A 639 substitution of Asp for Tyr in 1S0V (T7 RNA
Polymerase) results in a dramatic drop of enzymatic
activity. One would expect this decrease to be a result
of an alternation in the polymerase to bind to RNA and
loose selectivity. The active site’s Hydroxyl group will
bond with RNA’s addition oxygen on the Ribose 2C.
Hydroxyl
RNA polymerase
Tyrosine
RNA
DNA
Heme
Oxygen
Coordinating Histidine
Of these four polypeptide chain units, two are alpha and two are beta units. These different
units are complementary to one another. Although the alpha and beta chains have different
sequences of amino acids, they fold to form a similar 3D structure. Only noncovalent
interactions hold the four chains together. Myoglobins unit does not have a shape that is unique
in this fashion, thus it cannot associate with other forms to have a larger tetrameric structure.
Myoglobin is a globular protein, suggesting that it is more de
Noncovalent interactions hold the hemoglobin’s chains together.
Hemoglobin has a greater number of hydrophilic regions, shown in red. While Myoglobin is
more hydrophobic, suggesting it is less likely to interact with other surrounding proteins.