Endomembrane System Definition
Endomembrane system is a different type of membrane of organelles that are connected through a direct physical connection, or through the transfer of segments of the membrane in the form of vesicles. The endomembrane system includes the nuclear envelope, endoplasmic reticulum (ER), Golgi body, lysosome and vacuoles.
Mechanism of endomembrane system
The mechanisms of the endomembrane system are as follows:
- The nuclear envelope is in contact with the rough endoplasmic reticulum and the smooth endoplasmic reticulum.
- The endoplasmic reticulum produces a transport vesicle-shaped membrane, which will move towards the golgi body.
- In Golgi bodies or other organelles, modification of the molecular structure of the vesicles occurs. Next, the golgi body releases the vesicles that produce lysosomes and vacuoles.
- Vesicles produced by the endoplasmic reticulum can combine to expand the plasma membrane and produce secretory proteins or other products out of the cell.
This system has a variety of functions, including protein synthesis and modification as well as transport of proteins to membranes and organelles or to the outside of cells, lipid synthesis, and the neutralizing of certain types of toxins.
Endomembrane System Components
Nucleus
The nucleus of the cell is an important part of the cell that acts as a controller of cell activity. The nucleus is the largest organelle in the cell. The nucleus is about 10-20 nm in diameter. The nucleus is usually located in the center of the cell and is round or oval in shape.
In general, the cells of a single nucleus, but there are also those that have more than one nucleus. This nucleus is generally most conspicuous in eukaryotic cells. The average diameter is 5 μm. The nucleus has a membrane enveloping it called a membrane or nuclear envelope. This membrane separates the contents of the nucleus from the cytoplasm. The nucleus is necessary to control chemical reactions, growth, cell division.
The nucleus is bound by a pair of membranes. The sheath that is formed is not continuous, but contains pores. This may allow the material to pass from the nucleus. Inside the nuclear membrane nucleus there is a medium of half fluid (semifluid) in which chromosomes are suspended. Usually the chromosome appears as an elongated structure and is not easily observed with a light microscope. Under the usual circumstances, it is called chromatin. The nucleus is the controlling center of the cell.
The nucleus is also tasked with carrying synthesis commands in the DNA nucleus because it contains a DNA code to determine the sequence of amino acid proteins. Inside the nucleus, DNA is organized together with proteins into a material called chromatin. As the cell prepares to divide (reproduce), the tangled chromatin that is thread-shaped will roll, becoming thick enough to be distinguishable as separate structures called chromosomes.
This nucleus controls protein synthesis in the cytoplasm by sending RNA-shaped molecular messenger, messenger RNA (mRNA) is synthesized in the nucleus according to the commands given by DNA, mRNA then delivery of this genetic message to the cytoplasm through the nucleus pore.
While in the cytoplasm, the mRNA molecule will attach to the ribosome, here the genetic message is translated into the primary structure of a specific protein.
Nucleus Parts
- Nucleolus (nucleus child) that synthesizes a wide variety of RNA molecules (ribonucleic acid) used in ribosomal assembly.
- Nucleoplasm (nucleus fluid) is a substance composed of proteins.
- Chromatin granules are found in the nucleoplasm, clearly visible when the cell divides. At the time of splitting, chromatin granules thicken into threadlike structures called chromosomes. Chromosomes contain DNA (deoxyiribonucleic acid) that conveys genetic information through protein synthesis.
Nucleus Function
- The nucleus serves as the controller of all cellular activities.
- The nucleus serves to regulate cell division.
- The nucleus serves as a carrier of genetic information (DNA) that will pass on its properties through cell division.
Endoplasmic Reticulum (ER)
ER consists of membrane tubular nets and pockets called cisternae. An ER membrane separates cisternal and cytosol chambers. ER membrane is a continuation of the core membrane when the ER is attached to the core membrane. The ER is such a labyrinth of membranes that this endoplasmic reticulum covers more than half of the total membrane in eukaryotic cells.
There are two types of ER: smooth Endoplasmic Reticulum, SER) and rough ER (Rough Endoplasmic Reticulum, RER). In the smooth ER there is no ribosome in the outer membrane, while in the rough ER there is a ribosome in the outer wall of the membrane. Between these two types of ER is thought to be a close relationship, i.e. Rough ER can be converted into the smooth ER when it loses its ribosomes or vice versa.
The Golgi body (Golgi Apparatus)
The Golgi body (named after its discoverer, Camillo Golgi) is composed of a pile of flattened sacs from a membrane called a cisternae. There are usually three to eight cisternae, but there are a number of organisms that have Golgi bodies with dozens of cisternae.
The number and size of Golgi’s body depend on the type of cell and its metabolic activity. Cells that actively secrete proteins can have hundreds of Golgi bodies. These organelles are usually located between the endoplasmic reticulum and the plasma membrane. [1]
The side of the Golgi body closest to the nucleus is called the cis side, while the side away from the nucleus is called the trans side. When it arrives on the cis side, the protein is inserted into the lumen of the cistern. In the lumen, the protein is modified, for example by the addition of carbohydrates, characterized by chemical markers, and sorted so that it can later be sent to its respective destinations. [2]
Golgi body regulates the movement of different types of proteins; Some are secreted outside the cell, some are incorporated into the plasma membrane as transmembrane proteins, and some are placed inside lysosomes. Proteins secreted from the cell are transported to the plasma membrane inside the secretory vesicles, which release their contents by joining the plasma membrane in the process of exocytosis.
The reverse process, endocytosis, can occur when the plasma membrane strangles into the cell and forms an endocytosis vesicle that are carried to the Golgi body or elsewhere, such as lysosomes. [1]
Lysosomes
Lysosomes are membrane-bound sacs of hydrolytic enzymes used by cells to digest macromolecules. Lysosomes are round like spheres. Lysosomes contain enzymes that serve to digest food that enters the cell. Lysosomes are produced by rough ER and golgi bodies. Lysosomes contain hydrolytic enzymes such as proteases, nucleases, glycosidases, lipases, and phosphatase. These enzymes are made by ribosomes attached to the ER. Lysosomes also function to damage bad bacteria and destroy damaged organelles.
Lysosomes digest the material put into the cell and recycle the material from intracellular discharge. During phagocytosis, cells enclose food vacuoles with membranes that are internally detached from the plasma membrane. Food vacuoles combine with lysosomes, and hydrolytic enzymes digest those foods.
After hydrolysis, simple sugars, amino acids, and other monomers pass through the lysosome membrane to go into the cytosol as a nutrient for the cell. With the autophagy process, lysosomes recycle the molecular content of organelles. ER and golgi generally work together in producing lysosomes that contain active enzymes.
Lysosome function:
- Plays a role in intracellular digestion.
- Plays a role in the process of phagocytosis.
- Autophagy (swallowing and recycling damaged organelles).
- Autolysis (destruction of cells itself by freeing all lysosome contents).
- Pompe (absence of lysosome enzymes to break down polysaccharides so that glycogen accumulation can occur in liver cells).
- Tay-sachs (lipid digesting enzymes are inactivated or lost so that lipid condensation can occur that can affect the brain).
Learn more about 12 Lysosome Functions
Vacuole
Vacuoles (cell cavities) are webbed pockets. The membranes on the vacuole are called tonoplast. Vacuoles have different shapes and sizes depending on their function.
In plant cells, the vacuole is large and is a central vacuole. Central vacuoles are likely to help plant cells to grow.
With the absorption of water, the central vacuole can store vital substances and residual products of cell metabolism. The central vacuole in the flower serves to store pigments so as to attract pollinating insects. Another function of vacuoles is to store amino acids, organic acids, glucose, gas, crystalline salts, essential oils, and alkaloids.
Vacuoles are commonly found in plant cells. In single-celled animals there is known to be a pulsating vacuole (contractile vacuole). In addition to contractile vacuoles, there are also food vacuoles that are located in circulation because they serve to digest food and circulate the results of digestion. Food vacuoles digest foodstuffs in the form of phagocytosis solid particles or digest foodstuffs in the form of liquids in pinocytosis.
Learn more about The Function of The Vacuole
References
- ^ a b c d e f Russell, P.J.; Hertz, P.E.; McMillan, B. (2011) (dalam bahasa Inggris). Biology: The Dynamic Science. 1 (edisi ke-2). Belmont, CA: Cengage Learning. ISBN 9780538493727.
- ^ Kratz, R.F. (2009). Molecular & Cell Biology for Dummies. Hoboken, NJ: John Wiley & Son. ISBN 9780470531020.
- Image: LadyofHats, Public domain, via Wikimedia Commons
- Video: RicochetScience
