Ribosomes

Ribosomes - Protein Construction Teams

Cells need to make proteins. Those proteins might be used as enzymes or as support for other cell functions. When you need to make proteins, you look for ribosomes.Ribosomes are the protein builders or the protein synthesizers of the cell. They are like construction guys who connect one amino acid at a time and build long chains. 

Ribosomes are found in many places around the cell. You might find them floating in the cytoplasm (cytosol). Those floating ribosomes make proteins that will be used inside of the cell. Other ribosomes are found on the endoplasmic reticulum. Endoplasmic reticulum with attached ribosomes is called rough. It looks bumpy under a microscope. Those attached ribosomes make proteins that will be used inside the cell and proteins made for export out of the cell. 

Two Pieces Make the Whole

A ribosome is not just one piece. There are two pieces or subunits. Scientists named them 60-S (large) and 40-S (small). When the cell needs to make protein, mRNA is created in the nucleus. The mRNA is then sent into the cell and the ribosomes. When it is time to make the protein, the two subunits come together and combine with the mRNA. The subunits lock onto the mRNA and start the protein synthesis. 

The 60-S/ 40-S model works fine for eukaryotic cells. Prokaryotic cells have ribosomes made of 50-S and 30-S subunits. It's a small difference, but one of many you will find in the two different types of cells. Scientists have used this difference in ribosome size to develop drugs that can kill prokaryotic microorganisms that cause disease. 

Mixing and Matching Amino Acids

The process of making proteins is quite simple. We just explained that mRNA is made in the nucleus and sent into the cell. The mRNA then combines with the ribosome subunits. Another nucleic acid lives in the cell - tRNA, which stands for transfer RNA. tRNA is bonded to the amino acids floating around the cell. With the mRNA offering instructions, the ribosome connects to a tRNA and pulls off one amino acid. Slowly the ribosome makes a long amino acid chain that will be part of a larger protein.