Viruses

Chapter 18

What is a virus?

•Microscopic particle (microbe) that invades the cells of living organisms.

Basic Structure Virus• “Particles”• Core- nucleic acid (DNA or RNA)• Capsid- protein coat surrounds core

Are viruses living things?

Characteristic Yes/No Comments

Cells

Metabolism

Reproduce

Heredity

Homeostasis

Characteristic Yes/No Comments

Cells No particles – can not make proteins

Metabolism No too simple to obtain/make energy; only need it to reproduce - steal it from cells infect

Reproduce Yes Only inside host cell

Heredity Yes DNA or RNA

Homeostasis No No method for controlling internal environment

Are viruses Are viruses living living things?things?

Why should we study viruses?

In order to exist and reproduce,

a virus must invade

a living cell.

This living cell is referred to as a host.

In order to replicate, a virus

must invade a

living cell. This living

cell is referred to as a host.

Viral Replication

General Steps:

• Recognition

• Attachment

• Injection

• Assembly

• Lysis

How do viruses infect your cells?

Lytic Virus

•Examples:Common ColdFlu

•Replicates immediately and kills the host cell•You get sick right away.

How do viruses infect your cells?

Lysogenic Virus

•Examples:

HIV

Shingles•Does not kill host cell immediately•Viral DNA injected into host cell and then fuses with host cell DNA•Dormant period•You don’t get sick right away

VIRAL DNA

• All viruses are pathogens.• Animals, plants, fungi, protists, and bacteria can

all be infected by viruses.• Antibiotics do not work.• Antiviral medications• Vaccines are used as prevention only.• Vaccinations are ONLY useful against viruses

that do NOT evolve rapidly.• Flu shot- many different types- flu

Protection Against Viruses