Jewish population. It is known that a mutation associated with Hurler syndrome occurs more frequently between the Scandinavian and Russian peoples.
Diagnosis
Prenatal diagnosis is possible for all lysosomal storage disorders. Early detection of lysosomal storage diseases, either before birth or as soon as possible, is important because when therapies are available, either for the disease itself or for the associated symptoms, they can significantly limit the long-term course And the impact of the disease.
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