Ribosomes

1.0What are Ribosomes? 

A ribosome is a complex molecular machine found within all living cells, where it serves as the site of biological protein synthesis, also known as translation. Ribosomes link amino acids together in the order specified by messenger RNA (mRNA) molecules. This process is essential for the production of proteins, which are critical for the structure, function, and regulation of the body's tissues and organs.

2.0Structure of Ribosome

Ribosomes are composed of two major components: the small ribosomal subunit and the large ribosomal subunit. 

Each subunit consists of ribosomal RNA (rRNA) and proteins. The specific structure of ribosomes can vary between prokaryotes (such as bacteria) and eukaryotes (such as animals, plants, and fungi), but the fundamental principles of their operation are conserved across all domains of life.

3.0Ribosomes In Prokaryotes

Prokaryotic ribosomes are 70s particles, where "s" stands for Svedberg unit, a measure of the rate of sedimentation in centrifugation rather than size. This sedimentation rate reflects the size, shape, and density of the particles.

Subunits: The 70s ribosome is made up of two subunits: the 50s (large subunit) and the 30s (small subunit). The 50s Subunit is composed of a 23s rRNA molecule, a 5s rRNA molecule, and about 31 proteins while the 30s subunit is composed of a 16s rRNA molecule and about 21 proteins.

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4.0Ribosomes In Eukaryotes

Eukaryotic ribosomes are 80S in size, where "S" stands for Svedberg units, a measure of how fast particles sediment in a centrifuge. The 80S ribosome is made up of two subunits: the large 60S subunit and the small 40S subunit.

Ribosomal RNA and Proteins: Eukaryotic ribosomes are composed of ribosomal RNA (rRNA) and ribosomal proteins. The 40S subunit contains a single rRNA molecule (18S rRNA) and about 33 proteins. The 60S subunit contains three rRNA molecules (5S, 5.8S, and 28S rRNA) and about 49 proteins.

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5.0Function of Ribosomes

Ribosomes play a crucial role in the molecular biology of all living cells by acting as the site of protein synthesis. Here's an overview of their function:

Translation of mRNA: Ribosomes translate messenger RNA (mRNA) into proteins. mRNA, which is transcribed from DNA, carries the genetic information that specifies the amino acid sequence of the protein to be produced. 

Amino Acid Assembly: Ribosomes facilitate the sequential linkage of amino acids to form a polypeptide chain. They move along the mRNA strand, reading its nucleotide sequence in sets of three bases (codons), each of which specifies a particular amino acid.

Peptide Bond Formation: Ribosomes catalyze the formation of peptide bonds between adjacent amino acids using peptidyl transferase activity. This reaction occurs in the ribosome's large subunit, linking the amino acids together and extending the growing polypeptide chain.

Polyribosomes or Polysomes: Multiple ribosomes can simultaneously translate a single mRNA molecule, forming structures known as polyribosomes or polysomes. This process increases the efficiency of protein synthesis, allowing multiple copies of a protein to be produced rapidly from a single mRNA molecule.

Location: Ribosomes can be found floating freely within the cytoplasm (producing proteins that function within the cytoplasm) or attached to the endoplasmic reticulum (ER), forming the rough ER (producing proteins destined for secretion or for use in the cell membrane).