Describe those changes and the consequences for subsequent signaling by the G protein. Ligand occupied G protein receptor binds to the G protein and induces release of bound GDP from the a subunit. Small fat droplets in mammary gland cells come together and fuse to form larger fat droplets. Briefly explain the reason for this spontaneous process, an example of the hydrophobic interaction. Clustering together and fusion of fat droplets causes an increase in entropy due to a greater disorder in the water molecules.
Water molecules form a shell around fat with which hydorgen bonds are impossible.
Fusion of fat droplets decreases the area of this shell, freeing up water molecules to bond with each other. The resulting increase in probability of hydrogen bonding between water molecules accounts for the increase in entropy. Describe two different mechanisms by which the catalytic activity of an enzyme is physiologically regulated inside a cell. Binding of a ligand via noncovalent bonds to an allosteric site on the enzyme causes shape changes in the enzyme to increase or decrease catalysis. Covalent attachment of a phosphate to the enzyme causes shape changes in the enzyme to increase or decrease catalysis.