A large subunit and a small subunit. A small subunit and A large subunit
Prokaryotes have 70 S ribosomes, each consisting of a small (30S) and a large (50S) subunit. Their small subunit has a 16S RNA subunit (consisting of 1540 nucleotides) bound to 21 proteins. The large subunit is composed of a 5S RNA subunit (120 nucleotides), a 23S RNA subunit (2900 nucleotides) and 31 proteins. Eukaryotes have 80S ribosomes, each consisting of a small (40S) and large (60S) subunit. Their 40S subunit has an 18S RNA (1900 nucleotides) and 33 proteins. The large subunit is composed of a 5S RNA (120 nucleotides), 28S RNA (4700 nucleotides), a 5.8S RNA (160 nucleotides) subunits and 46 proteins. Ribosomes that are found in eukaryotic cells are tiny, round organelles that generate proteins from mRNA. Ribosomes are composed of protein and ribosomal RNA. The structure of the ribosome is composed of two subunits. One of the subunits is larger than the other. Ribosomes are produced in the nucleolus of the cell. The proteins that make up the ribosome are brought into the nucleolus and assembled into subunits. Afterward, the subunits are transported to the cytoplasm Each ribosome has a large component and a small component that together form a single unit composed of several ribosomal RNA molecules and dozens of proteins. The ribosome is responsible for translating encoded messages from messenger RNA molecules to synthesize proteins from amino acids. ribosome. The ribosome is a complex molecule made of ribosomal RNA molecules and proteins that form a factory for protein synthesis in cells. In 1955, George E. Palade discovered ribosomes and described them as small particles in the cytoplasm that preferentially associated with the endoplasmic reticulum membrane Ribosomes from different types of cells have the same basic structure but vary in size. Thus, all ribosomes are composed of two subunits. Each subunit contains a characteristic set of rRNA (ribosomal RNA) and ribosomal proteins. In the case of the eukaryotic ribosome, the two subunits are called the 40S (Svedberg unit) and the 60S subunits.  The ribosome has two subunits; a smaller one and a bigger one. The smaller one contains 21 proteins and one rRNA molecule, and the larger subunit contains 34 proteins and two rRNA molecules. Ribosomes are found in prokaryotes and eukaryotes (although they are a little different, they have the same function). Ribosomes are made of nucleolus. Some people might think that mRNA also helps to form the structure of the ribosome, but this is not the case. rRNA makes up the ribosome of a cell, while mRNA travels to the ribosome of a cell during protein synthesis in order to code for the amino acids. The ribosome (/ˈraɪbɵˌzoʊm/) is a large and complex molecular machine, found within all living cells, that serves as the site of biological protein synthesis (translation). Ribosomes link amino acids together in the order specified by messenger RNA (mRNA) molecules. Ribosomes consist of two major components: the small ribosomal subunit, which reads the RNA, and the large subunit, which joins amino acids to form a polypeptide chain. Each subunit is composed of one or more ribosomal RNA (rRNA) molecules and a variety of proteins. Eukaryotes have 80S ribosomes, each consisting of a small (40S) and large (60S) subunit. Their 40S subunit has an 18S RNA (1900 nucleotides) and 33 proteins. The large subunit is composed of a 5S RNA (120 nucleotides), 28S RNA (4700 nucleotides), a 5.8S RNA (160 nucleotides) subunits and 46 proteins. Distinguishing Characteristics: Ribosomes are typically composed of two subunits: a large subunit and a small subunit. Ribosomal subunits are synthesized by the nucleolus. These two subunits join together when the ribosome attaches to messenger RNA (mRNA) during protein synthesis.  Ribosomes are organelles composed of ribosomal proteins (riboproteins) and ribonucleic acids (ribonucleoproteins). The word ribosome is made from taking ‘ ribo ’ from ribonucleic acid and adding it to ‘ soma ’, the latin word for body. Ribosomes are bound by a membrane but they are not membranous. 
https://en.wikipedia.org/wiki/Ribosome http://www.brighthub.com/science/medical/articles/110037.aspx http://www.nature.com/scitable/definition/ribosome-194 http://www.nobelprize.org/educational/medicine/dna/a/translation/ribosome.html http://www.answers.com/Q/What_are_ribosomes_made_of https://en.wikipedia.org/wiki/Ribosome http://biology.about.com/od/cellanatomy/p/ribosomes.htm http://bscb.org/learning-resources/softcell-e-learning/ribosome/
what are ribosomes composed of