Ribosomes
introduction
Ribosomes are cell organelles in the cytosol. They are used to build proteins. The structure of proteins takes place in different stages within the framework of protein biosynthesis. Part of protein biosynthesis is translation; translation takes place on the ribosomes. Here the mRNA is translated into amino acid chains, from which proteins are ultimately built.
Ribosomes either occur as free ribosomes in the cytosol or form on the cytosolic side of the membrane of the rough endoplasmic reticulum (rER).
construction
Ribosomes are from one small and a larger subunit constructed, each of which consists of single-stranded rRNA and various proteins.
A distinction is made according to molecular weight eukaryotic ribosomes the 60 S and the 40 S Subunitswho put together a crowd of 80 p to have.
Prokaryotic ribosomes have a mass of 70 p and consist of one 50 S and a 30 S subunit.
The subunits are synthesized in the nucleolus of the cell nucleus and transported through the pores of the cell nuclear membrane into the cytoplasm, where they form the finished ribosomes.
Function of ribosomes
Ribosomes are complexes of ribosomal RNA (rRNA) and proteins. The function of ribosomes is to produce soluble proteins that meet the cell's own needs. All proteins occurring in a cell are synthesized on ribosomes.
Protein synthesis
The exact one Amino acid sequence is genetic in DNA determined and will be in the course of transcription in a messenger RNA (mRNA) translated. The mRNA released from the nucleus binds to the small subunit of a ribosome, whereupon the large subunit also binds and protein synthesis begins. The small subunit recognizes certain sequences in the mRNA, while the large subunit the individual amino acids are linked to form a protein chain.
The Rewriting the mRNA into a chain of amino acids is called Translation designated. The complete ribosome migrates along the mRNA, while a transfer RNA (tRNA) procures the right amino acid building blocks and connects them with one another.
The translation of proteins whose destination is outside the cell or which are intended for incorporation into the membrane takes place on rough endoplasmic reticulum (rER) instead, whereas proteins that are required in the cell itself are synthesized on free ribosomes.
Types of ribosomes
One distinguishes two forms of ribsomes:
- free ribosomes, which are scattered freely in the cytoplasm are present
- membrane-bound ribosomes of the rough endoplasmic reticulum (= rER)
Function of free ribosomes
In contrast to the membrane-bound ribosomes of the rER come free ribosomes scattered in the cytoplasm in front. This is the job of the free ribosomes Production of soluble proteinsthat are used to build the cell and are therefore not channeled out of the cell.
Size of ribosomes
Ribosomes usually have one Size of approx. 20 nm. Ribosomes can also be distributed as groups in the cytosol and are then referred to as polyribosomes, which can have different sizes.
