Sistem endomembran

Summary

This video lecture covers the endomembrane system in cellular biology, detailing key components such as the endoplasmic reticulum (both rough and smooth), ribosomes, Golgi apparatus, and lysosomes. It explains their structure, function, and interconnections, including how vesicles move within the system. Key processes like protein synthesis, glycosylation, and detoxification are highlighted, as well as the roles of lysosomes in digestion and cellular maintenance. The lecture also explores the importance of the Golgi apparatus in packaging and sorting proteins, alongside a discussion on disorders arising from lysosomal dysfunction.

Takeaways

• 😀 The endomembrane system is a collection of membranes that function together in cells, facilitating the transport and modification of materials.
• 😀 Key components of the endomembrane system include the nucleus, endoplasmic reticulum (ER), ribosomes, Golgi apparatus, lysosomes, and plasma membrane.
• 😀 The endomembrane system has two main pathways for material transport: the secretion pathway (inside to outside the cell) and the endocytic pathway (outside to inside the cell).
• 😀 The rough endoplasmic reticulum (RER) has ribosomes on its surface and is involved in protein synthesis, while the smooth ER (SER) lacks ribosomes and is involved in lipid metabolism and detoxification.
• 😀 Ribosomes are made of protein and RNA and can be free in the cytoplasm or bound to the rough ER, where they synthesize proteins.
• 😀 The Golgi apparatus modifies, packages, and transports proteins and lipids, including glycosylation processes, which add sugar molecules to proteins.
• 😀 Lysosomes are membrane-bound vesicles that contain enzymes responsible for digesting and breaking down waste materials and cellular debris.
• 😀 The lysosomal membrane is resistant to enzyme breakdown, protecting the cell from self-digestion, but can be compromised by certain substances like steroids or fat-soluble vitamins.
• 😀 The process of glycosylation starts in the ER and continues in the Golgi apparatus, where proteins are further modified before being secreted by exocytosis.
• 😀 Disorders in lysosomal function, such as enzyme deficiencies or membrane defects, can lead to diseases like lysosomal storage disorders, cancers, and other conditions.
• 😀 Lysosomes play a key role in cellular cleanup through processes like heterophagy (digesting materials from outside the cell) and autophagy (digesting internal cell components).

Q & A

What is the endomembrane system and what does it consist of?

The endomembrane system is a network of membranes within the cell that function together to transport materials. It consists of the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, various types of vacuoles, and the plasma membrane.

What are the two main pathways of vesicle movement in the endomembrane system?

The two main pathways of vesicle movement in the endomembrane system are the **secretion pathway**, where materials move from inside to outside the cell, and the **endocytic pathway**, where materials move from outside to inside the cell.

How does the rough endoplasmic reticulum (RER) function in protein synthesis?

The rough endoplasmic reticulum (RER) is studded with ribosomes, which are responsible for synthesizing proteins. These proteins are often destined for secretion or incorporation into cell membranes. The RER also assists in the glycosylation of these proteins.

What is the difference between rough ER and smooth ER?

The rough ER has ribosomes on its surface and is involved in protein synthesis, while the smooth ER lacks ribosomes and is involved in the synthesis of lipids, metabolism of carbohydrates, and detoxification of harmful substances.

What is the function of the Golgi apparatus?

The Golgi apparatus processes, modifies, sorts, and packages proteins and lipids from the ER for transport within or outside the cell. It also plays a key role in glycosylation and the formation of secretory vesicles.

What are lysosomes and what role do they play in the cell?

Lysosomes are membrane-bound organelles containing enzymes that break down cellular waste, foreign materials, and damaged organelles. They are involved in processes like autophagy (self-digestion) and heterophagy (digestion of materials from outside the cell).

How does protein synthesis on ribosomes occur?

Protein synthesis occurs on ribosomes, which consist of a small subunit (40S or 30S depending on the organism) and a large subunit (60S or 50S). The ribosome reads messenger RNA (mRNA) and links amino acids into a polypeptide chain according to the sequence encoded in the mRNA.

What is the relationship between ribosomes and the endoplasmic reticulum?

Ribosomes are either free in the cytoplasm or bound to the rough endoplasmic reticulum (RER). The ribosomes on the RER are involved in synthesizing proteins that are either secreted from the cell or integrated into its membrane.

What happens during the process of glycosylation in the Golgi apparatus?

During glycosylation in the Golgi apparatus, carbohydrates are added to proteins or lipids. This modification helps proteins to fold correctly, become functional, and be directed to the correct cellular destination.

What can happen when lysosomal function is compromised?

When lysosomal function is compromised, it can lead to various diseases, such as **lysosomal storage diseases**. These conditions occur when enzymes needed for digestion within the lysosome are missing or defective, resulting in the accumulation of undigested materials within the cell.