Question

In \(30 \mathrm{~S}\) and 40 S ribosomes, 'S'stands for (a) Sub-unit (b) Svedberg's unit (c) Single unit (d) Size

Short answer

The correct answer is (b) Svedberg's unit.

Step-by-step solution

Understand the options

First, evaluate each of the provided options. Are they acknowledged terms in relation to ribosomal structure?

Use your knowledge on ribosomes

According to understanding and biological study materials, 'S' in '30S' and '40S' stands for Svedberg units. Svedberg unit is a non-SI metric unit of sedimentation coefficient.

Choose the correct answer

Comparing the options and your knowledge on the topic, decide on the right answer.

Key concepts

Ribosomes

Ribosomes are essential cellular machines found within all living cells. They function as the site of biological protein synthesis, often referred to as translation.

The ribosome reads the genetic code from messenger RNA (mRNA) and, through a process known as polymerization, links amino acids together to form proteins. This process is critical for cell function and maintenance.

Ribosomes are composed of two subunits: a large one and a small one, each with a specific role in protein synthesis. These subunits are often represented by their sedimentation coefficients such as '30S' and '40S', particularly in prokaryotic cells such as bacteria. Eukaryotic cells tend to have larger ribosomes, typically 40S for the small subunit and 60S for the large subunit, combining to form the 80S ribosome. The 'S' stands for Svedberg unit, which is a measure of the sedimentation speed during ultracentrifugation, not an indication of size, weight, or any other physical property outside of this context.

Sedimentation Coefficient

The sedimentation coefficient, denoted by 'S', is a measure of how rapidly particles sediment in a centrifugal field. It reflects how fast a particle such as a ribosome will settle when subjected to centrifugation. The sedimentation coefficient is measured in Svedberg units, abbreviated as 'S', and is not a measure of size or weight but rather of how a particle behaves in a gravitational field.

It's important to note that the Svedberg unit is not additive. This means that the sedimentation coefficients of individual subunits of a ribosome do not necessarily sum up to the total Svedberg unit of the intact ribosome. For instance, bacterial 50S and 30S subunits combine to form a 70S ribosome, not an 80S. This is because the shape and other interactions between the subunits affect the sedimentation coefficient of the complete structure.

Biological Study Materials

Biological study materials, such as textbooks and scientific publications, are vital resources for understanding cellular structures like ribosomes. These materials commonly provide detailed descriptions and diagrams that help students visually comprehend complex biological concepts.

Many study materials also offer a historical perspective, revealing how scientific understanding has developed over time. For example, the discovery of the Svedberg unit came from the work of Theodor Svedberg, a Swedish chemist who received the Nobel Prize for developing the ultracentrifuge—a key tool that allows scientists to study the sedimentation rate of particles like ribosome subunits. Educational content should foster a comprehensive grasp of the relevance of these measurement units within the greater context of molecular biology.