Endoplasmic reticulum and golgi apparatus (video) | Khan Academy
We found that the ER, Golgi, and lysosomes were disorganized in fibroblasts . There was a significant difference between never‐smokers. Thus, in the late endosomes, the lysosomal hydrolases dissociate from the M6P. Lysosomes are membrane-bound spherical vesicles which contain hydrolytic enzymes that can break down virtually all kinds of biomolecules. At the same time .
It is a continuous membrane system consisting of tubules and sheets that begin at the nuclear membrane and extend throughout the cell. Despite its structure, the ER is a dynamic organelle that continuously changes based on the state of the cell, and is at the beginning of the eukaryotic endomembrane system.
Proteins are translated in the ER, where they can then be modified and packaged into vesicles bound for the Golgi complex. Through the Golgi, transported proteins can be further modified before sorting to their final localization at the lysosome or plasma membrane where the proteins function. Due to its important and central role in the cell, the ER has several mechanisms to ensure that homeostasis is maintained. The ER stress response activates a cascade of signals that allows the cell to respond to unwanted stressors Cao and Kaufman In eukaryotic cells, there are three major ER stress pathways that detect increased levels of unfolded proteins indicative of cellular stress.
Number two, the Golgi apparatus sorts and sends proteins to their proper destinations.
raznomir.info: Cell Structure: Lysosomes
And number three, the Golgi apparatus synthesizes certain molecules that need to be secreted from the cell. So, let's take a look at a protein that was synthesized in the rough endoplasmic reticulum, let's say that this part had a couple of ribosomes and there was a protein made.
Let's say this is the protein.
So, what will happen to it? So, this protein has to end up either at the lysosome or outside of the cell, or as a protein that's part of a cell membrane.
So, it'll butt off in a vesicle. Here's a vesicle butting off the endoplasmic reticulum.
Of course, the protein is inside of it. And that vesicle will merge with the Golgi apparatus, and the protein will end up inside the Golgi apparatus.
Endoplasmic reticulum and golgi apparatus
And this part of the Golgi apparatus is known as the cis stack. The cis stack is the part that's closest to the endoplasmic reticulum. Now, this protein that's in the Golgi apparatus will undergo modifications.
It'll get transferred to the middle part of the Golgi apparatus. The middle part is known as the medial stack. In the medial stack, it'll also be modified in different ways, and then, it'll eventually land up in this part of the Golgi apparatus. This part is known as the trans stack. The trans stack is the part that's furthest away from the endoplasmic reticulum.
And from the trans stack, a vesicle will kind of butt off and that vesicle will be holding the protein in it. And from here, this protein can take a couple of different paths. One thing that might happen to it is maybe it's destined to land up in the lysosome.
So, let's say this is a lysosome. So, in this case, the vesicle will move towards the lysosome, merge with it, and land up in the lysosome. I'm gonna digress for just a moment.
- The endomembrane system
If you recall earlier, I grouped together the endoplasmic reticulum with the Golgi apparatus, with the lysosomes, and I'm gonna add one more organelle to this group, the cell membrane. And the reason that I grouped all these organelles together is that they're all part of the secretory pathway.
Lysosomes - Little Enzyme Packages
Take a look at the protein we just spoke about. It was made in the endoplasmic reticulum where a vesicle butted off, then, the protein landed up in the Golgi apparatus, and then, another vesicle popped off and the protein ended up in the lysosome. So, all of these organelles have ways of transferring proteins between them.
The discs and tubules of the ER are hollow, and the space inside is called the lumen. Rough ER The rough endoplasmic reticulum rough ER gets its name from the bumpy ribosomes attached to its cytoplasmic surface. As these ribosomes make proteins, they feed the newly forming protein chains into the lumen. Some are transferred fully into the ER and float inside, while others are anchored in the membrane.
Inside the ER, the proteins fold and undergo modifications, such as the addition of carbohydrate side chains. These modified proteins will be incorporated into cellular membranes—the membrane of the ER or those of other organelles—or secreted from the cell.
If the modified proteins are not destined to stay in the ER, they will be packaged into vesicles, or small spheres of membrane that are used for transport, and shipped to the Golgi apparatus. The rough ER also makes phospholipids for other cellular membranes, which are transported when the vesicle forms. Micrograph and diagram of the endoplasmic reticulum.
Micrograph shows the rough ER as a series of membrane folds surrounding the nucleus.
Smooth ER The smooth endoplasmic reticulum smooth ER is continuous with the rough ER but has few or no ribosomes on its cytoplasmic surface. Functions of the smooth ER include: Synthesis of carbohydrates, lipids, and steroid hormones Detoxification of medications and poisons Storage of calcium ions In muscle cellsa special type of smooth ER called the sarcoplasmic reticulum is responsible for storage of calcium ions that are needed to trigger the coordinated contractions of the muscle cells.
There are also tiny "smooth" patches of ER found within the rough ER. These patches serve as exit sites for vesicles budding off from the rough ER and are called transitional ER 1 1. The Golgi apparatus When vesicles bud off from the ER, where do they go?