Metal Ions

Question 1

List the 4 strategies for elemental selection

Answer 1

1. Physical retention by membranes
2. Binding to cellular components such as proteins and polysaccharides
3. Incorporation via formation of kinetically stable covalent bonds
4. Removal from the aqueous phase by precipitation (biomineralisation)

Question 2

List 6 features of metal ion chemistry

Answer 2

1, Provide stable carriers of positive charge (e.g. the role of Na+, K+, ATPase in the p.d. across membranes)

2. They interact selectively with organic ligands - discriminating between ions e.g. specificity of bacterial K+ channel allows transport of K+ while rejecting the smaller NA+.
3. Form complexes with flexible stereochemistry
4. Ionic bonds can be altered by redistributing electric charge - in contrast to the kinetic stability of covalent bonds
5. Metal ions with high electron affinities have high polarising power (e.g. Zinc ions in carbonic anhydrase enzyme).
6. Some have variable oxidation states useful for redox reactions e.g. Fe and Mo in nitrogenase protein that converts nitrogen gas to ammonia.

Question 3

What do electrochemical functions of metal ions usually depend on?

Answer 3

Usually depend on the free movement of ions particularly Na and K ions.
Volume regulation in animal cells and propagation of action potentials.

Question 4

List the 3 Signalling function of Ca2+ ions

Answer 4

1. Release of neurotransmitters of synapses
2. Muscle contraction
3. Stimulation of glycogen breakdown

Question 5

Describe how the Ca2+ ion activates the regulatory protein calmodulin

Answer 5

1. Above a certain of cytoplasmic concentration of Ca2+, Ca2+ binds to and activates calmodulin.
2. The EF hand is a motif consisting of a helix, loop, and a second helix - and calmodulin is made up of 4 EF hands.
3. Binding of the ion induces conformational changes in the EF hands that expose hydrophobic surfaces.
4. Therefore, the two sets of two EF hands clamp down around specific regions of target proteins (these patches act as docking regions for the positively charged amphipathic alpha helices of target proteins).
5. The Ca2+ calmodulin complex stimulates a wide variety of enzymes, pumps, and target proteins.
   is important in CaM kinase II protein

Question 6

Describe the function of Zn2+ in the mechanism of carbonic anhydrase

Answer 6

1. Zinc facilitates the release of a proton from a water molecule to generate a hydroxide ion (water is bound to the positively charged Zinc ion)
2. The carbon dioxide substrate binds to the enzyme’s active site and is therefore positioned to react with the hydroxide ion.
3. OH- attacks the CO2 and converts it to the bicarbonate ion HCO3- and the release of the product regenerates the active site along with the addition of a molecule of water.

Question 7

Cytochrome c oxidase

Answer 7

Has 4 prosthetic groups containing metal ions

Catalyses the last step in the mitochondrial electron transport pathway

Question 8

What is Mo required for (catalytic function)?

Answer 8

Mo is required for nitrogen fixation

Question 9

What is Mn required for?

Answer 9

Mn is required for oxygen production

Question 10

What are Fe and Cu often used for?

Answer 10

Fe and Cu often catalyse reactions involving oxygen