Question

What kind of ribosome is seen in mitochondria? (a) \(80 \mathrm{~S}\) (b) \(70 \mathrm{~S}\) (c) Both (a) and (b) (d) None of these

Short answer

The type of ribosome seen in mitochondria is \(70 \mathrm{~S}\) (Option b).

Step-by-step solution

- Understanding Ribosomes

Ribosomes are minute particles involved in the production of proteins from amino acids. There are two types of ribosomes based on their sedimentation coefficients - \(70 \mathrm{~S}\) and \(80 \mathrm{~S}\). The \(70 \mathrm{~S}\) ribosomes are found in prokaryotes, mitochondria, and plastids of eukaryotes, while the \(80 \mathrm{~S}\) type is found in the cytoplasm of eukaryotes.

- Identify the Ribosome in Mitochondria

Mitochondria being an organelle of eukaryotic cells, but prokaryotic in origin, it possesses \(70 \mathrm{~S}\) type of ribosomes. It doesn't contain the \(80 \mathrm{~S}\) type.

- Choose the Correct Option

With the knowledge that mitochondria only contains the \(70 \mathrm{~S}\) type of ribosomes, the correct option from the ones given is option b - \(70 \mathrm{~S}\).

Key concepts

70S ribosome

A 70S ribosome is a complete ribosomal unit that measures 70 Svedberg units (S), a sedimentation rate commonly used in biochemistry to describe how quickly particles move in a centrifuge. This type of ribosome is typically found in prokaryotes, such as bacteria, but also exists in the mitochondria and chloroplasts of eukaryotic cells.

70S ribosomes are smaller and less complex compared to the 80S ribosomes found in the cytoplasm of eukaryotic cells. They are made up of two subunits: the smaller 30S subunit and the larger 50S subunit.

The smaller structure and different components may make the 70S ribosomes suitable for the simpler protein synthesis processes found in prokaryotic cells and specialized functions in organelles. Understanding the peculiarities of the 70S ribosome, particularly in organelles like mitochondria, provides essential insights into evolutionary biology and the origins of eukaryotic cells.

Organelle ribosomes

Organelle ribosomes are the ribosomes found within certain cell organelles, primarily mitochondria and chloroplasts. These ribosomes play a crucial role in the translation of proteins essential for the organelle's functions. Unlike cytoplasmic ribosomes, organelle ribosomes often exhibit characteristics similar to those of prokaryotic ribosomes.

Mitochondrial ribosomes are a classic example and are believed to have originated from ancestral prokaryotic cells due to their endosymbiotic relationship in evolution. Organelle ribosomes, such as the 70S ribosomes in mitochondria, suggest that these organelles descended from ancient bacteria, explaining their similarities in structure and function.

In chloroplasts, which are involved in photosynthesis in plant cells, ribosomes also present signs of a prokaryotic origin. Understanding organelle ribosomes helps scientists trace the evolutionary lineage of cells and illustrate the complex interactions within eukaryotic organisms.

Prokaryotic and eukaryotic differences

Prokaryotic and eukaryotic cells exhibit significant differences, particularly in their ribosomes, which are critical for protein synthesis. Prokaryotic ribosomes, found in bacteria and archaea, are typically 70S in size, composed of the 30S and 50S subunits. These ribosomes are less complex, reflecting their roles in simpler cellular organisms.

On the other hand, eukaryotic cells have larger, more complex 80S ribosomes, which consist of 40S and 60S subunits. These are present in the cytoplasm and are adapted for the more intricate processes necessary in eukaryotic cells.

Despite these differences, similarities exist. The presence of 70S ribosomes within eukaryotic organelles, such as mitochondria and chloroplasts, highlights the evolutionary connection between prokaryotic and eukaryotic cells. This is a vivid example of endosymbiosis, illustrating how modern eukaryotic cells likely evolved from ancestral cells that formed symbiotic relationships with simple prokaryotes. Understanding these ribosomal differences and connections helps clarify the evolutionary paths that have shaped modern cellular life forms.