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MBB163 > Mesnage (Spring) > Flashcards

Mesnage (Spring) Flashcards

1
Q

What is cardinal temp?

A
  • min and max temps that define limits of growth and dev of organism
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2
Q

How does bacterial growth change at temp changes?

A
  • at min temp, membrane gelling, transport processes so slow that growth can’t occur
  • growth increases w/ temp as enzymatic reactions occurring at increasing rates, until optimum reached
  • at max temp, proteins denature, cyto membrane collapses and thermal lysis
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3
Q

What are the different classes of MOs in terms of adaption to temperature, from lowest optimum to highest?

A
  • psychrophile
  • mesophile
  • thermophile
  • extreme thermophile
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4
Q

What are the requirements for bacterial growth?

A
  • temperature
  • pH
  • osmotic pressure
  • nutrients
  • oxygen
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5
Q

How are psychrophiles adapted to cold temps?

A
  • increased membrane fluidity –> higher content of unsat, polyunsat and methyl branched FAs, shorter acyl chain length (limit membrane cohesion)
  • prod of anti-freeze proteins (AFPs) –> bind to small ice crystals to inhibit growth by covering water accessible ice surfaces
  • prod of cryoprotectants –> Trehalase and exopolysaccharides
  • prod of cold adapted enzymes –> high prop of α helices, less weak bonds and interdomain interaction, giving greater flexibility
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6
Q

How are thermophiles adapted to high temps?

A
  • genome protection –> stabilisation of DNA by DNA binding proteins, intro of supercoils by reverse DNA gyrases, resistance to denaturation favoured by high GC%
  • mod of membrane composition –> ester linked phospholipids, single lipid layer (glycerol tetraethers)
  • prod of thermostable proteins –> hydrophobic interactions, higher prop of ionic interactions
  • existence of thermostable chaperonins –> thermosome
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7
Q

What are the metabolic adaptations of alkaliphiles?

A
  • resp chains pump Na+ out
  • H+/Na+ antiporters scavenge H+
  • Na+ driven ATPases export Na+
  • Na+ motive force powers motility, drives ATP synthesis and substrate symport
  • decarboxylases secrete Na+
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8
Q

What are the metabolic adaptations of acidophiles?

A
  • resp chains pump H+ out
  • H+/Na+ antiporters maintain pH below external pH
  • pmf powers motility, drives ATP synthesis and substrate symport
  • K+/H+ antiporters excrete H+
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9
Q

How do bacteria respond to osmotic stress?

A
  • reg of water movements by passive diffusion and aquaporins
  • prod of compatible solutes (betaine, Pro, Glu)
  • release of solutes by mechano-sensitive channels
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10
Q

What is the salt req in halophiles?

A
  • stabilisation of S-layer glycoprotein by Na+

- accum of K+ as compatible solute

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11
Q

What are the different classes of MOs in terms of adaption to salt conc, from lowest optimum to highest?

A
  • non-halophile
  • halotolerant
  • halophile
  • extreme halophile
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12
Q

What nutrients do bacteria req?

A
  • N
  • S
  • P
  • some vitamins
  • cofactors, eg. K+, Ca2+, Mg2+
  • trace elements (Fe, Cu, Zn)
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13
Q

What are the toxic forms of ROS?

A
  • superoxide (O2-)
  • H2O2
  • OH•
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14
Q

What is the overall reaction of O2 to form water?

A
  • O2 + 4e- + 4H+ –> H2O
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15
Q

What enzymes can detoxify ROS?

A
  • catalase/peroxidase –> convert H2O2 to H2O

- superoxide dismutase and catalase, and superoxide reductase and catalase –> convert O2- to H2O then H2O

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16
Q

Which bacteria req oxygen and why?

A
  • obligate aerobes –> catalase and SOD, only use O2 for resp
  • obligate anaerobes –> killed by normal atmospheric concs of O2
  • facultative aerobes –> catalase and SOD, can use O2 for resp
  • microaerophiles –> req O2 for resp
  • aerotolerant anaerobes –> only SOD, don’t use O2 for resp
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17
Q

How can bacterial growth be directly measured and what are some assoc problems and solutions?

A
  • microscopy –> counts live and dead cells, but can use dye to distinguish
  • flow cytometry (FACS) –> measures cell size, identify and count diff pops of cells
  • viable counts –> doesn’t reflect cell size or growth stage, usually underestimates no.
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18
Q

How can bacterial growth be indirectly measured and what are some assoc problems and solutions?

A
  • measure dry weight –> easy but time consuming, req high cell densities
  • OD –> differs between organisms, need standard curve, vol depends on growth stage, so cell no. estimate could be wrong, counts dead cells too
  • metabolic prod/protein levels
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19
Q

What are the 4 stages of bacterial growth and what occurs in each one?

A
  • lag –> metabolism starts but no division
  • log –> exponential increase
  • stationary –> deaths balance new cell prod
  • death –> pop decreases
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20
Q

What is the composition, structure and role of the outermost structure (S-layer) of archaea?

A
  • made of glycoprotein
  • 2D crystalline array
  • poss role in cell shape
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21
Q

What are the characteristics of the cell wall of archaea?

A
  • pseudomurein
  • not always present
  • heteropolymer (disaccharide-peptides)
  • similar to bacterial peptidoglycan
  • resistant to lysozyme
  • resistant to most antibiotics targeting bacterial peptidoglycan synthesis (penicillin)
22
Q

What are the characteristics of cytoplasmic membrane of archaea, and how does this differ from bacteria?

A
  • phospholipids contain no FA, isoprenes instead
  • phospholipids ether, not ester linked
  • membranes more stable than bacteria, present as monolayers or bilayers mix
23
Q

How are chromosomes organised and rep in archaea?

A
  • circular chromosome (and plasmids)
  • histones
  • multiple replication origins
  • encode pol B (eukarya) and D (specific to archaea)
24
Q

How does transcrip and RNA processing occur in archaea?

A
  • single RNA pol exist, similar to euk RNA pol II
  • presence of introns
  • genes organised in operons
25
Q

How does translation occur in archaea?

A
  • coupled to transcrip
  • involves several translation factors, like in eukarya
  • ribosomes are 70S particles
26
Q

What is the physiology of archaea like?

A
  • v diverse, reflects wide range of habitats
27
Q

What are the characteristics of (hyper)thermophiles?

A
  • inc Crenarchaeota and Euryarchaeota
  • high growth temp (80-120ºC)
  • most req elemental S for growth
  • often acidophiles
28
Q

What are the characteristics of halophiles?

A
  • mostly Euryarchaeota (few bacteria and euks)
  • found in evaporating ponds, Dead Sea etc.
  • req up to 5M NaCl for growth
29
Q

What are the characteristics of methanogens?

A
  • Eukarchaeota
  • found in anaerobic envs (rumen, gut, marine sediments)
  • use acetate/fumarate/CO2 as e- acceptor
30
Q

What are the methods of controlling bacterial growth?

A
  • heat
  • irradiation
  • filtration
31
Q

How can heat be used to control bacterial growth?

A
  • moist heat (boiling water/autoclave) –> 15 mins at 121º, under pressure for spores
  • dry heat (oven) –> direct flaming, incineration, >150ºC for 2 hours
  • pasteurisation (mild heat/HTST/UHT) –> temps below 100ºC to avoid casein aggregation
32
Q

How can irradiation be used to control bacterial growth and what is it used for?

A
  • not widely used for food
  • ionising –> food industry, med and lab equipment, DNA destruction via ROS
  • non-ionising –> surface decontam, DNA damage (breaks/dimers)
33
Q

How can filtration be used to control bacterial growth?

A
  • used to sterilise gases (air) or liquids that can be damaged by heat
  • porosity of filters can be chosen for specific apps (1mm-0.01μm)
  • nucleopore/membrane/depth filter
34
Q

What are the types of chemical antimicrobial control agents and what are they capable of?

A
  • sterilants and disinfectants used to destroy MOs on objects
  • sterilants completely eliminate all MO forms, inc spores, eg. ethylene oxide (g)
  • disinfectants kill MOs, not necessarily endospores, eg. alcohol (60-85%)
  • antiseptics and germicides applied on living tissue, inhibit growth or kill MOs, eg. handwash
35
Q

How does a bacteriostatic chemical antimicrobial control agent work?

A
  • stops reproduction of bacteria
36
Q

How does a bactericidal chemical antimicrobial control agent work?

A
  • kills bacteria, so only viable cell count decreases
37
Q

How does a bacteriolytic chemical antimicrobial control agent work?

A
  • bacteria destroyed, so no. cells counted reduced
38
Q

How can antimicrobial activity be measured by the disc diffusion technique?

A
  • inoculate plate w/ liquid culture of test organisms
  • discs containing antimicrobial agents placed on surface
  • incubate 1-2 days
  • test organism shows susceptibility to some agents, indicated by inhibition of bacterial growth and disease (zones of inhibition)
39
Q

What is the min inhibitory conc (MIC)?

A
  • lowest conc of drug inhibiting visible growth of test organism after overnight incubation
40
Q

What is the min bactericidal conc (MBC)?

A
  • lowest conc of drug killing >99.9% of test organism after overnight incubation
41
Q

What kind of chemicals can be used for antimicrobial control?

A
  • phenolic compounds –> local anesthetic at low concs, antibac but toxic at high temps, disrupt cytoplasmic membrane and denature proteins
  • alcohols –> active conc 60-85%, denature proteins, lipid solvent, disrupt cyto membrane
  • aldehydes –> alkylating agents, modify proteins and DNA causing cell death
  • 4º ammonium compounds –> interact w/ phospholipids of cyto membrane (cationic detergents)
  • halogen releasing agents
42
Q

What are the 2 types of halogen releasing agents? (chemicals for antimicrobial control)

A
  • Cl releasing –> sodium hypochlorite (in water ionises to prod Na+ and OCl-, in equilibrium w/ HOCl), formation of chlorinated bases in DNA, ox of proteins
  • I releasing (iodine/iodophors) –> v powerful, but stain, target DNA and proteins
43
Q

What role did Emmerich and Loew play in antibiotic discovery?

A
  • Pyocyanase shown to have antibac activity
  • prod large scale and app to patients
  • unstable, sporadic effectiveness and toxic
44
Q

What role did Ehrlich play in antibiotic discovery?

A
  • Salvarson
  • synthetic dye linked to arsenic
  • treated Syphilis
  • important toxicity and painful side effects
45
Q

What role did Domagk play in antibiotic discovery?

A
  • Prontosil red

- dye tested in vitro/in vivo (systematic screen)

46
Q

What role did Fleming play in antibiotic discovery?

A
  • Penicillin

- prod by fungus

47
Q

What are the major classes of antibiotics?

A
  • cell wall synthesis
  • DNA gyrase
  • RNA elongation
  • DNA directed RNA pol
  • protein synthesis (50S and 30S inhibitors and tRNA)
  • lipid biosynthesis
  • cyto membrane structure and function
  • folic acid metabolism
48
Q

What are the causes of antibiotic resistance?

A
  • misuse in human therapeutics
  • farming –> animals fed at subtherapeutic doses, far more than human consumption, dose req increased
  • agriculture –> treatment of tree and plant diseases
  • aquaculture
  • pets
49
Q

What are the factors that must be considered for the ideal antibiotic?

A
  • target –> selective toxicity and inhibition of essential process
  • stability and effectiveness –> pharmacokinetics and pharmacodynamics
  • cost
50
Q

How do β-lactams work?

A
  • inhibit peptidoglycan polymerisation mediated by D,D-transpeptidases
  • structural analogs of D-Ala-D-Ala C terminal residues in peptide stem
  • used by PBP as substrates and inactivate these enzymes irreversibly
51
Q

What are the resistance mechanisms of β-lactams?

A
  • inactivation by β-lactamases –> can cleave ring structure w/ nucleophilic attack by catalytic Ser, breaks ring and adds OH using water, preventing penicillin binding proteins from attaching
  • mutation of target enzyme –> reduce PBP affinity for β-lactams, so not able to target as well, can also overexpress PBP, so not enough to inhibit all of them
  • secretion of antibiotics (gram -ve bacteria) –> overprod diff systems to help reduce permeability of penicillin into cell, and to help push it out
  • mod of synthetic pathway targeted by β-lactams –> some bacteria don’t use D-Ala-D-Ala, so proteins can’t be affected by β-lactams

MBB163 (7 decks)

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