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Ecotoxicology > Ch.3 > Flashcards

Ch.3 Flashcards

1
Q

What are some examples of possible uptake and elimination routes for a toxin in an fish

A
  • Biotransformation
  • absorbing water
  • food
  • dermal uptake
  • loss from gills
  • loss from urine and feces
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2
Q

What is the black box approach

A

a simplified way of modeling the uptake and elimination of a substance within an organism,
-uptake and elimination are arrows outside the box with possible redistribution, biotransformation and detoxification inside the box

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3
Q

What is the main assumption for the black box approach

A

that there is only 1 method of uptake and elimination that is dominant

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4
Q

What are the main assumptions inherent in any mathematical model of uptake and elimination

A
  • uptake and elimination happen in one compartment
  • compartment is instantly and homogeneously mixed
  • kinetics and rate coefs are constant over time
  • no biotransformat or organism effects take place in this compartment
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5
Q

What is a compartment in mathematical modeling

A

a way to simplify an organism, sometimes the entire organism is represented by a compartment

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6
Q

True or False: a compartment is usually represented by an organ or other bordered area in the body

A

False, usually animals are represented by a three compartment system (fat storage, blood, and liver)

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7
Q

What are the typical 3 compartments in an uptake and elimination model

A
  • fate storage
  • blood (intestine in, urine out)
  • liver (biotransformation going out)
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8
Q

What kind of curve is represented most commonly

A

a sigmoid curve

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9
Q

what are the x and y axises of a sigmoid curve

A 
y = concentration 
x = duration of exposure
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10
Q

what are the stages of a sigmoid curve

A
  1. uptake mechanisms are more dominant
  2. elimination processes come into play
  3. uptake and elimination are in balence
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11
Q

What is the difference between steady state and equilibrium

A

steady state includes energy requiring processes while equilibrium does not

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12
Q

what is body burden

A

the steady state concentration expressed as mg contaminant per g of tissue or mg per individual

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13
Q

Why is prediction of contaminant accumulation necessary

A
  • effects are due to conc in target area not abs conc

- top predator exposures are often food related

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14
Q

Define bioconcentration

A

accumulation in/on an organism from water

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15
Q

define bioaccumulation

A

net amount of a contaminant on/in an organism from all sources

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16
Q

True or False: as models become more complex they become more predictive

A

False, it means more variables must be estimated that could result in less accuracy

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17
Q

what was to occur for a compound to be toxic

A

they have to come into contact with their site of action at a sufficient

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18
Q

what are some ways contaminants can enter an organism

A
  • skin (dermis)
  • gills
  • pulmonary surfaces
  • gut
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19
Q

what are some ways contaminants may entre a plant

A
  • roots
  • stomata
  • other epidermal surfaces
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20
Q

how many stomata can be on a single leaf

A

6 million

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21
Q

True or false: stomata open and close in response to many environmental signals

A

true

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22
Q

When do stomata open

A

in high humidity, light, low carbon dioxide

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23
Q

when do stomata close

A

dry, dark, high CO2

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24
Q

Where do stomata connect to?

A

to air spaces in the leaf and the internal cells (parenchyma)

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25
Q

what are parenchyma

A

thin walled cells with large central vacuoles

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26
Q

What are stomata involved in

A
  • photosynthesis
  • respiration
  • protein synthesis
  • storage
  • repairing plant tissues
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27
Q

how does a plant take in airborne pollutants from the environment

A

uptake via stomata -> pollutant moves to intracellular spaces around parenchyma - > compound dissolves into cell surface water->parenchyma cells can store, sequester or biotransform the compound

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28
Q

What are stomata connected to

A

the air spaces in the leaf and the internal cells

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29
Q

What is parenchyma

A

Thin walled cells with large central vacuoles

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30
Q

What are stromata involved in

A
  • Photosynthesis
  • Respiration
  • Protein synthesis
  • storage
  • repair of plant tissues
31
Q

What are the 3 general routes into cells

A
  • Lipid
  • Aqueous
  • Endocytotic
32
Q

Explain the lilipid route into the cell

A

-lipophilic contaminants and small uncharged polar molecules diffuse through the lipid bilayer

33
Q

Explain the aqueous route into the cell

A
  • Membrane transport proteins are involved
  • -> channels - porins may be gated or ungrated, barrel-shaped proteins
  • -> Carrier proteins -Can involve active transport mechanisms - Can be symporters, antiporters
34
Q

Explain Endocytotic as a route into the cell

A

-Taken up by endocytosis into vesicles and processed

35
Q

What must happen before a substance can be taken up into a cell

A

It must interact with the surface

36
Q

How does a substance interact with the surfaceinteract interact with the surface

A

Adsorption

37
Q

Explain Adsorption

A

The accumulation of a substance at a boundary of two phases (often the solution to solids)

38
Q

What is the resulting equilibrium from adsorption

A

an equilibrium between the bulk solution and the solid phase

39
Q

What force interactions are in adsorption

A
  • H bonding
  • Van der Waals
  • hydrophobic interactions
40
Q

How is adsorption described mathematically

A

Using the Freundlich equation

X/M = KC^(1/n)

41
Q

Explain the symbols in Freundlich equation

A

X/M = KC^(1/n)

X=Amount adsorbed
M = Mass of absorbent
K = Derived constant
C = [Solute] in solution after adsorption
n = Derived constant (less then or equal to 1
n is often close to 1 if the concentration of the solute is low

42
Q

What does it look like when you graph X/M on the y axis and C on the X axis

A

a classic sigma curve

43
Q

Can you linearize both sides

A

Yeah you log(X/M) = log K, + (logC/n)

44
Q

What is Freundlich isotherm mostly used for

A
  • Adsorption of liquids to solids
  • i.e. pollutants to sediments or soils
  • i.e. adsorption of compounds or soils to biota with a very large surface area to volume ration, particularly microorganisms
45
Q

What is the Langmuir equation

A

X/M = ((abC)/(1+bC))
X,M,C are the same as with the Freundlich isotherm
a = maximum adsorption amount
b = affinity (refliects bond strength

46
Q

What can the Langmuir equation describe

A

-Toxicant movement onto biological surfaces including a;gae gills and zoo plankton

47
Q

What are the models talked about in this unit simplifications of adsorption

A
  • Contaminant movement into the organism may be a multi step process
  • Rapid adsorption may be followed by a slower diffusion step
48
Q

What is adsorption influenced by

A
  • Structural composition of the chemical
  • Organic Carbon content of the soil
  • pH of the medium
  • Size of soil particle
  • Temperature
49
Q

What are the two types of diffusion

A
  • Simple

- Facilitated

50
Q

Explain simple diffusion

A
  • No energy input required
  • Molecules move across membrane down its concentration or electrical gradient
  • May include a channel protein: 1. May be gated or ungated. 2. Passage through the channel can be influenced by ion change or size
51
Q

Explain Facilitated Diffusion

A
  • energy input required
  • Molecules move faster than predicted down its concentration or electical gradient
  • carrier protein involved
  • may become saturated or inhibited
52
Q

What type of diffusion do large/ highly charged molecules require

A

-facilitated or carrier transport, or active transport to cross the cellular membrane

53
Q

What does diffusion of acids and bases depend upon

A

their pKa and the surrounding pH

- If the ratio of uncharged to change form is greater then 10:1, absorption into the cell will occur

54
Q

How can diffusion be expressed mathematically

A

By Fick’s Law (ds/dt) = -DA(dC/dx)
ds/dt = Rate of contaminant movement across a surface
D = diffusion coefficient
A= Surface area diffusion is occuring over
dC/dx = Concentration gradient (or electrochemical)

55
Q

True or False: Many models of bioaccumulation include calculations of rates of diffusion into or out of various compartments

A

True

56
Q

What is involved in active transport

A
  1. Energy required (either ATP or PMF)
  2. Carrier proteins involved
  3. May become saturated or inhibited (e.g. Na+/K+ pump (ATPase)) or (e.g. Cd2+ may be imported as Ca2+ analog)
57
Q

True or false: Endocytosis is an important route for contaminants ingested with food

A

True

58
Q

True or False: endocytosis is often receptor mediated

A

True

59
Q

True or False: endocytosis usually does not require energy

A

False

60
Q

Explain iron assimilation as a type of endocytosis

A
  • Fe3+ and perhaps other metals bind to transferrin (siderophore)
  • Metal: protein complex binds to receptor on cell surface
  • Bound receptor complex moves to clathrin coated pits on the cell surface.
  • Vesicle formed
  • Receptors are recycled.
  • Clathrin removed, endosome acidifies
  • Iron dissociated, transferrin and receptor are recycled.
  • Entire cycle 16 min (4 min to move receptors to coated pits, 5 min to form endosome, 7 min to sort and recycle receptors back to the surface).
  • Liver may uptake 20,000 iron atoms per minute by this process
61
Q

Explain first order kinetics

A
  • most commonlu observed and applied for bioaccumulation models
  • Reaction rate is most rapid with excess substrate (rate decreases with less sub)
  • reaction is basically irriversibe (A–> B)
  • Called first order because reaction velocity depends on the first order of magnitude of conc A
  • rate constant can be determined from slope of initial reaction vs [A]
  • if reverse reaction is occuring you also have to look at that
62
Q

Explain seccond order kinetics

A
  • Apply to reactions in which molecules of a reactant must come together
  • 2A->B
  • V=-k[A]^2
  • units of k are (mol/L)s^-1
63
Q

Explain zero order kinetics

A
  • USed to describe a saturated system in which the reaction rate is independant of the concentration of reactant
64
Q

Define Biotransformation

A

biologically mediated conversion of one chemical compound to another

65
Q

Does biotransformation often involve enzymes

A

Yes, saturation and inhibition are possible

66
Q

Explain Inhibition

A

Decrease in reaction rate due to interactions between enzymes and other compounds

67
Q

What are the two types of inhibition

A
  1. Competitive

2. Noncompetitive

68
Q

Explain competitive inhibition

A

inhibitory substance binds into active site, blocks substrate

69
Q

Explain noncompetitive inhibition

A

inhiibitory substance binds to another site on the enzyme

70
Q

Explain saturation in biotransformation

A

Although the velocity of an enzyme reaction increases as the concentration of reactants increases there will be a point ehen all enzymes are occupied and are working as quickly as possible

71
Q

What equation is used to describe saturation

A

Michaelis-Menten equation
V = ((VmazC)/(Km+C))

Vmax = Maximum Velocity
Km = Constant
C= Reaction Concentration
-This can be used to make various parameters earier to determine

72
Q

What is a Lineweaver-Burke plot

A

essentially its the inverse of the Michaelis-Menten equation (1/V vs 1/S)

73
Q

True or False: Biotransformation reactions can enhance elimination, detoxification, sequestration, redistribution and activation

A

True

Ecotoxicology (13 decks)

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