Understanding Lysosomes: Functions and Characteristics
Lysosomes are membrane-enclosed organelles containing digestive enzymes that break down various biomolecules. They maintain an acidic internal environment, protecting the cell from enzymatic activity. Lysosomes play a crucial role in cellular waste disposal, macromolecule digestion, and intracellular trafficking. Production, maintenance, and degradation processes of lysosomes contribute to cellular homeostasis.
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Lysosomes and microbodies Lysosomes are roughly spherical bodies enclosed by a single membrane. They are manufactured by the Golgi apparatus. It is found in both plant and animal cells, but is more common in animal cells, Lysosomes are not visible under a light microscope.
They contain different kinds of hydrolytic enzymes including : Lipase, which digests lipids Amylase, which digest carbohydrates (e.g., sugars) Proteases, which digest proteins Nucleases, which digest nucleic acids The size of lysosomes varies from 0.1 1.2 m. At pH 4.8, the interior of the lysosomes is acidic compared to the slightly basic cytosol (pH 7.2). The lysosome maintains this pH differential by pumping protons (H+ ions) from the cytosol across the membrane via proton pumps and chloride ion channels. l
the contents of the cell are protected from the digestive enzymes of the lysosome. First, the enzymes are enclosed in the lysosomal membrane and second, even if the enzymes were to leak out of the lysosome, they would not be active at the neutral pH of the cytosol
The production of lysosomal proteins suggests one method of lysosome sustainment. Lysosomal protein genes are transcribed in the nucleus. mRNA transcripts exit the nucleus into the cytosol, where they are translated by ribosomes. The nascent peptide chains are translocated into the rough endoplasmic reticulum, where they are modified. Upon exiting the endoplasmic reticulum and entering the Golgi apparatus via vesicular transport, a specific lysosomal tag, mannose 6-phosphate, is added to the peptides. The presence of these tags allow for binding to mannose 6- phosphate receptors in the Golgi apparatus, a phenomenon that is crucial for proper packaging into vesicles destined for the lysosomal system.
Three ways to degradation in lysosomes: Extracellular materials to be degraded in the lysosome are brought into the cell by either pinocytosis or phagocytosis. Pinocytosis, which occurs in all eukaryotic cells. These small vesicles carrying endocytosed molecules are initially delivered to membranous organelles called endosomes. Endosomes may actually mature into lysosomes when newly made acid hydrolases are delivered to the endosome.
Phagocytosis, which occurs in only specialized cell types, is the ingestion of large particles such as cell debris or whole microorganisms. Phagocytic cells engulf large particles by forming a large intracellular vesicle containing the engulfed particle.
Intracellular materials, such as old organelles, are brought into a lysosome by a process called autophagy. For example, when a mitochondrion comes to the end life, The newly enclosed mitochondrion then fuses with a lysosome, resulting in its degradation by the acid hydrolases
Lysosomal Storage Disease Lysosomal storage diseases are caused by the accumulation of macromolecules (proteins, polysaccharides, lipids) in the lysosomes because of a genetic failure to manufacture an enzyme needed for their breakdown. Neurons of the central nervous system are particularly susceptible to damage. The accumulated materials impair or kill the affected cells, resulting in skeletal or muscular defects, mental retardation, or even death.
Functions of Lysosomes 1-disposal system of the cell. To breakdown complex into simpler compounds (proteins, carbohydrates, lipids ). 2-repair the damages to the plasma membrane. They serve as membrane patch and help in sealing the wound in the plasma membrane. 3-Lysosomes are also involved in programmed cell death, or autolysis, which is a catabolic process involving degradation of the cells own components. This is the reason why lysosomes are often known as suicide sacs.
Microbodies A microbody is a type of organelle that is found in the cells of plants, protozoa, and animals. Organelles in the microbody family include peroxisomes, glyoxysomes, glycosomes and hydrogenosomes.
Peroxisomesis ;usually a vesicle with a spherical shape, ranging from 0.2-1.5 micrometers in diameter. Peroxisome are found in the cytoplasm of a cell, but they are only visible with the use of an electron microscope. They are surrounded by a single membrane and they contain a matrix of intracellular material including enzymes and other proteins. However, peroxisomes bud off from the endoplasmic reticulum, not the Golgi apparatus (that is the source of lysosomes).
http://upload.wikimedia.org/wikipedia/commons/thumb/c/cb/Peroxisome.svg/300px-Peroxisome.svg.pnghttp://upload.wikimedia.org/wikipedia/commons/thumb/c/cb/Peroxisome.svg/300px-Peroxisome.svg.png Some of the functions of the peroxisomes: Lipid metabolism and chemical detoxification are important functions of peroxisomes. Peroxisomes are responsible for oxidation reactions that break down fatty acids and amino acids. Peroxisomes oversee reactions that neutralize free radicals, which cause cellular damage and cell death. Peroxisomes chemically neutralize poisons through a process that produces large amounts of toxic H2O2, which is then converted into water and oxygen.
The liver is the organ primarily responsible for detoxifying the blood before it travels throughout the body; as a result, liver cells contain large amounts of peroxisomes Peroxisomes play important roles in plants., peroxisomes in seeds are responsible for the conversion of stored fatty acids to carbohydrates, which is critical to providing energy and raw materials for growth of the germinating plant. This occurs via a series of reactions termed the glyoxylate cycle.
How are different between lysosomes and peroxisomes? 1. Lysosomes contain hydrolase. This is the component or enzyme that is responsible for digestion. Peroxisomes, on the other hand, contain three oxidative enzymes such as catalase, D-amino acid oxidase, and uric acid oxidase. 2. Lysosomes are responsible for the digestion of cells while peroxisomes are responsible for the protection of cells against hydrogen peroxide. 3. Lysosomes were discovered in the 1960 s by Christian de Duve, a Belgian cytologist. Mr. Rhodin, on the other hand, first described peroxisomes in 1954
Glyoxysomes found in plants and also in filamentous fungi. As in all peroxisomes, in glyoxysomes the fatty acids are hydrolyzed to acetyl-CoA by peroxisomal -oxidation enzymes. Besides peroxisomal functions, glyoxysomes possess additionally the key enzymes of glyoxylate cycle (isocitrate lyase and malate synthase) which accomplish the glyoxylate cycle bypass.
Thus, glyoxysomes (as all peroxisomes) contain enzymes that initiate the breakdown of fatty acids and additionally possess the enzymes to produce intermediate products for the synthesis of sugars by gluconeogenesis. The seedling uses these sugars synthesized from fats until it is mature enough to produce them by photosynthesis. Glyoxysomes also participate in photorespiration and nitrogen metabolism in root nodules.
Vacuoles Vacuoles, like vesicles, are membranous sacs, but vacuoles are larger than vesicles. The vacuoles of some protists are quite specialized; they include contractile vacuoles for ridding the cell of excess water, and digestive vacuoles for breaking down nutrients. Vacuoles usually store substances,
such as nutrients or ions. Plant vacuoles contain not only water, sugars, and salts, but also pigments and toxic molecules. The pigments are responsible for many of the red, blue, or purple colors of flowers and some leaves. The toxic substances help protect a plant from herbivorous animals.
