Quick look: Golgi apparatus(or complex, or body, or ‘the ‘Golgi’) is found in all plant and animal cells and is the term given to groups of flattened disc-like structures located close to the endoplasmic reticulum. The number of ‘Golgi apparatus’ within a cell is variable. Animal cells tend to have fewer and larger Golgi apparatus. Plant cells can contain as many as several hundred smaller versions. The Golgi apparatus receives proteins and lipids (fats) from the rough endoplasmic reticulum. It modifies some of them and sorts, concentrates and packs them into sealed droplets called vesicles. Depending on the contents these are despatched to one of three destinations: Destination 1: within the cell, to organelles called lysosomes.
Destination 2: the plasma membrane of the cell
Destination 3: outside of the cell. The name behind the apparatus Debate about the existence of the apparatus continued even after 1913 when the term ‘Golgi apparatus’ was officially given to the ‘internal reticular apparatus’. It was not until 1954 that work in electron microscopy finally put the seal of approval on the existence of the organelle and the eponym ‘the Golgi’, was fully accepted. Going for Golgi. Where is the Golgi apparatus and what is it? Where is it? What is it? The Golgi apparatus is part of a manufacturing and supply chain In non-biological terms the Golgi apparatus can be divided into three main sections:
1) Goods inwards
2) Main processing area
3) Goods outwards
In terms of cell biology these sections, working from the rough endoplasmic reticulum (RER) outwards, are as follows: 1) Cis Golgi network (Goods inwards) 2) Golgi stack (Main processing area) 3) trans Golgi network (Goods outwards) Golgi apparatus – what does it do? The Golgi apparatus is rather like a food supermarket with an in store bakery. It takes in products from the Rough Endoplasmic Reticulum (RER) in what is called ‘bulk flow’ (the equivalent of a bulk delivery to the supermarket). These chemical products are transported to the Golgi apparatus in sealed droplets or sacs called vesicles and move to a ‘deliveries only’ part of the Golgi apparatus. In the Golgi apparatus the vesicles are delivered into the ‘unloading bay’ of the cis Golgi network. Here the ‘goods received’ are checked over. Any goods that have been wrongly delivered, including chemicals that should have stayed in the RER, are sent back, packed in vesicles to the rough endoplasmic reticulum. The proteins and lipids that have been correctly delivered are then passed into the cisternae of the Golgi stack and processed and sorted in an orderly sequence according to any ‘labels’ they bear. Some of the items from the rough endoplasmic reticulum go to the equivalent of the supermarket in store bakery and are converted into other products and re-labelled. In plants for example as much as 80% of biochemical activity in the Golgi cisternae can be devoted to producing chemicals such as pectin and polysaccharides used in making cell walls. The correct ‘labelling’ of products is critical. Inclusion cell (or I cell) disease, an inherited lysosome storage disorder in humans, is caused by a metabolic labelling error. The error causes chemicals to be despatched to the cell surface and secreted whereas the correct labelling would have despatched them to lysosomes. The lysosomes then accumulate material that should have been broken down. This accumulation causes the disorder. Moving through Golgi or Golgi moving? Golgi biochemicals. Where do they go? How do they get there? There are three main destinations for biochemicals released from the trans Golgi network: (1) inside the cell to the lysosomes; (2) the plasma membrane and (3) outside of the cell. In each case the destination is clearly linked to function. Using the food supermarket analogy, all the biochemicals transported away from the trans Golgi network have labels and barcodes built into them. They are all packed in vesicles and the construction of the vesicle or vessel is largely related to the vesicle contents, its destination and end use. Destination 1: inside the cell, ‘the lysosome line’ Destination 2: the plasma membrane, ‘the continuous secretion line’. Destination 3: outside the cell, ‘the regulated secretion line’ Certain triggers will make the vesicles fuse with the plasma membrane and release their contents in regulated bursts from the cell surface. Insulin release is an example of this when it is triggered by a rise in blood glucose level. Food intake is similar in that it triggers the release of mucus and digestive enzymes into the alimentary canal. Golgi and ‘clones’ Summary
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