MDCAT Acellular Life & Viruses 2026

Virus Structure

• Capsid (protein coat) + nucleic acid (DNA or RNA, never both)
• Some have envelope (lipid + glycoprotein)
• Obligate intracellular parasites — cannot replicate alone

Lytic vs Lysogenic

• Lytic — attachment → penetration → biosynthesis → assembly → lysis (host destroyed)
• Lysogenic — viral DNA integrates into host (prophage); replicates with host; can switch to lytic later

Common Viruses

Bacteriophage (T4 attacks E. coli), HIV (retrovirus, reverse transcriptase), influenza, polio, COVID-19 (SARS-CoV-2).