2) c) ii) Ligand Binding

Question 1

define a ligand

Answer 1

a ligand is a substance which can bind to a protein

Question 2

_ groups not involved in _______ ________ can allow _____ to ______

Answer 2

R groups not involved in protein folding can allow binding to ligands

Question 3

__________ _______ will have ___________ shape and chemistry to the ligand

Answer 3

Binding sites will have complementary shapes and chemistry to the ligand

Question 4

When a ligand binds to a protein-binding site what happens to the conformation of the protein?

Answer 4

When a ligand binds to a protein-binding site the conformation of a protein changes.
This binding causes a functional change in the protein

Question 5

allosteric sites exist between _________ _______ ______.

Answer 5

Allosteric sites exist between spatially distinct sites.

Question 6

Describe the process of the substrate molecule binding to an allosteric enzyme ACTIVE SITE and what happens as a result of this

Answer 6

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.

Question 7

Many allosteric proteins consist of _______ _________ (they have a _________ __________)

Answer 7

Many allosteric proteins consist of multiple subunits (have quaternary structure)

Question 8

Allosteric proteins with _________ subunits show ______________ in binding, in which ________ in ________ at _____ __________ alters the _________ of the remaining subunits.

Answer 8

Allosteric proteins with multiple subunits
show co-operativity in binding, in which
changes in binding at one subunit alter the affinity of the remaining subunits

Question 9

Allosteric enzymes contain a second type of site, called an __________ _______

Answer 9

Allosteric enzymes contain a second type of site, called an allosteric site

Question 10

What regulates the activity of the enzyme when it binds to the allosteric site?

Answer 10

Modulators regulate the activity of the
enzyme when they bind to the allosteric site.

Question 11

Allosteric interactions occur between _________ _______ ________.

Answer 11

Allosteric interactions occur between spatially distinct sites

Question 12

Positive modulator _________ the _________ _______ for the ________ whilst negative modulators _________ the _________ _________.

Answer 12

Positive Modulators increase the enzyme’s affinity for the substrate whilst negative modulators reduce the enzymes affinity.
(Upon binding a modulator, the conformation of an allosteric enzyme will change and this alters the affinity of the active site for the substrate.)

Question 13

Name an example which shows co-operativity

Answer 13

The binding and release of oxygen in
haemoglobin shows co-operativity.

Question 14

How does the binding of oxygen influence the other subunits on haemoglobin?

Answer 14

Changes in binding of oxygen at one subunit alter the affinity of the remaining subunits for
oxygen.
When an oxygen molecule binds to one of the four subunits of haemoglobin, it increases the affinity of oxygen for the other subunits.
When an oxygen molecule is released from one subunit it decreases the oxygen affinity of the other subunits - all the oxygens are released.

Question 15

What are the two factors which can affect the binding of oxygen to haemoglobin

Answer 15

temperature increase
ph decrease
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.