Viruses and Bacteria

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 VIRUSES???

• Viruses are REALLY small.

• They are much smaller than bacteria.

• They can only be seen with an electron microscope.

Bacteriophage

• Bacteriophages are viruses that infect bacteria

• Bacteriophage– Head – capsid and DNA– Tail – with fibers to attach to

bacteria

VIRUS SHAPES

• Round

• Rod-shaped

• Many sided

(icosohedral)

ROUND VIRUSES

• Herpes virus–There are two types:•Genital•oral

ROD-SHAPED

• Tobacco mosaic virus

Why viruses infect us?

All viruses are parasites. Parasites depend entirely upon other living organisms for their existence, harming these organisms in the process.

•Viruses take advantage of the nutrients and cellular machinery of their hosts.

Viruses Living ??

• Viruses have many of the characteristics of living things. – After infecting living cells,

viruses can reproduce, regulate gene expression, and even evolve.

Virus Specificity

•Specificity – usually infect specific organisms

– Cannot infect animals if it infects plants

– Some can infect wider variety– Rabies – all mammals, some

birds

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

Lytic infection:

•virus nucleic acid enters a bacterial cell

•makes copies of itself

• causes the cell to burst or lyse.

Lytic Cycle

Bacteriophage enzyme lyses thebacterium’s cell wall, releasingnew bacteriophage particles thatcan 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

Bacterialchromosome

Lytic Cycle

Section 19-3

Lysogenic Cycle

• viral nucleic acid is inserted into host cell’s DNA

• copied along with host DNA without damaging host.

• Viral DNA multiplies as host cells multiply so each

• generation of daughter cells is infected.

Lysogenic Cycle

Retroviruses• 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 Ex of a 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 & ARCHAEBACTERIA

The two bacterial kingdoms

Bacteria on a pin head

PROKARYOTIC CELLS

Classification of Prokaryotes

lacking a nucleus

•All prokaryotes were in kingdom Monera.

•Now – 2 kingdoms

– Eubacteria

– Archaebacteria

Eubacteria• “True” bacteria• largest Kindgom of

prokaryotes• generally surrounded by cell

wall composed of complex carbohydrates

• have a cell membrane (some have 2 cell membranes)

• Some have flagella for movement

• Found everywhere• Some produce disease• Some photosynthetic• some very useful – cheese is

just one example

Archaebacteria

• 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

Identifying Bacteria

• Cell Shape– Rod – bacilli– Sphere – cocci– Spiral – spirilla

Bacterial Shapes

Round Rod

Spiral

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

Reproduction

• Some can reproduce every 20 minutes• Held in check by food and production of

wastesTypes:

• Binary Fission • Replication of DNA and division in half• Asexual• Conjugation• 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

Importance of Bacteria

• Used in production of products we use every day• Yogurt• Cheese• Buttermilk• Sour cream• Pickles• Sauerkraut• Vinegar• Wine• Industry• digest petroleum• 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

Sewage decomposition

• Sewage treatment – bacteria is added directly to the raw sewage

• How does a septic tank work?

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

• Examples are:– Small Pox– Polio– Measles– AIDS– Mumps– Influenza– Yellow Fever– Rabies– Common Cold– Ebola etc…

Vaccine

• 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:– Diptheria– TB– Typhoid– Tetnus– Hansen disease– syphilis– cholera– bubonic plague– Flesh Eating Bacteria

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