The cell-free fluid portion of the blood is referred to as: plasma. Cells in the blood have limited life spans and are replenished through: bone marrow cells. Must use infected cell machinery to produce more viruses. Protein synthesis (they don"t have ribosomes on their own) How viruses gain entry: breaks in the skin, respiratory track, oral cavity, genital track. Non-enveloped virus (just a protein structure that surrounds genetic material that surrounds genetic material) (polio virus) Enveloped virus (has lipid membrane with proteins inside of it) (hiv) 4 general steps of life cycle of a virus: Absorption: virus (via molecules on the surface of the virus) binds to molecules on the surface of the cell. Enveloped: gets in by fusion of the membrane. Genetic material- dna or rna (directs synthesis of viral proteins) Proteins: nucleocaspid surround and thus protect the genetic material. Enzymes and recognition molecules- help virus infect a host cell and initiate its life cycle.