the diversity of viruses, bacteria, and fungi. eukaryotic cells (10–100 µm) prokaryotic cells...

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

Staphylococcus1 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

proteincoat

envelope(lipid bilayer)

spikes

coreproteins

reversetranscriptase

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

tobaccomosaic plant virusmeasles 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

coccus bacillus

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

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