Endomembrane System Parts and Functions

In this endomembrane system parts and functions post we have briefly explained endomembrane system organelles nucleus envelopes, lysosomes, vesicles, Golgi apparatus, and the endoplasmic reticulum.

Endomembrane System

Endomembrane system organelles (endo means “within”) is a group of organelles and membranes within eukaryotic cells. They work in concert to modify, package and transport lipids and proteins. Endomembrane system organelles comprises nucleus envelopes, lysosomes, vesicles, Golgi apparatus, and the endoplasmic reticulum. 

Although technically not within the cell, the plasma membrane is included in the endomembrane system because it interacts with the other endomembranous organelles, as you will see. The mitochondria membranes and chloroplasts are not part of the endomembrane system.

Endomembrane System Organelles and Functions

1. Endoplasmic Reticulum

The endoplasmic reticulum (ER) is a network of interconnected membranous sacs and tubules that modifies proteins and synthesises lipids. These two functions, however, are carried out in separate areas of the ER: the rough ER and the smooth ER, respectively.

The lumen or cisternae space is the hollow portion of the ER tubules. The ER membrane is a phospholipid bilayer embedded with proteins that is continuous with the nuclear envelope.

Endomembrane System Parts and Functions

Endomembrane System Organelles: Endoplasmic Reticulum

Rough ER

When seen using an electron microscope, the rough endoplasmic reticulum (RER) of endomembrane system organelles has a studded appearance due to the ribosomes attached to its cytoplasmic surface.

Ribosomes transport freshly generated proteins into the RER lumen, where they undergo structural changes like folding and side-chain acquisition. These changed proteins will be integrated into cellular membranes, such as the ER or other organelle membranes, or released from the cell (such as protein hormones enzymes). The RER also produces phospholipids for cellular membranes.

If the phospholipids or changed proteins aren’t meant to stay in the RER, they’ll be transported to their final destination by transport vesicles that sprout from the membrane of the RER.

Smooth ER

The smooth endoplasmic reticulum (SER) of endomembrane system organelles is connected to the RER, but its cytoplasmic surface includes few or no ribosomes. The SER is responsible for the synthesis of carbohydrates, lipids, and steroid hormones and the detoxification and storage of drugs and toxins. A specialized SER termed the sarcoplasmic reticulum is responsible for storing calcium ions in muscle cells, which are required to activate coordinated contractions.

2. Golgi Apparatus

The lipids or proteins contained in the transport vesicles must still be processed, packaged, and labeled before being delivered to their final destination. The Golgi apparatus of endomembrane system organelles is responsible for sorting, labelling, packaging, and distributing lipids and proteins. The CIS face is the receiving end of the Golgi apparatus, and the TRANS face refers to the opposite side.

The ER-derived transport vesicles proceed to the CIS face, fuse with it, and dump their contents into the Golgi apparatus lumen. Proteins and lipids undergo further changes as they move through the Golgi, allowing them to be sorted. The insertion of short chains of sugar molecules is the most common alteration.

Endomembrane System Parts and Functions

Endomembrane System Organelles: Golgi Apparatus

Phosphate groups or other small molecules are subsequently added to these newly changed proteins and lipids, allowing them to be guided to their right destinations.

Finally, the tagged and changed proteins are bundled into secretory vesicles that emerge from the Golgi’s TRANS face. Some secretory vesicles fuse with the plasma membrane and release their contents outside the cell, while others deposit their contents in other areas of the cell where they will be utilized.

Another example of shape following function is the profusion of Golgi in cells that release many things (such as salivary gland cells that produce digestive enzymes or immune system cells that secrete antibodies).

3. Lysosomes

Lysosomes of endomembrane system organelles are regarded as part of the endomembrane system and function as a digestive component and organelle recycling facility in animal cells. Lysosomes’ hydrolytic enzymes also destroy pathogens (disease-causing organisms) that enter the cell. Macrophages are a type of white blood cell part of your body’s immune system.

Endomembrane System Parts and Functions

Endomembrane System Organelles: Lysosomes

A segment of the macrophage’s plasma membrane invaginates (folds in) and engulfs a pathogen in the process known as phagocytosis or endocytosis.  The pathogen-infested region splits itself off the plasma membrane and transforms into a vesicle. A lysosome merges with the vesicle. The lysosome’s hydrolytic enzymes then destroy the pathogen.

Summary

1. The nuclear envelope, lysosomes, vesicles, the ER, Golgi apparatus, and the plasma membrane make up the endomembrane system organelles system. 

2. The proteins and lipids that make up the membranes are modified, packaged, tagged, and transported by these cellular components.

3. The RER alters proteins and produces phospholipids that are found in cell membranes. The SER is responsible for the synthesis of carbohydrates, lipids, and steroid hormones and the detoxification and storage of drugs and toxins.

4. The Golgi apparatus of endomembrane system organelles is responsible for sorting, labelling, packaging, and distributing lipids and proteins.

5. The budding of the RER and Golgi membranes of endomembrane system organelles results in the formation of lysosomes.

6. Pathogens are destroyed by lysosomes, which digest macromolecules, recycle worn-out organelles, and digest macromolecules.

Further Readings

Endomembrane System Parts and Functions