VIRUSES: Alive or Not?

RECALL: The SIX Characteristics of Life

• Made up of cells• Made up of similar

chemicals• Uses energy• Grows and develops• Responds to the world

around them• Reproduces

WHAT IS A VIRUS?• Virus: small,

nonliving particle that invades and then multiplies inside a living cell.– Do not use energy

to grow or to respond to their surroundings

– Cannot make food, take in food, or produce wastes

The common cold virus - Rhinovirus

Virus Shapes and Sizes• Vary in shape and

size– Round– Rod-like– Robot-like– Brick shaped

• Although they vary in size, all viruses are extremely tiny. The largest virus is no more than 250 nm long.

• What’s a nanometer?

Virus Structure1. Protein Coat

- each virus has unique proteins on its coat, the shape of the proteins determine which cells it will attack.

2. Genetic Material- Either DNA or

RNA

Viruses Can Only Multiply When They

are Inside a Living Cell• Viruses act

like a parasite because they destroy the host cells they take over when they multiply.

Two Types of Viruses• Once a virus enters the cell it takes over

the cell’s functions.• Some viruses take over right away, others

wait a while.– Active virus– Hidden virus

Examples of each kind:

Hidden – HIV, herpes

Active – Rhinovirus, Influenza, Chicken pox

How Do Viruses Multiply?

STEP ONE:ABSORPTION

The virus attaches itself to the cell membrane

                                                                                   

                   

How Do Viruses Multiply?

STEP TWO:ENTRY

The virus injects its genetic material.

How Do Viruses Multiply?

STEP THREE:REPLICATION

The cell starts to produce the virus’s proteins and genetic material.

How Do Viruses Multiply?

STEP FOUR:ASSEMBLY

New viruses assemble.

How Do Viruses Multiply?

STEP FIVE:RELEASE

The cell bursts open releasing new viruses.

Hidden Viruses Multiply Differently

• The only difference is that the hidden virus’ genetic material becomes a part of the organism for a while until it becomes active.

• See the difference here.• Cep-1021

REMEMBER THE STEPS

•ABSORPTION•ENTRY•REPLICATION•ASSEMBLY•RELEASE

Viral Diseases1. Can cause some short-term

sickness (Ex. Common cold)2. Can cause death (Ex. AIDS)3. Spread through physical

contact or inhaled droplets4. NO medications to cure

viruses.- medicines can treat the

symptoms- Our immune system (white

blood cells) is our first defense

Preventing VirusesVaccines: substance

that stimulates the body to produce chemicals that destroy viruses or bacteria.- may be dead or altered viruses- they activate the body’s natural defenses

How are Antibiotics and Vaccines

Different?ANTIBIOTICS

A chemical used to kill or slow the growth of bacteria

VACCINESVirus introduced into the body in order to put the body “on alert.” If the virus ever infects the body, the immune system recognizes it and destroys it.

Why get a Vaccine?

– How are vaccines beneficial? – Besides vaccines, what other

methods should be used to help prevent disease?

– Why do people still get the flu even though they’ve gotten the flu shot?

– Why not just get a SUPER Flu shot that covers them all?

EXAMPLES OF VIRUSES

• Polio• Small pox• Human

Papillomavirus• AIDS• Influenza• Herpes

How Viruses Effect Humans

• HPV

• More than 100

different strands

• Transmitted by

direct contact

• Symptoms: Warts or

none

• Very extreme case:

– Tree man

Measles – A Case Study• Symptoms: Measles symptoms usually show up in two stages.

– Stage 1: runny nose, cough, and a slight fever. As the infection progresses, the person's eyes become red and sensitive to light, and the fever rises.

– Stage 2 (3-7 days later) The fever reaches 103oF-105oF, and a red blotchy rash appears. The rash usually starts on the face and then spreads to the chest, back, and arms and legs,.The rash lasts for 4 to 7 days. Small white spots might also appear on the gums and inside of the cheeks.

• Measles is very contagious. An uninfected person can get measles simply by breathing the air in a room where an infected person has been. – The virus can live in the air for 2 hours after an infected person leaves a

room. Infected persons are usually infectious to others even before symptoms appear. (hidden virus)

• Complications: Pneumonia occurs in up to 6 percent of reported measles cases and accounts for 60 percent of deaths from measles. Encephalitis (inflammation of the brain) can also occur. – Infants under age 2 years and adults over age 20 have a greater risk of

complications.

• Prevention: Get vaccinated! – Not so easy for some.