Bacteria and Viruses Chapter 20

Biology II

3 Domains of Living Organisms

Section 1 - Bacteria

• Prokaryotes

– Oldest living things on Earth

• Date back 3.5 mya

– Single-celled organisms

• No membrane bound organelles

– 3 shapes

• Rod – bacillus

• Sphere – coccus

• Spiral – spirillum

• Divided into 2 main groups….. (both referred to as bacteria)

– Domain Archaea

– Domain Bacteria

**Bacterial Cell Shapes

• 3 basic shapes

– Bacillus (rod-shaped)

– Coccus (round-shaped)

– Spirillum (sprial)

Archaea & Bacteria

ARCHAEA

• Found in many places

–Mostly extreme environments

• Structurally different from bacteria

BACTERIA

• Can be found everywhere

• One square inch of skin hosts 100,000 bacteria

Bacterial Structure

• Have genetic material (DNA)

–A single chromosome clustered in a mass called a nucleoid

–Often have small extra loops of DNA called plasmids

• Have ribosomes

• Enzymes

• Can also form granules of stored nutrients to be used when in short supply

Bacterial Structure, cont.

• Membrane – lipid bilayers

• Rigid cell walls

– Can be 1 or 2 layers thick

• Cell wall made of a protein-carbohydrate compound called

peptidoglycan

– May also have a membrane covering peptidoglycan layer

• Presence of membrane allows us to group them using technique called Gram stain

– Gram positive - have a thick layer of peptidoglycan and NO outer membrane

– Gram negative – have a thin layer of peptidoglycan and have an outer membrane

Bacteria Structure

Gram-Positive Bacteria

• Gram stain involves two colors of dye

• First dye is dark purple

– Gram-positive dye trap the dark purple because peptidoglycan layer is very thick

• Second dye is pink

– Pink is absorbed, but cannot be seen because purple dye is much darker

• Appear PURPLE after staining…

Gram-negative Bacteria

• Thin peptidoglycan layer does not trap purple dye

• When pink dye is added, it is absorbed

• Appear pink after staining

• Out membrane of Gram-negative bacteria make them more resistant to host defenses and to medicines

Gram-Staining

Obtaining Energy and Nutrients

• Bacteria differ in how they obtain energy and nutrients

• They are typically grouped based on how they obtain energy

– *Photoautotrophs

– *Chemoautotrophs

– *Heterotrophs

–EACH WILL BE DISCUSSED INDIVIDUALLY

Photoautotrophs • Significant fraction of world’s photosynthesis carried out by

bacteria

– Get their energy from sunlight through photosynthesis

– Four major groups based on pigment:

• Purple nonsulfur bacteria

• Purple sulfur bacteria

– Oxygen free environment

• Green sulfur bacteria

– Oxygen free environment

• Cyanobacteria

– Major component of plankton that float in oceans

– Produce great deal of oxygen

– Probably formed Earth’s oxygen atmosphere

Chemoautotrophs

• Only organisms to obtain energy from inorganic sources

– Use molecules that contain sulfur or nitrogen

• Some that live in soil play great role in agriculture

– Nitrification – oxidize ammonia into nitrate

• Commonly used by plants

Heterotrophs

• Most bacteria are heterotrophs

• Together with fungi, heterotrophic bacteria are the principal decomposers of the living world

• Many are aerobic – live in presence of oxygen

– Some can live without

• Produce more than ½ of our antibiotics - Streptomyces

• Some can create poison in food – Staphylococcus

• Nitrogen-fixing – Rhiozbium

– Live within lumps on the roots of legumes

• Farmers rotate crops every few years with a legume to replenish soil with nitrogen

*Reproduction and Adaptation

• Reproduce by binary fission

• Exchange genetic material through conjugation, transformation, and transduction

• Survive harsh conditions by forming endospores

Binary Fission

• Usually asexually via binary fission

• Single cell divides into two identical new cells

• Mutation do occur during prokaryotic reproduction

– New forms emerge frequently

Paramecium….

Genetic Recombination

• Conjugation

– Occurs when two bacteria exchange genetic material

• 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

• Plasmids often convey antibiotic resistance

Conjugation

Endospores

• Form thick-walls around bacterial chromosomes and cytoplasm in harsh conditions

– Can survive MAJOR stress (boiling, radiation, and acid)

• Allow bacteria to germinate YEARS after they were formed

• END 20.1

Section 2 – Viruses

• **All living things:

–Are made of cells

–Are able to grow and reproduce

–Guided by DNA

• Smallest living organisms = prokaryotes

• Viruses are segments of nucleic acids contained in a protein coat

– Smaller than prokaryotes

• Must be viewed with electron microscope

Viruses, cont.

• Viruses are pathogens – cause disease

• Replicate by infecting cells and using the cells to make more viruses

• DO NOT have all the properties of life…

–Do not grow

–Do not have homeostasis

–Do not metabolize

• =NOT alive

Viral Structure

• All viruses have nucleic acid and a capsid

– Some have an envelope or tail fibers

Nucleic Acids

• Protein coat, or capsid may contain either RNA or DNA, but not both

– DNA viruses – warts, chickenpox, mononucleosis

• Makes copies by using the host cells’ enzymes and nucleotides

– RNA viruses – HIV, influenza, and rabies

• Viral RNA may be used to directly make more

• Can also be transcribed into DNA and then inserted into host cell’s DNA

Capsid

• Encloses its genetic material

• Proteins on the host cell recognize and have to match proteins on the capsid of a virus

– Like lock and key

• Made from proteins

Envelope

• Many viruses, like HIV, have a membrane, or envelope surrounding the capsid

• Gives virus overall shape

• Made of proteins, lipids, and glycoproteins

–Glycoproteins – proteins with attached carbohydrate molecules

Tail Fibers

• Bacteriophages – viruses that infect bacteria

– Complicated structure..

• Ex – T2 – has a capsid attached to a tail with tail fibers

–Act like a tiny syringe

» Inject the viral DNA into bacterial host

Viral Reproduction

• Rely on living cells (host cells) for replication

• **Can replicate by two different processes

– **lytic life cycle

– **lysogenic cycle

Lytic Cycle

• Lytic cycle – cycle of viral infection, replication, and cell destruction

– Viral DNA stays separate from hosts DNA

• After viral genes enter cell, they use host cells to:

– uses host cells organelles, enzymes, and raw materials to replicate viruses’ DNA and to make viral proteins

• Proteins are then assembled to form complete viruses

–Host cell is broken open and releases newly made viruses

• Called virulent viruses…

Lysogenic Cycle • Some viruses stay inside the cell during

an infection and do NOT make new viruses – Viral gene is inserted into host cell

chromosomes, which is called provirus

• When the cell divides, the provirus also divides – results in two infected host cells

• In this cycle, the viral genome replicates

without destroying the host cell. – Changes in environment can cause

virus to begin lytic cycle, results in cell destruction

• Called a temperate virus…

Lytic vs. Lysogenic Virus Replication

Viroids and Prions

• Emerging diseases caused by nonliving particles

– Can reproduce and cause disease

• Viroids – single strand of RNA (has no capsid)

– Can replicate inside a host’s cell to make new viroids

– Disrupt a cell’s regulation of growth

• Cause abnormal development in plants

• Prions – misshapen versions of proteins found in the brain

– Attach to normal proteins and cause them to take on the shape of the protein

• Misfolding leads to chain reaction and destroys brain function

– Ex – Creutzfeld-Jakob in humans and mad cow disease

– Transmitted by eating food contaminated with infected brain tissue

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Section 3 – Bacteria, Viruses, and Humans

• Not all bacteria and viruses are bad

• Play important roles in environment and industry

– Produce oxygen, make nitrogen available, help decompose dead organisms

– Foods (pickles, soy sauce, sourdough bread, yogurt)

– Used in cleaning up oil spills and in sewage treatment plants

• Impact humans in many ways

– Genetic research

– Viruses used in gene therapy

Koch’s Postulates and Disease Transmission

• Koch developed a technique for diagnosing cause of infection

– Still used today to identify pathogens

• Koch’s postulates:

– Step 1 – find and isolate the pathogen

– Step 2 – grow the pathogen

– Step 3 – infecting a healthy animals

– Step 4 – isolating the same pathogen

• Transmission

– Person to person (kissing, animal and insect bites), air, in contaminated food or water, utensils (toothbrushes, computer keyboards, kitchen sponges, and doorknobs.

Bacterial Diseases

• Pathology – scientific study of disease

• Cause disease in 2 ways

– Produce toxins (most common)

• Food poisoning

– Destroy body tissues

• Produce enzymes that break down the host’s tissues into nutrients the bacteria can use

Important Bacterial Disease

Antibiotics

• Chemicals that inhibit the growth of or kill microorganisms

• Development of Resistance

– The ability of bacteria to tolerate antibiotics

– Mutations for resistance occur

– Antibiotic resistance spreads when sensitive populations of bacteria are killed by antibiotics

• Causes resistant bacteria to thrive

• Consequences of Resistance

– Must constantly switch antibiotics to decrease resistance

– Fear that bacterial diseases will eventually become impossible to cure

****Antibiotic-Resistant Bacteria

• Susceptible bacteria are eliminated from the population, and resistant bacteria survive and reproduce, thus passing on their resistance traits

• Antibiotic Misuse

– If full course of antibiotic if administered, usually all targeted bacteria are killed = no chance for resistant strain to develop

• If treatment ends prematurely, some can survive

– ALWAYS TAKE THE FULL DOSAGE OF ANTIBIOTICS

• Multiple antibiotic resistance

– Patient is being treated with 2 or more antibiotics at once

• Selects for bacteria that have already acquired antibiotic resistant genes

• Antibacterial soap – routine use may favor resistance to antibacterial agents in soap

– Could reduce ability to treat common bacterial infections

Stop and Think

• 1. Describe the beneficial roles of bacteria and viruses in the environment, industry and research.

• 2. List the four steps in Koch’s postulates.

• 3. Explain two ways that bacteria cause disease.

• 4.Describe how antibiotic resistance spreads.

Viral Diseases

• cause disease in bacteria, plants, and animals.

• enter host cells to reproduce

– difficult to develop a drug that kills the virus without harming the living host.

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

• have been shown to cause some types of cancer.

– Hepatitis B (liver cancer)

– Epstein-Barr (Burkitt’s lymphoma)

– Human papilloma virus (HPV) (cervical cancer)

Viral Diseases, cont.

• Many symptoms of a viral infection, such as aches and fever

– result from the body’s response to infection.

• Many viral diseases can be prevented through vaccination.

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

Viral Diseases

Emerging Viruses

• are newly recognized

• have spread to new areas or to a new host

• diseases that have reemerged when a disease that was once considered under control begins to spread

• **Examples

– Bird flu – deadly to birds not humans

– SARS – sudden acute respiratory syndrome

– Hanta virus – rodents carry this

• Decline in vaccination thought to play role

Quick Quiz

• State if the following disease are caused by a bacteria or virus.

• Lyme disease

– Bacteria

• Measles

– Virus

• Stomach ulcers

– Bacteria

• Tetanus

– bacteria

• Avian Flu

– Virus

• AIDS

– virus

• Cervical cancer

– Virus

• Can all these diseases be cured by antibiotics?

• NO

Stop and Think

• 1. Explain why it is difficult to develop a cure for viral diseases.

• 2. Describe what an emerging disease is. Give an example.

• 3. If cold viruses invade your body your body’s immune system may destroy most but not all of the these viruses. How does your body’s immune system affect the evolution of the cold virus?