Lecture #7

Question 1

elemental mercury

Answer 1

Hg 0

Question 2

inorganic mercury

Answer 2

Hg(II) or HgCl2 (neutral, more dangerous) or HgCl4 2- (charged, more abundant)

Question 3

methyl mercury

Answer 3

CH3-HgCl (speciates to CH3-Hg-OH, both are neutral)

Question 4

dimethyl mercury

Answer 4

CH3-Hg-CH3

Question 5

global mercury cycle

Answer 5

-Hg in oceans/atmosphere is oxidized to Hg 2+ -bacteria take up Hg 2+ and convert it to elemental mercury under aerobic conditions -under anaerobic conditions, bacteria can convert methyl sulfides -> methyl mercury (main source of mm) -Hg in atmosphere is almost all elemental -light converts Hg 0 –> Hg(II) -most mercury in ocean is Hg(II)

Question 6

_______ do not cross lipid bilayers

Answer 6

charged molecules

Question 7

What is wrong with this image?

Answer 7

ocean pCl is 3, pH ~8 this is for the wrong pH, pH affects speciation

Question 8

Why doesn’t inorganic mercury get into cells even though it’s so abundant?

Answer 8

the majority of it is in a charged form at the pH and pCl of seawater, can’t cross membranes (only 5-10% is in the right form to cross over)

Question 9

inorganic mercury inhibits the growth of diatoms at ______?

Answer 9

-low salinity -inorganic mercury is more/less toxic depending on salinity

Question 10

why is inorganic mercury toxic to diatoms?

Answer 10

-enters the cell as HgCl2 but dissociates to Hg+ and Cl- once inside -associates with some of the proteins in the cell

Question 11

sulfhydryl groups

Answer 11

-reactive -Hg 2+ can displace the hydrogen on the SH group binding to proteins

Question 12

What compound is this?

Answer 12

cysteine (amino acid)

Question 13

Why does -SH binding matter for cell function?

Answer 13

-cell division is mediated by proteins called microtubules -can no longer divide

Question 14

inorganic vs. methyl mercury’s ability to enter a cell

Answer 14

-inorganic mercury tends to be stuck on the surfaces of things while methylmercury is more effective at getting into the cell -IM is stuck in membrane while MM gets out, hypothesis: the cell has a mechanism to remove inorganic mercury but not MM

Question 15

glutathione

Answer 15

-at low doses, protects cell from both types of mercury -when elimination is blocked, inorganic mercury becomes more toxic while MM is unaffected

Question 16

lipid bilayer contains

Answer 16

-transporters and channels that bring in nutrients, remove pollutants, or allow the cell to communicate with its neighbors

Question 17

Why is climate change increasing levels of methylmercury in fish?

Answer 17

warmer temps –> higher metabolisms –> eating and digesting more food –> more methylmercury