A supramolecular complex that serves to degrade damaged or unneeded proteins in the cell is called as
1. lysosome
2. flagella
3. proteasome
4. ribosome

Detailed Explanation:

Correct Answer: 3. Proteasome

Introduction to the Proteasome:

The proteasome is a large, multi-subunit complex in cells responsible for degrading damaged, misfolded, or unneeded proteins. It plays a crucial role in maintaining cellular health and homeostasis by regulating protein turnover, which involves breaking down proteins that are no longer needed or are harmful to the cell. The proteasome is essential for controlling various cellular processes, including the cell cycle, signal transduction, and stress response.

How the Proteasome Works:

1. Ubiquitin-Proteasome Pathway: Proteins targeted for degradation by the proteasome are first marked with a small protein called ubiquitin. This process is known as ubiquitination. Once a protein is tagged with ubiquitin, it is recognized by the proteasome for degradation.

2. Recognition and Degradation: The ubiquitinated protein is then directed to the proteasome, where it is unfolded and fed into the protease core of the proteasome. The protein is broken down into smaller peptides, which are then further processed into amino acids, ready to be recycled for the synthesis of new proteins.

3. ATP-dependent Process: The degradation process requires energy, which is provided by ATP. ATP helps in the unfolding of the protein and its translocation into the proteasomal core for degradation.

Structure of the Proteasome:

The proteasome consists of two main components:

• 20S Core Particle: This is the catalytic part of the proteasome where the actual breakdown of proteins occurs. It contains proteases that degrade the substrates.

• 19S Regulatory Particle: This particle is responsible for recognizing, binding, and unfolding the proteins that need to be degraded. It also removes the ubiquitin tags before the protein is fed into the core particle.

Why the Other Options Are Incorrect:

• Option 1: Lysosome: Lysosomes are membrane-bound organelles responsible for digesting extracellular materials, worn-out cell components, and other debris. While lysosomes contribute to cellular degradation, they are not involved in the selective breakdown of individual proteins, which is the role of the proteasome.

• Option 2: Flagella: Flagella are structures that help cells move, especially in single-celled organisms. They are not involved in protein degradation, making this option irrelevant to the question.

• Option 4: Ribosome: Ribosomes are responsible for protein synthesis, not degradation. They translate messenger RNA (mRNA) into proteins. Therefore, ribosomes do not play a role in degrading proteins.

Importance of the Proteasome:

• Cellular Regulation: By regulating protein levels, the proteasome controls key processes such as cell cycle progression, DNA repair, and responses to oxidative stress.

• Disease Implications: Dysfunction in the proteasome has been linked to various diseases, including neurodegenerative diseases (e.g., Parkinson’s and Alzheimer’s), certain cancers, and autoimmune conditions. Impaired protein degradation can lead to the accumulation of toxic proteins in cells, causing cellular damage.

• Therapeutic Target: Proteasome inhibitors, like bortezomib, are used as therapeutic agents in treating certain types of cancer, such as multiple myeloma, by preventing the degradation of proteins that regulate cell death.

Conclusion:

The proteasome serves as a critical supramolecular complex responsible for degrading damaged or unneeded proteins within the cell. Through the ubiquitin-proteasome pathway, it helps maintain protein homeostasis and ensures cellular function by regulating protein turnover.