Question

In the early days of research on protein synthesis, some scientists observed that their most highly purified ribosome preparations, containing almost exclusively single ribosomes, were less active than preparations that were less highly purified. Suggest an explanation for this observation.

Short answer

Highly purified ribosomes are less active because they lack the efficiency of polysomes and necessary associated factors present in less purified preparations.

Step-by-step solution

Understand the Role of Ribosomes

Ribosomes are essential for protein synthesis. They translate messenger RNA (mRNA) into proteins by linking amino acids together in a specific sequence.

Consider the Nature of Purification

Highly purified ribosome preparations contain mostly single ribosomes, while less highly purified preparations may contain ribosomes in their native, functional states, such as polysomes.

Analyze Ribosome Activity

Single ribosomes are less efficient in translation because they cannot form polysomes. Polysomes (multiple ribosomes bound to a single mRNA) enhance the efficiency and speed of protein synthesis.

Effect of Purification

Overly purifying ribosomes might strip away associated factors or conditions necessary for optimal function, reducing their activity compared to less purified preparations which still retain these elements.

Conclusion

The observation can be explained by the fact that single ribosomes in highly purified preparations are less efficient in synthesizing proteins than ribosomes in less purified preparations, where ribosomes are likely in the form of polysomes and retain associated protein synthesis factors.

Key concepts

ribosomes and protein synthesis

Ribosomes are like miniature factories within cells, dedicated to producing proteins, which are vital molecular machines and structural components. The process of protein synthesis begins when ribosomes translate messenger RNA (mRNA) into polypeptide chains, which then fold into functional proteins. Ribosomes consist of two subunits — a large subunit and a small subunit — that work together to read the sequence of codons on an mRNA strand.

Each codon, a sequence of three nucleotides, specifies a particular amino acid. Transfer RNA (tRNA) molecules bring the appropriate amino acids to the ribosome, where they are linked together by peptide bonds. This chain elongates as the ribosome moves along the mRNA, ultimately producing a complete protein.

Effective protein synthesis is critical to cell function and survival. Accuracy and speed are important, as errors can result in malfunctioning proteins that could cause cellular harm. Therefore, the organization and function of ribosomes are finely tuned to maximize the efficiency and fidelity of protein synthesis.

polysomes

Polysomes, also known as polyribosomes, are clusters of ribosomes simultaneously translating a single mRNA strand. This arrangement significantly boosts the efficiency of protein synthesis since multiple ribosomes can produce multiple copies of a protein at the same time.

Polysomes are formed when an mRNA is long enough to accommodate several ribosomes spaced along its length. Each ribosome in a polysome is at a different stage of translation, creating a production line that increases the overall output of protein. Polysomes are usually found in cells that synthesize large amounts of proteins, such as secretory cells or rapidly dividing cells.

The presence of polysomes indicates a cell’s active engagement in high-level protein production. This is especially important during periods of growth, development, or response to environmental cues. In laboratory settings, the detection and study of polysomes can reveal much about a cell's translational activity and protein synthesis capacity.

purification impact on ribosome function

Purification of ribosomes involves isolating them from other cellular components to study their function in detail. However, it's important to recognize that the ribosome's activity might be affected depending on the degree of purification.

In the study mentioned, highly purified preparations contained mostly single ribosomes, which were less active. This reduced activity can be attributed to several factors:

• Single ribosomes cannot form polysomes, which are more efficient in protein synthesis than individual ribosomes.
• Highly purified ribosomes may lose essential associated factors necessary for optimal function, such as proteins, RNA molecules, and other cofactors that aid translation.
• Certain cellular conditions, like ion concentrations and energy supply, that support ribosome function might be altered during purification.

These factors collectively result in the decreased activity observed in highly purified ribosome preparations. Understanding the impact of purification is crucial for designing experiments that accurately reflect the natural state and function of ribosomes in cells.