Biology 112BACTERIA AND

VIRUSES

Smallest and most common microorganisms

Unicellular organisms that lack a nucleus

They can be divided into two separate groups

Eubacteria

Archaebacteria

PROKARYOTES

Live almost everywhere

Usually surrounded by a cell wall that protects it from injury as well as determines its shape Cell wall contains peptidoglycan, a carbohydrate

Cell membrane inside the cell wall that surrounds the cytoplasm

Some have a second membrane which further protects it from damage

EUBACTERIA

Have cell walls, lack nuclei and lack the peptidoglycan that is present in eubacteria

There are different lipids existing in their cell membranes

The DNA sequencing is more similar to eukaryotes than prokaryotes May be the ancestors of eukaryotes

Most live in harsh environments, including mud, digestive tracts, volcanoes

ARCHAEBACTERIA

ShapeRod-shaped (bacilli), spherical (cocci), spiral/corkscrew (spirilla)

Composition of Cell WallsThick peptidoglycan walls (gram positive) or thinner walls with a second outer lipid layer (gram negative)

MovementSome do not move at all, others have flagella, which are whiplike structures while others still lash, snake, spiral and glide

IDENTIFYING PROKARYOTES

Heterotrophs (ex. E coli)

Autotrophs (ex. Cyanobacteria)

FOURTH IDENTIFYING CHARACTERISTIC OF PROKARYOTES

(OBTAINING ENERGY)

Heterotrophic ProkaryotesEat other organisms for energy as well as a supply of carbonCalled chemoheterotrophs

Others are autotrophs to obtain their energy but also eat other organisms for their necessity for carbonCalled photoheterotrophs

HOW PROKARYOTES OBTAIN ENERGY - HETEROTROPHS

Use light energy to convert carbon dioxide and water to carbon compounds and oxygenFound where light is availablePhotoautotrophs

Make organic carbon molecules from carbon dioxide but do not require lightUse energy from chemical reactions involving ammonia, hydrogen sulfide, nitrites, sulfur or ironPresent in harsh environments

Chemoautotrophs

HOW PROKARYOTES OBTAIN ENERGY - AUTOTROPHS

They undergo cellular respiration, fermentation or both

Those that require a constant supply of oxygen are called obligate aerobes

Those that do not require it (or may even be killed by the presence of oxygen) are called obligate anaerobes

Those that can survive with or without oxygen are called facultative anaerobesDo not require it but are not harmed by it either

As a result, they can survive almost anywhere

HOW PROKARYOTES RELEASE THEIR ENERGY

How fast they grow and reproduce depends mostly on availability of food and the production/elimination of waste products

When a prokaryote has doubled in its size, it may divide in half through a process called binary fi ssion (daughter cells are identical to single parent cell – asexual reproduction)

Conjugation occurs when a bridge forms between two cells and genetic material can be passed between the two

Spore formation , called endospores, may form within a prokaryote A thick wall forms around the DNA and a portion of the

cytoplasm Spore may remain dormant until more favorable conditions

occur

GROWTH AND REPRODUCTION

Critical for maintaining the living worldSome are producers as well as

decomposersOthers have uses in human survival

DecomposersBacteria recycles nutrients which maintains balance in the environment

Without them, sewage systems would not be able to eliminate all its waste and disease would spread

IMPORTANCE OF BACTERIA

Nitrogen fixersPlants need nitrogen to make amino acids (building blocks of protein)

Nitrogen (N2) must be changed to ammonia (NH3) or other nitrogen compounds (nitrates) before it can be used by living things

This process is known as nitrogen fixation

IMPORTANCE OF BACTERIA

Human uses

Food industry Lactobacillus is used for the preservation of dairy

Industry Sulfate-reducing bacteria in the petroleum industry

Waste removal Bacteria that converts waste into fuel

Mining Bacteria that leaches copper from mines

Synthesize drugs and chemicals for improved health Vaccines

IMPORTANCE OF BACTERIA – HUMAN USES

Viruses are composed of parts of nucleic acid, protein and lipids

Reproduction only occurs by infecting living cells

Great variety in their size and appearance

All viruses infect cells the same way – by entering healthy cells and once inside, use the organelles of the infected cell to produce more viruses

It is typically composed of DNA, RNA and a protein coat

VIRUSES

Protein coat is also called a capsidContains proteins that enable the virus to enter the host cell

Binds to receptors on a healthy cell and “tricks” the cell into allowing it to enter

Once inside, viral genes are exposed to the cell

The healthy cell ‘reads’ the genetic information and then may, as a result, get destroyed in the process

The host cell may also make copies of the virus

STRUCTURE OF A VIRUS

Viruses are highly specific to the host cell it is infecting

As a result, viruses which target plants may not contain the proteins in their capsids to gain entry to an animal cell

Viruses that attack bacteria are called bacteriophages

VIRUSES ATTACK DIFFERENT ORGANISMS

Some viruses replicate themselves immediately once inside the host cell and kill the cell

Others do not replicate in such a way that destroys the host cell immediately Lytic Infection

Virus enters cell, replicates itself, and causes the cell to burst

Destroys the cells DNA, uses the cell to make viral proteins and viral DNA, then releases viral particles

Lysogenic Infection Incorporation of the viruses DNA with the host cell

DNA and replicates along with the host cell’s DNA Viral DNA is called a prophage which may lay

dormant for an indefinite amount of time

VIRAL INFECTION