Question

What kind of ribosome is present in mitochondria? (a) \(70 \mathrm{~S}\) (b) \(80 \mathrm{~S}\) (c) \(40 \mathrm{~S}\) (d) \(60 \mathrm{~S}\)

Short answer

The type of ribosome present in mitochondria is \(70 \mathrm{S}\), so the correct answer is (a) \(70 \mathrm{S}\)

Step-by-step solution

- Understanding Ribosomes

Ribosomes play a critical role in protein synthesis in any cell. Different types of cells contain different types of ribosomes, which can be distinguished by their sedimentation coefficients. The sedimentation coefficient is linked to the ribosome's size and shape.

- Researching the ribosome type in mitochondria

Research the types of ribosomes present in different parts of the cells. Mitochondria, being an ancient symbiotic bacterium incorporated into eukaryotic cells, have their own ribosomes. These ribosomes have a structure and composition close to the ribosomes of prokaryotic cells.

- Identifying the correct sedimentation coefficient

Identify the sedimentation coefficient of the ribosome type that is found in mitochondria. Prokaryotic ribosomes, which are present in mitochondria, are smaller than eukaryotic ribosomes. They have a sedimentation coefficient of \(70 \mathrm{S}\).

Key concepts

Ribosome Sedimentation Coefficient

The ribosome sedimentation coefficient is a measure of a ribosome's size and shape that is essential for understanding its role in protein synthesis.

During the ultracentrifugation process, ribosomes are separated based on their density and mass. Scientists measure this in Svedberg units (S), where the sedimentation rate reflects how quickly a ribosome settles when subjected to centrifugal force.

The size of the ribosome can affect its functionality and its interaction with messenger RNA (mRNA) and transfer RNA (tRNA) during protein synthesis. For instance, in a eukaryotic cell, ribosomes can be either 80S (found in the cytosol) or 70S (found in the mitochondria). The 'S' stands for Svedberg units, indicative of their rate of sedimentation. The 70S ribosomes, similar to their prokaryotic counterparts, are composed of two subunits: 50S and 30S, indicating that during the centrifugation, prokaryotic ribosomes sediment separately as these two distinct subunits.

Protein Synthesis

Protein synthesis is a fundamental biological process where cells build proteins based on genetic instructions.

This complex process occurs in several stages, which include initiation, elongation, and termination. First, mRNA delivers the genetic blueprint from the DNA to the ribosome. Here, the ribosome reads the information found on the mRNA and, with the help of tRNA, which brings in amino acids, begins to assemble the protein in a process called translation.

Throughout translation, tRNA molecules pair with specific codons on the mRNA strand, ensuring the correct sequence of amino acids is formed. The ribosome facilitates the formation of peptide bonds between amino acids, gradually synthesizing the nascent protein chain. Upon completion, the finished protein undergoes folding and, if necessary, post-translational modifications before it can become fully functional.

Prokaryotic Ribosomes

Prokaryotic ribosomes are the cellular machinery for protein synthesis in bacteria and archaea.

Unlike eukaryotic cells, prokaryotes only possess 70S ribosomes. These are split into two subunits when not active: the larger 50S and the smaller 30S subunits. Each subunit is made up of its respective ribosomal RNA (rRNA) and proteins. Interestingly, mitochondria in eukaryotic cells also contain 70S ribosomes, reflecting their evolutionary ancestry related to prokaryotes. This unique characteristic supports the endosymbiotic theory which suggests that mitochondria were once independent prokaryotic organisms that entered into a symbiotic relationship with their host cells.

Understanding the structure and function of prokaryotic ribosomes is essential for the development of antibiotics, as many of these drugs specifically target bacterial ribosomes without affecting eukaryotic (80S) ribosomes, thereby selectively inhibiting bacterial protein synthesis with minimal impact on the host organism.