Viruses and ProkaryotesChapter 20.1-20.3

Difference between Bacteria and Viruses

A virus is a strand of DNA or RNA surrounded by a protein coat (CAPSID)

Viruses are not considered to be alive!!

Bacteria are one-celled microorganisms

BOTH ARE INFECTIOUS!

Any disease-causing agent is known as a PATHOGEN

Viral Structure

Structure: genetic material surrounded by a capsid (protein shell).

Different shapes and sizes

Capsids surrounded by lipid envelope or protective outer coat

Why aren’t Viruses Alive?

CAN ONLY REPRODUCE BY INFECTING OTHER

LIVING CELLS

How do viruses enter cells?

Viruses enter host cells in various ways

Eukaryotic viruses fuse with host cell membrane

Eukaryotic viruses enter through endocytosis

When virus is taken in through endocytosis, the virus is now able to reproduce.

Lytic Infection

Viruses cause two types of infections:

First Type:

LYTIC: causes host cell to burst, or lyse

host bacterium

The bacterophage attachesand injects it DNA into a host bacterium.

The host bacterium breaks apart, or lyses. Bacteriophages are ableto infect new host cells.

The viral DNA directs the hostcell to produce new viral parts.The parts assemble into newbacteriophages.

The viral DNA forms a circle.

Lysogenic InfectionSecond Type:

LYSOGENIC: does no immediate harm

Prophage: phage DNA that is inserted into host cell DNA

The viral DNA is called a prophagewhen it combines withthe host cell’s DNA.

Although the prophage is notactive, it replicates along withthe host cell’s DNA.

Many cell divisions produce acolony of bacteria infectedwith prophage.

The prophage may leave thehost’s DNA and enter thelytic cycle.

Bacteriophages

Viruses that infect bacteria

ex: T-bacteriophage, which infects E. coli bacteria

Pierce host cells and inject their DNA into viral hosts

capsid

DNA

tail sheath

tail fiber

Prokaryotes

• Unicellular organisms that lack a nucleus

• DNA not membrane bound and is located in cytoplasm

• Either ARCHAEA or BACTERIA

Bacteria

• Wall protection

• Flagella

• Peptidoglyclan cell wall (polymer of sugars and amino acids)

Archaea

• Walls lack peptidoglycan

• More like eukaryotes than bacteria genetically

• Live in extreme environments (salty, hot, methane-rich)

Great Salt Lake

Prokaryote Structure and Function

• Prokaryotes vary in:

• Size

• Shape

• Mode of movement

• Way obtain and release energy

Size, Shape, and Movement

• Shapes: Bacilli, cocci, spirilla

• Bacilli: rod shape

• Cocci: spherical

• Spirilla: spiral, coiled

Energy Used by Prokaryotes: Nutrition &

Metabolism• Heterotroph: take in nutrients

• Photoheterotroph: use light energy and take in nutrients

• Photoautotroph: use light energy to convert carbon dioxide into carbon compounds

• Chemoautotroph: use energy released by chemical reactions to make food

Energy Released by Prokaryotes

Growth and Reproduction in

Prokaryotes• Reproduce by BINARY

FISSION (asexual)

• When growth conditions are unfavorable, prokaryotic cells form an ENDOSPORE (thick, internal wall that encloses the DNA)

Recombination in Prokaryotes

• Mutations: cause prokaryotes to evolve

• Conjugation: exchange of genetic information when a hollow bridge forms between 2 bacterial cells and genetic material (plasmid) moves from one cell to the other.

Importance of Prokaryotes

• Decomposers

• Producers

• Nitrogen fixers

• Food production

• Drugs and antibiotics

What is a Pathogen?

Microorganisms (viruses and bacteria) that cause disease

Bacterial Pathogens

• Bacteria cause disease by destroying living cells or by releasing chemicals that upset homeostasis

• Damage host tissue

• Release toxins

Methods for controlling bacteria: removal, disinfectants, food storage and

processing, sterilization by heat, vaccines, and antibiotics!

What is the Benefit of a Vaccine?

Vaccines are made from weakened pathogens and stimulates the body’s OWN immune response

Immune system gets MEMORY of pathogen

Made from killed or weakened microbes or certain parts of microbes

Viral Diseases• Viruses cause disease by directly destroying

living cells or by affecting cellular processes in ways that upset homeostasis

Viral DiseasesSome can be prevented with vaccines

Examples of Viral Infections:

Cold

Influenza

SARS

HIV

Mono

Rabies

Smallpox

Common Cold

> 200 different viruses cause cold symptoms each season

High mutation rate

Symptoms last between 5-7 days

InfluenzaWhy is the spread difficult to control?

FLU virus

Spreads quickly, causes local epidemics

20% of American population infected with flu virus per year

Different types of flu viruses affect different species

H1N1 (Swine Flu/Spanish Flu of 1918)

Others infect pigs, birds, horses, etc.

SARS

Severe Acute Respiratory Syndrome

Coronavirus: cause respiratory or enteric infections

8096 infected and 774 deaths from 11/2002-7/2003

Symptoms: Fever, GI problems, cough, sore throat, shortness of breath

HIV/AIDSHuman Immunodeficiency Virus

Lysogenic and Lytic Infection

Retrovirus: contain RNA and uses reverse transcriptase enzyme to make DNA (RNADNA)

Viral DNA enters host nucleus and incorporates itself into host DNA strand and remains dormant for years

When active, however, new viral parts are made, viruses bud or lyse through host cell and infect other host cells.

Mononucleosis

Caused by Epstein-Barr Virus (EBV)

Same family as the Herpes Virus

Has a lytic and a latent cycle

Increases WBCs in bloodstream

Symptoms: severe fatigue, sore throat

In US, 95% of adults 30-40 years old have antibodies against EBV

RabiesCauses acute encephalitis (swelling of the brain)

Most commonly transmitted through bites from animals infected with the virus

Virus travels to the brain via peripheral nerves

Once symptoms begin to show (usually after a few months), the disease is usually fatal.

IF BITTEN BY RABID ANIMAL: need 4 doses of Rabies Vaccine and 1 dose of Human Rabies Immunoglobulin

SmallpoxUnique to humans

Found in blood vessels of skin, throat, and mouth

In 18th century, virus killed 400,000 Europeans; During 20th century, virus killed 300-500 million people throughout the world

Vaccine available

As of NOW, Smallpox is the only infectious disease to be completely eradicated.

What is a Viroid?

Infectious particle

Cause disease in plants

Passed through seeds or pollen

Made only of single-stranded RNA

What is a Prion?

ALSO Infectious

Proteins that can cause other proteins to fold incorrectly

Infections BUT contain NO GENETIC MATERIAL!

Mad Cow Disease

degeneration in the brain and spinal cord