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.
DNA is found in the nucleus of cells (the N of DNA) associated with chromosomes. The genes, segments of DNA, are copied by enzymes to make RNA. RNA is then translated by a very large complex of enzymes into proteins. Some of these proteins are the very enzymes that make RNA and translate the RNA into proteins.