Viruses

and

Bacteria

What is a virus?

Virus: An infectious particle

that is nonliving.

The word virus comes

from the Latin word

meaning “________”. poison

All viruses are parasites.

All viruses require a host.

Parasites live in or on other

living organisms, causing

them harm.

Parasites:

Host:

The host is the living

organism the parasite

lives on.

Martinus Beijerinck

Dutch Scientist

1898

Beijerinck is considered the

founder of _________.

Virology is:

The study of viruses.

virology

In 1898, he used

filtration

experiments to

prove that:

an agent

smaller than a

bacterium was

causing tobacco

mosaic disease.

He was the first

to name these

very small

particles

“________”. viruses

Wendell Stanley

American biochemist

1904 - 1971

In 1935, Stanley

was able to isolate

crystals of the

tobacco mosaic

virus.

Living organisms

do not crystallize,

so Stanley inferred

that viruses were

not “_____”. alive

Stanley was

awarded the Nobel

Prize in chemistry.

Characteristics of VirusesViruses are _____________.

Most can be seen only with

an _________________.

extremely small

electron microscope

A viruses is active only when

______________. inside a living cell

When removed

from a living cell, it

_______ all

activities, but

retains its ability to

_____________.

ceases

infect the cell

They may be crystallized and stored

indefinitely, but even after longs

periods of time, they retain:

their ability to infect a living cell.

Viruses vary widely in terms of size and structure,

but they all have one thing in common:

They enter living cells and use the machinery of

the cell to produce more viruses.

Viruses are non-cellular.

1 – Head

2 – Capsid

3 – DNA or RNA

4 – Tail fibers

5 – Base plate

6 – Sheath

1. They are not made of cells and

have no cell parts.

2. Viruses consist of two parts:

DNA or RNA surrounded by a

protein coat.

3. Capsid –

The protein

coat that

surrounds

the DNA or

RNA .

The

Viral

Capsid

The capsid is made of

_______ that enable the

virus to enter a host cell.

proteins

The capsid has a particular

_____ that must match

________ on the surface of a

_________.

shape

receptors

host cell

When the virus attaches to

these receptors, the cell is

“tricked” into:

letting the virus inside.

Viruses can reproduce, but

only _______________.

They

reproduce

inside a cell by

getting the cell

to produce

viral parts

instead of cell

parts.

inside a living cell

Since viruses must bind precisely to ________ on the

__________, they are highly specific to the cells they

infect.

proteinscell surface

Plant viruses can only

infect plant cells.

Animal viruses can only

infect animal cells.

Viruses of eukaryotes are

usually tissue specific.

Example: Human cold

viruses infect only the cells

lining the upper respiratory

system, ignoring all other

tissues.Bacteriophages

are viruses that

infect only

certain types of

bacteria.

Viruses are not affected by any

known _______. antibiotic

Anything that

will kill the

virus will also

kill the host.

Living Characteristics of Viruses:1. They can reproduce--but only

inside a living cell.

2. They can mutate or change.

3. They have DNA or RNA.

Their genome may consist of

only four genes, or up to a

hundred genes.

Non-living Characteristics of Viruses:

1. They are non-cellular.

2. They have no metabolism.

They have no food or energy

requirements.

3. They can be crystallized and

dehydrated and stored

indefinitely. They come to

"life" only when injected inside

a living cell.

1. Since viruses have no enzymes

and no cell parts, they force the

host cell to:

___________________.

2. A viral infection begins when:

the genetic material (DNA or

RNA) of a virus makes its way

into a host cell.

3. Once inside, the virus _______

the cell, reprogramming the cell.

start making viral parts

hijacks

4. The viral genome takes over the

________ and makes the host cell

start producing _________.

host cell

viral parts

5. The host cell will begin to make copies of the _________

and producing the ______________.

viral DNAprotein capsids

6. The host cell assembles the parts

into viruses.

7. The reproductive cycle ends with:

the exit of hundreds or thousands of

viruses from the infected host cell.

8. This often ________ the host cell.

Each of these viral progeny has the

capacity to infect neighboring cells

thereby spreading the infection.

destroys

The Two Reproductive Possibilities:

1. Once a virus is inside a host cell, two

different processes may occur.

2. Some viruses replicate themselves

immediately, killing the host cell.

3. Other viruses replicate themselves in a way that

does not destroy the host cell.

4. These two processes

are called:

a) The lytic cycle

b) The lysogenic cycle

In a lytic infection, a virus:

enters a cell, makes copies of itself,

and causes the cell to burst.

Bacteriophage T4 is an

example of a bacteriophage

that causes a lytic infection.

Now, let’s learn

the steps to the

lytic cycle!

Attachment. Tail fibers

are used to attach to

receptor sites on the

surface of the host cell.

Entry. Phage DNA is

injected. Empty capsid

remains outside. Host

cell DNA is destroyed.

Synthesis. The

host cell is directed

to produce viral

genomes and

protein capsids.Assembly. The viral DNA or

RNA is assembled inside the

protein coat.

Release. The cell

swells, bursts, and

releases 100’s of new

viruses.

A phage that

reproduces only by a

lytic cycle is called a

virulent phage.

1. In this type of viral reproduction:

the host cell makes copies of the viral genetic

material indefinitely.

2.The virus incorporates its DNA into the DNA of the

host cell. The viral DNA is then ________ along with

the host cell’s own DNA.

3. Lysogenic viruses do not __________________. A

lysogenic virus may remain ________ for some

period of time.

replicated

kill the cell right away

inactive

Bacteriophage

(phage)

Phage attaches and

injects its DNA.

Bacterial

chromosome

Certain features

determine whether:

Lytic cycle

is induced

Lysogenic cycle

Is entered

LYSOGENICLYTIC

Viral DNA is

incorporated into the

bacterial chromosome,

forming a prophage.

Prophage

Bacterial cell divides by binary

fission normally. The viral

genome is copied and passed to

daughter cells.

Many cell

divisions may

occur, producing

a large

population of

bacteria that are

infected with the

prophage.

Daughter cell

with prophage

New viruses are produced.

The host

cell bursts,

releasing the

new viruses.

Prophage:The viral DNA

embedded into the

host cell’s DNA.

The prophage may remain part of the host

__________________ before becoming

active.

for many generations

Eventually, certain environmental conditions

(chemicals, radiation) may trigger the switchover from

the ________ cycle to the ____ cycle.lysogenic lytic

Retroviruses

Retroviruses have

____ as their

genetic information

rather than _____. DNA

RNA

• These viruses have an enzyme called

__________________, which transcribes their ____ template

into ____. The newly made DNA then enters the

___________ and integrates into the DNA of a chromosome.

• In this way, the retrovirus may remain dormant for some

length of time.

• It will eventually become ______, causing the host

cell to make ___________, and causing the _____

of the host cell.

• Retroviruses are responsible for some types of

cancer.

• The AIDS virus is a retrovirus.

reverse transcriptase RNA

DNA

cell’s nucleus

active

new viruses death

Comparison of Viruses and Cells

Have DNA or RNA

and a protein capsid

Only within a host cell

Cell membrane,

cytoplasm, nucleus,

cytoplasmic organelles

Reproduce independently,

either sexually or

asexually

DNA or RNA

None

No

No

Yes

DNA

Yes, in multicellular organisms

Yes

Yes

Yes

Viral Diseases

There is little that can be done to

cure a viral infection.

Antibiotics are effective against _______, but not

against _______.

bacteria

viruses

A few new drugs have been

developed that interfere

with the reproduction of the

virus, but they only seem to

slow the effect of the virus.

They do not provide a cure.

The battle against viral diseases lies in

the use of vaccines.

Vaccines:Contain a harmless

variation of the

pathogen.

Our immune system launches a

response to the harmless form,

thereby learning to _________ it the

next time that we are _______ to it.

recognize

exposed

When we are exposed to the

"real" pathogen, our immune

system can respond __________

since it has already _______ to

recognize the pathogen.

much fasterlearned

Colds

Hepatitis

Flu

AIDS

Chicken poxWest Nile

Virus

1. They are known for their extreme ________ and small_____.

2. They are much smaller than a _____.

3.They consist of ___________________________, but they

have no __________. They are tiny molecules of

_________________.

4.They have only been identified in plants. But, they are

suspected of causing some diseases in animals for which no

pathogen has ever been isolated.

5.The important lesson we have learned from viroids is that:

a molecule can be an infectious agent and cause

disease.

simplicity

virus

small, circular molecules of RNAprotein coat

naked circular RNA

size

1. These are disease-causing particles that:

do not contain DNA or RNA.

2. They are tiny bits of _______.

3. Prions cause degenerative brain diseases such as

_______________.

4. How can a protein, which cannot replicate itself, be a

pathogen?

The leading hypothesis is that a prion is a

______________________ normally present in brain

cells. When a prion enters a cell that contains the

normal form of the protein, the prion converts the normal

protein to the prion version.

protein

Mad Cow Disease

misfolded form of a protein

The Bacteria

The bacteria are

___________.prokaryotes

A prokaryotic cell:

does not have a

true nucleus or

membrane-bound

organelles.

Prokaryotes dominate the

biosphere. Their collective

biomass outweighs all

eukaryotes combined by at least

10 fold.

cholera

Some are _______ and cause

diseases, but most bacteria are

________________. A

relatively small number of

species cause _______.

harmful

benign or beneficial

disease

They are successful because

of their rapid cell division

(reproduction) and their great

metabolic diversity. They can

double their numbers every

___________ and live in

environments that:

support no other forms of life.

20 minutes

Domain:

Archaea

Kingdom:

Archaebacteria

Domain:

Bacteria

Kingdom:

Eubacteria

Classification of Prokaryotes

Strep

Archaea

The bacteria are separated into two different _______:domains

These are the “true” bacteria.

There is great variety in the organisms that belong to this kingdom. These bacteria are found in every environmenton Earth.

The eubacteria have a cell wall that contains a polysaccharidecalled peptidoglycan.

Eubacteria

Archaebacteria1. Under a microscope,

Archaebacteria look very

_______ to the eubacteria.

They are:

equally small, lack nuclei, and

have cell walls.

2. Chemically, the Archaebacteria

are ____________.

3. The Archaebacteria lack the

_____________ found in the

eubacteria. They also have

different _______________.

4. The Archaebacteria live in:

extremely harsh environments.

similar

very different

peptidoglycans

membrane lipids

Suitable temperature: 80-100 °F.

Moisture

Suitable food source

Darkness

Space to grow

Bacteria are found almost everywhere. The

best environment for growth has:

Bacteria are very large in

comparison to a virus.

Prokaryotes are identified by

several characteristics:

1. Shape

2.The materials composing

the cell wall

3. The way they move

4.The way they obtain

energy

Bacteria exist in three basic shapes:

1. Cocci are

spherical.

2. Bacilli are

rod-shaped.

3. Spirilla are

spiral

shaped.

Movement

Some bacteria are ______ and

others do not move at all.

Some move by means of

_______, whip-like structures

used for movement.

motile

flagella

Some lash or snake forward.

Others glide slowly over a layer

of slime they secrete.

Most bacteria are ________.

Some are ________________________.

harmless

pathogenic (cause diseases)

Soil

bacteria

Label the structures seen in the prokaryotic cell:

1 – cell wall

2 – cell membrane

3 – peptidoglycans

4 – flagella

5 – pili

6 – single, circular

chromosome

(DNA)

7 – ribosomes

The cytoplasm does not contain any…

…..membrane bound organelles.

The chromosome consists of ….

…..one single, circular, continuous molecule of DNA.

The cytoplasm is filled with many _________.ribosomes

A ________ may be present

outside of the ________. It is

composed of a gluey

_____________.

It enables prokaryotes to

adhere to their:

substrate or to other

individuals in the colony.

Some capsules protect

against __________. Some

capsules shield pathogenic

bacteria from:

attacks by their host’s

immune system.

capsulecell wall

polysaccharide

dehydration

Flagella: long whip like structure

used for movement.

Pili are shorter and thinner than

flagella. Pili serve to attach

bacteria to:

1)a food source

2)the surface of a liquid

3)another bacteria during

reproduction.

How Do Bacteria Obtain

Energy?

Most bacteria are ___________.

They do not have the ability to

_________________.

The heterotrophic bacteria are

further divided into….

….saprophytes and parasites.

heterotrophs

make their own food

Saprophytes:

a.Saprophytes live on dead organic matter.

b.Saprophytes are very important as

decomposers.Parasites:

a.A parasite is an

organism that invades

plants and animals and

lives off of them.

b.Host: The organism

that the parasite is living

off of.

A few bacteria are __________. They have

the ability to __________________.

autotrophsmake their own food

Photoautotrophs:

Photosynthetic organisms that use light energy from

the sun to convert carbon dioxide and water into the

organic molecule glucose, and oxygen.

Chemoautotrophs:

Use the energy from inorganic

reactions as a source of energy

to build molecules of glucose.

Growth and ReproductionIf conditions are favorable for growth,

bacteria can grow and divide at incredible

rates.

Many bacteria can divide every

__________ (under ideal conditions).

If reproduction continued unchecked at

this rate, a single prokaryotic cell could

give rise to a colony….

….outweighing Earth in three days.

20 minutes

In reality, prokaryotic reproduction is limited by:

a) the eventual exhausting of food supply

b) being poisoned by their own metabolic waste

c) competition from other microbes

d) being consumed by other organisms

Binary fission is a

type of asexual

reproduction where:

one cell undergoes

cell division to form

two cells.

When the bacterium

has grown to nearly

double its size:

it replicates its DNA

and divides in half.

Two identical

daughter cells

are formed.

During conjugation, a _____________

forms between two bacterial cells.

hollow bridge

Through this tube,

genes move from

one cell to the other.

There is no increase in numbers;

but they have redistributed the

_________________. The

transfer of genetic information

increases ______________ in

future populations.

Now they can go back to binary

fission and increase their

numbers.

genetic information

genetic diversity

Endospore FormationWhen conditions for growth become

__________, many bacteria form

structures called __________.

unfavorable

endospores

An endospore is formed ____________.

The contents of the _________ draw up

together and a ________ is formed

around it.

inside of a cell

cytoplasm

thick wall

These endospores can….

….survive extreme dryness, heat or cold.

They can remain _______ for months or

years while waiting for favorable growth

conditions to return.

dormant

The Importance of Bacteria

Bacteria are vital to

maintaining the living world.

The prokaryotes can easily

survive without the

__________, but the

eukaryotes are totally

dependent on the

___________.

eukaryotes

prokaryotes

Bacteria

Are

Decomposers

All living things

depend upon a

constant supply of:

carbon, nitrogen,

and other essential

elements. These essential

elements must

be recycled

when an

organism dies.

Bacteria are ___________

that help to _______ these

essential chemical elements.

decomposers

recycle

When an organism

dies, it is attacked

by bacteria and

broken down into

simpler materials.

Nitrogen

Fixation

Plants and animals must

have ________ to build

___________. Amino

acids are needed to build

________.

nitrogen

amino acids

proteins

Nitrogen gas makes up about 80% of Earth’s atmosphere, but….

….plants and animals are not capable of using nitrogen gas directly.

In a process called ______________,

bacteria are able to convert

____________________, a form that

plants can use.

nitrogen fixation

nitrogen gas into nitrates

Plants take up these ______

through their ______ and use

them to build ____________.

nitrates

rootsplant proteins

Animals eat the plants, and convert the

_____ proteins into _______ proteins.plant animal

When an organism dies, bacteria __________

the organism, returning this nitrogen to the

__________ to be used again.

decompose

ecosystem

Human Uses For Bacteria

Bacteria are used to

produce a wide variety of:

foods and beverages.

Examples: sour cream,

yogurt, cheese.

Some bacteria can

digest oil and are

helpful in cleaning up

oil spills.

Bacterial Diseases in Humans

Some bacteria are _________.

A pathogen is a disease-causing agent.

pathogens

Bacteria produce diseases in one

of two ways:

Some bacteria:

damage the

cells and tissues

by breaking

down the cells

for food.

Other bacteria:

release toxins

or poisons in

the body of the

host.

Many of the

diseases caused

by bacteria can

be prevented

with the use of

vaccines.

Vaccine:

A weakened or killed form of the

pathogen that stimulates the body’s

immune system to produce antibodies.

Once the body has “learned”to make the correct antibody,

the body will be able to

respond rapidly if infected

with the living, active form of

the pathogen.This rapid response of

the immune system is

called ________.immunity

AntibioticsAntibiotics are

compounds that:

kill bacteria.

They are effective

against _______,

but have no affect

on ______.

bacteria

viruses

Symbiotic Relationships between Organisms

Symbiosis is a _________________ association

between organisms of different species.

There are three types of symbiotic relationships:

• Mutualism

• Commensalism

•Parasitism

close and permanent

Mutualism:

The relationship

is beneficial

to both species.

Commensalism:

A relationship in which one

species benefits from the

association while the other is neither harmed

nor helped.

Parasitism:

A relationship in which one

species benefits and the other is

harmed.