CHAPTER 16Prokaryotes and Viruses

PROKARYOTIC LIFE BEGAN ON A YOUNG EARTH

Stromatolites are composed of thin layers of sediment pressed tightly together resembling layers in an onion.

The first organisms are found in these layers.

They are called cyanobacteria.

STROMATOLITES ARE LIVING FOSSILS

HOW DID LIFE BEGIN?

There are many questions about how life began.

It is a total mystery but there are theories. The Miller-Urey experiment showed that

inorganic molecules can create organic ones. Water is boiled into steam. Methane, ammonia and hydrogen gas were

present on early Earth. Putting water vapor together with these

compounds and putting an electric charge through them makes organic compounds. Pg. 357

MILLER-UREY EXPERIMENT

HOW DID LIFE BEGIN?

Organic polymers have been made in lab conditions by dripping amino acids on hot surfaces.

The heat evaporates the water leaving behind high concentrations of amino acids bonded together.

THE RNA WORLD HYPOTHESIS

What was the original process of copying hereditary information?

DNA strands can only copy themselves with the help of enzymes but single RNA strands can copy in solutions containing nucleotides without enzymes.

This theory is called the RNA World theory. This could have been the basis for the first

replication. Experiments have shown that pre-cells or

bubbles made of lipids can form around RNA polymers in a solution.

WHERE DID LIFE BEGIN?

It is a mystery where live originated but some likely sites have been identified.

Some sites could be shallow water or moist sediments.

During Earth’s early history, the land surface may have been too hot for molecules or pre-cells to survive.

The discovery of deep-sea hydrothermal vents raised the possibility that energy and chemicals can from vents.

Today’s deep sea vents are populated by a huge diversity of life.

Most of this life is prokaryotic organisms.

DIVERSITY OF PROKARYOTIC LIFE

Archaea comes from the Greek word meaning ancient.

Populate the most extreme places on Earth. Many Archaea are called extremophiles

which means lovers of the extreme. Thermophiles live in boiling hot springs. Halophiles live in salt environments. Others live in volcanic lava, glaciers and

environments where no oxygen is present.

ARCHAEA

DIFFERENCES BETWEEN BACTERIA AND ARCHAEABACTERIA

Bacteria are prokaryotes that differ from Archaea in different ways.

1. There are key differences in the DNA and RNA.

2. There are differences in their types of RNA polymerases.

3. Introns are absent in bacteria but are present in some Archaea.

4. Certain antibiotics kill bacteria but have no effect on Archaea.

5. Bacterial cell walls contain peptidoglycan that is not present in Archaea or eukaryotes.

STRUCTURE AND FUNCTION OF BACTERIABacteria are distinguished by shape, type of cell wall and motility type.

BACTERIA HAVE THREE SHAPES.

Cocci- spherical shapes that are sometimes formed in chains, clumps or clusters, Strep throat and pneumonia are this type

Bacilli- rod shaped such as E. coli that live in your intestines.

Spirochete- curved or spiral shape, this type causes Lyme disease

CELL WALL STRUCTURENearly all bacteria have a cell wall outside their plasma membrane.

PURPLE OR PINK?

Bacteria are stained with two dyes, purple and pink to determine which antibiotics will work for each kind.

Gram positive retain the purple dye in their cell walls.

Gram negative do not retain the purple dye but retain the pink dye instead.

Some antibiotics will only work for one kind.

Gram positive

Gram negative

BACTERIAL MOTILITY Flagella- a long thin filament anchored

to the plasma membrane , may be one or many anchored all over the bacteria

Pili- shorter and thinner filaments that help bacteria stick together in clumps

NOTE: The flagella and pili are different than the kinds you will observe in eukaryotes.

BACTERIAL REPRODUCTIONAnybody good at math?

Better use a calculator!

MOST BACTERIA CAN COPY THEMSELVES EVERY 20 MINUTES!

Binary fission-DNA duplicates and moves to opposite ends of the cell, then the cell divides

This method allows quick reproduction and is much simple than mitosis.

Allows for quick passing of mutant genes. (More on this later!)

GENETIC VARIATION Since bacteria do not undergo meiosis, they do not

exchange genetic information, however, they can do other things.

Transformation occurs when some bacteria take up pieces of DNA from the environment and incorporate it into its genetic material.

In conjugation, two bacterial cells temporarily join and directly transfer genetic material between them.

Plasmids are separate rings of DNA apart from the cell’s main chromosomes.

Transduction is when viruses that infect bacteria carry their genes to another.

They are called bacteriophages. Some bacteria can survive extended periods of very hostile

conditions by forming specialized resting cells called endospores.

BACTERIAL REPRODUCTION

Modes of NutritionType Energy Carbon

Photoautotroph Sunlight CO2

Chemoautotroph Inorganic chemicals

Photoheterotroph Sunlight

CO2

Organic compounds

Chemoheterotroph Organic compounds

Organic compounds

Modes of Nutrition Fossil evidence indicates that the photoautotrophic

mode of nutrition is very ancient. Cyanobacteria generate oxygen as a waste product of

their photosynthesis. Oxygen is toxic to many organisms. It attacks organic

compounds. Many early bacteria went extinct as the oxygen was

created by cyanobacteria. Some anaerobic bacteria or non-oxygen using

bacteria, survive in areas where oxygen did not reach. Their descendants are still alive today in oxygen-free

environments.

Modes of Nutrition The rest of the organisms adapt to oxygen living. Many prokaryotes perform essential function by

breaking down or decomposing organic waste products and dead organisms.

Some species of bacteria convert nitrogen gas in the air to nitrogen compounds in the soil and water.

The converted nitrogen can be used by plants. Humans have discovered many ways of using

prokaryotes. For example, the use of organisms to remove

pollutants from water, air and soil is called bioremediation.

Genetic engineering of prokaryotes helps pharmacies create antibiotics and proteins for use in humans. Insulin is made this way.

How Bacteria Cause Illness

Bacteria and other microorganisms that cause disease are called pathogens.

Most pathogenic bacteria cause disease by producing poisons.

Some bacteria produce proteins that cause illness while others produce cell wall secretion that lead to fever, aches and shock.

Defense Against Bacterial Diseases

Since the discovery of bacteria, many disease have declined.

This is due to better health and sanitation procedures.

Much of the decline is due to antibiotics.

Diseases/Illnesses Caused By Bacteria MRSA TSS (Toxic Shock

Syndrome) Pneumonia Gonorrhea Meningitis Salmonella E. Coli Cholera Bubonic plague Botulism Peptic ulcer Anthrax

Typhoid Staph Strep throat Sepsis Chlamyadia Tuberculosis Syphilis Leprosy Diphtheria Tetanus Rocky mountain spotted

fever Lyme disease

VIRUS STRUCTURE

The structure of a virus is well suited to its function; entering a host cell and reproducing.

A virus is composed of a relatively short piece of nucleic acid DNA or RNA surround by a protein coat.

Since a virus doesn’t have its own cellular machinery, it must use the host cell’s machinery to make copies of itself.

VIRUS REPLICATION

Viruses that infect bacteria called bacteriophages reproduce in 2 ways.

In the lytic cycle, the phage attachs to the host cell and injects its DNA.

The host cell’s enzymes and synthesis machinery make copies of the viral DNA and the viral proteins.

The viral proteins and nucleic acids then assemble themselves inside the host cell making copies of the original infecting virus.

The host cell then bursts open and these offspring infect new host cells and repeat the cycle.

VIRUS REPLICATION

In the lysogenic cycle, a virus injects it genes into the host.

The viral DNA then adds itself directly to the host cell’s DNA.

Each time the host cell reproduces, the viral DNA is copied along with the host’s DNA.

Occasionally, the viral DNA separates from the host DNA and starts a lytic cycle.

New phages are made and released.

LYTIC AND LYSOGENIC CYCLES

T-4 BACTERIOPHAGE

VIRUSES AND DISEASE

Some viruses use RNA as their genetic material.

Some viruses that use RNA are flu, the common cold, measles, mumps, HIV, and polio.

DNA viruses are herpes and hepatitis. The way viruses cause disease is radically

different from bacteria infections. A virus uses the equipment of a host cell to

reproduce therefore approaches to control and cure infection are different from bacterial infection controls.

VIRAL DISEASES/ILLNESSES

Common cold (rhinovirus)

AIDS (HIV) Measles Mumps Herpes (Many forms

including chicken pox) HPV (Human

Papilloma Virus) Hepatitis (A,B,C) Mono

Bird flu Ebola and Marburg Smallpox Dengue Fever Yellow Fever Polio Lassa Fever Meningitis (some

forms) West Nile

HIV: A RETROVIRUS

HIV is a virus that causes AIDS. It is particularly dangerous because it attacks

our own immune system, the very thing meant to protect us.

HIV is different because it is called a retrovirus.

A retrovirus synthesizes DNA from RNA which is the opposite of what normally happens.

An HIV virus carries 2 copies of RNA instead of DNA.

The RNA then uses an enzyme called reverse transcriptase to form DNA from the RNA.

HIV: A RETROVIRUS

The DNA integrates into the host DNA and takes over.

The viral DNA can be dormant for years but occasionally it is transcribed into RNA again and new viruses are made.

While the virus is inactive, the disease symptoms are not evidence.

Only when the virus reproduces and destroys host cells does an individual get AIDS.

HIV LIFE CYCLE

HIV

WHERE IN THE WORLD?

DEFENSE AGAINST VIRAL DISEASES

The immune system is critical to fighting infections and provides the basis for a major medical weapon for preventing certain viral and bacterial infections from occurring.

This weapon is called the vaccine. Vaccines are deactivated varieties or small

pieces of pathogens that stimulate the immune system to defend against the actual pathogen.

THE FIRST VACCINE

The first vaccine was made against the virus that causes smallpox, an often fatal disease.

Edward Jenner, a physician, discovered that milk maids who had been exposed to cowpox, a mild disease, were resistant to smallpox.

The two diseases were so similar that the immune system couldn’t tell them apart.

Jenner injected people with cowpox which then causes resistance to smallpox.

Currently, smallpox has been eradicated. NOTE: Smallpox the disease is gone but not

the virus. It’s “on ice” in a lab somewhere.