Introduction to mitochondrial ribosomes

Mitochondrial ribosome is a kind of ribosome existing in eukaryotic mitochondria, which is responsible for the translation process in organelle mitochondria. The sedimentation coefficient of mitochondrial ribosome is between 55s and 56s, which is the smallest ribosome in sedimentation coefficient. The differences in composition and physical and chemical properties of mitochondrial ribosomes in different organisms are greater than those of cytoplasmic ribosomes.

Second, the size of mitochondrial ribosomes.

The sedimentation coefficient of mitochondrial ribosomes is smaller than that of 70S ribosomes, but mitochondrial ribosomes are not degenerate 70S ribosomes or "sub-ribosome particles". In fact, the mass and volume of mitochondrial ribosomes are larger than those of 70S ribosomes.

The reason why the sedimentation coefficient of mitochondrial ribosomes is small is largely due to its high protein content and small RNA molecules.

Composition and gene expression of mitochondrial ribosomes

I. Composition

Generally, mitochondrial ribosomes are composed of 28S ribosome subunits (small subunits) and 39S ribosome subunits (large subunits). Among these ribosomes, rRNA accounts for about 25% and ribosomal protein (RP) accounts for about 75%. The protein content of mitochondrial ribosomes is the highest. Mitochondrial ribosomes contain 2-3 kinds of rRNA and 85 kinds of RP. ?

Another study holds that human mitochondrial ribosomes contain only 78 kinds of RP. Mitochondrial ribosomal proteins ("MRP") can be divided into primary binding proteins and secondary binding proteins according to their sequences that bind to rRNA during ribosomal self-assembly.

Among mitochondrial ribosome 39S subunits, L7, L 13, L 14, L2 1, L26 and L44 have been proved to be primary binding proteins, while L8, L1,L28, L35 and L40.

Second, gene expression.

The components of mitochondrial ribosomes are encoded by two genomes belonging to the nucleus and cytoplasm respectively, so mitochondrial ribosomes need the co-expression of the two genomes. Genes encoding mitochondrial ribosomes in mammalian nuclei evolve faster than those encoding 80S ribosomes. ?

All ribosomal proteins in mitochondrial ribosomes are encoded by nuclear genes and synthesized by 80S ribosomes. These ribosomal proteins need to be transported from cytoplasmic matrix to mitochondria to complete the assembly of mitochondrial ribosomes.