Question

Sugar groups may be added to proteins in which of the following? a. smooth endoplasmic reticulum b. rough endoplasmic reticulum c. Golgi apparatus d. lysosome

Short answer

c. Golgi apparatus

Step-by-step solution

Identify Where Glycosylation Occurs

Glycosylation is the process of adding sugar groups to proteins. This process primarily takes place in the endoplasmic reticulum (ER) and the Golgi apparatus.

Review the Functions of Rough and Smooth ER

The rough ER has ribosomes attached to its surface and is involved in protein synthesis and initial glycosylation steps. The smooth ER lacks ribosomes and is not directly involved in these processes; it is more associated with lipid synthesis and detoxification.

Examine the Role of the Golgi Apparatus

The Golgi apparatus is the primary site where glycosylation is completed and modified before the proteins are transported to their final destinations.

Exclude the Incorrect Options

Lysosomes are mainly involved in degradation and recycling of cellular components. They do not play a significant role in glycosylation.

Select the Correct Answer

Based on the information, the Golgi apparatus (option c) is the correct answer for where sugar groups are added to proteins.

Key concepts

endoplasmic reticulum

The endoplasmic reticulum (ER) is a vital cell organelle that plays a significant role in the synthesis and modification of proteins. There are two types: rough ER and smooth ER. The rough ER gets its name from the ribosomes attached to its surface, giving it a 'rough' appearance. These ribosomes are essential for protein synthesis.

The rough ER is also involved in the initial stages of glycosylation, the process of adding sugar groups to proteins. This modification is crucial because it helps proteins fold properly and become stable. It begins in the rough ER, where basic sugar groups are added.

On the other hand, the smooth ER lacks ribosomes and is involved in other cellular processes like lipid synthesis and detoxification. Unlike the rough ER, the smooth ER does not play a direct role in glycosylation.

Understanding the functional differences between the rough and smooth ER is key to knowing where early glycosylation steps occur.

Golgi apparatus

The Golgi apparatus is another essential organelle involved in protein maturation and glycosylation. Once proteins are synthesized and partially glycosylated in the rough ER, they are transported to the Golgi apparatus.

In the Golgi apparatus, glycosylation is completed and refined. This means that initial sugar groups added in the ER are modified and extended, making them more complex and functional. Think of the Golgi apparatus as a 'processing center' for proteins, ensuring they are correctly modified and ready for their specific roles in the cell.

The Golgi apparatus also sorts and packages these glycosylated proteins into vesicles, which are then transported to their final destinations, such as the cell membrane, lysosomes, or secretion outside the cell.

lysosome

Lysosomes are organelles mainly involved in the degradation and recycling of cellular waste, not in glycosylation. They contain enzymes that break down various biomolecules, including proteins, lipids, and carbohydrates.

While lysosomes are essential for maintaining cellular health by removing and recycling damaged components, they do not add sugar groups to proteins. Instead, their function is to degrade these proteins into simpler molecules that the cell can reuse.

This distinction is crucial for understanding why lysosomes are not involved in the glycosylation process. Their primary role lies in breakdown and clearance, contrasting the synthesis and modification activities seen in the endoplasmic reticulum and Golgi apparatus.