Midterm 2

Question 1

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.

Answer 1

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).

Question 2

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.

Answer 2

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

Question 3

Embryos lack defenses against chemicals.

Answer 3

false

Question 4

Transporters refold denatured proteins.

Answer 4

false

Question 5

Many lethal pesticides act on the same biological pathways.

Answer 5

true

Question 6

Cytochromes produce calcium waves.

Answer 6

false

Question 7

ABCB1 is present on all sides of a polarized cell.

Answer 7

false

Question 8

The thermal limit (lethal temperature) can be set by heat shock proteins.

Answer 8

true

Question 9

Cells have defenses against mercury.

Answer 9

true

Question 10

The Ames assay detects -SH binding.

Answer 10

false

Question 11

Neutral organic molecules can diffuse across lipid bilayers.

Answer 11

true

Question 12

ABC transporters use membrane potential to power transport.

Answer 12

false

Question 13

The apical surface of a polarized cell faces the blood/internal side.

Answer 13

false

Question 14

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

Answer 14

cytochrome p450s

Question 15

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

Answer 15

membrane proteins that pump chemicals out of cells

Question 16

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

Answer 16

aryl hydrocarbon receptors

Question 17

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

Answer 17

glutathione

Question 18

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

Answer 18

all of the above

Question 19

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

Answer 19

increase in the cytoplasm

Question 20

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

Answer 20

a mutagen

Question 21

Which of the following is NOT a type of epithelium: -squamous -cuboidal -stratified -desmosomal -none of the above

Answer 21

desmosomal

Question 22

Where does methylation of inorganic mercury occur in the ocean? -anoxic sediments -oxic sediments -the water column -all of the above

Answer 22

anoxic sediments

Question 23

Identify the structure:

Answer 23

dioxin

Question 24

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

Answer 24

Through transporters

Question 25

The fluidity of a cell membrane is largely influenced by what? -The specific proteins that are present -The type of junctions present -The relative abundance of unsaturated fatty acids -All of the above

Answer 25

all of the above

Question 26

There has been an inorganic mercury spill on the edge of San Diego Bay. The City of San Diego has contacted you for recommendations on how to rapidly reduce its toxicity. Which of the following is the best idea to reduce mercury toxicity: -Pour salt over the spill site. -Pour dilute acid over the spill site. -Pour freshwater over the spill site. -Pour methyl mercury over the spill site.

Answer 26

Pour salt over the spill site.

Question 27

Mercury is deposited into the oceans as: -Mercury II (Hg 2+). -inorganic mercury (HgCl2). -methyl mercury (CH3HgCl). -mercuric sulfides (HGS). -elemental mercury (Hg0).

Answer 27

Mercury II (Hg 2+).

Question 28

Which of the following molecules readily crosses a membrane? HgCl2 HgCl4 (2-) CH3HgCl HgCl2 and CH3HgCl none of the above

Answer 28

HgCl2 and CH3HgCl

Question 29

Cells at environmental barrier tissues are organized into sheets known as epithelia. Please describe the two-dimensional organization of several neighboring cells in a columnar epithelium (1). What is different about the apical and basolateral sides and what type of junction that keeps these two domains separated (2 points). List two additional types of junctions (1) and their functions (1).

Answer 29

In a columnar epithelium, the cells appear to be tall and semi-thin rectangular shapes. They are arranged side by side and the tissue is only one cell thick. The apical side is facing toward environment and basolateral is toward the blood. There are tight junctions between cells to ensure that no compounds can pass between them, keeping the apical and basolateral sides separate. Additional junctions include gap junctions, which allow passage of small molecules between cells, and adherens junction, which connect actin bundles between cells, and desomosomes, which join intermediate filaments.

Question 30

Uncoupling of oxidative phosphorylation is a mechanism by which pesticides can be toxic. You have been hired by Sargenta and asked to test a newly developed pesticide called “Beetlejuice” that promises to kill a destructive beetle. You are charged with determining if the pesticide works by targeting oxidative phosphorylation. 1. a) You collect some beetles and make cell extracts in the blender. What organelle do you need to isolate from these cells (1)? b) You make an extract of this organelle and find that its ATP levels are high. Do you conclude that oxidative phosphorylation is targeted, or not (1)? c) Farmers have reported to Sargenta that beetles are developing resistance to Beetlejuice. You collect several thousand of the resistant beetles from their fields and find that the levels of Beetlejuice in their cells are very low. Which mechanism do you suspect to be responsible for causing the beetles to become resistant to the pesticide (1)? 2. How could you test the hypothesis that your proposed mechanism is correct (2)?

Answer 30

a) You would need to isolate the cells’ mitochondria. b) This extract indicates that the oxidative phosphorylation was not targeted. c) It is likely an ABC transporter removing the chemical from the cell, causing resistance in a similar manner to tumor resistance to cancer drugs. d) If the concentration of Beetlejuice outside of the cells is high, then it is likely that a transporter is being used to pump the compound outside of the cell.

Question 31

Match the following transcription factors/receptors and genes they turn on. Heat shock factor Arylhydrocarbon receptor Nuclear hormone receptor Drug transporters Heat shock proteins Cytochrome P450

Answer 31

Heat shock factor - Heat shock proteins Arylhydrocarbon receptor - Cytochrome P450 Nuclear hormone receptor - Drug transporters

Question 32

Briefly explain how the cellular location and binding partners of heat shock factor change during heat stress.

Answer 32

When a threshold temperature is met in the cell, the heat shock factor dissociates from the heat shock proteins so they can go address the issue. The heat shock factor is then free to travel to the nucleus of the cell and bind to DNA, encoding for the production of more heat shock proteins.

Question 33

The Krogh principle stipulates that for every question there is suitable organism in which to study it. There have been at least six Nobel Prizes awarded for basic research/discoveries in marine organisms. List the common names of three organisms used in these discoveries and the associated discovery (3). For two of these explain the specific biological feature of the organism that enabled the discovery (2).

Answer 33

Action potential was first able to be observed in giant squid axons. These large squids allowed for the study of action potentials because their neurons were large enough that scientist could place sensors on different regions and observe how the action potential worked. Sea urchins were studied to find out more about the cell cycle. Cyclins were first observed in sea urchins. This was readily understandable due to the readily observed embryos of sea urchins, as they spawn large amounts of eggs and sperm into the water column, which then develop outside of the parents’ bodies. This makes observation far easier and the different parts of the cell cycle could be studied. Jellyfish were also studied to find the compounds responsible for biofluorescence (green fluorescent protein). This compound was then extracted and manipulated to cause biofluorescence in multiple colors.