Microbe Diversity Flashcards
Viruses – a borrowed life
Viruses are not cells
Viruses are very small infectious particles consisting of nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope
Viruses called bacteriophages can infect and set in motion a genetic takeover of bacteria, such as Escherichia coli
Viruses lead “a kind of borrowed life” between life-forms and chemicals
Viruses reproduce only in host cells
Viruses are obligate intracellular parasites, i.e. they can reproduce only within a host cell
Each virus has a host range, a limited number of host cells that it can infect
Virus reproduction
Once a viral genome has entered a cell, the cell begins to manufacture viral proteins*
The virus makes use of host enzymes, ribosomes, tRNAs, amino acids, ATP, and other molecules
*Viral nucleic acid molecules and capsomeres spontaneously self-assemble into new viruses
Viruses as pathogens
Diseases caused by viral infections affect humans, agricultural crops, and livestock worldwide
Viruses may damage or kill cells by causing the release of hydrolytic enzymes from lysosomes
Some viruses cause infected cells to produce toxins that lead to disease symptomsOthers have envelope proteins that are toxic
Vaccines
Vaccines are harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the actual pathogen
Viroids
circular RNA molecules that infect plants and disrupt their growth
Prions
slow-acting, virtually indestructible infectious proteins that cause brain diseases in mammals
Prions propagate by converting normal proteins into the prion version
Prokaryote structure
Most prokaryotes are unicellular, although some species form coloniesMost prokaryotic cells are 0.5–5 μm, much smaller than the 10–100 μm of many eukaryotic cells [1 mm = 1000 μm]
*Prokaryotic cells have a variety of shapes
*The three most common shapes are spheres (cocci), rods (bacilli), and spirals
*Prokaryotes = bacteria and archaea
*Archaea share certain traits with bacteria and other traits with eukaryotes
Prokaryotic cell wall
maintains cell shape, provides physical protection, and prevents the cell from bursting
Eukaryote cell wall
made of cellulose or chitin
Bacterial cell wall
contain peptidoglycan, a network of sugar polymers cross-linked by polypeptide
Archaea contain
polysaccharides and proteins but lack peptidoglycan*Using
Using the Gram stain
bacterial species classified into Gram-positiveand Gram-negative groups based on cell wall composition
Gram-negative bacteria
have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant
Fungi
*Fungi are diverse and widespread
*Fungi are heterotrophs but do not ingest their food
*They secrete exoenzymes that break down complex molecules, and then they absorb the smaller compounds
*Can be decomposers, parasites, mutualistic symbiont
Fungi origin
*Fungi and Animalia as sister kingdoms
*Molecular evidence that fungi and animals diverged from a common unicellular, flagellated ancestor
*Fungi probably evolved before the colonization of land by multicellular organisms
Undisputed fossils of fungi dated 460 million years oldFungi were among the earliest colonizers of land, probably as symbionts with early land plants
Fungi structure
*The morphology of multicellular fungi enhances their ability to absorb nutrients
*Fungi consist of mycelia, networks of branched hyphae, adapted for absorption
Most fungi have cell walls made of chitinSeptate fungi have hyphae divided into cells by septa, with pores allowing cell-to-cell movement
*Coenocytic fungi lack septaSeptate hyphaCoenocytic hypha
