Question

Sedimentation coefficient of mitoribosomes of higher plants is
A. 80S
B. 70S
C. 65S
D. 55S

Answer 1

Hint: Mitochondria is a cell organelle. In addition to it, mitochondria consist of circular DNA and all the enzymes which are required for the process of synthesis of DNA which is the genetic material in all organisms. It is a protein complex that is active in the ribosome. Translation of mRNA is done using the mitoribosome.

Complete answer:
Mitoribosomes are also called mitochondrial ribosomes. Like cytoplasmic ribosomes, mitoribosomes also have two subunits. In mitochondria protein complexes are present and their main function as riboprotein is to translate mitochondrial mRNAs which are encoded in mtDNA. They are large (mtLSU) and small (mt-SSU). Mitochondrial proteins are synthesized through cytoplasmic ribosomes. The small subunit is responsible for the complementarity between tRNA anticodon and mRNA whereas the large subunit catalyzes the formation of peptide bonds. 80S ribosomes are also called eukaryotic ribosomes. They sediment faster than the prokaryotic ribosome. 70S ribosome is found in plants and animals which is made up of two subunits that is small subunit 30S and large subunit 50S. It is found in all eukaryotes and also in some prokaryotes.
So, option B: 70S is the correct answer. As it is the sedimentation coefficient of mitoribosomes in higher plants. Their main function is peptidyl transfer and peptidyl hydrolysis in the mitochondria.

Note: In mammals 55S mitoribosomes are found which is formed by small subunit 28S and large subunits 39S. The S in the naming of the ribosome stands for svedbergs which is a unit used to measure how fast the molecules move during centrifuge in a centrifugal machine.