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 chromosomes of the nucleus in a cell and it carries hereditary information. RNA is located in the cell but not in the nucleus. Just as proteins consist of long chains of amino acids, DNA and RNA consists of nucleic acid chains called nucleotides. Nucleotides are composed of three units: base, sugar (monosaccharide) and phosphate. Bases are found in both DNA and RNA. As seen below, they are adenine, cytosine, guanine, thymine, and uracil.