The Endoplasmic reticulum is a network of tubules, vesicles and sacs that are interconnected.They serve specialized functions.
Cell biology (formerly cytology, from the Greek kytos, "contain") is a scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level. Cell biology research encompasses both the great diversity of single-celled organisms like bacteria and protozoa, as well as the many specialized cells in multicellular organisms such as humans, plants, and sponges.
Knowing the components of cells and how cells work is fundamental to all biological sciences. Appreciating the similarities and differences between cell types is particularly important to the fields of cell and molecular biology as well as to biomedical fields such as cancer research and developmental biology. These fundamental similarities and differences provide a unifying theme, sometimes allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types. Therefore, research in cell biology is closely related to genetics, biochemistry, molecular biology, immunology, and developmental biology.
The endoplasmic reticulum (ER) is a type of organelle in the cells of eukaryotic organisms that forms an interconnected network of flattened, membrane-enclosed sacs or tubes known as cisternae. The membranes of the ER are continuous with the outer membrane of the nuclear envelope. Endoplasmic reticulum occurs in most types of eukaryotic cell but is absent from red blood cells and spermatozoa. There are two types of endoplasmic reticulum, rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). The outer (cytosolic) face of the rough endoplasmic reticulum is studded with ribosomes that are the sites of protein synthesis. Rough endoplasmic reticulum is especially prominent in cells such as hepatocytes where active protein synthesis is occurring. The smooth endoplasmic reticulum lacks ribosomes and is concerned with lipid metabolism, carbohydrate metabolism, and detoxification]citation needed[ and is especially abundant in mammalian liver and gonad cells. The lacey membranes of the endoplasmic reticulum were first seen in 1945 by Keith R. Porter, Albert Claude, and Ernest F. Fullam.
The Golgi apparatus (//), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. It was identified in 1897 by the Italian physician Camillo Golgi and named after him in 1898.
Part of the cellular endomembrane system, the Golgi apparatus packages proteins inside the cell before they are sent to their destination; it is particularly important in the processing of proteins for secretion.
A biological membrane or biomembrane is an enclosing or separating membrane that acts as a selectively permeable barrier, within or around a cell. It consists of a phospholipid bilayer with embedded , integral and peripheral proteins used in communication and transportation of chemicals and ions. The cellular membranes should not be confused with isolating tissues formed by layers of cells, such as mucous and basement membranes.
The endomembrane system is composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles. In eukaryotes the organelles of the endomembrane system include: the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vacuoles, vesicles, endosomes and the cell membrane. The system is defined more accurately as the set of membranes that form a single functional and developmental unit, either being connected directly, or exchanging material through vesicle transport. Importantly, the endomembrane system does not include the membranes of mitochondria and chloroplasts.
The nuclear envelope is a membrane containing two layers, that encompasses the contents of the nucleus. The endoplasmic reticulum (ER) is a synthesis and transport organelle that branches into the cytoplasm in plant and animal cells. The Golgi apparatus is a series of multiple compartments where molecules are packaged for delivery to other cell components or for secretion from the cell. Vacuoles, which are found in both plant and animal cells (though much bigger in plant cells), are responsible for maintaining the shape and structure of the cell as well as storing waste products. A vesicle is a relatively small, membrane-enclosed sac that stores or transports substances. The plasma membrane, also referred to as the cell membrane, is a protective barrier that regulates what enters and leaves the cell. There is also an organelle known as the spitzenkörper that is only found in fungi, and is connected with hyphal tip growth.
Vesicular-tubular cluster (VTC), discovered in 1984 also referred to as the ER-Golgi intermediate compartment (or ERGIC), is an organelle in eukaryotic cells. This compartment mediates trafficking between the endoplasmic reticulum and Golgi complex, facilitating the sorting of cargo. The compartment was first defined as the location within the cell of the mannose-binding membrane lectin called ERGIC-53.
In mammalian organisms, COPII vesicles that have budded from exit sites in the endoplasmic reticulum lose their coats and fuse to form the vesicular-tubular cluster (VTC). Retrieval (or retrograde) transport in COPI vesicles returns many of the lost ER resident proteins back to the endoplasmic reticulum. Forward (or anterograde) transport moves the VTC contents to the cis-Golgi network, the receiving face of the Golgi complex. This process is thought to occur by one of two processes. One is known as cisternal maturation where the VTC simply matures into the cis-Golgi network. In another COPI vesicular transport moves VTC material to the receiving face of the Golgi apparatus. A fuller explanation of the two processes is described (see Golgi complex). Evidence exists for both processes and it may be that both occur simultaneously in cells.