Answer: A double-layered membrane called the pericardium surrounds your heart like a sac. The outer layer of the pericardium surrounds the roots of your heart's major blood vessels and is attached by ligaments to your spinal column, diaphragm, and other parts of your body.
Answer: linear or circular. include genes encoding viral proteins: capsid, envelope proteins, any polymerase not found in the host cell. viruses may have a lipid envelope.
