Bacteria & Viruses

DO NOW:

What are the characteristics of viruses? Bacteria? What

kingdom do each of these belong? Are they living? Why or

why not?

What do you already know?

• What are the differences between viruses and bacteria?

• Are all bacteria harmful?• When you get a cold, should you

take an antibiotic to help you get better?

• What’s the best and easiest thing to do to avoid getting sick?

Bacteria

• Bacteriology is the study of bacteria• Bacteria are prokaryotic, unicellular

organisms containing DNA and ribosomes.• Bacteria have ALL the characteristics of living

things.• Bacteria have the greatest percentage of the

biomass on Earth!

Bacterial Structure• Basic structure of bacteria:

Ribosome

PiliDNAFlagellum

Peptidoglycan*

Cellwall

Cellmembra

ne

Bacterial Structure• Bacteria have three distinct shapes:

spherical(cocci)

rod-shaped(bacilli)

spiral(spirilla)

Bacteria• Bacteria have a variety of important uses:

– Help make interesting food (buttermilk, yogurt, cheese, sauerkraut, pickles, and olives, etc…)

– Decompose organic matter (recycle nutrients from dead organisms; break down sewage into simpler compounds)

– Nitrogen fixation (chemically changes nitrogen gas, N2, into ammonia, NH3, so plants can make amino acids)

– Human health (bacteria on skin help prevent infection & bacteria in gut helps digest food & make vitamins)

– Biotechnology (used to make antibiotics, insulin, human growth hormone, vitamins, and other drugs)

How Do Pathogenic Bacteria Work?

• Bacteria produce disease in one of two ways:• Using cells for food: The bacteria break

down healthy cells for food, destroying tissues

• Releasing toxins: The bacteria produce a toxin (poisonous protein) that is released into the bloodstream where it can travel throughout the body, disrupting normal activity and damaging tissues

Bacteria• A rather vocal minority (less than 1%) of

bacteria cause disease in humans, animals, and plants.

• Bacteria can cause a variety of diseases:– Food Poisoning – Scarlet Fever– Tuberculosis – Whooping Cough– Cholera – Bacterial Meningitis– Syphilis – Pneumonia– Ulcers – Leprosy– Strep Throat – Tetanus

Viruses• Virology is the study of viruses• Viruses are “biological entities” containing

either DNA or RNA that require another cell to survive.

• Viruses have some, but not all, of the characteristics of life.

*So are viruses living or non-living?*• Viruses seem to exist only to make more

viruses!

Viral Structure

• All viruses have the same basic structure:

Nucleic acid core

(DNA or RNA)

Capsid (Protein

coat)

How Do Viruses Work? In order to replicate and make copies of itself,

viruses need a host cell. Any living cell can become a host cell (human, animal, plant, and even bacterial cells!)

Without a host cell, viruses cannot function (i.e.-are harmless!)

Although any cell can theoretically become a host cell, specific viruses will only infect specific cells(EX: HIV will only infect human T cells, a part of your immune system)

How Do Viruses Work?• Attach: The capsid of the virus binds to receptor

proteins on the surface of a host cell, tricking the host cell into thinking it’s not a foreign invader.

• Inject: The virus then injects its genetic material (DNA or RNA) into the host cell.

• Assemble: The viral genes are expressed, turning the host cell into a virus-making factory.

• Repeat: The host cell eventually bursts, releasing the hundreds of newly formed viruses to infect surrounding cells!

lysogenic cycle is a viral replication cycle in which the virus's nucleic acid is integrated into the host cell's chromosome, a provirus is formed and replicated each time the host cell reproduces, the host cell is not killed until the cycle is activated. At this time the virus remains quiet for a very long time and it is said to be hidden. lytic cycle is a viral replication cycle in which a virus takes over a host cell's genetic material and uses the host cell's structures and energy to replicate until the host cell bursts, killing it. This cycle kills the host cell almost right away.

Viruses

• Viruses can cause disease in humans, animals, plants, and even bacteria!

• Viruses can cause a variety of diseases:– Common cold – Polio– Hepatitis A, B & C – Influenza– Herpes – Mumps– Mononucleosis – Measles– Warts – Viral Meningitis– Chickenpox – AIDS

Protection• There are a few big ways to protect yourself

against pathogens (disease causing agents)– Antibiotics (drugs to kill bacteria)– Antivirals (drugs to treat viruses)– Vaccination (using your body’s own immune

system to preemptively guard against attack)

Antibiotics• Antibiotics can only be used to treat bacterial

infections!• Target specific structures on bacteria to kill them.• First made from a fungus (penicillin), now most

are made artificially.• Unfortunately, antibiotic resistance (where the

antibiotic doesn’t kill the target bacteria anymore) is becoming a major problem.

Antivirals• Antivirals can only be used to treat certain viral

infections!• Does not “kill” or disarm the virus permanently; only

shortens symptoms by 1-2 days.• Usually only prescribed to patients with life

threatening symptoms or those that have a greater chance of developing complications (because of their age or they have a high-risk medical condition).

• Just like antibiotics, there is evidence of antiviral resistance too!

Vaccination

• Vaccines can only be used to prevent infections (both viral and bacterial) from leading to disease.

• “Trick” your immune system to make antibodies that destroy foreign “bodies” or particles (such as bacteria and viruses). Your body remembers how to make these antibodies when the real thing invades.

• Made from a weakened virus, inactivated virus, or by using only part of the virus/bacteria itself.

To Review....

• What are the differences between viruses and bacteria?

• Are all bacteria harmful? Explain.• When you get a cold, should you take an

antibiotic to help you get better? Why?• What’s the best and easiest thing to do to

avoid getting sick?