Primerano Exam 1 Flashcards
Zoonotic Infection
Exogenous microbes transmitted from animals to human
fomites:
inanimate objects which harbor the microorganisms, e.g. infants toys, shared toothbrushes.
Nosocomial infections.
Crowded conditions, poor sanitary practices, and impaired defense systems in hospitalized patients
Sterile tissues.
blood, deep tissue, and alveoli in lung.
bacteriocins
toxic bacterial proteins that kill other bacteria
Koch’s Postulates
1) The bacterium should be found in all people who have the disease. Also, the bacterium or its products should be found in parts of the body affected by the disease.
2) Bacterium should be isolated from the lesions of an affected person and able to be maintained in pure culture.
3) The pure culture, inoculated into a susceptible human volunteer or experimental animal, should reproduce the disease symptoms.
4) Same bacterium should be reisolated in pure culture from the infected animal or human.
Problems with Koch’s Postulates
1) Ignores the role of the host. Susceptibility and resistance can have a genetic basis and reduces the extent of correlation expected in postulate #1.
2) Fastidious organisms are harder to culture. Many organisms can’t be cultured at all.
3) Variability (in virulence) of a single bacterial species. Organisms can acquire new virulence traits by genetic exchange (e.g. lysogenic conversion).
4) We can’t ethically inoculate humans with dangerous/lethal for experimentation.
5) Polymicrobial infections.
Prokaryotes:
cells lack a membrane bound nucleus
Eukaryotes:
cells which have a defined nucleus
Bacteria are
unicellular prokaryotic organisms and as such lack a nuclear envelope as well as membrane-bound organelles.
cell wall
Fungi are
eukaryotic organisms which have a well-defined nucleus, membrane-bound cytoplasmic organelles and a cell wall
Fungi include
yeasts (unicellular), molds (multicellular and filamentous), and dimorphic fungi which can switch from yeast to mold.
Parasites (broad definition)
prokaryotic, eukaryotic or viral organisms that require a living host for at least part of their life cycle and cause disease to the host.
Parasites (narrow definition)
unicellular or multicellular eukaryotic organisms that require a living host for at least part of their life cycle and cause disease in the host.
Viruses are
intracellular parasites that lack cell structure; generally consist of nucleic acid genome surrounded by a protein coat; require a cellular host for replication.
Prokaryote Ribosome structure
70S Ribosomes (30S + 50S)
Prokaryote translation begins with
Translation begins with N-formylmethionine
Prokaryote respiration occurs where
Respiration occurs in plasma membrane
Viroid vs. prion
Viroids consist of RNA genome without any protein components
Prions are infectious agents consisting only of protein.
Flagella are required for what process?
movement of cell, toward a nutrient or away from a toxic substance, a process called chemotaxis
Flagella are composed of what protein?
flagellin
Pili (fimbriae) do what
thin, rigid appendages allow cells to adhere to host cell or other bacterial cell surfaces.
Pili (fimbriae) are composed of what protein?
composed of proteins called pilins;
Bacterial Capsule is made up of what?
Glycocalyx
Glycocalyx made up of what?
usually polysaccharide (but occasionally protein) confers resistance to phagocytosis gives colony a smooth or shiny appearance
Nucleoid:
discrete area containing the bacterial chromosome and plasmid DNA; bacterial DNA is
organized by histone-like proteins. No membrane is present
Cytoplasmic inclusion bodies:
sites where nutrient macromolecules (usually polysaccharides like glycogen) are stored as large microscopically visible complexes
Endospores:
heat-resistant, dehydrated multi-layered cells that are rich in calcium dipicolinate; formed within the cell by a process called sporulation; endospores germinate into growing cells when adverse conditions wane
Bacterial Cell Envelope =
Plasma membrane + cell wall + intervening material
Function of Plasma (Cytoplasmic or Inner) Membrane
(1) site of active transport
(2) respiratory chain components
(3) site of synthesis for phospholipids, peptidoglycan, LPS and capsular polysaccharides
Peptidoglycan structure of backbone
Glycan backbones consist of alternating N-acetylmuramic acid (M) and N-acetylglucosamine
What type of linkages are on peptidoglycan?
B-1,4 linkage
What enzyme cleaves B-1,4 linkage of peptidoglycan?
lysozyme
What allows peptidoglycan to form a ‘sacculus’ in G+ bacteria?
terminal D-alanine of tetrapeptides is covalently linked by a glycine pentapeptide
Muranyl Dipeptide
fragment of peptidoglycan: adjuvant, pyrogen (fever-causing), and somnagen
permeases
are required for active transport of nutrients (against a concentration gradient)
sites for the synthesis for the biosynthesis of peptidoglycan and outer membrane components (like LPS in g- organisms)
Plasma or Inner Membrane
Where is LPS located?
G- bacteria on outer most leaflet
Lipid A portion
is responsible for endotoxic activity; anchors LPS molecule in the outer leaflet
Core Polysaccharide contains
unusual eight carbon sugar 2-keto-3-deoxyoctulosonic acid (KDO); core is essential for LPS structure and bacterial viability
The O antigen forms basis for
serotypes of bacterial strains
LPS and LTA are both what?
amphipathic
LTA can induce coagulation reactions but cannot do what/
cause fever (is not pyrogenic)
Porins are
protein complexes that form channels that allow passive diffusion of small charged molecules.
Found only in outer membrane of g- bacteria
Braun lipoprotein
covalently anchors the outer membrane to peptidoglycan. Inner leaflet of outer membrane.
Omp proteins
stabilize the outer membrane and act as specific receptors
What part of bacteria has been sequenced for identification?
16S ribosome
Adhesins
(Afimbrial adhesins). Bacterial surface proteins which mediate intimate contact with the host cell
Gram + and gram- bacteria
Biofilms.
The formation of dense, multiorganism layers on a surface. Especially significant in implants, etc
Invasions:
causes the formation of pseudopod-like structures, which mediates bacterial engulfment.
How do bacteria survive phagocytosis?
Some bacteria are able to produce catalase + SOD and have lysozyme resistant cell wall
Siderophores/enterobactins
chelate iron effectively and bring inside cell.
Diphteria Toxin is what kind of toxin?
AB Toxin
Pore former (hemolysin)
acts to lyse the cell by permitting rapid H2O entry in response to the osmotic gradient. Cholesterol is often the target allowing entry/insertion into the host cell membrane.
Phospholipase.
Enzymatically removes the charged head of phospholipids. This acts to destabilize the cell membrane, also resulting in cell lysis.
Septic shock
Bacterial products hyperactivate the complement cascade leading to hypotension, DIC and organ failure.
superantigens
antigen which binds to the MHC class II on phagocytes. This protein also binds to receptors on many T cells, with the release IL-2 and other interleukins. Septic Shock
Sepsis is a problem caused by
bacteremia of both gram negative and gram positive origin
LPS (endotoxin) results in what systemic effects?
DIC Thrombosis
Hypotension -> shock
Fever
Hypoglycemia
Fermentation Defined
Glycolytic pathway followed by NAD+ regeneration
Glycolysis Net equation
Glucose + 2 NAD + 2ADP + 2Pi —-> 2 pyruvate + 2 NADH + 2H + 2ATP
What generates much of the total ATP under aerobic conditions
Oxidative phosphorylation
Central metabolism provides intermediates for
nucleotide, amino acid and vitamin biosynthesis
Nitrogen Fixation
N2 —-> NH3
Ammonia assimilation
Many bacteria are able to assimilate NH3 into amino acids by various reactions.
Organisms that require these molecules added to the growth medium are called
auxotrophs
Those that have no requirements beyond simple C, N and S sources are called
prototrophs.
Strict Aerobes require
oxygen for growth since little or no ATPgenerated via fermentation.
Strict Anaerobes
little or no ATP via electron transport; lack superoxide dismutase, catalase and peroxidase, hence, oxygen is toxic.
Aerotolerant anaerobes
aerobic and anaerobic
possesses Catalase and SOD - - or Mn++
Ferments in presence or Absence of O2
Facultative anaerobes
aerobic and anaerobic
catalase and SOD
Respires with O2 and ferments in absence of O2
Microaerophilic organisms
require or prefer low [O2]
no anaerobic
no catalase
only does oxidative phosphorylation
General Secretory System
transports proteins to the gram-positive extracellular space or to the periplasm of gram-negative organisms.
located in cytoplasmic membrane and recognizes precursor proteins with hydrophobic N terminus (signal peptide)
What passes through bacterial membrane by passive diffusion?
Very small molecules, water and gases.
Energy independent channels (porins) transport what?
small hydrophilic solutes to pass through the outer membrane
Glycerol transport is mediated by what found in the cytoplasmic membrane of gram-negatives
glycerol facilitator protein (facilitated diffusion)
mechanism of the transport of glucose and other sugars go through bacterial membranes how?
Group translocation via PTS system
Siderophores are
macromolecules that bind iron in the medium and transport it inside the cell
Pathogenicity Islands:
cluster of genes encoding proteins involved in pathogenesis
GC content of island is often different than the host genomes
Semi‑conservative replication
each daughter duplex DNA molecule is composed of one parental strand and one newly‑synthesized strand
oriC
single site on chromosome where all DNA replication is initiated.
Bidirectional replication
Two replication forks begin at oriC and travel in opposite directions around the circular chromosome
DNA Polymerases
All bacterial polymerases share 5’ to 3’ polymerase activity and 3’ to 5’ exonuclease (proofreading) activity which is necessary for maintaining a lower error rate.
Supercoiling:
Bacterial chromosome has negative superhelicity which means that it can readily convert to a molecule with unwound helical regions. Negative superhelicity is absolutely required for DNA replication.
RNAP does what?
single enzyme transcribes all four types of RNA (not true in eukaryotes)
sigma factor
initiation site specificity to holoenzyme, so that holoenzyme recognizes -10 and -35 positions of the promoter.
Rho factor
assists in termination in some genes
consensus sequence is
the sequence found most frequently in a survey of a large number of sequences
the more similar a sequence is to the consensus, the stronger the
promoter.
PolyA tails in prokaryotes. true or false?
false
Two subunits of bacterial ribosome
30S + 50S (70S)
30S plays a role in
translation initiation and has
site for tRNA binding.
50S primary function
Primary function = peptide bond formation (transpeptidase)
tRNA synthetases catalyze
addition of amino acid to tRNA
degenerate
that is more than one codon can code for a given amino acid
The rate of translation initiation is controlled by a sequence present in the 5’ non translated region of all prokaryotic mRNAs
ribosome binding site or Shine-Dalgarno (S‑D) sequence.
the A site
Accepts incoming charged tRNA.
P site
is the site where peptidyl tRNA sits.
transpeptidation step
Transfer of peptidyl residue to free amino group of charged tRNA molecule in the A site.
Peptidyl transferase activity is located
in the 50S subunit
Coupling
can only occur in prokaryotes. Nucleus physically separates the processes of transcription and translation
What reactions require energy consumption in transcription/translation
- Active transport
- DNA AND RNA SYNTHESIS
- tRNA CHARGING
- PEPTIDE SYNTHESIS (INITIATION AND ELONGATION)
sequential use of carbon sources is called
diauxic growth.
