What is an organelle?
Think of an organelle as a "tiny organ" that is a component of a cell. The organelle usually contains a membrane which helps create a compartment where certain cellular activities can occur without interference from other elements in a cell.
A specific thing in an organelle that has a specific job
Ribosomes are composed of a large subunit and a small subunit. When these two subunits combine, they form a complete ribosome that is capable of converting genetic code found in RNA into a sequence of amino acids. The ending result is a protein structure.
Under a microscope, ribosomes appear to be tiny bead-like structures. These are present in all living cells, including prokaryotes and eukaryotes. These can function in two ways. First, ribosomes can float freely within the cell's cytoplasm. Otherwise, ribosomes can also be attached to a cell structure that is known as the endoplasmic reticulum.
As the cell's protein factories, ribosomes locate and combine disparate amino acids using peptide bonds in order to create more complex polypeptide structures (proteins). Once an RNA sequence enters a ribosome, it programs that ribosome with instructions for producing a specific protein. That ribosome can then absorb amino acids and combine them in the specific order necessary to convert disparate amino acids into a complex chain of amino acids called proteins.
What do ribosomes do?
Ribosomes are where RNA is translated into protein. This process is called protein synthesis. Protein synthesis is very important to cells, therefore large numbers of ribosomes are found in cells. Ribosomes float freely in the cytoplasm, and are also bound to the endoplasmic reticulum (ER).