Bacteria & Viruses

Bacteria & Viruses Mr. Humes Chapters 23 & 24

Prokaryotes • Single celled organisms that do not have a membrane bound nucleus

Domain Archaea • Differ from bacteria in the make up of cell walls, lipids, genetics, and metabolism • Methanogens • Convert H2 and CO2 into methane gas for energy, anaerobic • Found in deep waters, mud, and sewage • Halophiles • Live in high salt concentrations • Thermoacidophiles • Live in acidic environments with high temperatures

Domain Bacteria • Most prokaryotes are bacteria • Occur in many shapes and sizes • Bacilli – rod shaped • Cocci – sphere shaped • Streptococci – chains of spheres • Staphylococci – grapelike clusters of spheres • Spirilla – spiral shaped

Gram Stain • Bacteria are grouped by characteristics of their cell walls • Technique called gramstaining • Gram-negative bacteria • Cells appear red under microscope • Gram-positive bacteria • Cells appear purple under the microscope

Important Bacterial Groups • Proteobacteria – aerobic and anaerobic • Rhizobium – nitrogen fixing bacteria found in the roots of legumes. Fix nitrogen into ammonia for plants to use • ex: E.coli • Gram-positive bacteria • Streptococcus - causes strep throat • Clostridium botulinum - causes botulism, release toxins into environment • Lactobacilli - turns milk sour and makes yogurt • Bacillus anthracis - makes the biological weapon anthrax • Actinmyocetes- form of bacteria that make antibiotics

Important Bacterial Groups • Cyanobacteria - make own food through photosynthesis • Lack a nucleus and membrane bound organelles • Believed to be the first oxygen producing organism on Earth and responsible for putting O2 into our atmosphere • Spirochetes - responsible for syphilisand Lyme disease • Chlamydia - another STI

Biology of Prokaryotes • Cell Wall - made of peptidoglycan instead of cellulose • Cell membrane - regulates what enters and leaves the cell • DNA -circular loop attached to the cell membrane • It is not enclosed in a nucleus • Capsule - an outer covering of the cell that protects bacteria from dry harsh conditions

Biology of Prokaryotes • Pili - short hair like projections on the surface that allow to attach to other bacteria and to host cells • Endospores – a form some bacteria become when in unfavorableconditions • Flagella - long hair like projections that help the bacterium move • Some bacteria release a slime layer and move through it

Bacteria and Health • Pathology - scientific study of disease • Bacteria and other organisms that cause disease are called pathogens • Some bacteria cause disease by making certain poisons called toxins • Exotoxins - Toxic substances that bacteria secrete into their environment • Ex: Tetanus is caused by the bacteria Clostridium tetani • Endotoxins - Toxic substances that are not released until the cell dies • Can cause fever, body aches, diarrhea, hemorrhage, and weakness

Bacteria and Health • Antibiotics affect bacteria by interfering with certain cellular activity • Penicillin blocks the ability to build new cell walls • Tetracycline blocks protein synthesis • Antibiotics are made naturally by some fungi and bacteria • Antibiotic resistance is a major problem • Mutationshave allowed bacteria to become resistant to some antibiotics

Viruses • Non-living particles made up of nucleic acid and a protein or lipid coat • Lack key characteristics of life • Can not reproduce on their own • No metabolism • No homeostasis • Do not grow

Virus Characteristics • Viruses basic structure • Nucleic acid (DNA or RNA) • Protein coat surrounding the genome called capsid • Some contain a bilipid membrane surrounding capsule called an envelope • Classified by their structure • Whether they contain DNA or RNA • Whether the nucleic acid is single or double stranded • Ex: ssRNA in HIV • Whether they contain an envelope over their capsid

Replication • Since viruses are not alive, they cannot reproduce on their own • Must recognize a host cell, infect the cell, and replicate using the enzymes and organelles from the host

Replication • DNA Viruses • DNA gets transcribed into mRNA and make proteins using organelles and amino acids from host cell • DNA from virus inserts itself into host’s genome • Called a provirus

Replication • RNA Viruses • RNA strand serves as the mRNA to make proteins • Some viruses can perform reverse transcription where RNA gets coded into DNA and then inserts into host genome • Called retrovirus

Viruses infecting Prokaryotes • Bacteriophages • Viruses that infect only bacteria • Made of a protein capsid, tail fibers, and nucleic acid

Lytic Cycle of Viruses • Lytic – to break • Viruses that reproduce by this process are called virulent • Virulent viruses destroy their host cells • Virus releases the nucleic acid into the host, the host cell then produces viral proteins and assembles new viruses, new viruses burst the cell and repeat the process • Ex: common cold, influenza

Lysogenic Cycle • This process is when the virus hides in the host’s genome • Can hide for days, months, or years • The viral nucleic acid is inserted into the host’s genome, remains there and the cell continues its normal function, the viral nucleic acid can then become lytic and begin to produce new viruses • Ex: herpes virus, mononucleosis Sneaky Ninja Virus

Viral Diseases • Chickenpox and Shingles • Caused by the same virus • Multiplies in the lungs and travels to blood • Contagious through direct contain with the skin and in the air • May stay in the nerve cells as a provirus • Can later cause shingles in its lytic cycle form

Viral Diseases • Acquired Immune Deficiency Syndrome (AIDS) • Human immunodeficiency virus (HIV) causes AIDS • Destroys the immune system • Can be spread by sexual contact or contact with bodily fluids such as blood • Virus integrates itself into host’s genome by reverse transcription and is lytic (targets helperTcells of immune system)

Prevention & Treatment • Vaccinations • Contains harmless version of virus that is introduced to the body • By exposing the cells to the virus, this builds an immunity for it • Best treatment for viral infection is the body’s own immune system • Drug Therapy • Some anti-viral drugs can help by interfering with nucleic acid synthesis • Not as common since viral infections take place within the patient’s owncells

Bacteria & Viruses