Biological Molecules 5: Metals Flashcards
What must a molecule have in order to act as a ligand?
An atom with a lone pair of electrons
What is a ligand?
A group that binds to a specific site on a target molecule to form a complex
What is a bidentate ligand?
A group where two atoms have a lone pair
How does charge influence strength of a ligand?
Metals with multiple charges (i.e. >1) will have stronger electrostatic attraction
How many of the amino acid side chains can act commonly as ligands?
Eight
What are the most common amino acid ligands?
Histidine
Methionine
Cysteine
What are the five main metallic elements present as cations in biology?
Sodium
Potassium
Magnesium
Calcium
Iron
What are the less common trace elements found in biology?
Chromium
Magnesium
Cobalt
Nickel
Copper
Zinc
Molybdenum
What oxidation state is iron typically found in?
2+ or 3+
What oxidation state is copper typically found in?
1+ or 2+
What oxidation state is zinc always found in?
2+
Where are Mg2+ ions found?
In complexes with nucleotides
In isomerases
Chlorophyll
Rubisco
Where are Ca2+ ions found?
Signalling
Receptor/ion channels
Kinases
Where are molybdenum ions found?
In complexes used for nitrogen fixation and oxygen atom transfer
Where are manganese ions found?
In complex enzyme used to split water
Where are iron ions found?
Electron transfer proteins
Oxygen transport and activation
Nitrogen fixation
Ferritin
Where are copper ions found?
Electron transfer
Oxygen transport
Oxygen activation
Where are nickel ions found?
Hydrogenase enzymes (in bacteria)
Where are cobalt ions found?
Vitamin B12 (involved in methionine synthesis)
Where are zinc ions found?
Numerous enzymes (e.g. peptidases, carbonic anhydrase)
Zinc fingers (regulation of gene expression)
What is the role of the Na+/K+ pump?
Used to balance charges inside and outside the cell
Concentration gradient is maintained by ATP consumption by Na/K pump
Na+ re-entry into cell is coupled to glucose co-transport
Salts concentration is tightly controlled to maintain protein folding and electrostatic associations
What does carbonic anhydrase do?
Catalyses the conversion of carbon dioxide in muscles to soluble carbonic acid
Allows the carbon dioxide to dissolve effectively and be transported to the lungs
In the lungs, carbonic anhydrase can catalyse conversion back to CO2 for exhaling
Formation of carbonic acid lowers pH in red blood cells causing haemoglobin to lose oxygen
Consumption of carbonic acid in the lungs causes pH to rise and haemoglobin to bind to oxygen more strongly
What is the role of zinc in carbonic anhydrase?
Speeds up the deprotonation of water to make a hydroxyl nucleophile
Zn2+ acts as a Lewis acid (electron pair acceptor)
Over 100 million times faster than the uncatalysed reaction
Essential for life
Describe the structure of haemoglobin.
Protein made up of four subunits
4 active sites that bind to oxygen cooperatively
Alpha-2 Beta-2 tetrameric structure
Protein chains are 2 pairs which are similar but not identical
How does haemoglobin work?
Uses a haem-based Fe(II) to co-ordinate oxygen reversibly
Can do this without reducing oxygen
It is bound and released in equilibrium
The haem and iron are attached to the protein by a single His ligand
A second His in the active site helps co-ordinate oxygen
Describe the binding curve of haemoglobin.
Sigmoidal
Helps in uptake and release in high and low oxygen respectively
Very efficient transporter
Describe what happens when oxygen binds to haemoglobin.
Iron becomes smaller and is pulled into the haem plane, moving His slightly
Affecting the conformation of the haemoglobin tetramer
In the T-state the tetramer has low oxygen affinity
In the R-state, it has high affinity
When is the tetramer of haemoglobin most stable?
When all subunits are R or T
Therefore binding of one triggers binding of more
Same applies for release
What is bioenergetics?
The study of energy storage and release in biological systems
