Ribosomes are composed of a large and small subunit that join together when attached to messenger RNA in the cytoplasm to assemble amino acids into proteins based on the nucleotide sequence. Diamond-Blackfan Anemia is a rare inherited disease caused by mutations in ribosomal protein genes that results in not enough red blood cells being made. Ribosomes are about 40% protein and 60% nucleic acid and occur both as free particles and attached to the endoplasmic reticulum in cells.