The Diversity of Viruses, Bacteria, and Fungi

Eukaryotic cells (10–100 µm) Prokaryotic cells (0.2–10 µm) cyanobacterium Viruses (0.05–0.2 µm) Escherichia coli Staphylococcus 1 µm

Viruses

Defining Characteristics A virus is a noncellular infectious agent. Viruses are major pathogens and infect virtually all living organisms from animals to bacteria. The two defining characteristics of a viruses are:  A viral particle consists of a protein coat wrapped around a nucleic acid core (the Genome).  A virus CANNOT reproduce itself. Its reproduction is dependent upon the host cell.

glycoproteins protein coat envelope (lipid bilayer) spikes core proteins reverse transcriptase genetic material (viral RNA) coated with protein

viral RNA protein subunits of coat helical virus polyhedral virus

DNA protein coat sheath base plate tail fiber complex virus

rabies virus herpes virus bacteriophage tobacco mosaic plant virus measles virus Copyright © 2005 Pearson Prentice Hall, Inc.

Ebola virus particles

Treating Viral Infections Because viruses use the host cell machinery in order to reproduce, the illnesses that they cause are difficult to treat. Viruses also have high mutation rates, which makes it inevitable that when a population of viruses is being treated with an antiviral drug, a mutation will arise that will result in resistance to the drug.

Prokaryotes (Bacteria)

Characteristics of Prokaryotes Prokaryotes are microscopic (too small to be seen without a microscope) Most abundant organisms on earth. Metabolically diverse Do not contain membrane bound nuclei or organelles Usually have a single chromosome Most contain a cell wall Reproduce by fission Come in three basic morphologies

Prokaryotic Cell Morphology coccusbacillus spirillum

The Prokaryotic Cell bacterial flagellum pilus capsule cell wall plasma membrane cytoplasm DNA ribosomes in cytoplasm

The Cell Wall A semi-rigid structure that helps the cell maintain its shape and resist rupturing. Composed of peptidoglycan molecules The cell wall is often enclosed by a glycocalyx or a sticky mesh composed of polypeptides, polysaccharides, or both. It helps the cell attach to surfaces such as teeth and mucous membranes and protect against phagocytosis.  When highly organized and firmly attached it forms a capsule  When less organized and loosely attached it forms a slime layer.

Endospores When some rod-shaped bacteria encounter inhospitable conditions, they form protective structures called Endospores. An Endospore forms inside of a bacterium and contains genetic material and a few enzymes encased within a thick protective coat. Endospores are resistant to extreme environmental conditions.

endospore bacterium

Two Kinds of Prokaryotes Archaebacteria – the bacteria that live under extreme conditions. Divided into 3 categories  Extreme Halophiles – live in high salt environments  Methanogens – Produce methane gas and live in oxygen free environments such as the gut and swamps  Extreme Thermophiles – live in extremely high temperatures (> 80°C). Eubacteria – the most common bacteria. Can be divided into two sub-groups:  Gram-positive  Gram-negative

The Gram Stain A staining technique called the Gram stain is commonly used in identification of bacterial species.  Expose to a purple dye and then iodine  Wash with alcohol  Counterstain Gram-positive cells stain purple Gram-negative cells stain pink

Bacillus subtilis Gram positive E. coli Gram negative

Eubacteria Photoautotrophs – Cyanobacteria: aerobic cells that engage in photosynthesis. Some convert nitrogen gas to ammonia for use in biosynthesis. Chemoautotrophs – derive energy by combining oxygen with inorganic molecules such as sulfur, ammonia, and nitrite. Chemoheterotrophs – derive energy by breaking down organic compounds.

Prokaryotic Growth and Reproduction Growth is measured by the increase in the number of cells in a population. Under ideal conditions cell division can occur in as little 10 to 30 minutes in some bacteria and as long as 15 hours in other bacteria. Prokaryotic cells reproduce by a mechanism called Fission.

parent DNA molecule DNA copy DNA replication completed DNA replication begins Bacterium before DNA replication bacterial chromosome

Membrane growth moves DNA molecules apart New membrane and cell-wall material deposited Cytoplasm divided in two

Bacteria and Human Health: Good Bacteria Some bacteria are beneficial to other organisms  Lactobacillus used to make pickles, yogurt, sauerkraut, and buttermilk.  Actinomyces used as a source of antibiotics  Various bacterial components are used in vaccines  Escherichia coli makes vitamin K and compounds that help us digest milk.

Bad Bacteria: Pathogens Pathogens are bacteria or parasites that threaten our health and well-being. They synthesize toxins that cause disease symptoms.  Some E. coli strains cause diarrhea  Clostridium botulinum causes botulism, C. tetani causes tetanus  Borrelia burgdorferi causes Lyme disease  Streptococcus variants cause pneumonia and strep throat.  Treponema pallidum – syphilis  Neisseria gonorrhoeae - gonorrhea

Fungi

Fungi obtain their nutrients from other organisms. Fungi propagate by spores. Most fungi can reproduce both sexually and asexually.

Fungi and Us Fungi attack plants that are important to people. Fungi cause human diseases. Fungi can produce toxins. Many antibiotics are derived from fungi. Fungi make important contributions to gastronomy.  Wine and beer are made using yeasts  Yeasts make bread rise  Research details of both….

Firm cell walls (generally of “chitin”) “Spores” as reproductive bodies Unique chromosomes and nuclei Includes molds, yeasts, rusts, and mushrooms

hyphae - the vegetative bodies of most fungi, constructed of tiny filaments mycelium -an interwoven mat of hyphae

Human hair Fungal hypha