Bacteria constitute a large domain of prokaryotic microorganisms.

What is a Virus?• A virus is a noncellular particle made up of genetic material and protein that can invade living cells • Structure – Core of nucleic acid surrounded by a protein coat c

Viruses and Prokaryotes

What is a Virus?

• A virus is a noncellular particle made up

of genetic material and protein that can

invade living cells

• Structure

– Core of nucleic acid surrounded by a protein coat called a capsid

– Capsid can be DNA or RNA, but not both

– Core can be several to several hundred genes

SO HOW BIG ARE

• Bacteriophages are viruses that infect bacteria

• Bacteriophage

– Head – capsid and DNA

– Tail – with fibers to attach to bacteria

SHAPES MAY DIFFER BUT…

T4 Bacteriophage Tobacco Mosaic Virus

Influenza Virus

RNA Capsid

Surface proteins Membrane

envelope

RNA

Capsid proteins

• All viruses have

• 1 Chromosome-like part that carries hereditary information – The Core

• 2 Protein coat: Protects hereditary information and provides the shape!

The Capsid

• Tobacco mosaic

virus

MANY SIDED

• bacteriophage

E coli bacteria

Is this why viruses infect us?

• YES!

• Viruses need living

organisms in order to

reproduce and form more

viruses!

virus Injecting DNA

Virus Size

• Size – 20 to 400 nanometers (one

nanometer is one billionth of a meter)

• Specificity – usually infect specific

VIRUSES ARE SPECIFIC IN THE CELLS THEY INFECT

Rabies: only nervous system cells of mammals

Common cold: infects cells on airway passage to lungs

Tobacco mosaic virus : only tobacco plants… not wheat or corn

Lytic Infection

• Cause cells to lyse or burst

1 Infection – chance contact virus with right kind of bacterium Virus attaches to bacterium and injects its DNA Most times, complete virus particle does not enter.

2 Growth – Bacterium can’t tell difference between bacterial and viral DNA RNA polymerase causes mRNA to be made from cell for

virus Viral DNA takes over and produces more DNA and viral

proteins.

3 Replication – Virus uses bacterial material to make thousands of copies of the protein coat and DNA Cell becomes filled with virus particles (All three stages can happen with E coli within 25

minutes!)

4 DNA serves as central point for virus particles to be assembled

Cells fill with virus and lyse (burst) New viruses can now infect new cells.

SO HOW DO VIRUSES CAUSE

DISEASE?

Bacteriophage enzyme lyses the

bacterium’s cell wall, releasing

new bacteriophage particles that

can attack other cells.

Bacteriophage proteins and

nucleic acids assemble into

complete bacteriophage

particles

Bacteriophage takes over bacterium’s metabolism, causing synthesis of new bacteriophage proteins and nucleic acids

Bacteriophage injects DNA into bacterium

Bacteriophage attaches to bacterium’s cell wall

Bacteriophage Bacteriophage DNA Bacteriophage protein

Bacteriophage protein coat

Bacteriophage DNA

Bacterial chromosome

Lytic Cycle

Section 19-3

• RNA viruses

• When they infect a cell, they produce DNA

copies of their RNA genes.

• Retroviruses have their genetic information

copied backwards RNA  DNA

• One retrovirus is HIV Others cause cancer in

animals and humans.

• The theory is that viruses were not the first living things They are dependent on living things to

survive.

EUBACTERIA AND ARCHAEBACTERIA:

The two bacterial

kingdoms

Bacteria on a pin head

• “True” bacteria

• largest Kindgom of prokaryotes

• generally surrounded by cell wall composed of complex carbohydrates

• have a cell membrane (some have 2 cell

• Archaebacteria includes organisms that live in very harsh environments

• Methanogens – live in oxygen free

environments – mud, digestive tracts of animals

• Extremely salty environments

• Hot springs

Bacterial Shapes

Arrangement

• 2 cocci – diplococci

• long chains – streptococci

• clumps, clusters – staphylococci

Cell Wall

• Chemical nature – Gram staining

• Hans Christian Gram

• 2 dyes – crystal violet (purple) and safranine

(red)

– bacteria either take one or the other

– If only one thick layer of carbohydrate and protein molecules outside the cell membrane – picked up

crystal violet – appeared purple – GRAM POSITIVE – If cell had 2nd, outer layer of lipid and carbohydrate – picked up safranine – appeared red GRAM

NEGATIVE

Bacterial movement

• propelled by flagella

• lash, snake, or spiral forward

• no movement

Bacterial Respiration

• Obligate aerobes – require oxygen

• Obligate anaerobes – must live in

absence of oxygen

– example is Clostridium botulinum

• Facultative anaerobes – can live with or without oxygen

• Some can reproduce every 20 minutes

• Held in check by food and production of wastes

• Sexual – involves the exchange of genetic material

• Long bridge of protein forms between the cells

• Donor genetic information transferred to recipient

through bridge

• Recipient cell has different genes at the end than it did

to begin with

• remove wastes and poisons from water

• synthesizing drugs – through genetic engineering

Symbiotic Relationships

(mutuallism)

• E coli in humans – help us digest food – make vitamins we can’t, we give them a home, food, and transportation

• Bacteria in the intestines of cattle allow them to break down cellulose (in grass and hay)

Bacteria in the Environment

• Bacteria are like the stage hands that allow the show to go on without being seen (or always given the credit)

• Bacteria recycle and decompose dead material

• Saprophytes – organisms that use the complex molecules of a once living

organism as their food source

Nitrogen Fixation

• All organisms are TOTALLY dependent on

monerans for Nitrogen

• All Plants need nitrogen to make amino acids NH2)

(-• Because animals eat plants, they get their

proteins from plants

• What percentage of the air is Nitrogen?

• Plants, and most other organisms cannot use this directly

• Need Nitrogen to be “FIXED” chemically as

ammonia

Nitrogen Fixation

• Scientists can make synthetic nitrogen containing

fertilizers by mixing Nitrogen and Hydrogen gases,

heating to 500 degrees C and compressing it to 300 X normal atmospheric pressure – dangerous, expensive, time consuming

• Many cyanobacteria can take nitrogen from the air and convert it to a useable form – this is called Nitrogen

Fixation

• Bacteria are the only organisms that can do this.

• Some plants have a symbiotic relationship with nitrogen fixing bacteria

• soybean – Rhizobium grows in nodules around roots

Diseases caused by Viruses and Monerans

• only a small number of viruses and

bacteria can cause disease

• Pathogens – organisms that cause

disease

• All viruses infect living cells

• Disease occurs when infection causes

damage to the cells

Viruses and Disease

• The body’s own defenses must be used

• Vaccine – dead or weakened viruses that stimulate the bodies defense system

• Symptoms can be treated sometimes, but once someone is infected by a virus, there

is not much science can do

Bacteria and Disease

• Bacterial diseases include:

2 ways bacteria cause disease

1 Damage cells and tissues of infected

organisms directly by breaking down cells

2 Releasing toxins (poisons)

• Many bacteria can live without a host organism

(on a petri dish)

• Rickettsiae cannot live outside a host cell They

have leaky cell walls

• Rickettsiae cause Rocky Mountain Spotted

Fever, typhus, and Legionnaire’s disease

• Measures to fight bacterial infection

include:

– Antibiotics – drugs and natural compounds that attack and destroy bacteria in the body – NOT Effective against viruses