MedChem 310 Exam #2

plasma membrane

selectively permeable barrier, mechanical boundary of cell, nutrient and waste transport, location of many metabolic processes (respiration, photosynthesis), detection of environmental cues for chemotaxis

gas vacuole

an inclusion that provides buoyancy for floating in aquatic environments

ribosomes

protein synthesis

inclusions

storage of carbon, phosphate, and other substances

nuclei

localization of genetic material (DNA)

periplasmic space

in typical gram-negative bacteria, contains hydrolytic enzymes and binding proteins for nutrient processing and uptake; in typical gram-positive bacteria, may be smaller or absent

cell wall

proteciton from osmotic stress, helps maintain cell shape

capsules and slime layers

resistance to phagocytosis, adherence to surfaces

fimbriae and pili

attachment to surfaces, bacterial conjugation and transformation, twitching and gliding motility

flagella

swimming and swarming motility

endospore

survival under harsh environment conditions

what is the carbohydrate component of peptidoglycan

helical glycan chairs consisting of dissacharid subunit with N-acetylmuramic acid (NAM) and N-acetylglucosamie (NAG)

what is the peptide compoent of peptidoglycan

pentapeptide chains attached to NAM-carboxyl group as amides

D/L-Ala, diamino acid, D-Glu building blocks

peptide chains involved in crosslinking glycan polymers

what are the two types of crosslinks between peptide chains

direct connection of peptide chains

connection of peptide chains via peptide inter bridges

what are the lipolysaccharide functions

negatively charged outer membrane surface

membrane stabilization

permeability barrier

host cell immune response

toxic reactions in host (lipid A)

what is the gram-positive bacteria cell wall structure

thick peptidoglycan layer

one plasma membrane

small periplasmic space with few protains (cell wall synthesis)

what is the gram-negative bacteria cell wall structure

thin peptidoglycan layer

two plasma membranes (inner and outer membrane)

outer membrane layer consisting of lipopolysaccharides

large periplasmic space with secreted proteins (eg nutrient activation and transport, cell wall synthesis)

fluid mosaic model

membranes provide an environment in which membrane proteisn “float”

what is the bacterial membrane structure

phospholipids

hopanes

glycolipid

integral protein

peripheral membrane protein

oligosaccharide

integral membrane protein

phospholipids

bacteria change the fatty acid composition of phospholipids to adapt to temperature change

hopanes

sterol analogs of bacteria

maintain membrane fluidity

integral protein

channeling or transporting membranes across the membrane

peripheral membrane protein

support, communication, enzymes and molecule transfer in the cell

oligosaccharide

cell recognition and cell adhesion

integral membrane protein

movement of molecules across them and the transduction of energy and signals

what composes of the 50S subunit

5S rRNA

LSU proteins

23S rRNA

what composes of the 30S subunit

SSU proteins

16S rRNA

what are the bacterial plasmids

conjugative plasmids

R plasmids

Col plasmids

virulence plasmids

metabolic plasmids

conjugative plasmids

transfer of DNA from one cell to another

R plasmids

carry antibiotic resistance genes

Col plasmids

produce bacteriocins substances that destroy closely related species

virulence plasmids

carry virulence genes

metabolic plasmids

carry genes for enzymes

what is the chain of infection

agent → virulence → exposure → dose → susceptibility

reservoir

the environment/host where an infectious agent normally resides

inanimate objects: soil

animate objects: cats

zoonosis

a disease that can be transmitted from animals to humans

direct contact with animal

animal products/waste

exposure

various forms of infection/transmission

indirect: airborne (dust), food contamination, surface contamination

direct: human/animal contact, vector (between reservoirs)

overview of infeciton process

what are the conditions bacterial pathogens must survive in infected host to cause disease

suitable environment

nutrients

protection from host defense

why do bacterial pathogens employ virulence factors

find/establish environments and niches

evade host defense

acquire nutrients

what are cytosolic viruelnce factors

adaptive metabold, physiological and morpholigical shifts

response to host immune stress

waht are cell associated virulence factors

attachment and evading the host immune system

what are secreted virulence factors

attachment

damage the host

establish suitable environment

protection against host immune system

what is the objective of adherance and colonization factors

bacteria, fungi, and protozoa require a protal of entry to access nutrients

what are the 5 adherance mechanisms

pili and fimbriae

capsule

cell envelope proteins

lipopolysaccharides O-antigens

secreted polysaccharides

what is the portal of entry for adherence and colonization factors

skin

respiratory system

gastrointestinal system

urogenital system

conjunctiva of the eye

extracellular pathogens attach to intercellular spaces with intracellular pathogens invade host cells

pili and fimbriae adherence mechanism

initial host cell contact and bacteria-bacteria or interaction and movement during colonization

capsule adherence mechanism

capsular polysaccharides

cell envelope proteins adherence mechanism

often cell-type specific interaction

lipopolysaccharides O-antigens adherence mechanism

gram-negative bacteria

secreted polysaccharides adherence mechanism

attach by forming a sticky, adhesive layer on the cell surface or by being excreted into the surround environment; bacterial glycosyltransferases catalyze the transer of sugar to build complex polysaccharide chains, which are then secreted outside the bacterial cell

infectivity

ability to establich a discrete focal point of infection

invasiveness

ability to spread to adjacent or other tissues

clostridium tetani

produces toxins and enzymes eg. collagenase (protein degradation)

noninvasive because does not spread between tissue

bacillus anthracis

produces substantial virulence factors (eg. capsules and toxins)

highly invasive

streptococcus sp.

span the spectrum of virulence factors and invasiveness

ex. hyaluronidase (carbohydrate degradation)

how does active penetration alter the host

attaching EC matrix and basement membrane of integuments/intestinal linings

degrading carbohydrate-protein complexes

disrupting host cell surface

what enzymes are associated with attaching EC matrix and basement membrane of integuments/intestinal linings

hyaluronidase

collagenase

what enzymes are associated with degrading carbohydrate-protein complexes

proteases

the glycocalyx

what enzyme is associated with disrupting host cell surface

phospholipase C in clostridum sp

what is passive mechanisms related to

lesions, ulcers, wounds, abrasions, burns

arthropod vectors

tissue damaged by other organism (animal bite)

what does the secretion of reactive oxygen species (eg. H2O2) do

damage epithelial cells

invading bacteria might reach the circulatory system (lymphatic system, blood)

toxin release → organ failure/sepsis

what are exotoxins

travel from the site of infection to other tissues or target cells

toxic in nanogram per-kilogram of body weight concentrations (eg botulinum toxin)

grouped by mechanism of action or protein structure

what are the types of exotoxins

AB toxin

channel (pore)-forming toxins

superantigens

what is an AB toxin

“B” binds to a host cell receptor determines the cell type of toxin will affect

“A” enters the cell and has enzyme activity that causes the toxicity, exerts deleterious effect

what are some examples of AB toxins

diphtheria toxin

botulinum toxin (botox)

what is diphtheria toxin

toxin uses B subunit to bind clathrin-coasted pits on cell curface

intact toxin is endocytosed and pH change from ATPase activity causes the subunits to separate

location of separation is often called a compartment of uncoupling of receptor and ligand (CURL)

B subunit is recycled

active toxin (A) exerts its effect on its target

how does the active toxin of biphtheria toxin exert its effect on its target

protein A catalyzes ADP-ribosylation of eukaryotic elongation factor 2 (eEF2)

ADP-ribosylation prevents mRNA during translation by eEF2 in host cell ribosome

what is botulinum toxin (botox)

produced clostridium botulinum

can cause paralysis

neurotransmitter release: electrical signals travel to the neuromuscular junction (NMJ)

acetylcholine release: at the NMJ, acetylcholine binds to receptors on the muscle cells causing contraction

block the release of acetylcholine, preventing the muscles from contraction

muscle paralysis or reduced muscle contraction

among the most toxic compound known

what are channel (pore)-forming toxins

secreted protein monomers

disrupt membranes so that the cell lyses/dies

examples of channel (pore)-forming toxins

secreted protein monomers (cholesterol-dependent cytolysins from gram-positive bacteria)

secreted synergistic peptides (enterococcal cytolysis from enterococcus faecalies)

what is the mechanism for channel (pore)-forming toxins

inserts itself into the host cell membrane to form a pore

multiple membrane pores results in an osmolarity shift as water enters the cell and cytoplasmic contents move out

resulting effect of the toxin is cell lysis

what are super antigens

hyperactivates the immune system

nonspecific activation of T cells by a superantigen in the absence of antigen

crosslinking MHC-II of macrophages with T-cell receptor

stimulates release of large anounts of cytokines

what is the result of superantigens

host is overwhelmed and it results in shock/death

inflammation, toxic shock

weakens host

enables bacterial dissemination

what is Lipid A

an endotoxin

biologically active component of lipopolysaccharides (LPS) the main components of the outer membrane of gram-negative bacteria

highly toxic (ng/kg body weight) when released into bloodstream

bound by toll-like reseptor 4 on marcophages

innate immune response (recognition of gram-negative bacterial infection)

release of high amounts of lipid A during a servere infection

severe immune response, organ failure, sepsis

what are the bacterial strategies to evade the host immune system

prevention of detection

attack on host immune proteins

biofilms

how do bacteria use prevention of detection to evade the host immune system

mucous production on bacterial capsule to prevent binding by immune cells

surface protein production

protein M - group A streptococci (GAS), causes strep throat, binds immune system proteins and fibrinogen (clotting substrate) to evade phagocyte binding and immune response

protein A - staphylocossuc aureus, binds antibodies on the heavy-chain end which usually binds to phagocyte

O-antigen changes - gram-negative bacteria can alter the length of polysaccharide chains of LPS to evade immune detection

pill/surface protein changes

how do bacteria attack host immune proteins

secretion of proteases to degrade immune proteins

what are biofilms and how do they work

provide a unique environment for bacteria to exchange genetic information and collectively resist antimicrobial agents and host defense mechanisms

bacterial pathogens form biofilms for improved resistance to antibiotics and host immune system during host colonization - chronic infectious diseases

clusters of bacteria that are attached to a surface and/or each other and embedded in a self-produced matrix (proteins, polysaccharides, environmental DNA) - protection from host immune cells and proteins

biofilms offer advantage of protection, shared nutrients and rapid exchange of plasmid DNA - slower metabolism makes bacterial pathogens more persistent

biofilm attack by phagocytes can cause tissue damage

how de we classify antibiotics

broad spectrum

narrow spectrum

minimum inhibitory concentration

minimum bactericidal concentration

bacteriostatic

bactericidal

broad spectrum antibiotics

inhibition of both gram-positive and gram-negative bacteria

narrow spectrum antibiotics

inhibition of only a few genera of either gram-negative or gram-positive bacteria

minimum inhibitory concentration (MIC)

prevents visible growth of a bacterium (in virtro culture with drug)

minimum bactericidal concentration (MBC)

lowest concentration of an antibiotic agent that kills a bacterium (in vitro subculture without drug)

bacteriostatic antibiotic

MBC/MIC > 4, MBC concentration too high for safe in vivo dosage

bactericidal antibiotic

MBC/MIC < 4, MBC concentration can be safely administered in vivo

what drugs inhibit cell wall synthesis

beta-lactams (penicillins, cephalosporins, carbapenems, monobactams)

vancomycin

bacitracin

cell membrane (polymyxins)

what drugs inhibit nucleic acid synthesis

folate synthesis → sulfonamides, trimethoprim

DNA gyrase → quiolones

RNA polymerase → rifampin

what drugs inhibit protein synthesis

50S subunit → macrolides, clindamycin, linezolid, chloramphenicol, streptogramins

30S subunit → tetracyclines, aminoglycosides

what is the structure of beta-lactams

feature of beta-lactam (=4 membered cyclic amide, aka azetidinone)

beta-lactam antibiotics are classified by the ring fused to the beta-lactam

what is the reactivity of beta-lactams

amide has no planar bond character due to the fused ring and beta-lactam stereochemistry creating a V-shaped ring system

strained ring system

more reactive than peptide bond amides eg. to nucleophilic attack to the lactam carbonyl group

what is the mechanism of action for beta-lactams

inhibit transpeptidase domains of penicillin-binding proteins (PBP), which catalyze the crosslinking of peptide chains of peptidoglycan during cell wall biosynthesis

role of PBP transpeptidases in the formation fo 4→ 3 peptidoglycan cross-links

mimic D-Ala-D-Ala substrate of penicillin-binding proteins

irreversible inhibition

what is the structure of penicillin

penam core structure (=beta-lactam + fused thiazolidine)

what does the R group on beta-lactam ring substituent have no effect on in penicillin

acid stability and intact drug absorption in GI tract

stability against bacterial beta-lactamase (resistance mechanism)

blood concetrations

antibacterial activity

more info on acid stability and intact drug absorption in GI tract for penicillin

acid stable penicillin are oral drugs

under acidic conditions (eg. at stomach pH) the carbonyl of the R-acyl substituent can attack the beta-lactam intramolecularly as a mucleophile, open the ring and inactivate the drug

an electron-withdrawing R-group reduces nucleophilicity of the R-acyl carbonyl and therefore increases acid stability of the drug

more info on stability against bacterial beta-lactamase (resistance mechanism) for penicillin

beta-lactamases (aka penicillinase) - serine proteases can catylze hydrolysis of beta-lactams

can be regenerated from covalently bound beta-lactam adduct → inactivation of many beta-lactams

secreted into medium (gram-positive bactera) or into periplasmic space (gram-negative bacteria)

large R group incrases resistance to beta-lactamases

more info on blood concentrations for penicillin

less hydrophobic R decreases binding of penicillin to plasma proteins and thus, increases blood plasma drug concentration

more info on antibacterial activity for penicillin

R group can change the antibacterial spectrum of penicillin eg. more hydrophilic R enables transport through gram-negative outer membrane porins (hydrophilic pore)

ampicillin = broad spectrum antibiotic

what are cephalosporins

cefem core structure

broad spectrum including many very dangerous bacteria

often lack oral activity

z-oxime on R1-group increases stability against beta-lactamase

bactericidal

what are carbapenems

potent broad-spectrum activity