Red blood cells and platelets do not contain nucleus. Red blood cells, or erythrocytes, are specialised cells that circulate through the body and deliver oxygen to the tissues. In humans, red blood cells are small and biconcave, and do not contain mitochondria or a nucleus when mature. Because of the lack of nuclei and organelles, mature red blood cells do not contain DNA and cannot synthesise any RNA, and consequently, cannot divide and have limited repair capabilities.