Unit 1: Ligand Binding Flashcards
(13 cards)
What’s a ligand?
A ligand is a substance that can bind to a protein
What happens as a result of ligand binding
As a ligand binds to a protein-binding site the conformation of the protein changes
This change in conformation causes a functional change in the protein
Whats an allosteric enzyme?
Allosteric enzymes are enzymes that are regulated by changing their conformation and contain a second type of site, called an allosteric site.
Whats a modulator?
Modulators regulate the activity of the enzyme when they bind to the allosteric site
What happens after a modulator binds to an allosteric enzyme?
Following binding of a modulator, the conformation of the enzyme changes and this alters the affinity of the active site for the substrate
Whats the difference between positive and negative modulators?
Positive modulators increase the enzyme’s affinity for the substrate, whereas negative modulators reduce the enzyme’s affinity.
How does haemoglobin show cooperativity with oxygen?
When the first oxygen ligand binds to one of the subunits it alters the conformation of the haemoglobin. Thisincreases the affinity of the other subunits for oxygen making it easier for the other 3 oxygen molecules to bind to the other 3 subunits.
How does temperature and pH affect the binding of oxygen to haemoglobin?
A decrease in pH or an increase in temperature lowers the affinity of haemoglobin for oxygen, so the binding of oxygen is reduced. Reduced pH and increased temperature in actively respiring tissue will reduce the binding of oxygen to haemoglobin promoting increased oxygen delivery to tissue
What can the addition or a removal of a phosphate cause?
A reversible conformational change in the protein
What is the addition or removal of a phosphate a common form of?
Post-translational modification
What do kinases do?
Protein kinases catalyse the transfer of a phosphate group to other proteins
What do phosphatases do?
Protein phosphatases catalyse the reverse reaction
How does the binding of a substrate to one active site of an allosteric enzyme affect the affinity of other substrates?
The binding of a substrate molecule to one active site of an allosteric enzyme increases the affinity of the other active sites for binding
of subsequent substrate molecules. This is of biological importance because the activity of allosteric enzymes can vary greatly with small changes in substrate concentration
