Question

REFLECT AND APPLY 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 lack essential translation factors, reducing activity.

Step-by-step solution

- Understand Ribosome Purification

Purifying ribosomes means isolating them from other cellular components. In the context of early research, more highly purified ribosomes would mean fewer associations with other molecules.

- Consider Ribosome Activity

Ribosome activity refers to their ability to synthesize proteins. Activity can be influenced by the presence of other molecules such as mRNA, tRNA, and various enzymes and factors that assist in translation.

- Analyze the Effect of Purification

When ribosomes are highly purified, they may lose associated factors necessary for optimal protein synthesis. These factors could include initiation factors, elongation factors, or even mRNA and tRNAs that were co-purified in less pure preparations.

- Draw a Conclusion

Highly purified ribosome preparations might be less active because they lack essential translation factors and substrates that are removed during the purification process. These factors are necessary for efficient protein synthesis.

Key concepts

Protein Synthesis

Protein synthesis is the process by which cells build proteins based on the instructions coded in their DNA. This process starts in the cell nucleus where DNA is transcribed into messenger RNA (mRNA). The mRNA then travels to the ribosome, the cell's protein factory.
Ribosomes read the sequence of the mRNA and translate it into a specific sequence of amino acids, creating a polypeptide chain.
This translation involves several steps:

• Initiation: The small ribosomal subunit binds to mRNA. Special proteins called initiation factors help the ribosome find the start codon.
• Elongation: Transfer RNA (tRNA) molecules bring amino acids to the ribosome, which assembles them into a growing polypeptide chain.
• Termination: The process ends when the ribosome encounters a stop codon, signaling the completion of the protein.

This multi-step process is crucial for cell function, as proteins are essential for almost all cellular activities.

Ribosome Purification

Ribosome purification is the process of isolating ribosomes from other cellular materials. In research, achieving highly purified ribosomes can be valuable for studying their structure and function.
However, the extent of purification can influence ribosome activity. Removing ribosomes from their natural cellular environment might also strip away necessary components:

• mRNA: The template carrying genetic information.
• tRNA: Molecules that bring amino acids during translation.
• Translation factors: Proteins that assist in various stages of protein synthesis.

In early studies, scientists noticed less active ribosomes when they were highly purified. This is because essential translation factors and substrates were likely removed, disrupting the protein synthesis process.
Maintaining a balance in purification is critical for retaining ribosome activity while still being able to study them effectively.

Translation Factors

Translation factors are proteins that play a key role in protein synthesis. They help ribosomes in the different stages of translation. There are several types of these factors, each with a specific function:

• Initiation Factors (IFs): Help the ribosome and mRNA begin the process. They assist in the assembly of the initiation complex, making sure the ribosome is correctly positioned to start translation.
• Elongation Factors (EFs): Aid in the addition of amino acids to the growing polypeptide chain. For instance, EF-Tu helps tRNA enter the ribosome and EF-G moves the ribosome along the mRNA strand.
• Release Factors (RFs): Recognize stop codons and help release the newly formed protein, terminating the translation process.

During ribosome purification, these factors can be lost, leaving ribosomes less efficient at building proteins. Their presence is vital for optimal ribosome function and effective protein synthesis.