IMPORTANT DISCOVERIES 👨🔬
and BACTERIAL STRUCTURE
SCIENTIFIC TERMINOLOGY
PREDICT HORIZONTAL GENE TRANSFER
criteria for xenologs
GC content
% of G + C in genome can be determined by measuring the melting temperature of DNA
vary wide range among prokaryotes (20% - 80%)
useful taxonomic tool
unusual codon usage
degenerate codons
meaning: >1 codons specifies a single aa are not used at equal frequency
phylogenetic tree give information regard
evolutionary relationship - VGT
evidence for HGT
IMPORTANT DISCOVERIES
VAN LEEUWENHOEK
PASTEUR
KOCH
observe & describe microorganisms
extensive microscope user
advances
can detect range of sizes using scale-specific technique
viruses 20 - 200 nanometers
bacteria 0.2 - 2 micrometers
he was able to magnify object 300x
History
spontaneous
Biogenesis: Pasteur's experiment
BACTERIAL STUFFS
BACTERIAL LOOK
STRUCTURES OF BACTERIAL CELLS
ANTIBIOTICS PENETRATION
ACTION OF COMMON ANTIBIOTICS
highest lens in a light microscope is 100x
for a very long time, scientists believed microorganisms arise spontaneously from nonliving matter
Aristotle : simpler invertebrates could arise from spontaneous generation
Francesco Redi disproved this theory
Showed contamination occurs because of microbes in the air
disproved spontaneous generation
technique -aseptic techniques
prevent contamination by unwanted microorganisms
GERM THEORY
microorganisms in disease was not immediately obvious to people
Koch showed relationship between
specific microbes Bacillus anthracis
disease : anthrax
POSTULATION
experimental steps
- suspected pathogen must be present in disease and absent in healthy
- suspected pathogen can be grown in pure culture
- cells from pure culture have to cause disease
- suspected pathogen must be reisolated and shown to be the same as original
importance
developed pure culture methods
growth on solid media
isolation of pure cultures
used scientific method to prove causation disease
limitation
some agents cannot be isolated in pure culture
mycobacterium lepare
chlamydia trachomatis
viruses
some agents are host specific
not all individual show the same degree of infection
unethical experiments
PROKARYOTE OVERVIEW
Planctomycetes - membrane-enclosed DNA anammoxomsomes for anoxic ammonia oxidation
some bacteria & archaea - cytoskeleton proteins
some bacteria - extensive & complex intracellular membranes
prokaryotes is not accurate anymore
CYTOSKELETON PROTEIN
FtsZ - cell division
MreB - provide structure
MbI - localize protein in a particular location
CreS - intermediate filament
SIZE
bacteria and archaea vary in size and shape
1 - 2 micrometer wide
2 - 10 micrometer long
why small?
to increase in S/V ratio -> increase diffusion of nutrients
SHAPE
Rods - bacilli
circular - cocci
spiral
single bacillus
diplobacilli
streptobacilli
coccobacillus
diplococci
straphylococci - grape like
streptococci - chain like
dimension
tetrad
sarcinae
vibrio - comma
spirilla - 2 or more twists
spirochetes - corkscrew-shaped
CELL WALL
shape bacteria
protect from
contribute to cause diseases
some antibiotics act here
osmolarity
toxic compound
more important, keep from rupturing - hypotonic
help bacteria survive /from shrinking - hypertonic
components
network of peptidoglycan - repeating polysaccharide attached to polypeptides
subunit
sugar
3 amino acid
D-glutamic acid
D-alanine
meso-diaminopimelic acid (DAP)
fomation
NAM & NAG alternate
cross-linked with peptides of adjacent strand
peptide crosslink
pentaglycine interbridge
GRAM STAIN
gram + strain: purple
gram - stain: pink/red
thick layer of peptidoglycan
no outermembrane
20 - 80nm thick
thin layer of peptidoglycan
outermembrane
2-7 nm thick
teichoic acids - negatively charged
peptidoglycan bound to S-layer proteins
lipopolysaccharides (LPS)
lipoproteins
phospholipids
lipid A
O side chain : polysaccharide
glucosamine
fatty acids
phosphate / pyrophosphate
may act as an endotoxin after Gram - bacteria die
EXCEPTION THAT CANNOT BE STRAINED WITH GRAM STAIN
MYCOBACTERIA
mycolic acids
mycoplasma
smallest bacteria - resembles obligate symbionts
no cell wall
resistant to osmotic pressure - has sterols in membrane
contain
lipoglycans
long chain polysaccharides in cell membrane
similar to gram (-) but no lipid A
(magnetosome)
some are involved in moving internal items
MamK - actin-like protein - assemble magnetosome
CELL WALL
CELL MEMBRANE
made of phospholipids
transport: permeable barrier
simple diffusion
passive transport
fast - non polar
slow - small polar molecule, hydrophobic (no charged)
active transport
concentration gradient
cell wall synthesis
folic acid metabolism
DNA gyrase
cytoplasmic membrane structure
RNA elongation
DNA-directed RNA polymerase
protein synthesis
tRNA
transpeptidation
- bactoprenol - inserts cell wall precursors
- autolysin breaks bond btw NAM & NAG
- transglycosylase - synthesize new NAM & NAG and add them to the old chain
final step of biosythesis
peptide crosslink between NAM in adjacent chains - release D-alanine
blocked by penicillin and ampicillin
beta-lactam antibiotics
prevent peptiglydocan crosslinking
weaken cell wall structure
inhibit transpeptidation
ampicillin
active against many bacteria
acid resistant
penicillins, cephalosporins
FEEDING MECHANISM
GRAM BACTERIA
passive transport
outermembrane - porin trimer
plasma membrane - active transport system
active transport
outermembrane +peptidoglycan - TonB-dependent receptor
plasma membrane - ExbD And ExbB something
enter thru porin
if in a neutral environment, ampicillin is deprotonated and becomes charged
vancomycin
bidn to D-Ala, D-Ala terminal end
block cross linking by steric hindrance
gram (-) bacteria
naturally resistant to penicillin & vancomycin due to outermembrane
have to structurally modify
drug itself - charged residues bind to porins
bacteria outermembrane
peptidoglycan
periplasm
plasma membrane
phospholipids form a lipid bilayer - 2 parallel rows
phospholipid have
polar head - phosphate group & glycerol : hydrophilic
nonpolar tail - fatty acid : hydrophobic
sulfa-drugs
difuse thru cell membran e
pKa = 7 - 10
if cannot diffuse, molecules can be transferred thru carriers
RIBOSOME
site of protein synthesis
float free in cytoplasm
70S -2 subunits
30 S
rRNA 16S
50S
rRNA 23S
rRNA 5S
macrolides
bind near 50S peptidyl transferase site
block enlongation
excellent site for selective toxicity
different in structure from eukrayotes
drug: chloramphenicol - prevent formation of peptide bond
tetracyclines - interfere binding of tRNA with mRNA codon
these antibiotic not taken up by gram -
can cause aplastic anemia
produced from destruction of bone marrow
aminoglycosides - broad spectrum drug - effective against gram +, gram -, chlamydia & rickettsia
bind calcium
cause teeth discoloration
30S inhibitor
50S inhibitor
N-acetylmuramic acid (NAM) - unique in bacteria/ not exist in archaea
N - acetylglucosamine (NAG)
the core polysaccharide : joined to lipid A
steroid
bacteria doesn't have steroid aka cholesterol
some have hopanoids (steroid like, stability across the temperature ranges)
important in mycoplasma
actinomycetes - more related to gram + but cannot be stained with gram stain
which means fatty acids that form waxy layer in addition of peptidoglycan
cannot cross the outermembrane
charged residues bind to ones on porins