Viruses Chapter 18, Section 2

Pre-assessment Before watching the video clip, answer the following questions: Is a virus a living thing? 2. Why do viruses have specific shapes and sizes? Link to Section Launcher Video Clip

Viruses A nonliving strand of genetic material within a protein coat. Are not all harmful but are known to infect and harm all types of living organisms. Very small

Living or Nonliving? Organisms are living if : grow and reproduce, made up of cells, have DNA, maintain homeostasis

Living or Nonliving? Viruses DO NOT maintain homeostasis & DO NOT metabolize They CAN NOT live without being inside of a host NO true cells – no nucleus, cytoplasm, or organelles DO reproduce VIRUSES ARE NOT LIVING!

Diagram of Virus

Structure of a Virus Viruses can have different arrangements All viruses have at least two parts: Capsid – outer layer of all viruses, made of protein Genetic material - inside of the capsid (may be DNA or RNA, never both)

Classification of Viruses Shape (spherical, polyhedral, rod, helical, many sided with tail) Nucleic acid (RNA or DNA) Type of host affected (bacteriophage - virus that infects bacteria) How they are transmitted (vector)

Viral Replication Rely on living things to replicate (must enter a host to replicate) During replication, viruses can evolve and change 2 replication cycles: 1) lytic cycle 2) lysogenic cycle Visualizing Replication Cycles Link

Lytic Cycle Kills the host, enters host and immediately begins to produce more viruses. Viruses that replicate by lytic cycle often produce active infections like the common cold or influenza

Lytic Cycle

Lysogenic Cycle Doesn’t kill the host, enters host and becomes part of the DNA and causes no immediate harm until right conditions (can be dormant for months or years) Example: Herpes Simplex I

Retroviruses Has RNA instead of DNA. Ex: HIV Link to Retrovirus Animation

Human Virus Table

Virus Examples Polio Herpes Pink eye Cold sores Smallpox Warts Chicken pox AIDS Common cold

Viruses and Disease Vaccines- weakened viral particles that prevent viral disease by producing antibodies Viruses can cause cancers - hepatitis B (liver cancer), HPV virus can cause cervical cancer

Prions A prion is a protein that can cause infection or disease. Prions normally exist in cells. Normal prions are shaped like a coil. Mutations in the genes that code for these proteins occur, causing the proteins to be misfolded. Mutated prions are shaped like a piece of paper folded many times. They can cause normal proteins to mutate. Abnormal prions infect and burst nerve cells in the brain, leaving spaces that make the brain look like a sponge