Chp 1 Microbial World and Chp 3 Bacterial Cells

Bacteria and archea

Both are single-celled organisms, look similar under the microscope. Contain no membrane bound nucleus, prokaryotes. Do not contain any other organelles. Cytoplasm is surrounded by rigid cell wall. Despite their common features, these two domains are highly different from one another.

Key differences unique to archaea

Chemical composition of cell wall, found in extreme environments - extreme temperatures, environments with high concentrations of salt

Gram-negative outer membrane - LPS

Constructed of a lipid bilayer: LPS serves as barrier to a large number of molecules, LPS is medically significant - toxic when injected, also called "endotoxin"

Gram-negative outer membrane

Constructed of a lipid bilayer: much like cytoplasmic membrane but made of lipopolysaccharides not phospholipids

Viruses

Contain protein coat surrounding nucleic acid, termed obligate intracellular parasites - must have host machinery to replicate, inactive outside of host, frequently kill host cells, all forms of life can be infected by viruses

Vibrio

Curved rod

Pairs

Diplococci. Ex: Neisseria honorrhoeae

Gram-negative outer membrane - O-specific polysaccharide

Directed away from membrane, used to identify certain species or strains

Clusters

Division along several random planes form clusters. Ex: species of Staphylococcus

Packets

Division along two or three perpendicular planes form cubical packets. Ex: Sarcina genus

Pair or chain

Divisions along a single plane may result in pairs or chains of cells

Spirochete

Helical shape

Chains

Streptococci. Ex: species of Streptococcus

Gram positive

Stained purple

Gram negative

Stained red or pink

Colony

A population of bacterial cells arising from a single cell is called a colony. Visible with the naked eye

Examples of eukaryotes

Algae, fungi, protozoa

Basic structure of peptidoglycan

Alternating series of two subunits: NAG or NAM, joined subunits form glycan chain: glycan chains held together by string of four amino acids - tetra-peptide chain

Gram-negative outer membrane - Lipid A

Anchors LPS molecule in lipid bilayer, plays role in recognition of infection - molecule present with gram negative infection of bloodstream

Examples of prions

Animal disease: scrapie, mad cow disease Human disease: Creutzfelt-Jakob Kuru

Pleomorphic

Bacteria able to vary shape

Nomenclature

Binomial naming system - two word naming system. First word is genus name - always capitalized. Second word is species name - not capitalized. When writing full name, genus usually abbreviated. Full name always italicized or underlined

Prions

Infectious proteins - contain no nucleic acids, responsible for 6 neurodegenerative diseases, infections are always fatal

Gram-negative cell wall

More complex than gram-positive, contains a thin layer of peptidoglycan: sandwiched between outer membrane and cytoplasmic membrane

Bacteria

Most common type of organism in human infection. Members are widely diverse.

Gram stain

Most widely used procedure for staining bacteria, used to separate bacteria into two major groups, differential staining is based on differences in cell wall structure

Binary fission

One cell divides into two. Each cell is genetically identical to the first

Eukarya

Organisms contain membrane bound nucleus. Contains internal organelles - organisms are more complex, may be single cell or multi-cellular

Lipopolysaccharide - LPS layer

Outer membrane

Prokaryotes

Pre nucleus

Morphology of prokaryotic cells - shape

Prokaryotes exhibit a variety of shapes. Most common are coccus and bacillus

Morphology of prokaryotic cells - groupings

Prokaryotic cells may form groupings after cell division. Cells adhere together after cell division for characteristic arrangements. Arrangement depends on plane of division - esp. in the cocci

Periplasm of gram-negative cell wall

Region between outer membrane and cytoplasmic membrane

Gram-positive cell wall

Relatively thick layer of PTG - up to 30 sheets, teichoic acid components of PTG

Bacterial cell wall

Rigid structure, surrounds cytoplasmic membrane, determines shape of bacteria, prevents cell from bursting, unique chemical structure, distinguishes Gram-positive from Gram-negative

Peptidoglycan - cell wall

Rigidity of cell wall is due to peptidoglycan - compound found only in bacteria

Bacillus

Rod or cylinder shaped, cell shape not to be confused with bacillus genus

Prominent features of archaea

Same shapes, multiply through binary fission, move by means of flagellum

Coccobacillus

Short round rod

Viroids

Simpler than viruses - still require the host cell for replication, consist of a single short piece of RNA, smaller than viruses, generally cause plant diseases

Porins

Small molecules or ions pass through channels

Prominent features of bacteria

Specific shapes, rigid cell walls, multiply by binary fission, some bacteria are motile

Coccus

Spherical

Spirillum

Spiral shaped

Medical significance of LPS

Toxic when injected - endotoxin

Size in the microbial world

Tremendous range in size

Eukaryote

True nucleus