Midterm 2 Flashcards
Describe the global mercury cycle. For each stage of the cycle indicate the form (species) of mercury that is most abundant, its source and how it moves to the next location. Indicate the major and minor sources of mercury in the environment and the source and form of mercury that bioaccumulates. Once mercury is in the ocean it moves between different forms, please describe how pH and pCl govern the speciation of mercury and how this affects its bioavailability.
Atmosphere: major sources are coal-burning (50-70%) and volcanic eruptions, put out elemental uncharged mercury (Hg(0)). In the atmosphere UV radiation will convert this to the ionic form Hg(II), which adsorbs to particles and is deposited in the ocean.In the ocean, around 90% of this mercury will remain in inorganic forms such as HgCl2 and HgCl42- (discussed more below). Around 10% will be converted to more dangerous organic forms, methylmercury (mostly) and dimethylmercury by bacteria in anoxic sediments. Organic mercury bioaccumulates because both common forms of methylmercury are uncharged, meaning that it can cross cell membranes, and normal cellular defenses like glutathione are less effective against organic mercury than against neutral inorganic mercury.Once mercury is in the ocean, pH affects speciation because if there are fewer hydrogen ions (high pH) drawing chloride, the composition of mercury species in the ocean will be shifted towards HgCl42-. pCl affects speciation because if more Cl- is available to react with mercury (low pCl) mercury will be shifted towards HgCl42-. In seawater, the pCl alone (pCl=3) would push mercury to be predominantly in HgCl2 (neutral) form, but the high pH (pH=8) causes about 95% of inorganic mercury in the ocean to be charged.Charged molecules cannot easily diffuse across membranes, lowering the bioavailability (this is why low salinity causes mercury to be more toxic to diatoms- more of it is in neutral form).
Describe the structure and function of an ABC transporter. What does ABC stand for? What other genes are present in the family? Name the different parts of a transporter protein and describe their function. Name three of the families of transporters and how they differ in structure and function. Give some examples of where each transporter is expressed in the body.
ABC transporter = ATP Binding Cassette transporter ABC transporters are a superfamily consisting of eight subfamilies, named A-H.ABC transporters are made up of two main parts: the nucleotide binding domains (NBDs) and transmembrane domains (TMDs). At nucleotide binding domains, hydrolysis of ATP occurs in order to release stored energy to transport drugs against concentration gradients.Transmembrane domains (made up of transmembrane spans) are hydrophobic sections of the ABC transporter embedded in the plasma membrane and determine what the ABC transporter can bind. (This is where compounds bind to the ABC transporter).The three families most relevant to drug transport are: ABCB: 12 TMs + 2 NBDs, binds small hydrophobic molecules in their unmodified state (promiscuous), upregulated in leukemia, also seen in gills, liver, kidneys, brainABCC: 17 TMs + 2 NBDs, transports modified compounds (such as metals conjugated to glutathione), seen in lungs, liverABCG: (6 TMs + 1 NBD) x 2- dimerize (it takes two to make one transporter)Plant metabolites- alkaloids, hydrophobic molecules, expressed in mammary tissue sending compounds into the milk
Embryos lack defenses against chemicals.
false
Transporters refold denatured proteins.
false
Many lethal pesticides act on the same biological pathways.
true
Cytochromes produce calcium waves.
false
ABCB1 is present on all sides of a polarized cell.
false
The thermal limit (lethal temperature) can be set by heat shock proteins.
true
Cells have defenses against mercury.
true
The Ames assay detects -SH binding.
false
Neutral organic molecules can diffuse across lipid bilayers.
true
ABC transporters use membrane potential to power transport.
false
The apical surface of a polarized cell faces the blood/internal side.
false
Which of the following cellular strategies/defenses can degrade/oxidize a chemical? -heat shock proteins -aryl hydrocarbon receptors -multidrug transporters -cytochrome P450s -glutathione -all of the above
cytochrome p450s
Multidrug transporters are: -enzymes that degrade chemicals -receptors that recognize chemicals and initiate gene responses -molecular chaperones -membrane proteins that pump chemicals out of cells -all of the above
membrane proteins that pump chemicals out of cells
Which of the following cellular strategies/defenses bind the toxicant dioxin and initiate a gene response? -heat shock proteins -aryl hydrocarbon receptors -multidrug transporters -cytochrome P450s -glutathione -all of the above
aryl hydrocarbon receptors
Which of the following strategies/defenses bind molecules that react with –SH groups? -heat shock proteins -aryl hydrocarbon receptors -multidrug transporters -cytochrome P450s -glutathione -all of the above
glutathione
Which of the following strategies/defenses can be up-regulated/increased in response to toxicants? -heat shock proteins -multidrug transporters -cytochrome P450s -glutathione -all of the above
all of the above
You are investigating the effects of a toxicant that causes cells to release the signaling molecule inositol triphosphate within cells. This signaling molecule opens calcium channels in the endoplasmic reticulum. As a result, you expect calcium levels to: -remain unchanged in both the cytoplasm and endoplasmic reticulum -increase in the endoplasmic reticulum -increase in the cytoplasm -increase in the cytoplasm and in the endoplasmic reticulum -none of the above
increase in the cytoplasm
You perform the Ames assay on your toxic compound and find it causes the mutant bacteria used in this assay to survive without histidine. You conclude the compound is: -a calcium channel poison -an endocrine disruptor -an inhibitor of the electron transport chain -a mutagen -harmless
a mutagen
Which of the following is NOT a type of epithelium: -squamous -cuboidal -stratified -desmosomal -none of the above
desmosomal
Where does methylation of inorganic mercury occur in the ocean? -anoxic sediments -oxic sediments -the water column -all of the above
anoxic sediments
Identify the structure:

dioxin
alpha-Amanitin enters cells… -Through transporters -By diffusion -On carrier proteins -In mercury complexes -None of the above
Through transporters