The predominant cells in blood are the red blood cells (RBC) which contains a protein called hemoglobin. Hemoglobin is the principal determinant of the color of blood. Arterial blood and capillary blood are bright red, as oxygen imparts a strong red color to the heme group.
Concept 21 RNA is an intermediary between DNA and protein. DNA is found mostly in the cell nucleus, but another type of nucleic acid, RNA, is common in the cytoplasm. Watson and Crick proposed that RNA must copy the DNA message in the nucleus and carry it out to the cytoplasm, where proteins are synthesized. Crick also predicted the existence of an adaptor molecule that reads the genetic code and selects the appropriate amino acids to add to a growing polypeptide chain.
Extracellular RNA. Extracellular RNA (also known as exRNA or exosomal RNA) describes RNA species present outside of the cells from which they were transcribed. In Homo sapiens, exRNAs have been discovered in bodily fluids such as venous blood, saliva, breast milk, urine, semen, menstrual blood, and vaginal fluid.