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

  1. suspected pathogen must be present in disease and absent in healthy
  1. suspected pathogen can be grown in pure culture
  1. cells from pure culture have to cause disease
  1. 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

  1. bactoprenol - inserts cell wall precursors
  1. autolysin breaks bond btw NAM & NAG
  1. 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