viruses and bacteria · structure consists of a single piece of nucleic acid (either dna or rna)...

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Viruses and Bacteria

What is a virus?

Noncellular particle made up of genetic material and protein that can invade living cells (influenza, HIV, hantavirus, Ebola…)

Do viruses fit in our definition of life?

NO. Viruses cannot be placed in a kingdom as they are not cellular and cannot carry any form of metabolism. They are considered to be obligate intracellular parasites: they can only express their genes and reproduce within a living cell as they lack the structures necessary for independent activity and reproduction.

Where do they come from?

As they are dependent on living organisms, it is likely that they developed after living cells (possibly from bits of genetic material of living cells)

Structure

Consists of a single piece of nucleic acid (either DNA or RNA) surrounded by a protective protein coat called a capsid.

Extremely small (0.01-0.4 µm), compared to prokaryotic cells (1-10 µm), and eukaryotic cells (10-100 µm)

Come in a variety of shapes – rods, helical, cubical etc.

Viral Specificity:

Very specific with respect to host selection (grouped into plant, animal and bacteriophages)

Can only infect a host cell that has a specific receptor on its surface for the virus’ capsid.

Defense against Viral Attack:

First line - skin and mucous membrane which also lines the gastrointestinal and respiratory passageways. The skin is tough and the acidic nature of the stomach is a great disinfectant.

Second line – White blood cells and related cells (called phagocytes) converge on the invaders and proceed to “eat them”. Phagocytes typically collect in one place causing puss to eliminate the waste.

Defence con’t

Antibodies – specific in their actions and will only attack virus’ which they are identified for – ie chickenpox antibody will only attack a chickenpox virus. A virus will stimulate the production of a specific antibody and is the basis of vaccination where an inactivated virus – usually the protein coat – is injected into the blood stream to stimulate the production of antibodies.

Interferons – Proteins produced by the body’s cells when the cells are infected by viruses to “interfere” with the viruses ability to infect other cells

Viruses

Viruses – non cellular particle made up of genetic material and protein that can invade living cells.

Structure – composed of a core of nucleic acid surrounded by a protein coat called a capsid to protect the nuclear core. The nucleic acid core is either DNA or RNA – never both.

Bacteriophages are virus that invade bacteria and contain a capsid, a nucleic acid core and a flagella.

Types of Viruses

Tobacco mosaic virus-rod shaped

Bacteriophages- tadpole shaped

Multiple sided-helical or cube shaped

Lytic Cycle

Life Cycle of a Lytic Virus

Step 1: Infection

-Virus is activated by chance contact with the right kind of host cell

-The virus injects its DNA into cell

Life Cycle of a Lytic Virus

Step 2: Growth

-RNA polymerase (enzyme that makes messenger RNA from the cells own DNA) makes RNA from the genes of the virus

-This RNA shuts down and takes over the infected host cell.

Life Cycle of a Lytic Virus

Step 3: Replication

-Once the virus takes over it uses the material of the host cell to make thousands of copies of its own protein coat and DNA

Life Cycle of a Lytic Virus

Step 3-Replication cont’d

Eventually the cell becomes filled with hundreds of viral DNA molecules causing the host cell to lyse (burst) releasing hundreds of virus particles to infect other cells

Examples: the common cold or a Rhinovirus

Happy Monday!!! Quiz

1. What are the three types of viruses covered in class? (3 marks)

2. What are the two major parts that make up a virus? (1 mark)

3. Outline the 4 steps involved in a lytic virus cycle. (4 marks)

4. Name a virus utilizes the lytic cycle for its replication. (1 mark)

5. Are viruses living? What kind of parasites are they? (1 mark)

Answers!

1. Tobacco mosaic virus, bacteriophage, helical/cube shaped.

2. Capsid + DNA or RNA

3. A. Virus is activated and injects its DNA.

B. RNA polymerase incorporates viral DNA into RNA and shuts down the host cell.

C. The Viral DNA tells the host cell to make copies of itself.

D. Once the cell has made enough copies the cell bursts (lyses)

Answers Con’t

4. Rhino Virus

5. No. Obligate Intracellular Parasites

Lysogenic Infection

Lysogenic Infection

DNA of the virus is inserted into the DNA of the host cell where it is known as a prophage where it may remain part of the DNA of the host cell for many generations.

Lysogenic Infection

The presence of this DNA can block the entry of other viruses into the cell and may even add useful DNA to the host cells DNA.

Lysogenic Infection

The virus, triggered by a change in temperature or availability of nutrients will eventually have its DNA become active, remove itself from the DNA of the host cell and promote the formation of new viruses.

Eg. Cold sore/

Herpes Virus

Retroviruses

Contain RNA so when they infect a cell they produce a DNA copy of their RNA genes which is inserted into the DNA of the host cell.

Retroviruses

They have the name retrovirus because their DNA is copied backward from RNA to DNA.

Retroviruses

These viruses are responsible for some types of cancer in animals and humans and AIDS

Monerans-Prokaryotic Cells

Prokaryotes – cells that do not have a nucleus

Placed in the kingdom Monera and divided into four phyla – Eubacteria, Cyanobacteria, Archaebacteria, and Prochlorobacteria.

Monerans-Prokaryotic Cells

These groups share enough similarities to be called bacteria or one celled prokaryotes.

They are considerably smaller than eukaryotes because they lack the membrane – enclosed organelles that are found in most eukaryotic cells.

Eubacteria

Eubacteria: Largest of all Moneran Phyla

Generally surrounded by a cell wall composed of complex carbohydrates, which protects the bacterium from injury

Within the cell wall is a cell membrane that surrounds the cytoplasm

Eubacteria cont’d

Some Eubacteria have flagella that are involved in the movement of the bacteria

Many live in the soil, infect larger organisms to produce disease, while others are photosynthetic

Eubacteria: Label your diagram

Cyanobacteria

Those bacteria that belong to this phyum are all photosynthetic and are also known as blue green bacteria because of a blue pigment called phycocyanin.

Cyanobacteria contain chlorophyll a (thus the green colour) and membranes that carry out the light reactions of photosynthesis. These membranes are much simpler than the chloroplasts found in plants.

Cyanobacteria cont’d

These organisms are found in fresh and salt water and on land, some are capable of surviving extremely hot temperatures and are found in hot springs, while others are able to thrive in the freezing temperatures of the Arctic where they are able to grow on snow.

Archaebacteria

Archaebactera – organisms that live in extremely harsh conditions like the digestive tracts of organisms and in thick mud.

These bacteria produce methane and are called methanogens.

Other Archaebactria live in the salt flats and in hot environments where the water can reach boiling temperatures.

Prochlorobacteria

Prochlorobacteria – contain chlorophyll a and b which makes them similar to the chloroplasts in plants (causing them sometimes to be called Prochlorophyta –phya = plants).

To date only two species of prochlorobacteria have been discovered.

Identification of Monerans

Cell Shape, Cell Wall, Movement

Cell Shape – Bacteria have three basic shapes – rod, sphere, and spiral

Spirilla (spiral shaped) Bacilli (rod shaped) Cocci (sphere shaped)

Identification of Monerans

Cell shape, Cell Wall, Movement

Cell Wall – Because of the thick layer of carbohydrates and protein on the cell wall Gram positive bacteria absorbs the crystal violet and appear purple under the microscope. Those bacteria with a second, outer layer of lipid and carbohydrate molecules took up safranin and appeared red under the microscope (are referred to as Gram negative bacteria).

What does Gram staining look like?

This photo of bacteria under the microscope shows stained bacteria. Scientists uses staining to help identify different species of bacteria. The purple bacteria are Gram Positive bacteria. The red bacteria are Gram Negative bacteria.

Identification of Monerans

Movement – some are propelled by one or more flagella, others snake or spiral forward, while others glide slowly on a layer of slime like material that they create themselves. Finally, some bacteria are not able to move at all.

Cell shape, Cell Wall, Movement

How Monerans obtain ENERGY

Autotrophs versus heterotrophs

Autotrophs – can obtain energy either by trapping it from sunlight like green plants (phototrophic autotrophs such as cyanobacteria or photosynthetic eubacteria) or from inorganic molecules like hydrogen sulfide, nitrites, sulfur, and iron (chemotrophic autotrophs such as Nitrosomonas uses ammonia and oxygen to produce energy).

How Monerans obtain ENERGY

Autotrophs versus Heterotrophs

Heterotrophs – obtain energy by taking in organic material and break them down to absorb them and are referred to as chemotrophic heterotrophs. The majority of bacteria, as well as most animals, are heterotrophs.

Autotrophs and Heterotrophs

Growth and Reproduction

Binary Fission, Conjugation, Spore Formation

Binary Fission – occurs once a bacterium has almost doubled in size. It replicates its DNA and divides in half producing two identical daughter cells

Growth and Reproduction

Binary Fission, Conjugation, Spore Formation

Conjugation – a form of sexual reproduction in which a long bridge of protein forms between and connects two bacterial cells. Part of the genetic information from the donor is transferred to the other cell, the recipient. The recipient now has a different set of genes from those that it had before the conjugation event thus increasing its genetic diversity.

Growth and Reproduction

Conjugation in Bacteria

Growth and Reproduction

Binary Fission, Conjugation, Spore Formation

Spore Formation – occurs when growth conditions becomes unfavorable. The bacterial form a type of spore called an endospore which has a thick internal wall that encloses its DNA and a portion of its cytoplasm. The spore can remain dormant for months until the conditions become favorable again for continued growth. This is not a form of reproduction as no new offspring is produced.

Growth and Reproduction

Spore Formation in Bacteria

How are bacteria involved in the world around us?

2 important ways: Nutrient Flow, Nitrogen Fixation

Nutrient Flow – bacteria recycle and decompose dead material. Saprophytes use the materials of once living organisms as their energy source. Eventually the nutrients return to the ground enriching the soil. Bacteria are also utilized in sewage decomposition to break down human waste, discarded food, organic garbage and some chemical waste.

How are bacteria involved in the world around us?

2 important ways: Nutrient Flow, Nitrogen Fixation

Nitrogen Fixation – All organisms on earth rely on bacteria for usable nitrogen. These nitrogen fixing bacteria convert the N2 in the air to NH3, a form which plants can use to turn the nitrogen into amino acids. Rhizobium are bacteria that live in the nodules on the roots of bean plants. As they fix the nitrogen for the plant the plant provides nutrients and a home.

Bacteria and the Nitrogen Cycle