CEL - Endomembrane System [LESSON]

Endomembrane System

Now, we will learn about the organelles specific to the endomembrane system, which is the system responsible for the synthesis and transport of proteins from the DNA code. The endomembrane system (endo- = “within”) is a group of membranes and organelles in eukaryotic cells that works together to modify, package, and transport lipids and proteins. It includes a variety of organelles, such as the nuclear envelope and lysosomes, which you may already know, and the endoplasmic reticulum and Golgi apparatus. Recall the functions of these organelles from the last lesson.

Now, watch the following video on the Endomembrane System.

You can see from this video that the basic pathway for protein production and secretion is sequential.

Click through the activity to look at the Endomembrane Sequence pathway.

Protein destinations

Proteins that are going to be secreted out of the cell, embedded into the cell membrane, or embedded into an organelle membrane must use the endomembrane system described above. There are two types of ribosomes. The ribosomes that produce proteins that are delivered to the endoplasmic reticulum as described here are called bound ribosomes. They are called this because they are bound to the ER and they deliver proteins to the ER after production. The other option is called a free ribosome – these ribosomes are loose in the cytoplasm and create proteins that will stay in the cytoplasm of the cell. It is unnecessary for these to use the ER and Golgi since they do not have to travel through or into a membrane. A great example of this would be all of the enzymes used in glycolysis of cellular respiration since this entire series (ten enzyme steps) is completed in the cytoplasm.

Vesicle Transport

Microtubules of the cytoskeleton provide tracks for motor proteins called kinesins and dyneins, which transport vesicles around the interior of the cell. The kinesins “walk” along the microtubule (this uses a lot of ATP) as pictured below. They drag a vesicle behind them with the protein inside to its next destination.

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