VIRUSES AND BACTERIA

Bacteria

The word bacteria is so familiar that we will use it as a common term to describe prokaryotes.

Prokaryotes come in many sizes and shapes, they are unicellular organisms that lack a nucleus.

Classified into two kingdoms….Eubacteria and Archaebacteria

Eubacteria

The larger of the two kingdoms Live almost everywhere…water, land,

and within the human body. Very diverse with many different

lifestyles.

Eubacteria

They contain a cell wall which is made of a carbohydrate called peptidoglycan.

Also have a cell membrane and cytoplasm.

Some include flagella for movement.

The pili are involved in cell-to-cell contact.

Archaebacteria

They are alike to eubacteria in the fact that they are small, lack nuclei, and have a cell wall but chemically they are quite different.

They LACK the carbohydrate called peptidoglycan in their cell walls.

The DNA sequences of key archaebacterial genes are more like those of eukaryotes than those of eubacteria.

Scientists reason that archaebacteria my be the ancestors of eukaryotes.

Archaebacteria

They live in harsh environments.

Some produce methane gas.

They can live in oxygen free environments.

Some live in thick mud, intestines of animals, hot springs, or extremely salty environments.

Identifying Prokaryotes

Prokaryotes are identified by characteristics such as Shape Chemical Nature of Cell Walls Movement How they obtain energy.

Prokaryotes by Shapes

Rod-Shaped prokaryotes are called bacilli

Prokaryotes by Shapes

Spherical prokaryotes are called cocci

Prokaryotes by Shapes

Spiral shaped prokaryotes are called Spirilla

Prokaryotes by Shapes

Prokaryotes by Shapes

Prokaryotes by Movement

Some move some do NOT

Some have flagella while others lash, snake, or spiral forward.

Still others glide slowly along a layer of slime like material they secrete.

Prokaryotes by Metabolic Diversity

Bacteria will vary depending on their source of energy and whether or not they use oxygen for cellular respiration.

Heterotrophs or Autotrophs

Prokaryotes that are Heterotrophs

Some heterotrophic prokaryotes must take in organic molecules for both energy and a supply of carbon they are called chemoheterotrophs. Most animals (humans too) are chemoheterotrophs.

A smaller group of heterotrophs prokaryotes are called photoheterotrophs. These organisms are photosynthetic BUT they also need to take in organic compounds such a carbon sources.

Prokaryotes that are Autotrophs

Some groups of autotrophs called photoautotrophs use light energy to convert carbon dioxide and water to carbon compounds and oxygen in a process similar to that of green plants.

These live in an environment where light is abundant like near the surfaces of lakes, streams and oceans.

Ex: cyanobacteria

Prokaryotes that are Autotrophs

Other prokaryotes make organic carbon molecules from carbon dioxide but do NOT require light. They are called chemoautotrophs.

Instead, they use energy directly from chemical reactions involving ammonia, hydrogen sulfide, nitrites, sulfur, or iron.

Some chemoautotrophs live in deep in the darkness of the ocean. They obtain energy from hydrogen sulfide gas that flows from hydrothermal vents on the ocean floor.

Prokaryotes- Energy

Bacteria need a constant supply of energy. This energy can be released by the process of cellular respiration and fermentation or BOTH.

Obligate Aerobes- require constant source of oxygen Ex; Mycobacterium tuberculosis…cause tuberculosis

Obligate anaerobes- must live in the absence of oxygen. Ex: Clostridium botulinum found in soil…it can grow in canned

food because it does not require oxygen Facultative anaerobes- can survive with or without

oxygen. Because of this they can live just about anywhere. Ex: E.coli—lives anaerobically in the large intestines and

aerobically in sewage or contaminated water.

Prokaryotes- Binary Fission

When a bacterium has grown so that it has nearly doubled in size, replicates its DNA and divides in half, producing 2 daughter cells.

This is known as binary fission.

Does not exchange genetic info….asexual reproduction.

Prokaryotes- Conjugation

During Conjugation, a hollow bridge forms between two bacterial cells, and genes move from one cell to the other.

This transfer of genetic information increases genetic diversity in populations of bacteria.

Prokaryotes- Spore Formation

Ex: Bacillus anthracis…which causes the disease anthrax is one such bacteria.

During harsh conditions some bacteria have developed a structure called a spore.

This spore will enclose a portion of the bacteria’s DNA and cytoplasm.

It can remain dormant for months or years until more favorable conditions.

This allows the bacteria to survive.

Viruses!! Viruses can be very

difficult to understand.

A biologist, Wendell Stanley in 1935 inferred that viruses were NOT alive.

Viruses are particles of nucleic acid, protein, and in some cases lipids.

Viruses differ widely in terms of size and structure

They all enter living cells and once inside use the machinery of the infected cell to produce more viruses.

Most viruses are so small then cannot be seen without an electron microscope.

A typical viruses is composed of a core of DNA or RNA surrounded by a protein coat called a capsid.

The simplest viruses contain only a few genes whereas the most complex may have more than a hundred genes.

Viruses!!

Viruses!! The capsid includes proteins that enable

a virus to enter a host cell. Once inside the, the viral genes are

expressed. Sometimes the genetic program causes

the host cell to make copies of the virus, and in the process the host cell is destroyed.

Because the virus must bind to certain proteins on a cell surface and then use a host’s genetic system MOST viruses are highly specific to the cells they infect.

Viruses!! Plant viruses infect plant cells Animal viruses usually only infect certain

related species Viruses that infect only bacteria are

called bacteriophage.

Virus Structures Bacteriophage

Virus Structures Tobacco Mosaic

Virus

Virus Structures Influenza

Virus

Viral Infection Once the virus is inside the host cell two

different process may occur. Lytic Infection or Lysogenic Infection

Viral Infection Lytic Infection- a virus enters a cell , make a

copy of itself, and causes the cell to burst. Lysogenic Infection-, a virus integrates its

DNA into the DNA of the host cell, and the viral genetic information replicates along with the host cells DNA

The viral DNA that is embedded in the host’s DNA is called a prophage. It may remain in the host cell for many generations before becoming active.

Assignment- Draw, color, and label Figure 19.10 on page 481

Retroviruses Some viruses contain RNA as their genetic

information are called Retroviruses. When they infect a cell they must use their

RNA to create a DNA copy, which can then be inserted into a host cell.

They get their name “retro” meaning backwards because usually we go from DNA to RNA and in this cause it goes backwards…RNA to DNA

The virus that causes acquired immune deficiency syndrome (AIDS) is a retrovirus.

Diseases caused by Bacteria and Viruses

Bacteria and viruses are everywhere in nature.

Its pathogens--disease causing agents that get all the attention.

Bacteria can cause disease in one of two ways.

1. The bacteria damage the cells and tissues of the infected organisms directly by breaking down the cells for food. Ex: Tuberculosis

2. Other bacteria release toxins that travel throughout he body interfering with the normal activity of the host. Ex: Strep throat and

diphtheria

Preventing Bacterial Disease

Some bacterial diseases caused by pathogenic bacteria include Lyme disease, tetanus, strep throat and tooth decay.

Many such disease can be prevented by stimulating the body’s immune system with a vaccine.

A vaccine is a preparation of weakened or killed pathogens.

When injected into the body, a vaccine sometimes prompts the body to produce immunity to the disease.

Preventing Bacterial Disease

Antibiotics can also be used once the bacterial infection does occur.

Antibiotics are compounds that block the growth and reproduction of bacteria.

Penicillin and tetracycline are antibiotics. The dramatic increase in human life

expectancy during the past two centuries can be attributed to the better understanding on how to prevent and cure bacterial infections.

Controlling Bacteria

Although most bacteria are harmless and many are beneficial, the risks of bacterial infection are great enough to warrant efforts to control bacterial growth.

There are various methods used to control bacterial growth, including sterilization, disinfectants, and food processing.

Viral Disease in Humans

Like bacteria, viruses produce disease by disrupting the body’s normal equilibrium.

The virus will attack and destroy certain cells in the body, causing symptoms.

Unlock bacterial diseases, viral diseases cannot be treated with antibiotics.

The best way to protect against viruses is prevention often by the use of vaccines.

The symptoms of the infections can often be treated but NOT the viruses.