Question

A cell, which is very active in the synthesis and secretion of proteins, would be expected to have (a) equal amount of RER and SER (b) more SER than RER (c) more RER than SER (d) more Golgi bodies and no ER.

Short answer

The cell with high activity in protein synthesis and secretion would have (c) more RER than SER.

Step-by-step solution

Understanding Cell Organelles Function

Recognize that Rough Endoplasmic Reticulum (RER) is involved in the synthesis of proteins that are usually secreted by the cell, while Smooth Endoplasmic Reticulum (SER) is involved in lipid synthesis and detoxification processes. Golgi bodies are involved in modifying, sorting, and packaging proteins for secretion.

Determining Organelle Activity Relation with Protein Synthesis

Determine that a cell active in protein synthesis and secretion would require a significant amount of RER for protein synthesis. Although both RER and SER are important for cell function, the emphasis on protein synthesis and secretion highlights the role of RER.

Choosing the Correct Option

Based on the information from the previous steps, select the option that indicates a higher presence of RER to support the high level of protein synthesis and secretion.

Key concepts

Rough Endoplasmic Reticulum (RER)

The Rough Endoplasmic Reticulum (RER) is a crucial organelle in the process of protein synthesis.
The RER is studded with ribosomes, which give it a 'rough' appearance under a microscope. These ribosomes are the sites where proteins are assembled from amino acids based on the instructions encoded in mRNA.

During protein synthesis, the newly formed polypeptide chains are threaded into the lumen of the RER where they undergo folding and post-translational modifications.

• Important for the production of membrane-bound and secretory proteins.
• Acts as a quality control hub, ensuring only properly folded proteins move forward.
• Associated with the synthesis of glycoproteins due to the addition of carbohydrate side chains.

As cells involved in high levels of protein secretion have increased demands for protein synthesis, they correspondingly have a larger amount of RER to meet this demand.

Smooth Endoplasmic Reticulum (SER)

In contrast to the RER, the Smooth Endoplasmic Reticulum (SER) has a different set of functions and lacks ribosomes on its surface.
The SER plays a vital role in detoxification processes, carbohydrate metabolism, and the synthesis of lipids and steroids.

Key functions include:

• Synthesis of phospholipids and cholesterol, crucial for cell membrane formation.
• Detoxification of drugs and poisons by adding hydrophilic groups to make them easier for the body to excrete.
• Storage and release of calcium ions, important in muscle contraction and other cellular responses.

Cells that are highly active in protein synthesis do not necessarily require large amounts of SER, as its functions are less directly involved in the synthesis and modification of proteins.

Golgi bodies

Golgi bodies, also known as Golgi apparatus or Golgi complex, are a series of flattened, membrane-bound sacs known as cisternae.
They are the packaging and distribution center of the cell for proteins synthesized in the RER.

Functions of the Golgi bodies include:

• Modifying proteins received from the RER, which might include adding sugar molecules to form glycoproteins.
• Sorting and packaging proteins into vesicles for transport to their destination, either inside or outside the cell.
• Formation of lysosomes, which are vesicles filled with digestive enzymes.

Cells with high rates of protein secretion typically have extensive Golgi networks to efficiently handle the volume of proteins being modified and shipped out.

Protein Secretion

Protein secretion is the final step in the path of a protein from its synthesis to its destination outside the cell.
Proteins destined for secretion are first synthesized in the RER, then moved to the Golgi apparatus for modification and packaging into secretory vesicles.

Once properly packaged, the secretory vesicles are transported to the cell membrane. Through a process called exocytosis, the vesicles fuse with the cell membrane releasing their content (proteins) into the extracellular space.

• Crucial for maintaining intercellular communication.
• Important in immune responses with the secretion of antibodies.
• Allows cells to export products like hormones and enzymes.

Cells highly active in protein secretion therefore require well-developed organelles associated with this pathway, namely RER and Golgi bodies to efficiently process and secrete proteins.