microbiology - microorganisms Flashcards
definition of microorganisms
small
usually free living unicells or cluster
fungi, algae, protozoa, bacteria, archaea
common features of cells
basic unit of all living organisms
cell envelope
nucleic acids
ribosomes
cytoplasm
prokaryotic and eukaryotic
importance of cell membranes
barrier between cell and environment
structural component of cell
site of crucial biochemical reactions
lipid bilayer
hydrophobic fatty acids linked by ester bonds
hydrophilic heads
lines up in bilayer
also contains lipid components
sterols and hopanoids
cell membrane in archaea
hydrophobic fatty acids ether linked to hydrophilic head (glycerol)
ether linkages more chemically stable than ester
can resist extreme conditions eg temperatures
fatty acids often branched
called isoprenoids
monolayer - cyclic tetra ether lipids can join tail to tail and form a monolayer
cell walls
often constructed from polysaccharides
cellulose (glucose) - plants, algae and some fungi
chitin - fungi
mannans and xylans - fungi and plants
bacterial cells walls
peptidoglycan
- polysaccharide chains cross linked by peptides
cell wall in archaea
pseudopeptidoglycan
different peptide cross links between disaccharides
some cell walls made of glycoprotein, protein and polysaccharides
- forms s-layer
- hexagonal array of proteins or glycoproteins
gram stain
cell wall structure basis for differentiation of 2 groupings of bacteria
based on staining procedure
cells stained with dye, binds to cell
stained cells treated with alcohol
extracts dye from negative cells
sample stained again
stains extracted cells - negative
results of gram stain
purple = gram positive
pink = gram negative
gram positive cells
purple stain
cell membrane
thick peptidoglycan layer
dye binds tightly
gram negative cells
pink stain
thin peptidoglycan layer
dye doesn’t bind as well
most have second outer membrane
lipopolysaccharide
lipid A
found in outer membrane
anchor for polysaccharides on gram negative cells
overall structure known as lipopolysaccharide
used in immunological testing
different pathogens have different sugar chains on outside
nucleic acids
DNA
RNA - r,m,t,si
nucleotide structure
phosphate
5 carbon sugar - ribose or deoxyribose
RNA has hydroxyl at 2
DNA has hydrogen at 2
organic bases
- purines or pyrimidines
joining of nucleotides
phosphates attach to carbon 5 of sugar
hydroxyl group on carbon 3 forms ester bonds with phosphate group
= sugar phosphate chain
3 hydrogen bonds - CG
2 hydrogen bonds - AT
- those with more CT pairs are stronger and more temperature resistant
difference between nucleotide and nucleoside
side = sugar and base
tide = sugar, base and phosphate
pyrimidines
single ring structure
cytosine
thymine
uracil
purines
twin ring structure
adenine
guanine
NAD(P)
nictinamide adenine dinucleotide
oxidant in biochemical reactions
reduced form NADH used in energy metabolism
NADPH used in photosynthesis
ribosomes
in all cellular forms of life
large and small subunits
prokaryotes - 70s
eukaryotes - 80s
control protein synthesis and translation
also found on RER
prokaryotic cell structures
pili and fimbriae
gas vesicles
heterocysts
capsule
endospores
sheath
pili and fimbriae
protein made of pilin
binding and attach cell surfaces
eg proteins on cell surfaces
transferal of genetic material
gas vesicles
hold gases in aquatic cells
alter boyency to position for optimum conditions for photosynthesis
different wavelength reach different depths
heterocysts
only in some photosynthetic bacteria
fixation of nitrogen gas
capsule
extracellular polysaccharide capsule
pathogens make them to protect from digestion by phagocytes
physical barrier to protect cells from environment
endospores
produced by bacteria in extreme conditions
very heat resistant
contain cells DNA
used for dispersal in fungi
produce endospores in response to extreme conditions
germinate and produce new cell when conditions return to favourable
sheath
outside cell wall
provides physical barrier to protect cell from iron oxides coating cell wall
