Microorganisms Chapter 20 Sec. 2 Viruses. Are viruses alive? Viruses are so small they can only be seen with an electron microscope. But is a virus alive?

Microorganisms

Chapter 20

Sec. 2 Viruses

Are viruses alive?

Viruses are so small they can only be seen with an electron microscope.

But is a virus alive?

– Viruses can only reproduce by infecting a host cell.– Viruses do not grow, instead they are assembled.– Viruses are not made of cells.– Viruses do not carry out metabolic processes to maintain

homeostasis.

But, viruses do have genetic material – DNA or RNA

Viral Structure

Basic structure:

– Nucleic acid core (RNA or DNA)

– Protein coat or capsid – a protein sheath that surround the nucleic acid core

– Some viruses have an envelope – a membrane that surrounds the capsid

• has receptors to help the virus bind to host cells

– Nucleocapsid – envelope that covers the nucleic acid

– Tail fibers – some viruses called bacteriophages that infect bacterial cells have a tail with tail fibers.

Viral Structure Continued

Glycoproteins – proteins on the outside of the envelope which attach to carbohydrate molecules on host cells.

Reverse Transcriptase – only in RNA viruses – transcribes (translates) the viral RNA into viral DNA and is then inserted into host cell.

Tail fibers – some viruses called bacteriophages that infect bacterial cells have a tail with tail fibers.

Virus Shape

Viruses have many different shapes.

Virus Categories

Viruses are split into two categories based on their nucleic acid core:

– DNA viruses either insert their DNA into the host cell or the DNA remains separate, but uses the host’s enzymes and nucleotides to make new copies of its DNA and more viruses.

• The DNA may be single-stranded or double stranded.• Examples include: smallpox and Hepatitis B

– RNA viruses use reverse transcriptase to transcribe their RNA into DNA, insert the DNA into the host cell’s DNA, and then is transcribed into viral mRNA to make new viruses.

• Most often called retroviruses• Examples include: HIV, Rhinovirus

Viral Reproduction

Viruses can only reproduce inside a host cell.

Two cycles by which viruses can reproduce:

– Lytic life cycle– Lysogenic life cycle

Lytic Cycle

Virus attaches to host cell’s membrane and injects its nucleic acid into the host cell.

The viral nucleic acid takes over protein synthesis, creating new viruses.

The host cell bursts, lyses, and releases the newly formed viruses and then dies.

Viruses that reproduce only by the lytic cycle are called virulent.

Lytic Cycle

Lysogenic Cycle

The viral DNA becomes part of its host cell’s DNA.

– This virus is called a prophage.

When the host cell replicates its own DNA, it also replicates the provirus.

– New cells that are produce contain the provirus

– New viral particles are NOT assembled and the host cell is not destroyed.

After a period of time – days, months, or even years – the provirus may leave the host’s DNA and enter a lytic cycle.

– Sometimes the virus never enters the lytic cycle and becomes a permanent part of the host’s DNA

A virus whose reproduction includes the lysogenic cycle is called a temperate virus.

Lysogenic Cycle

Combined Lytic and Lysogenic Cycles

Viroids and Prions

Viriods and prions are molecules that are able to reproduce and cause disease.

Viroids are a single strand of RNA without a capsid.

– The RNA of a viroid is much smaller than that of a viruses.

– Replicate inside a host’s cell to make new viroids

– Disrupt a cell’s regulation of growth

– Some viroids have caused abnormal development and stunted growth in plants such as cucumbers and potatoes.

Viroids and Prions Prions are mistake

versions of proteins that are found in the brain.

– They attach to normal proteins and cause them to take on the shape of the prion.

– The normal protein then stops functioning.

– This causes a chain reaction of misfolding among the other proteins which destroys brain tissue.

Prions ContinuedCause a disease in humans known as Creutzfeldt-Jakob disease

You may also be familiar with Mad Cow Disease in cows.

Another disease is chronic wasting disease in deer and elk

Microorganisms

Chapter 20

Sec. 1 Bacteria

Prokaryotes

Let’s recall what a prokaryote is . . . .

Single-celled, no membrane bound organelles, no nucleus

Oldest living things on Earth

Fossils date back 3.5 billion yrs ago

Divided into two major groups– Archea– Bacteria

Archea

Found in many places, including extreme environments such as salt lakes and hot springs.

– methanogens, halophiles and thermoacidophiles

Structurally they are different from Bacteria.

Some Archaean molecules are more similar to those found in eukaryotes.

Includes cyanobacteria which helped produce oxygen through photosynthesis to make the current Earth atmosphere

Oldest fossil is 3.5 billion years old and found in Western Australia.

Eubacteria

Most prokaryotes belong to this domain.

Virtually found everywhere.

Broken into groups based on three shapes.

– Spirillum, coccus, and bacillus.

Bacterial Structure

Bacterial DNA is a single chromosome clustered in a mass called a nucleoid.

May have extra loops of DNA called plasmids.

– Bacterial plasmids are used in current medical research to help find cures for diseases.

Bacterial Structure

Ribosomes and other enzymes

Cell membrane

Flagella for movement

Pili to adhere to surfaces

Bacterial Structure

Bacterial Structure

Rigid cell wall

– Made of peptidoglycan, a protien-carbohydrate compound

– Presence or absence of a cell wall helps biologist to group bacteria

– Use a technique called gram-staining to identify two groups of bacteria

• Gram-positive or gram-negative

Gram-Staining

Dies (crystal violet and safranin) are used to stain the peptidoglycan layer of the bacterial cell.

Gram-staining helps doctors decide what type of antibiotics can be used to treat the infection.

More on Gram-Staining

Anthrax bacteria (purple rods) in cerebrospinal fluid sample. The other cells are white blood cells.

A Gram stain of mixed Staphylococcus aureus (Gram positive) and Escherichia coli (Gram negative).

Anthrax bacteria (purple rods) in cerebrospinal fluid sample. The other cells are white blood cells.

Anthrax bacteria (purple rods) in cerebrospinal fluid sample. The other cells are white blood cells.

A Gram stain of mixed Staphylococcus aureus (Gram positive) and Escherichia coli (Gram negative).

Anthrax bacteria (purple rods) in cerebrospinal fluid sample. The other cells are white blood cells.

How do Bacteria obtain energy?

Bacteria are grouped based on their energy sources.

3 groups

– Photoautotrophs – energy from photosynthesis

– Chemoautotrophs – energy from inorganic compounds

– Heterotrophs – energy and nutrients from other organisms

Bacterial Reproduction

Bacteria reproduce using 3 different methods.

1) Binary Fission – single cell divides into two identical cells

2) Endospore Formation – formation of a thick-walled stucture that protects the bacterial DNA and a small bit of cytoplasm from harsh conditions

• Can survive boiling, radiation, and acid

• Can survive for hundreds of years

Bacterial Reproduction continued

3) Genetic Recombination – ways that bacteria can form new genetic combinations

• Conjugation occurs when two bacteria exchange information.

• Transformation occurs when bacteria take up DNA fragments from their environment.

• Transduction occurs when genetic material (such as a plasmid) is transferred by a virus.

Microorganisms

Chapter 20Sec. 3 Bacteria, Viruses and Humans

Viruses, Bacteria, and Humans

Pathology – the study and the diagnosis of disease.

– Pathogen – anything that causes a disease.

– Toxin - a poison that is produced by bacterial pathogens and that damage cells.

• Ex: Botulism occurs when canned food is contaminated with endospores of the bacterium Clostridium botulinum

Bacterial Disease

Bacteria cause disease by producing toxins or by destroying body tissue.

– Ex: Group A streptococcus bacteria produce strept throat, but if untreated the bacteria can get into muscle or skin tissue and cause necrotizing fasciitis (when the flesh dies off).

We treat bacterial diseases with antibiotics.

Antibiotics

First discovered by the scientist Alexander Fleming in 1927.

– penicillin

Antibiotics – a drug that kills or slows the growth of bacteria.

– Ex: amoxicillin, zithromycin, ciprofloxacin

– Each antibiotic targets a specific group or specific bacteria

Antibiotic Resistance

Antibiotic resistance – as time goes on many bacteria are becoming resistant to antibiotics because of overuse of the antibiotic or mutations for resistance.

– Overuse of hand-sanitizers and not taking the recommended dose are contributing factors

Useful Bacteria

Bacteria make oxygen, decompose organisms, and make nitrogen available to other organisms

– Ex: nitrogen fixing bacteria combine nitrogen and oxygen and make it available for plants.

Bacteria help humans digest food and exist virtually on every inch of the human body. Nodules on roots of this soy

bean plant are full of nitrogen fixing bacteria.

Nodules on roots of this soy bean plant are full of nitrogen fixing bacteria.

Nodules on roots of this soy bean plant are full of nitrogen fixing bacteria.

Useful Bacteria Continued

Bacteria are used in many industries such as sewage treatment facilities and cleaning up oil spills.

Bacteria are also used to make a variety of foods.

– Ex: pickles, yogurt, soy sauce, and sourdough bread

Viral Disease

Because viruses enter host cells to reproduce, it is difficult to develop a drug that kills the virus without harming the living host.

Viruses can be transmitted by any action that brings virus particles into contact with a host cell.

– Ex: common cold, Influenza A and B, and HIV

Vaccines

Vaccine – is a weakened form of a pathogen that prepares the immune system to recognize and destroy the pathogen.

Most common types:

– Killed virus – uses killed virus to create an immune response

• Ex: influenza and hepatitis

– Live – attenuated virus – uses live, but modified virus to create an immune response, but the virus does not get the person sick.

• Ex: measles and mumps

Developed Vaccines

Since viruses have the ability to enter into the host cell they are also able to mutate quite rapidly.

This makes producing vaccines sometimes difficult.

Some viruses have been shown to cause some types of cancer.

– Ex: Hepatitis B (liver cancer) and Human papilloma virus (cervical cancer).

– Gardasil vaccine – given to teenage girls to protect against cervical cancer